Eckhard Karden Advanced Power Supply and Energy Management Ford Research & Advanced Engineering Europe.

Transcription

1 How Harmful Are Carbons in Enhanced Flooded Batteries for High Temperature Use Cases? R&D Symposium on Lead-Based Batteries, 7th Advanced Automotive Battery Conference Europe 31 January 2017, Mainz, Germany Eckhard Karden Advanced Power Supply and Energy Management Ford Research & Advanced Engineering Europe

2 CONTENT Challenges for automotive lead acid batteries Why carbon? Risks and side effects Gassing Tests: standards versus drive cycles Recommendations for high temperature durability tests Recommendations for additive screening & research Summary & Outlook 2 31 Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

3 CHALLENGES FOR AUTOMOTIVE LEAD ACID BATTERIES Dynamic charge acceptance (DCA) brake energy recuperation in micro-hybrids: fuel economy, CO 2 emissions Shallow cycling at partial state-of-charge (PSOC) increasing charge throughput (comfort loads, stop/start) absorbent glass mat (AGM) and enhanced flooded batteries (EFB) have achieved very good robustness against cyclic wear and early sulphation failure SOC recovery may, however, get very slow during battery life (lazy battery: AGM and EFB) Weight Lithium-ion technology offers significant weight savings, at (currently) technical shortfalls and (permanently) higher cost Lead acid technology still has attractive advantages low cost materials mature technology & processes safe, robust (e.g C), simple to manage low self-discharge efficient recycling established OEM-grade pack weights as shown do not include battery sensors (lead acid), thermal management (lithium-ion), etc.?? 3 31 Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

4 courtesy of Sielemann, AABC Europe 2015 WHY CARBON? Novel additives, particularly for the negative electrode, often: various modifications & particle structures of carbon achieve various benefits that are all linked to charging kinetics: +C Dynamic charge acceptance (DCA) time scale: 2 s s recuperation: 2.5 to 3 fold improvement demonstrated in lab and on road Shallow cycling / PSOC time scale: 2 min... 1 h 17.5% DoD cycling: EFB meet AGM cycle life targets at lower cost weight reduction opportunity for moderate cycling requirements! lazy battery time scale: 3 months... 3 years faster recovery after quiescent drain and rest periods cycle life 17.5% DoD 27 C Different benefits have been demonstrated with different additive combinations (not one magic black powder so far). significantly improved by advanced carbon additives 4 31 Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

5 weight loss / (g/ah) RISKS AND SIDE EFFECTS OF CARBONS Many carbons have been rejected by OEMs so far because they accelerate gassing and water consumption in established tests: NA gassing: collect gas for 30 after 20h overcharging C EU water consumption: weight loss weeks overcharging C SAE J2801: shallow low-throughput cycling with 108 h/w charging C Early field evidence does not confirm high water consumption: high-volume stop/start programs in Japan and India taxi fleet tests (Exide: Las Vegas, Furukawa: Bangkok) Most suppliers (of batteries and carbons) study extensively water loss during steady-state overcharge as critical constraint for additive selection and specification: loading wt%, impurity levels in interaction with other additives (e.g. expanders). At the same time, EU/NA OEMs call for further reduction in steady-state water consumption to improve hot-climate durability (warranty). How meaningful is steady-state overcharging as a test condition to determine water consumption under hot-climate field conditions? Las Vegas taxi fleet Exide Group Size 96R SLI EFB EFB+C type1 EFB+C type2 typical performance BCI 96R: k mi service life / miles 5 31 Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

6 vol % flow ml/min U / V GASSING TEST EXPERIMENT: STANDARDS VERSUS DRIVE CYCLES We recorded in-situ gas flow and H 2, O 2 concentrations for 13 state-of-the-art EFB (with and without novel additives: ±C) with an electronic gas analysis system (egas) during continuous overcharging (EN ) and during a simulated aggressive drive cycle (HO2) with 3.5h charging at 75 C per working day and 3.5 C n discharge throughput per week details: see next presentation from D.U. Sauer H 2 water consumptions (WC) during steady-state overcharging vs. dynamic microcycles in simulated hot field operation O 2 WC per charging time is always much higher despite T-adjusted voltage (explanations include: transient unsymmetric polarizations, spatial current distribution, self-discharge) Correlation of WC during steady-state overcharging with WC during microcycling is weak for all EFB±C EFB+C: often 3x higher WC(EN), but only % higher WC(HO2) 3 g/ah spec. limit (a) SLI (b) EFB (c) EFB+C (d) AGM (a) SLI (b) EFB (c) EFB+C (d) AGM gas flow rate per species vs. electric charge balance gassing reactions + grid corrosion account for only about half of the parasitic current integral for all EFB±C most likely explanation: oxygen recombination cycle 6 31 Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

7 RECOMMENDATIONS FOR HIGH TEMPERATURE DURABILITY TESTS Verify our results with other hot-climate vehicle usage scenarios other reference use cases simulated in laboratory (4 8 weeks are enough to establish robust WC trend) vehicle fleets, e.g. taxi (measure weight or electrolyte levels several times during service life) Harmonize test methods (not necessarily pass requirements) globally between standardization regions (EN / SAE / JIS /...) with OEM battery specifications Current / A Temp1 Assumptions for 90%ile hot-climate customer usage profile HO2 = Hot Overcharge version2 ambient 75/30 C day/night cycle 5 days 4 h/d trips (5 3.5h charging) per week high discharge throughput (3.5 C n per week) temperature-adjusted charging voltage V non-accelerated test: quiescent loads, self-discharge Voltage / V F , TS000008, HO60a70a Is it possible to create one unified high-temperature key life test? agree upon weights of overcharge, cycling, stand-time parameters like temperature and voltage should accelerate test but not introduce artefacts cover water consumption, grid corrosion, degradation of separator and expander,... Charge / Ah Time / d CENELEC TC21X WG3 provides a forum for coordinated test development and validation Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

8 H 2 : C log. charging current / (ma/ah) O 2 : C RECOMMENDATIONS FOR DEVELOPMENT OF EFB WITH HIGH DCA (EFB+C) Mechanisms of parasitic reactions in EFB must be understood: Gas flow and weight loss do not match with electric charge balance. Oxygen recombination cycle is hardly negligible in state-of-the-art EFB. Can, and should, cell design aid or hinder oxygen transport? O 2 charging voltage (e.g. 2.4 V/cell) O2 Parasitic reactions in EFB should be studied using direct continuous gas measurements, rather than weight loss alone hydrogen evolution oxygen evolution egas can be minimized in size, even for in-vehicle measurements. Test cells and single plate tests are needed after our battery-level tests, for example varying geometry parameters of diffusion-limiting current, or for example studying interactions during self-discharge [Rüetschi 1958] neg. polarization / mv OCV 2.14V grid corrosion pos. polarization / mv Additive screening & research must utilize application-relevant test methods. Lack of correlation has been found for DCA as measured by single pulses after discharge into PSOC, and WC as measured by steady-state overcharging. Battery and material suppliers have to quickly establish co-operative work streams like definition of best practices for material screening. from cabinet to portable device %H 2 %O 2 courtesy of Hosaka (Hitachi Chemical), Eberbach Workshop Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?:

9 SUMMARY & OUTLOOK Battery requirements in 12 V power supply and microhybrid applications are evolving quickly, enabling CO2 emissions reduction, as well as new electric functions (autonomous driving). To defend a leading position in automotive low-volt battery applications, the lead acid battery industry need to quickly establish collaboration with the car industry, to develop test methods for new applications and technologies within their industry, to develop and demonstrate next generation EFB or AGM with minimal weight at uncompromised user-level performance substantially increased DCA in sustained PSOC operation uncompromised high temperature durability under field conditions the cost, maturity, robustness, safety, and recycling advantages maintained New findings about parasitic reactions in EFB open doors for joint development of globally harmonized high-temperature battery durability tests coordinated research toward a better understanding of risks and side effects of carbon (and other novel lead acid battery materials) Expected shares for Europe, North America, and China combined car markets (reprinted from [1], using data from [2]). [1] H. Budde-Meiwes, Dynamic Charge Acceptance of Lead-Acid Batteries for Micro-Hybrid Automotive Applications, Aachen, 2016 [2] C. Rosenkranz, D. Weber, J. Albers, in: AABC Europe, Mainz Jan 2017 How Harmful Are Carbons in EFB for High Temperature Use Cases?: