Flooded starting-lighting-ignition (SLI) and enhanced flooded batteries (EFBs)

5 Flooded starting-lightingignition (SLI) and enhanced flooded batteries (EFBs): state-of-the-art 1

2

M. Gelbke 1, C. Mondoloni 2

Akkumulatorenfabrik Moll GmbH þ Co. KG, Bad Staffelstein, Germany PSA PEUGEOT CITROE¨N, Centre Technique La Garenne-Colombes, La Garenne-Colombes, France

5.1 History of leadeacid batteries in combustion engine cars Leadeacid batteries have been, for over 100 years, the favourite energy storage system for internal combustion engine (ICE) vehicles. Moreover starting-lighting-ignition (SLI) batteries dominate the worldwide consumption of lead. No other leadeacid battery is produced in such high numbers as starter batteries. About 40% of world consumption of lead is used for SLI batteries [1]. SLI describes the main part of the multiple function of the leadeacid battery in a car, although the function has progressed over the years. Initially the battery was used for supporting only the lights. It worked as a stand-alone solution and had to be regularly recharged out of the car. In 1913 the first board net was developed by BOSCH (‘BOSCH Licht’). It consisted of an alternator, a controller and a battery. First, it was used only for lighting and driving the windshield wipers. During the 1920 and 1930s battery electric ignition was developed and introduced [2]. A special starter system to crank the engine by using power from the battery became state-of-the-art, step-by-step replacing manual crank systems. Up to the 1950s 6-V batteries were dominant in the automotive application. The range of requirements that the leadeacid battery in automotive use has to fulfil today is much wider than in any other battery application:  Operate in discharge/charge mode and buffer mode alternatively;  Discharge at some mA over hours and days;

LeadeAcid Batteries for Future Automobiles. http://dx.doi.org/10.1016/B978-0-444-63700-0.00005-2 Copyright © 2017 Elsevier B.V. All rights reserved.

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Discharge at more than 1000 amps for milliseconds and seconds; Discharge at 5e30 A over minutes; Charge with limited voltage; Compensate for voltage fluctuations in the board net; Operate over a temperature range from 30 C to þ75 C; Be resistant to vibration according to vehicle design.

The application of the battery in a car today is marked by a further extension of functions and higher power consumption. This more rigorous duty will be discussed in detail in Section 5.2. Leadeacid batteries in passenger cars are now 12-V block batteries usually rated from 40 up to 110 Ah capacities. Board net systems most commonly make use of a single battery. For some special applications, however, board nets with two batteries (one as SLI and the other as power support for other consumers) are in use. Batteries for trucks have to supply more energy than batteries for cars. Crank power has to be higher, vibration resistance has to be increased significantly and loads with current consumptions of some amps must be supported regularly for periods of several hours. To cope with such duty special designs with higher capacity, from 100 up to 230 Ah, are applied. In general two 12-V batteries connected in series are used to support the 24-V board net of trucks. There have been, and continue to be, many attempts to replace leadeacid batteries by other storage systems, but as yet without final success. Apart from the capability to perform the wide requirement set mentioned above, leadeacid batteries can be produced in large quantities at an acceptable price. International, regional and national standards bodies such as IEC (world), BCI (USA), JIS (Japan), EN (Europe), GB/T (China) and others moderate starter battery designs, performance requirements and test methods. Product ranges are based on modular use of uniform flat electrodes (plates). This makes production of electrodes in large quantities possible. Thanks to the economies of scale and the modest material costs leadeacid batteries are relatively cheap. Finally, leadeacid starter batteries are very easy to recycle. Consequently, in the market there is now a closed loop for material usage. More than 90% of batteries sold will be recollected after use and reworked to raw material for new batteries with low energy consumption in a quite simple process. There is no other storage system that has these endless resources. Batteries in passenger cars have a lifetime expectancy between 2 and 7 years (depending on climate conditions, application and battery placement inside of car). Battery Council International (BCI) statistics for the US market have shown that mean battery lifetime increased from 36 months in 1962 to

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55 months in 2010 [3]. But developments in automotive battery applications have caused average life to be reduced to 51 months in 2015 [3]. Generally, the battery still meets the endurance expectations of customers. The reliability of the battery is a key issue, however, because a car is out of function when it has a flat battery. Further increase of reliability of the battery and reliable end-oflife prediction are challenging tasks requiring further development. Preferred failure modes for leadeacid batteries in conventional ICE cars are:  grid corrosion and drying out (overcharging the battery-mainly at high temperatures);  sulfation and active-mass shedding (undercharging the battery at low temperatures and extended cycling and micro-cycling);  mechanical damage by vibration (especially under severe road conditions and in trucks). Several leadeacid battery technologies are in use today:    

flooded flat plate batteries valve-regulated flat plate absorptive glass-mat (AGM) batteries valve-regulated gel batteries valve-regulated spiral batteries

Table 5.1 compares different leadeacid battery designs for automotive applications.

5.2 Board net architecture and car requirements on batteries 5.2.1 Electric power system and board net The global electrical power system to cover the various electric demands that may appear on conventional or micro-hybrid vehicles with ICEs can be simply illustrated by the architecture board net of schematic shown in Fig. 5.1. The main active components in the board net presented are limited to: 12-V battery, electro-magnetic starter and alternator (that can be considered as the main generator) and loads. The negative pole of the circuit is always the chassis of the car. Often, several circuits with specific loads exist in parallel protected by different fuses. For closing the circuits of the board net different switches [KEYs (KEYs are called board net circuit closing/opening switches managed over car key)] are installed. The alternator and the starter are situated near the engine. The battery could be placed near the engine or far away in the trunk or under the seats in the passenger compartment. The latter option is becoming

151

Parameter Typical weight

Flat plate Monobloc flooded batteries SLI Flat plate flooded and EFB batteries advanced EFB Flat plate VRLA AGM

Spiral cells VRLA AGM

Flat plate VRLA gel

17e19.5 kg (EFB 18.5.19.5 kg)

20e21.5 kg

20.5e21.5 kg

21 kg

21 kg

Example typical size

w9.2 L: L3 278 3 175 3 190 mm w480e680 Ae6672 Ah Ah

9.2 L: L3 278 3 175 3 190 mm w680e760 Ae70 Ah

w9.2 L: L3 278 3 175 3 190 mm 760 Ae70 Ah

w8.7 L,BCI D34 254 3 173 3 200 mm 765 Ae55 Ah

w9.2 LLES650/G60 278 3 175 3 190 mm 460 Ae60 Ah

Power density and specific power at 18 C, 10s

w220e290 Wkg1 400e600 WL1

w270e310 Wkg1 600e680 WL1

w300e310 WL1 600e680 WL1

w350e400 WL1 900 WL1

w170e190 WL1 400 WL1

Energy density and specific energy at 25  C; C20

w46e44 Wh kg1 86e95 Wh L1

w40e42 Wh kg1 90 Wh L1

w40e41 Wh kg1 90 Wh L1

w31 Wh kg1 75 Wh L1

w34 Wh kg1 78 Wh L1

Internal resistance@ 25  C; 100%SoC

3.8.4.7 mOhm

3.0.3.4 mOhm

3.2.3.5 mOhm

2.8 mOhm

5.0 mOhm

Self-discharge rate

Low (w3e6% per month)

Low (w3.3% per month)

Low (w3% per month)

Very low (w2.3% per month)

Very low (w2%/ month)

Temperature range

30e75 C

30e75 C

30e60 C

30e60 C (þ75 C)

30e75 C

Good

Very good

Very good

Excellent

Weak (20%)

5e7 years

5e7 years

5e7 years

5e7 years

5e7 years

V50e150 kWh1 V8e10 kW1

X 1.3

X 1.6

X 2.5

X 2.8

SLI for passenger car for micro-hybrid vehicles with recuperation only

For micro-hybrid vehicles with stopestart

For micro-hybrid vehicles with stopestart taxi cars with many consumers

High power and deep cycle for special vehicles and construction machines

Very deep cycle board net batteries in vehicles (with seasonal application)

Cold cranking at 18 C Operational lifetime Cost

Application

LeadeAcid Batteries for Future Automobiles

152

Table 5.1 Comparison of different automotive battery designs

LeadeAcid Batteries for Future Automobiles

Figure 5.1 General layout of Electric Power System (EPS) and board net with Electric Energy Management (EEM); G-generator; A-alternator

increasingly popular because of the limited space under the hood and the high temperatures in the vicinity of the engine. More sophisticated architectures for micro-hybrid cars (with integrated alternator-starter and or ultracapacitors, dual-battery systems, DC/DC converters, etc.) are also active areas of development. The main functions of the Electric Power System (EPS) of conventional cars are:  Start the ICE;  Ensure the quality and availability of electric energy supplied to electrical components and consumers (loads) in the different operation modes of the vehicle; Additional functions for micro-hybrid cars:  Contribute to the decrease in fuel consumption and the reduction of CO2 emissions of vehicles;  by reducing the mechanical coupling of the alternator on the accessory belt;  by mechanical energy recuperation (regenerative braking);  by allowing to switch off the engine at car stop events via the stop/start (STT) function;

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 Restart engine after STOP events (car engine “OFF”) of the STT function;  Furnish other electric assistance/charging boost/engine torque assist. The EPS has to guarantee all the special voltage and current profile requirements during all of the different car operation modes: 

Key ON (Close board net circuit switch via car key set at “ON”), board net booting and engine crank In the case of micro-hybrid cars additional: engine restart after stop event in an active board net

Cranking mode

Key ON and generator OFF (engine and generator “OFF”, a very limited number of board net loads are active only) In the case of micro-hybrid cars: engine OFF at STOP event and support all loads of completely active board net from battery

Stop mode



Key ON generator ON (engine and generator support board net, i.e. car is driving)

Driving mode



Key OFF (engine off, car key is switched off, battery supports all small loads (Controller, car safty devices ect.) which are active at parking car also)

Parking mode



Restart of stop function in STT

Stop in STT function

Up to the 1990s, board nets were characterized by loads, generator and battery working ‘independently’, i.e., without net communication and any active control by controllers. At the beginning of this century a board net with an Electrical Energy Management (EEM) had to be introduced due to the demands of:  the increasing number of loads;  the associated increase of energetic needs for engine ON and OFF situations, in particular taking into account quiescent currents;  the replacement of mechanical control functions by electric devices;  the introduction of electric functions which are essential for safety and functionality of the car (x-by wire);  the higher requirements on voltage stability in the board net;  the limited potential increase of generator power. Table 5.2 illustrates the reasons for the increase of energy and power consumption in different operation modes. Today, electrical energy consumption for a 1 h driving cycle for cars of different classes has been increased to:  C segment: 130e180 Ah (gasoline)/220e250 Ah (diesel)  B segment: 90e130 Ah (gasoline)/180e200 Ah (diesel).

154

Extra power needed at Key ON modes Equipment/device

Trend of usage/power increase Cranks/restarts

Engine precrank

General application

X

Fuel pump

General application

X

Suspensions Power-assisted steering (1 kW)

Generator ON

Generator OFF

Needed at rest mode Key OFF

X X X

General application

X

þ250/300 W at 2020 (forecast)

X

X

X

Especially for premium cars

X

X

X

Telematics and multimedia (radio/GPS nav./Internet on board)

þ25% power consumption increase for each car generation

X

X

X

Lighting devices, permanent day light

þ25% power consumption increase for each car generation

X

X

Power heating to satisfy comfort needs or specific function as electrical seats (could be thermal preconditioning, engine postventilation)

þ25% power consumption increase over 10 years

X

Power heating with engine more efficient (vacuum pump) and to answer depollution strategy (SCR powering)

þ150 W necessary to satisfy the transition from V5 to V6 CAFE standard

X

Motor cooling-fan Air conditioning (stronger cooling)

X

X

X

Other engine OFF functions permanent electric consumption of the vehicle (more calculators, alarm, multimedia, diagnosis over the year etc..) Car transformation devices

X

X

X

X

LeadeAcid Batteries for Future Automobiles

Table 5.2 Increase of consumers energy requirement at modern board net

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Development in Power needs at board net of diesel car 3,5

Power (KW)

3 2,5 2 Average 1,5 1

Maximum

0,5 0 1995

2000

2005

2010 YEAR

2015

2020

2025

Figure 5.2 Development of power needs at KEY ON at diesel cars.

Power as well as energy consumption is expected to increase constantly over the next few years. It can be seen from Fig. 5.2 for the example of diesel cars which represents the worst case. A power consumption requirement of 2.5e3 kW can be predicted for 2020 which means that generators will need to supply about 180e200 A in average conditions (engine at about 2000 rpm and 60 C) even for middle class cars. The generator is dimensioned in the Key ON mode for different climatic scenarios (machine temperature significantly affects the output current of the alternator) in order that the Ah balance remains always positive (battery state-of-charge [SoC] should not decrease). Voltage (power output) can be controlled. In particular, the alternator dynamic (response time) is rather low (about 150 ms) so that the battery must supply peaks in power demand to keep the voltage at the consumer board net sufficient (>12 V) in the event of sudden load increases, for example to satisfy:    

robotized gear box: 60 A/20 ms; piloted suspension: 70 A/200 ms; power-assisted steering: 110 A/100 ms; safety brake: 95 A/200 ms.

Over the years there has been an increase in battery size. But this increase has been limited due to space and weight constraints. The EEM has to manage the higher energy consumption especially during key off phases without recourse to much bigger batteries. EEM has been implemented through the introduction of board nets consisting of a bus system, micro-controller controlled loads, generators and batteries as well as software, including energy and battery management algorithms operated at special control devices. 156

LeadeAcid Batteries for Future Automobiles

With the help of EEM it is possible to manage:    

generator or battery power supply; consumers in the different driving modes; consumers in the generator OFF modes; charging of the battery appropriately according to the battery status, power supply and car status.

These intelligent board nets are nowadays the basis upon which micro-hybrid operations in combustion engine cars rely.

5.2.2 Battery primary functionalities As part of the EPS, the 12-V SLI leadeacid starter battery basic functions are:  supply the power to starter necessary to crank the ICE;  buffer the voltage output of the alternator at board net level;  filter the voltage ripples at the alternator output;  supply power and energy in complement to the alternator when necessary;  support loads during parking and stop phases;  supply energy in emergency mode during generator (alternator) break down. In a conventional ICE car, the standard SLI battery is permanently charged during the driving mode and it is very unlikely that the battery is cycled during normal operation. Battery SoC remains high (>90%) and quite constant. During parking phases SoC will be lowered by discharges with very small currents in the mA range to serve quiescent loads. Taxi operation is characterized by regular discharges with currents of some amperes over longer times. These discharges take place in cars with auxiliary heating or other electric loads operating at stop phases. Generally, the batteries in higher equipped cars are cycled more than those in lower range cars. The charging voltage is fixed and adjusted to battery technology, temperature and battery position within the car.

5.2.3 Performance parameters of batteries in conventional cars EPS requirements assign to the battery the ability to supply and absorb electric power and energy within a voltage functionality range that depends on the different driving modes:  charging voltage in the range of 13e15 V;  minimum discharge voltages depending on vehicle driving mode and board net layout, but typically above 6 V (inrush starting current)/9 V (starting)/12 V (driving).

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LeadeAcid Batteries for Future Automobiles

International standards and OEM specifications fix general the requirements for automotive batteries:  nominal Cold Cranking current, initial voltage drop after a certain time, (e.g., 10 s); cold crank current (CCA) (Ah) and time to 6 V (to describe behaviour battery during engine start);  nominal capacity Cn (Ah) (to describe the ability to support small loads over time);  water consumption level (to define the maintenance level);  charge-acceptance (to describe ability to be recharged during driving);  endurance ability when exposed to medium cycling (to describe cycle-life when SoC is floated over battery lifetime);  endurance ability against overcharge (to measure resistance to corrosion);  resistance to deep discharge (to describe behaviour after over discharges which can happen during extended parking phases);  tilting and vibration resistance (to describe mechanical robustness and safety against acid leakage). Additionally, specific conditions of application influence classic automotive battery design:  customer should not be forced or allowed to top up electrolyte level and/ or battery is placed in compartments with limited ventilation; battery to be ‘maintenance free’;  battery is placed just in front of hot engine causing an operational temperature range between 32 C and þ75 C during driving mode (at hot climates still higher); battery to be resistant to severe thermal environment;  battery is placed in narrow compartments or in the passenger compartment, gases and acid sprays from charging have to be transported away for safety reasons; battery to have a special ventilated lid including a central degassing system and flame arrestor;  battery is placed far away from engine and starter which can cause power loss during charging and cranking; wiring in the car must prevent voltage losses and a battery to must have better recharge ability at lower voltage as well as higher cranking current (¼lower internal resistance);  battery is placed in areas/cars with high vibration or used as mechanical pulse damper; battery to have special design (special fixed groups, special separators and strap designs);  battery has to survive very low temperatures or quick thermal changes; to adopt material for boxes and lids as well as internal resistance of battery. Battery position in the car, profile of usage in a car (layout of board net), thermal environment and mechanical stresses determine failure mode and

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lifetime of battery very strongly. Batteries installed in an area of higher temperature fail because of corrosion and dry out, batteries installed far away from engine suffer from sulfation and premature ageing of activemasses because of undercharging. Climate zones in which cars will be operated can accelerate these different failure modes.

5.2.4 Parameters for battery selection 5.2.4.1 Crank-ability selection During a crank, the battery should be able to deliver a current according to a particular voltage pattern. Fig. 5.3 shows the principal voltage and current profiles during crank. The voltage profile obtained during the whole starting of an ICE is a key factor in the evaluation of a crank system (starter, battery and cable) for a certain engine compartment (engine, pinion, oil):  Initial step (t < 10e20 ms): The voltage minimum during the inrush current is a pure electrical response of the ‘starter/battery’ subsystem (depending on the internal resistance of the battery, the voltage drop of the cabling and the moment the engine fires). It is typically not acceptable for the voltage to drop below 6.2 V during this step (the minimum set point is determined by the controller layout of the board net).  Ramp up of engine: The current and voltage profiles result from the electromechanical power/energy demands to start the rotation of starter, pinion and engine as well as the ignition behaviour of the

Figure 5.3 General pattern of current and voltage slope during car cranking.

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combustion engine. It is typically not acceptable for the voltage to drop below 9 V during this step. Depending on engine type (gasoline/diesel) and size, starter type and temperature, the peak current during car engine starting can reach very different values. Typical readings are in the range of 500e1500 A. The ability of a battery to comply with this requirement is assessed from its CCA parameter. For instance an L2 or L3 battery labelled in the range (540e640 A) or (680e760 A) can be used to provide initial currents of up to 700e1000 A. Battery nominal cold crank (CCA) standardized test methods are designed to simulate real cranking. They are helpful for the preselection of a battery, but cannot replace real world measurements or calculations. In practice, car manufacturers have developed interactive multi-component Simulink simulation systems and/or do trials with real systems in climate chambers. Key factors for parameterization of starter performance models includes battery parameters such as internal resistance (Ri), open-circuit voltage (OCV) and extrapolated voltage at current zero (Eo) that represents the electromotive force of the battery (U ¼ Eo þ Ri  I). All of these parameters depend on SoC and temperature. Measurements of voltage drop are required for each battery type and, as shown at Fig. 5.4, depend on current for different SoCs and temperatures.

Figure 5.4 Initial voltage drop at discharges with different currents at different SoCs and temperatures for SLI L3 12 V 70 Ah Icc ¼ 720 A battery.

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LeadeAcid Batteries for Future Automobiles

voltage graph during crank U@ different SOC, T-- simulation (fit) vs. readings (bat) 12 11 10 U (V)

9 8

Ubat / T=25 / SOC% =80 Ufit / T=25 / SOC% =80 Ubat / T=-10 / SOC% =80 Ufit / T=-10 / SOC% =80 Ubat / T=-18 / SOC% =80 Ufit / T=-18 / SOC% =80 Ubat / T=-30 / SOC% =80 Ufit / T=-30 / SOC% =80

7 6

-0,1

-0,05

5

0

0,05

0,1 t (sec)

0,15

0,2

0,25

0,3

Figure 5.5 Voltage profile of real starts under different conditions e comparison of readings and simulation.

To consider dynamic behaviour (polarization) and battery ageing, correction factors for Ri have to be introduced into the modelling. Such data will be generated by measurements on new and aged batteries at different SoC and temperature. With these adjustments models can be used for selecting battery type and size instead of measurements. Fig. 5.5 presents the voltage profile during real crank measured at a battery with SoC ¼ 80% at different temperatures in comparison to simulations.

5.2.4.2 Battery capacity selection Different scenarios of battery behaviour in a car at stop mode after vehicle production will be considered according to an energy reserve calculation: i)

Scenarios before car delivery to the final customer  Estimate battery condition during the different park storages before final commercialization (major discharge by self-discharge and quiescent current of the car). ii) Typical customer scenarios  Activation profiles of systematic consumers/controllers/alarms, etc. Car remaining at rest for a relative long period of time (3e4 weeks)eaverage quiescent current <530 mA / airport parking scenario;  Short continuous activation events for higher consumers (lightning, warnings, automatic adjustments, etc.) for minutes or hours / board net wake up scenarios.

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In all cases it is necessary to define an acceptable range of SoC in which the battery can remain without affecting the later performance of the car (i.e., engine cranking still possible, no premature ageing, etc.). Battery size is chosen according to these current consumptions, minimum SoC level, discharge profiles and acceptable discharge times. Typical upper SoC level for calculation will be set to 80% SoC. An example of the determination of battery size in a worst case scenario is as follows: i) Considering 20 Ah consumption over 1 month (average current 28 mA) including a high quiescent current (alarm) and the residual self-discharge current during parking time; and ii) Considering acceptable SoC range would be between 80% and 50% SoC (DSoC  30%):  20 Ah for a 50 Ah battery / delta SoC ¼ 40% / not acceptable  20 Ah for a 60 Ah battery / delta SoC ¼ 33% / not acceptable  20 Ah for a 70 Ah battery / delta SoC [ 28.5% / acceptable

5.2.4.3 Battery design and technology selection Apart from parameters such as crank ability and capacity, battery selection has to follow special requirements according to endurance and lifetime. The criteria applied to reach the final battery definition for a given car configuration are summarized in Fig. 5.6.

Figure 5.6 Battery selection criteria.

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For micro-hybrid cars, it is also necessary to take into account the ICE hybridization level which will affect selection of the battery technology type, SLI, enhanced flooded battery (EFB), advanced EFB, AGM. AGM choice may be favoured by frequent cycling duty.

5.2.5 Specificity of electric energy management in microhybrid cars The term micro-hybrid could be defined as a special form of EEM which uses an active managed storage device (mainly a battery) to achieve an additional fuel saving. There are different strategies and board net layouts for managing power and energy flow during driving and stop mode to meet this goal, but all these strategies make use of a storage device (battery) temporarily as a source and a sink of electric power. The main strategies are:  recuperation (to define as feeding back energy from deceleration of car to EPS)  stopestart (STT) (indicated by support of consumers during stop phases from battery and recharge during driving mode)  combinations of both strategies  temporary battery assists the generator as power source during special car operations An EEM with a special subfunction to continuously monitor and manage the need for electric energy as well as the SoC of the battery is necessary to satisfy ‘energy recuperation with or without STT’. During this operation the battery is held in a partial state-of-charge (PSoC) and the SoC will be floated dependent on the car operation status in order to combine:  energy recovery optimization (braking/deceleration phases)  STT function availability  battery life preservation Ideally, energy transfer towards the battery is achieved with an alternator that is voltage-controlled by a battery monitoring system (BMS) according to the battery PSoC set point. Battery SoC is monitored and fixed in a typical set point range [80e85%] to have efficient energy recuperation and to maintain an appropriate energy reserve. During charge recuperation steps, dynamic charge-acceptance of the battery should be high enough to absorb energy and recharge the battery in a short time. Energy will be taken from the battery (and the alternator is cut off or reduced) if the SoC of the battery is above the PSoC set point. For vehicles with recuperation only (i.e., without the STT function), this special battery feature can be adapted to a low or medium micro-cycling duty (<0.5% depth-of-discharge [DoD]) with a total lifetime Ah turnover

163

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Figure 5.7 Profile of 50 h driving of micro-hybrid car with recuperation only (no stopestart); slope of IBat, UBat, Ri and SoC of L2 12 V 60 Ah battery.

that can be above 12,000 Ah (200 Cn of a 60 Ah battery). Flooded batteries such as premium SLI or basic EFB can satisfy this endurance target according to the different strategies developed by car manufacturers. Typical driving profiles (voltage, current, internal resistance and SoC over time) for a micro-hybrid car with recuperation only are given in Fig. 5.7. Fig. 5.7 shows graphs for voltage, current, internal resistance Ri and SoC of 50 h driving of a 1.6 L diesel engine car equipped with an L2 EFB 12 V 60 Ah battery. Voltage at the alternator output is adjusted continuously to satisfy the battery PSoC management strategy. An issue at this operation is that the resulting dynamic charge-acceptance can be very low. Detailed analysis of driving under the PSoC strategy shows that the battery dynamic charge-acceptance (or recharge ability) can be very easily reduced:  after long periods of storage  after continuous ‘micro-cycling’

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 after long period of charge  at low temperatures Because of this car manufacturers have had to develop a boost charging strategy to prevent the risk of progressive sulfation of the negative plate [4]. A system of monitoring the internal resistance of the battery is in use to check the battery state-of-health. Improvement of the dynamic charge-acceptance (DCA) has become a task for battery development. Fig. 5.8 presents a typical driving profile for a car with combined recuperation and STT. The current and voltage of an L3 VRLA 12 V 70 Ah battery as well as car speed are plotted for a 1.6 L diesel STT engine car over a 30 min driving cycle (cf. Worldwide Harmonized Light-Duty Vehicle Test Cycle; WLTC). During stop phases (engine and alternator off) where loads will be supported by battery only, the battery usage is characterized by a significantly deeper micro-cycling (>1.5% DoD) with more self-heating (due to higher effective [root mean square] current) and a cumulated energy throughput between 35,000 and 56,000 Ah (500e800 Cn for a 70 Ah battery). Advanced EFBs or AGM batteries are necessary to satisfy this target according to the different requirements and strategies developed by car manufacturers.

Discharge at car stop

recuperation Ubat (V)

16 15 14 13 12 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1.4

1.6

1.8

Ibat (A) et Vehicle Speed (Km/h)

100

2 × 106

50 0 -50 0

0.2

0.4

0.6

0.8

1

1.2

150

2 × 106

Speed (Km/h)

100 50 0 0

200

400

600

800

1000

1200

1400

1600

1800

2000

Figure 5.8 Profile of 30 min driving of micro-hybrid car with recuperation and stopestart (STT) function; slope of Ubat and Ibat of L3 AGM battery 12 V 70 Ah; slope of car speed.

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LeadeAcid Batteries for Future Automobiles

Besides improvement of DCA an increase in cycling endurance of batteries during micro-hybrid operation is important.

5.2.6 Battery technology selection for micro-hybrid cars The micro-hybrid application requires batteries with improved high-rate discharge behaviour, increased DCA at PSoC and strongly extended microcycle life with low and constant internal resistance throughout life. Different micro-hybrid strategies require different enhancements of these performance parameters to meet a 5-year battery lifetime goal in every case. To choose the battery technology for a car application, it is necessary to define the expected endurance in micro-cycling, and low and medium DoD cycling according to typical application profiles in a car. Fig. 5.9 presents cycling endurance of different automotive batteries in different DoD cycling. It can be seen that standard SLI battery, AGM battery and EFBs of different layouts have very different cycling abilities, which also change with different DoDs. The graph indicates too that the performance of a certain battery technology (for instance, flooded batteries) can vary widely. The evaluation of the micro-cycling behaviour is most important for choosing the right battery technology. The car manufacturer has to establish from a statistical analysis of typical user profiles which cycling endurance is required. Typical expectations of car manufacturers are

Figure 5.9 Cycling endurance in dependence on depth of discharge for different battery designs (for enhanced flooded battery are given different stages of development).

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LeadeAcid Batteries for Future Automobiles

about 50,000 cycles (or 800 Cn) for an L3 70 Ah battery type. The different standards (SBA, EN) or the car manufacturers’ own tests are used to evaluate the battery in 1.5e2% DoD micro-cycling depending (or not) on the battery size. It is important to note that the micro-cycling endurance is very dependent on charge-acceptance behaviour during the IU [IU-Charge names a charging procedure with constant current charge first up to fixed voltage followed by constant voltage charge (according to German DIN Standard 41772)] charging steps. The higher it is the better able it is to address sulfation issues that can rapidly lead to battery premature failure. For choosing battery size the internal resistance and the DCA behaviour are paramount. EN 50342-6 sets out to create performance classes to make the choice of a suitable battery easier. It is worth noting that although the choice of battery technology (flooded or sealed) contributes to the different performance levels, it is not of itself a criterion of selection. Table 5.3 presents requirement levels for batteries for the micro-hybrid application.

5.2.7 Reliability of batteries in micro-hybrid application Today, battery quality and reliability levels in micro-hybrid cars are such that intrinsic manufacturing defects remain at a level similar to that achieved by the best SLI batteries for conventional cars (<100e500 ppm/24 months in service).

Table 5.3 Performance requirement levels for batteries in micro-hybrid application Test

Level M1

Level M2

Level M3

Normalized mean Rdyn (calculated by dU/dI) increase 1.5 after 8000 cycles End of step voltage U(EOS)300A  9.5 V Ce  50% of Cn after 8000 cycles

EN 50342-6

MHT micro-hybrid test 2% DoD e behaviour test

EN 50342-6

17.5% DoD cycle test

9 units

15 units

18 units

EN 50342-6

50% DoD cycle test

150 cycles

240 cycles

360 cycles

OE specs for batteries ‡ L2 size in general

1.5e2% DoD Shallow microcycling endurance test

>8000 cycles (i.e., 200 Cn on L3 70 Ah) /EFB or high performed SLI (for energy recuperation only without STT)

>30,000 cycles (i.e., 500 Cn on L3 70 Ah) /EFB

>50,000 cycles (i.e., 800 Cn on L3 70 Ah) /advanced EFB; AGM

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Pareto (80/20 rule) analysis indicates that manufacturing defects of microhybrid batteries are dominated by the following failure causes: 

50% damaged or deformed plates

/leading to short-circuit



40% envelope or separator deformation

/leading to short-circuit



5% poor plate-welding

/leading to capacity loss or explosions



<5% poor TTP (transition through partition, realized by intercell welding process)

/leading to open-circuit (brake down)

During the same 24 months in service period, it is more difficult to report a quantitative analysis about the cause of defects during utilization (i.e., plate sulfation, grid corrosion or active-mass shedding/softening). Failure mode status today indicates:    

50% of batteries irreversibly sulfated/deep discharged 30% of batteries early sulfated during the vehicle lifetime <15% of the expected failure modes, overcharge/cycling <1% of thermal runaway

Further analysis after gathering more experience from the field will clarify the picture in the future. First indications, however, do show that micro-hybrid operation changes the failure modes for automotive batteries significantly towards sulfation and premature mass ageing.

5.3 Flooded automotive battery design and production technologies: status and latest improvements Flooded automotive battery design and production technology has to provide batteries with medium life expectation, high reliability and robustness as well as excellent cold crank which can be produced with a minimum of material consumption, weight and costs in very high volumes.

5.3.1 Flooded battery design development In general, design of the flooded automotive (SLI) battery has not been changed over the last 90 years. It is a Fauré pasted flat plate design. The latest development the so-called EFB e in principle uses the same design today. It is important to note that EFB is not a specific design or technology. EFB could be defined as a collection of several different design and process improvements aimed at overcoming the limits of the classic automotive

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flooded battery in order to extend its performance range and make it suitable for micro-hybrid applications. EFB production is the result of process improvements and product design optimization on the basis of a sounder knowledge about the flooded battery and its performance-limiting parameters. A variety of goals have been addressed and a range of solutions and results achieved. Further development of EFB is still in progress. A very big advantage of the similarity in design of the EFB and the SLI batteries is that often the same production machinery can be used with high productivity and output. For this reason, the substantial performance increase of the EFB is not accompanied by an equivalent increase in costs. In this respect, EFB manufacture is very different to AGM battery production. General SLI battery design is illustrated in Fig. 5.10. The battery box contains several cells. Each cell contains a group of plates (plate-block), assembled from alternately stacked positive and negative electrodes (plates) interleaved with separators. The modern separator is designed as a porous plastic pocket which envelopes one of the electrodes and isolates it electrically from those plates of opposite polarity on either side of it. Plates of each polarity are parallel-connected via so-called straps. From cell to cell the straps are welded through the cell wall (intercell welding or TTP) to create a series connection. Cells are filled with dilute sulfuric acid (acid density

Figure 5.10 General design of starter battery.

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between 1.26 kg/L and 1.30 kg/L). The battery box is sealed by a lid which has openings for degassing and may have access for electrolyte replenishment and inspection of cells. Plate electrodes consist of grids formed from lead alloys and active-masses. These masses are inserted into the grids in a pasting process and dried under special conditions to form porous electrodes that are supported by grids which also act as current-collectors. Positive and negative masses are activated in so-called formation processes that produce electrochemically active Pb sponge at the negative and a porous PbO2 structure at the positive plate. Development of SLI battery design and production technology over the years has concentrated on the increase of productivity, the reduction of lead consumption, the increase of endurance (mainly by improving corrosion resistance) and cold crank performance, the reduction of water loss (to reduce maintenance requirements) and the increase of reliability. This has been achieved by:  usage of new materials (plastic box and lids with special designs, new lead alloys, PE separators);  improvement of grid design;  optimization of mass recipes and battery layout (new expanders for negative masses and lower paste density for higher cold crank, change of mass quantities and ratios to overcome premature capacity loss (PCL) effects);  introduction of continuous grid and plate-making technologies;  establishing of automatic battery assembly lines;  introduction of modern cost- and energy-efficient formation.

5.3.2 Development of electrode production technology Driven by market demands, a lot of work in the development of design and production technology has concentrated on grid-making technology. Grid design and methods of production are interconnected. They exercise a very strong influence on productivity, material consumption, corrosion resistance, reliability and electrical performance of battery. Table 5.4 compares different grid production technologies in terms of grid quality and production efficiency. It can be seen from the data presented in Table 5.4 that each technology has pro and cons. Grid production technology influences grain structure and corrosion behaviour as does alloy composition. Traditional book mould casting can supply grids with high corrosion resistance, best current distribution and highest grid/mass contact area and adhesion. Casted grids are produced with low scrap rates, but lowest productivity. Casting technology imposes grid thickness limitations that cause the lead consumption per grid to be higher than for other technologies.

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Table 5.4 Comparison of different grid-making technologies and designs Grid-making technology

Book mould cast Continuous casted

Expanded, rolled strip

Expanded, strip not rolled

Punched

Grid design/ distribution of internal resistance

Wire design/grain structure crosssection

Wire design/grain structure e longitudinal section

Surface/crosssection of wire

Material consumption per wire of same thickness H ¼ 0.9 mm and width B ¼ 0.9; concast B ¼ 1.3 mm

100

133

154

154

154

Surface area per wire of same weight

100

75

55

55

55

Very low (30e38 grids/minute)

High (up to 500 grids/minute)

High (up to 500 grids/minute)

Very high (up to 700 grids/ minute)

High (up to 500 grids/minute)

45e60

40e50

25e45

25e45

35e45

Productivity in production

Possible single grid weights for 110 mm grid height [g]

(Continued)

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Table 5.4 Comparison of different grid-making technologies and designsdcont'd Grid-making technology

Book mould cast Continuous casted

Expanded, rolled strip

Expanded, strip not rolled

Punched

Material efficiency (remelting material, dross generation)

DDDD

DDDDD

DDD

DDD

D

Energy efficiency of production (from melting cycles per piece)

DDDD

DDDDD

DD

DD

D

Corrosion resistance of positive grids

DDDD

D

DDD

DD

DDDDD

Current distribution over grid (achievable with optimal design)

DDDDD

DDDD

DD

DD

DDDDD

Conductivity at grid/mass transfer area

DDDDD

DDDDD

DDD

DDD

DD

Mechanical grid mass adhesion

DDDDD

DDDD

DDD

DDD

DD

Vibration resistance/ mechanical stability

DDDDD

DDD

DD

D

DDD

DD

DD

DDDDD

DDDDD

DD

Failure risk at enveloping and assembly

Continuous grid making increases productivity very strongly and offers the possibility of lowering grid weights dramatically by reduction of grid thicknesses. These technologies mainly require special PbCa alloys. The PbCaalloy composition influences corrosion behaviour, water loss and other performance parameters of the battery. Grid punching causes significant improvement in corrosion resistance and good current distribution over grid height. But the material and energy efficiencies of this process are quite low due to the energy required for remelting and a high drossing rate. Moreover, process driven grid wire design characteristics reduce grid/mass contact area significantly, which increases transfer resistance. This decreases cold crank and high current discharge performance.

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Grids without a frame (expanded metal) have the worst current distribution, a higher tendency to grid growth (short-circuit risk) and a higher failure risk during battery assembly and in the field. On the other hand, expanded metal grids and plates can be produced with the highest speeds and the lowest material consumption. All grids produced from rolled strips have a very fine grain structure and an improved corrosion behaviour, which is important for positive plates. The concast process enables the production of thinner casted grids with a frame (i.e., better current distribution and higher reliability in the assembly process) and a higher grid surface with high speed and best material efficiency. But the grain structure of grids produced by this method does not allow concast grid application for positive grids because of very bad corrosion behaviour. In summary, especially for positive grid production an optimal technology has not been found up to now. Each plate-making technology requires an adjustment of battery layout, materials and other battery production steps to get high quality products. Grid design and plate-making technology are important for the improvement of flooded automotive batteries for microhybrid applications which require low resistance and excellent current distribution over plate height.

5.3.3 Flooded battery performance limits and improvements for the micro-hybrid application As mentioned in Section 5.2 micro-hybrid applications require batteries with substantially improved cycling endurance, significantly higher chargeacceptance, increased high discharge performance and lower internal resistance over whole time of battery life in comparison with SLI batteries. Normally battery designs are optimized according to high discharge performance or good cycling endurance alone. Denser positive masses supply higher cycling endurance, but worse cold crank capacity. Improvement of automotive batteries for micro-hybrid application has to increase both features simultaneously. This requires new mass recipes and changes in battery design. Plate and active-mass surfaces have to be increased as well as conductivity of current-collectors and straps.

5.3.3.1 PSoC cycling and acid stratification During deeper cycling, classic flooded batteries can suffer from premature ageing caused by acid stratification. Earlier efforts to reduce water loss during normal operation (especially the introduction of PbCa alloys) to achieve ‘maintenance-free products’ aggravated this problem.

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distribution of acid density @ IU recharge of conventional PbCa battery after C20-discharge Imax= 23,75A Umax= 16V, Charging time 24h, AD over height of cell and charging time height of measuring point at cell 0%= acid level 100%= cell bottom

1400 1350

acid density [mg/ccm]

1300 0% 15% 20%

1250 1200 end of charge

1150

stratification after 24H IU-charging: ADmax-ADmin=103mg/ccm

30% 40% 50% 60% 70% 80% 90% 100% *70%

1100 1050

*60% U(t)

1000 0

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

time t [h]

Figure 5.11 Acid stratification during IU charging according to EN 50342_1; Imax ¼ 5x C20/20, Umax¼16 V; acid density distribution of height of cell depending on charging time; 0% ¼ top of acid level; 100% ¼ bottom of cell; conventional PbCa battery12 V 72 Ah.

Each charge of a flooded battery with limited voltage (IU-characteristics) after discharge with higher DoD causes a gradient of acid concentration over the plate and cell height. This so-called acid stratification persists if there is not a strong gassing at the end of charge. Fig. 5.11 presents the distribution of acid densities, measured according method descriped at [5], over time and cell height in a cell during IU-charge with maximum voltage 16 V after a discharge with DoD ¼ 100% Cn with I ¼ C20/20 A in a classic PbCa starter battery. The graph shows that during recharge there is a very different acid concentration over the height of the cell with increased density at the bottom of the cell (100% depth-measuring point) and much lower acid density at the upper part of the cell (0% depth-measuring point). Acid concentrations will only be equalized during a gassing phase after the cell is fully charged, and even then equalization will seldom be complete. Under real world conditions the charging voltage of 13.8e14.8 V is much lower than is presented in the example in Fig. 5.11. Thus the tendency to acid stratification without equilibration by gassing is more severe than is implied in the figure. Acid stratification reduces cold crank performance and charge-acceptance significantly. Further, the higher acid concentration which is present after charge at the cell bottom leads to mass sulfation and incomplete charge at the bottom of the cell and reduced capacity during the next discharge. As a result of this asymmetric mass utilization, local sulfation and local deep discharge of electrode areas the battery ages prematurely [6]. These processes are very

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heavily influenced by temperature, discharge current density and depth of discharge [7]. Thus the failure mode of premature ageing caused by acid stratification dominates at lower temperatures (cold climate zones), at lower charging voltages (battery placed in the trunk without properly adjusted charging strategies) and during deeper discharges (i.e., cars with a lot of consumers during the ENGINE OFF mode). To overcome this limitation is essential for the micro-hybrid application because of the increased DoD of cycling in PSoC. Fig. 5.12 presents a comparison of the acid stratification tendency of a classic SLI battery versus that of an advanced EFB during a PSoC cycling test at 27 C with a DoD of 17.5%. The graph shows the EoDV and the acid density at the upper and lower parts of the cell as functions of dependence of cycle number. The example indicates that due to its very low acid stratification tendency the PSoC cycling lifetime of the advanced EFB (right graph) is more than five times higher than that of the SLI battery, which is characterized by a continuously increasing acid stratification (left graph). It is important to note that the general layout of the battery and the plates as well as the composition and consistency of the active-materials all serve to influence the acid stratification tendency of each design. Consequently, the survival of the active-material and electrodes in a particular acid stratification environment also depends on all details of the cell design. Thus the cycling performance of individual battery designs can differ from the example in Fig. 5.12 significantly, e.g., SLI batteries with weaker design can have half the lifetime indicated in Fig. 5.12 or less. Many EFB designs today also may have lower cycling endurance than is presented here. There are different ways to increase PSoC cycling endurance and to prevent premature ageing by acid stratification in EFB batteries:  Increase paste density (a more dense mass is more resistant against deep discharge).  Fix the active-masses more firmly in place by using shims or special separators (to prevent active-mass shedding) [8].  Compress the plate-block of the cell (to prevent active-mass shedding) [9].  Add additives to the masses (to change the charge and discharge behaviour of the active-masses) [6,10].  Use plate designs with improved current distribution (to prevent unequal local charge/discharge) [6].  Use modified cell designs with special electrolyte mixing devices. These are intended to exploit the physical acid movements that occur during car acceleration/deceleration to mix the electrolyte and equalize acid concentrations of the cell during car driving [11,12].

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176 Figure 5.12 Comparison of cycle-life and tendency to acid stratification of classic SLI versus advanced EFB; cycling at 50% SoC with 17.5% DoD at 27 C, charge time limited IU-charge with Umax ¼ 14.4 V; left, starting-lighting-ignition (SLI); right, Enhanced Flooded Battery (EFB).

LeadeAcid Batteries for Future Automobiles

Generally, several design changes are in use together. This strategy is needed, for instance, because improvement of cycling endurance by increasing positive paste density causes a decrease in cold crank performance. So compensation by other design features is necessary. Or, as a second example: physical acid mixing during car driving does not prevent sulfation of the masses during micro-cycling (see below) or during parking of a car with a battery that is still prone to acid stratification. The whole requirement set that must be satisfied differs according to the different micro-hybrid strategies. Consequently, there is no single, universal, EFB battery design. There are many different designs and approaches. On the other hand, it is possible that lessons learned for EFB could also applied to the improvement of SLI batteries.

5.3.3.2 Micro-cycling Batteries in stopestart operation, STT, will be charged and discharged with a variety of quite different current densities:  discharge with I ¼ 5.50 A at T > 0 C  discharge at room temperature with I ¼ 300e500 A for less than 1 s (restart)  recharge with IU characteristics and Imax ¼ 100.150 A at Umax ¼ 14e14.4 V maximum  DoD 1e2%. Acid stratification does not occur under these conditions, but heavy sulfation of plates due to a rapid reduction in charge-acceptance happens. Under certain conditions it is also found that negative lugs corrode and can be damaged (so-called lug thinning is a new failure mode). The application and the ageing processes that result under these conditions are simulated by several micro-cycling tests (SBA S0101 according Japanese standard, microhybrid test MHT according EN 50342-6 and others). Degradation of the negative plate and increase of internal resistance with cycling are typical failure modes during these laboratory tests. Fig. 5.13 presents the difference between the negative plate sulfation of a classic premium SLI battery and that of an advanced EFB during SBA micro-hybrid cycling after the test. During the SBA test the battery was cycled at 27 C in units which consisting of 3600 microcycles, followed by 48 h pause each ( for details of microcycles see Fig. 5.13). Tests had to be terminated when battery voltage at discharge with I ¼ 300 A is lower than 7.2 V. SLI battery failed after 12 units, testing of EFB was stopped after 19 units without battery failure. The analysis presented in Fig. 5.13 indicates that surface sulfation of negative plates is the reason for the lifetime limitation. This sulfation

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Figure 5.13 Sulfation of negative plates during micro-cycling, comparison of PbSO4 e distribution at negative plates of SLI plate versus EFB. One SBA-test unit consists of 3600 cycles with DCH I ¼ 45 A, tDCH ¼ 59 s/DCH I ¼ 300 A, tDCH ¼ 1 s/CHA Imax ¼ 100 A; Umax ¼ 14.0 V; tCHA ¼ 60 s followed by 48 h pause.

causes the lug thinning which was responsible for fail of SLI battery [13]. By changing the current distribution at the negative electrode during microcycling the endurance of the EFB is dramatically improved. Simultaneously there is a change of internal resistance and charge-acceptance of the advanced EFB during micro-cycling, which differs significantly from other designs. Fig. 5.14 compares the micro-cycling behaviour of an advanced EFB with those of a premium quality SLI battery and an AGM battery during an MHT micro-cycling test according EN 50342-6. In general, the internal resistance of batteries during micro-cycling increases. This means that the ability of charge peak absorption decreases and restart behaviour, indicated by the end of discharge voltage at IDCH ¼ 300 A, deteriorates. In contrast to the fast continuous increase of relatively high internal resistance of an SLI battery an AGM battery has a lower resistance and a weaker increase over cycling. The internal resistance of the advanced EFB stays stable at a quite low level e after an initial ramping up. This indicates a good and stable crank performance and a constant high current

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Figure 5.14 Development of EoDV at 300 A and internal resistance of different battery designs LN5 during micro-hybrid test (MHT) according to EN 50342-6 (battery size LN5 according to EN 50342-2); comparison of high quality SLI battery with AGM and advanced EFB (Adapted from MOLL).

peak acceptance over a very wide range of micro-cycling. In this case the EFB can perform better than an AGM battery during micro-cycling. The improvement in micro-cycling performance is mainly a result of the addition of carbons and other ingredients to the negative masses as well as adjusting the recipes and plate-production parameters. Grid design of both electrodes influences behaviour significantly too.

5.3.3.3 Dynamic charge-acceptance For brake energy recuperation an excellent acceptance of power peaks (currant I ¼ 100e200 A; time ¼ some seconds) is required. As discussed in

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Figure 5.15 Dynamic charge-acceptance of different battery designs according to [14], I_recu:recuperation current during test pulses (see [14]); enhanced flooded battery (EFB gen.2) with improved negative masses.

Section 5.2, leadeacid batteries lose this ability during use in certain operation modes. For simulation of this field phenomenon there has been developed a special test method [14] which is now incorporated in new European standard for batteries for micro-hybrid application EN 50342-6. Fig. 5.15 presents the different behaviour of a poor SLI battery, an AGM battery and EFBs of different layouts (generations of development) that have been optimized for DCA. Fig. 5.15 shows that the EFB ‘generation 2’ has significantly higher chargeacceptance than the SLI and AGM batteries during this ‘real world test’. Improvements in DCA of the EFB ‘gen.2’ are a result of a recipe change and the addition of carbons to the negative mass.

5.3.3.4 Additives: the future potential During last 15 years a lot of scientific work has been done to clarify how carbon additives prevent premature sulfation of negative masses during PSoC and high-rate discharge PSoC cycling. There are a lot of studies and models, but no comprehensive theory [13,15]. Nevertheless, a wide variety of carbon additives are in use with quite different goals and a surprising improvement of several different performance features. Additives (not only carbons) are an important design feature of EFBs and an extraordinary improvement of performance has been achieved. But their application has to

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be accommodated in a more extensive range of design and process changes. Additives always change several performance parameters simultaneously. The interdependence of different additives and the general design for different battery performance parameters is complex. But on the other hand it opens a huge potential for further battery improvement. Today this potential is not exploited completely because of the lack of a fundamental understanding of different additive modes of operation. Future development is driven by the need for further improvement in DCA and micro-cycling endurance as well as by the fact that additives that improve these properties often increase water loss at same time. Water loss (gassing) must remain as low as possible to maintain the maintenance-free status of batteries. To get high DCA, excellent micro-cycling behaviour and low water loss seems to be possible by choice and combination of suitable additives and by adjustment of processes. Finally, it should be pointed out that EFB designs can be adapted to typical micro-hybrid operations easier than AGM. This is because the complex internal recombination mechanism at AGM that will be influenced by additives additionally. It can therefore be predicted that the variety of successful mass modifications of AGM batteries will be less than those for EFBs.

5.4 Market trends In contrast to the case of mild- and full-hybrid electric cars ICE vehicles with micro-hybrid operations are the most efficient technical solution for making the first level of reduction in fuel consumption. With an additional cost of about V100e200 (stopestart function) fuel consumption can be reduced by 5e10%. By way of comparison the fuel reduction offered by full-hybrid cars lies in the range 25e35% with additional costs between V2200 and V3200 per car at best [16] and up to V4500e5500 in extended versions. Additionally, cars using micro-hybrid strategies can be introduced into the market very fast because there is no need for extended development and general change in car concept. Since the forecast for world new car sales in 2015 is about 76.4 million units (compare: sales of electric cars in 2014 was 304,000 vehicles; mild- and fullhybrids less than 2 million pieces worldwide in 2014) and respecting that growth rate of world vehicle production is estimated at 2.6%/year [17] it is evident that the introduction of micro-hybrid functions to ICE vehicles will provide the biggest contribution to CO2 emissions reduction. 7.6 million of the 21 million cars sold in 2012 in Europe had the stopestart function already. The forecast for the European market suggests a market share for stopestart of 66% in 2016 and of 100% in 2019. Very different is the

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current situation in the United States where in 2014 only 6% of new cars sold were equipped with stopestart [16]. Modifications of technical solutions have to be introduced in order to get a higher customer acceptance there (for example: no switching off of air-conditioning during stop). These modifications are on the way as are solutions to extend the stopestart function [18]. The market in Japan is also different: The high market share of 20% of sales in 2014 for full-hybrids may be at least partially attributable to customer subsidies. The biggest market, China, is also undergoing change. 50,000,000 45,000,000

world

40,000,000

Units

35,000,000 30,000,000 25,000,000 20,000,000 15,000,000 10,000,000 5,000,000 0 EFB units

2012 2013 2014 2015 AGM units supercapacitor units

2016 2017 Li-ion mild units

2018 Li-ion micro units

25,000,000

EU

15,000,000 Units

Units

20,000,000

10,000,000 5,000,000 0

2012

2013

EFB units

2014

AGM units

Li-ion mild units

2015

2016

2017

2018

supercapacitor units

6,000,000

Li-ion micro units

2013

2014

2015

AGM units

2016

2017

2018

supercapacitor units

Li-ion micro units

6,000,000

US

5,000,000 4,000,000 Units

Units

2012

Li-ion mild units

5,000,000 4,000,000 3,000,000

3,000,000

Japan

2,000,000

2,000,000

1,000,000

1,000,000 0

China

EFB units

8,000,000 7,000,000

9,000,000 8,000,000 7,000,000 6,000,000 5,000,000 4,000,000 3,000,000 2,000,000 1,000,000 0

2012

2013

EFB units Li-ion mild units

2014

AGM units

2015

2016

2017

2018

supercapacitor units

Li-ion micro units

0

2012

2013

2014

EFB units Li-ion mild units

2015

AGM units

2016

2017

2018

supercapacitor units

Li-ion micro units

Figure 5.16 Market trend for use of storage devices at mild and micro-hybrid application according to Lux Research, Inc. [19].

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Additionally there are a lot of developments aimed at introducing 48-V board net solutions to increase fuel economy via e-boosting and more efficient recuperation at moderate extra costs (estimated at 25e50% of fullhybrid extra costs) [16]. This could influence the market beyond 2020. Fig. 5.16 reports a market trend forecast for storage devices up to 2018 for mild and micro-hybrid applications worldwide and at biggest regional markets according to Lux Research, Inc. [19]. Fig. 5.16 shows the tremendous growth of the market for storage devices in the micro-hybrid application as well the different battery technologies that will dominate in different regional markets. Due to technical advantages like higher temperature resistance and better micro-cycling behaviour of most developed EFBs and due to lower costs as well as the possibility to use existing production technologies EFBs will gain a strong and increasing share of the market.

Abbreviations, acronyms and initialisms AGM Absorptive glass-mat BCI Battery council international BMS Battery monitoring system CCA Cold-cranking amps (current) CHA Charge DCA Dynamic charge-acceptance DCH Discharge DoD Depth-of-discharge EEM Electric energy management EFB Enhanced flooded battery EN European Standard GB/T Chinese voluntary national standards IEC International electrotechnical commission ICE Internal combustion engine IU European term used to describe a method of constant-currenteconstant-voltage charging JIS Japanese Industrial Standards MHT Micro-hybrid test OCV Open-circuit voltage OEM Original equipment manufacturer PCL Premature capacity loss PSoC Partial state-of-charge SLI Starting-lighting-ignition SoC State-of-charge STT Stopestart TTP Through-the-partition VRLA Valve-regulated lead-acid WLTC Worldwide Harmonized Light-Duty Vehicle Test Cycle

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LeadeAcid Batteries for Future Automobiles

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