Abstract:A novel electrical circuit analogy is proposed modelling electrochemical systems under realistic automotive operation conditions. The model is developed for a lithium ion battery and is based on a pseudo 2D electrochemical model. Although cast in the framework familiar to application engineers, the model is essentially an electrochemical battery model: all variables have a direct physical interpretation and there is direct access to all states of the cell via the model variables (concentrations, potentials) for monitoring and control systems design. This is the first Equivalent Circuit Network -type model that tracks directly the evolution of species inside the cell. It accounts for complex electrochemical phenomena that are usually omitted in online battery performance predictors such as variable double layer capacitance, the full current-overpotential relation and overpotentials due to mass transport limitations. The coupled electrochemical and thermal model accounts for capacity fade via a loss in active species and for power fade via an increase in resistive solid electrolyte passivation layers at both electrodes. The model's capability to simulate cell behaviour under dynamic events is validated against test procedures, such as standard battery testing load cycles for current rates up to 20 C, as well as realistic automotive drive cycle loads.

Thermal gradients arising inside a battery pack for automotive applications are calculated for 200 A discharge via a multiparticle thermal-electrochemical coupled high fidelity model for a 12P7S 4.8 Ah cell pack. The effect of such gradients at the cell level are studied in a first approximation under a corresponding discharge at 15 A, by discretising the cell into units at fixed temperatures throughout the discharge. The immediate time evolution of load distribution through the various parts of the cell shows a complex behaviour, dependent on parameters such as temperatures, state of charge and load characteristics.

One of the biggest causes of degradation in lithium-ion batteries is elevated temperature. In electric vehicle, particularly hybrid vehicle applications this can be very difficult to manage, and without fundamentally redesigning the cell is the province of the battery pack engineer. Yet how battery pack design affects both cell performance and degradation has been very poorly studied in the past. The latest work of the electrochemical science & engineering group at Imperial College London on understanding how thermal gradients affect performance and degradation, and how thermal techniques can be used to detect and diagnose path dependent degradation will be presented. State-of-the-art models that can reproduce the diagnostic outputs and  can be embedded in battery management systems and could therefore be used for diagnostic and even prognostic purposes in real world battery packs will also be presented. Recent work exploring the effect of cell surface cooling and cell tab cooling is shown, reproducing two typical cooling systems that are used in real-world battery packs. It is shown that cooling method alone can significantly affect useable capacity. For new cells at C/20 discharge, very little difference in capacity was seen, however, at 6C discharge surface cooling led to a loss of useable capacity of 9.2% compared to 1.2% for cell tab cooling. Furthermore, after cycling the cells for a 1,000 times at 6C discharge and 2C charge, surface cooling resulted in a degradation rate three times higher than cell tab cooling. Using incremental capacity analysis, electrochemical impedance analysis and thermal models of cells, it is shown that this is due to thermal gradients being perpendicular to the layers for surface cooling leading to higher local currents and faster degradation, but in-plane with the layers for tab cooling leading to more homogenous behaviour. Aged cells were put with new cells in a parallel pack configuration with cooling where measuring the current flowing through each individual cell is often impractical. Using a novel diagnostic method based on simple cell surface temperature measurements developed by our group, a diagnosis method capable of quantitatively determining the state-of-health of individual cells simultaneously during both charge and discharge by only using temperature and voltage readings, and whilst cells are being thermally managed, will be shown. Our latest models account for complex electrochemical phenomena that are usually omitted in battery models such as variable double layer capacitance, the full current-overpotential relation and overpotentials due to mass transport limitations in the double layer. The coupled electrochemical and thermal model accounts for capacity fade via a loss in active species and for power fade via an increase in resistive solid electrolyte passivation layers at both electrodes. The model's capability to simulate cell behaviour under dynamic events is validated against test procedures, such as standard battery testing load cycles for current rates up to 20 C, as well as realistic automotive drive cycle loads, and ageing up to 1,000 cycles including reproducing incremental capacity analysis results. References: Module design and fault diagnosis in electric vehicle batteries, Journal of Power Sources, Vol:206, 2012, Pages:383-392 The effect of thermal gradients on the performance of battery packs in automotive applications, Journal of Power Sources, Vol:243, 2013, Pages:544-554 The effect of thermal gradients on the performance of lithium-ion batteries, Journal of Power Sources, Vol:247, 2014, Pages:1018-1025 Differential thermal voltammetry for tracking of degradation in lithium-ion batteries, Journal of Power Sources, Vol:273, 2015, Pages:495-501 Novel application of differential thermal voltammetry as an in-depth state-of-health diagnosis method for lithium-ion batteries, Journal of Power Sources, Accepted 23rdDecember 2015

This paper presents the energy consumption results from the 2012 RAC Future Car Challenge. It discusses measurement techniques for the different types of powertrain and draws conclusions about their applicability to different vehicle segments. The energy consumption of a plug-in hybrid vehicle is analysed in detail to illustrate separately electric versus fuel energy consumption. The ChallengeThe RAC Future Car Challenge (FCC) is a motoring event promoted by the Royal Automobile Club in which the challenge for participants and their vehicles is to consume the least energy possible over a 63-mile route from Brighton to London. The event is open to internal-combustion engine (sub-110 gCO 2 /km), hybrid, range-extended/plug-in hybrid and pure-electric vehicles. These are grouped by 'Euro Car Segment' (mini, small, medium, large, executive, luxury, sport, multi-purpose and sports-utility) and type of build (prototype or series production) for the awards. This paper analyses the energy consumption results from the 2012 FCC -the third Challenge. The most significant change in the 2012 FCC compared to the two previous events (in 2010 and 2011) was the inclusion of motorway driving. The aim of this was to make the FCC drive cycle reflect realworld driving conditions as closely as possible.The paper will first briefly outline the methodology employed (Section 2) and illustrate the drive cycle in terms of speed and distance (Section 3). Section 4 then provides the energy consumption results for all the vehicles that were measured. In order to make like-for-like comparisons, the results are analysed in terms of fuel/propulsion type, vehicle class and weight. Data collected from previous FCCs (2010 and 2011) as well as from the 2012 FCC is used to examine energy consumption trends over time.Section 5 discusses the energy measurement methods and energy consumption results of a prototype plug-in hybrid vehicle, of which three were entered in the Challenge. This allows for a discussion of energy management optimisation and driver impact on vehicle performance under different conditions. Finally, Section 6 draws conclusions. MethodologyAs in previous years, vehicles with different types of powertrain, fuelled by various energy sources and emitting no more than 110 g/km CO 2 , participated in the 2012 FCC.The 'transition' from conventional internal-combustion engine (ICE) powertrains to pure electric vehicle (EV) configurations is illustrated in Figure 1, with Table 1 listing the adapted FCC categorisation. Essentially, three combinations are possible (see Figure 1, from left to right):(1) the vehicle runs solely on liquid fuel; (2) the vehicle runs on a combination of electric energy and liquid fuel; or (3) the vehicle runs solely on electric energy. The allowed time frame to complete the route was set to a minimum of 2h15min and a maximum of 3h. (further details in the Rules and Regulations [1]) Figure 1 -Vehicle classification by drivetrain configuration

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