Battery system

Abstract

A method of controlling battery temperature in a system comprising a battery 22, a power controller 21, a first heat exchanger 24 in thermal communication with the controller, a second heat exchanger

Description

Field of the Invention The present invention relates to a battery system, a method of controlling battery temperature in a battery system and a use of the battery system for controlling the temperature of a battery at a temperature suitable for discharging or charging the battery. Background Lithium-ion batteries are generally designed for optimal operation in temperatures between 20°C and 45°C due to limitations of the materials used for positive and negative electrodes. If lithium-ion batteries operate beyond this range, their performance is limited. This may take the form of reduced energy, power, and cycle life. If fast charging mechanisms are used for a battery cell below the optimal temperature, it may cause damage to the lifetime capacity of the cell. This is especially problematic in applications such as electric vehicles, which are frequently operated in cold temperatures, or for high-rate batteries which may have a narrower optimal operating temperature window. According to research carried out by the American Automobile Association (AAA, 2019), an ambient temperature of-7°C results in a 12% decrease in average EV range, indicating a reduction in effective battery capacity, and an 8% decrease in average equivalent fuel economy, compared to tests on the same range of vehicles at 24°C. There is therefore a need for battery systems which can efficiently control battery temperature within its optimal range. Summary of the Invention At its most general, the present invention provides a method of controlling battery temperature, by transferring thermal energy from the power controller used to discharge / charge the battery, to the battery. Generally, the present invention relates to a method of controlling battery temperature in a battery system, the battery system comprising a battery and power controller, the method comprising transferring thermal energy from the power controller to the battery. Power controllers are electrical system used to control and condition power discharged from a battery or used to charge a battery. Power controllers include inverters, power converters, buck and boost circuits. Power controllers may also be known as power electronics. In operation, the power controllers of a system produce heat due to inevitable inefficiencies such as resistance within the components. This means that they require a cooling system, conventionally a fan which blows air across the components. The heat generated by the power controller is commonly wasted. In a first aspect of the invention there is provided a method of controlling battery temperature in a battery system, the battery system comprising: a battery, a power controller for controlling and / or conditioning power charged or discharged from the battery, a first heat exchanger in thermal communication with the power controller, and a second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication; the method comprising: transferring thermal energy from the power controller to the first heat exchanger, transferring thermal energy from the first heat exchanger to the second heat exchanger, and transferring thermal energy from the second heat exchanger to the battery. In some embodiments, the battery system further comprises a temperature controller, and the method further comprises: adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger using the temperature controller, to control the battery temperature. In some embodiments, the battery system further comprises a third heat exchanger in thermal communication with the first and / or second heat exchangers, and the method further comprises: transferring thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, wherein transferring thermal energy to the third heat exchanger is simultaneous and / or sequential with transferring thermal energy from the first heat exchanger to the second heat exchanger. In a second aspect, there is provided a battery system for controlling battery temperature, the battery system comprising: a battery, a power controller for controlling and / or conditioning power charged or discharged from the battery, a first heat exchanger in thermal communication with the power controller, and a second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication and the battery system is configured to transfer thermal energy from the first heat exchanger to the second heat exchanger. ln a third aspect, there is provided a use of the battery system of the second aspect for controlling the temperature of a battery at a temperature of 12 °C or more, preferably 20 °C or more, more preferably from 25 to 45 °C, yet more preferably from 30 to 40 °C. In another aspect there is provided a use of the battery system of the second aspect in a mobile charging device, a static charging device, or an electric vehicle. The present invention includes a power controller which controls / conditions power which is discharged from the battery, and excess heat from the power controller is used to heat the battery. The power controller may be heated as a result of charging or discharging the battery. Alternatively, the power controller may have been heated using power from an external power source (e.g., a charger, to which the battery system is attached). Heating using power from an external power source may be known as pre-heating. A battery typically has an optimal temperature range, which is the temperature range at which the battery performs most efficiently. Outside of this optimal range, the battery performance is limited. The optimal temperature range may be the temperature range at which the battery has its highest specific capacity, its lowest internal resistance, or its highest coulomb efficiency. The optimal temperature range may also be the temperature range at which the battery has its best long term capacity retention, such as long term capacity retention at high charge rate. For example, the optimal temperature range may be the temperature range over which the battery has over 90% of its peak capacity. Preferably, the optimal temperature range is the temperature range over which the battery has over 90% of its peak capacity at a C-rate of 10C or more, such as 20C or more. The optimal temperature range may be the temperature range over which the battery has a capacity retention of at least 80% at 5C maintained over at least 1,000 cycles. Preferably, the optimal temperature range may be the temperature range over which the battery has a capacity retention of at least 80% at 10C maintained over at least 1,000 cycles. The optimal battery temperature range may be 12 °C or more, preferably 20 °C or more, yet more preferably from 25 to 50 °C, even more preferably from 30 to 45 °C. Where two or more batteries are present, the optimal battery temperature range of the two batteries may be the same or different. The optimal temperature range is often different to the ambient temperature, so the battery is not normally within the optimal temperature range when the battery system is not in use. Therefore, the temperature of the battery needs to be controlled to bring it inside the optimal temperature range. Although the battery may heat itself during charging or discharging, this ‘internal’ heating is inefficient. The internal heating requires a large amount of the batteries stored energy to produce heat, so the battery capacity is depleted more quickly, and the usable capacity of the battery is deceased. This internal heating is also slow, so requires discharging or charging of the battery for a prolonged period at non-optimal temperatures. This may reduce the long term performance of the battery. Standalone heaters may also be used to heat the battery. However, a standalone heater requires additional components to be included in the battery system, which may only be used for a small portion of the batteries lifetime. This increase the bill of materials and complexity of the battery system. The standalone heater also needs to be powered by an external power source or by the battery itself. The present invention uses the thermal energy generated by the power controller to control the temperature of the battery. The battery is charged or discharged using the power controller, and thermal energy from the power controller generated during charging or discharging is transferred to the battery. As a result, the battery is able to be heated to its optimal temperature without the need for a separate battery heater, and without relying on only internal heating of the battery. Accordingly, the battery system allows the battery to reach its optimal temperature more quickly, minimising the time the battery is cycled at non-optimal temperatures. This is also achieved without secondary heater components, by repurposing the heat released from the power controller components used to control charge / discharge of the battery itself. The system may include a thermally conductive interface between the heat transfer fluid and the power controller. Power controller includes a switching device, such as a transistor, (e.g., a metal-oxide-semiconductor field-effect transistor (MOSFET)). Preferably, the thermally conductive interface is adjacent to the switching device, such as a MOSFET. Summary of the Figures The present invention is described with reference to the figures listed below. Figure 1 shows a block diagram of a known system. The dashed lines indicate signalling connections, solid lines indicate the flow of coolant, and lines with alternating dashes and dots indicate electrical power flow. Figure 2a shows a block diagram of a system according to an example embodiment of the invention, during discharge of the battery. The dashed lines indicate signalling connections, solid bold lines indicate the flow of coolant, and lines with alternating dashes and dots indicate electrical power flow. Figure 2b shows a block diagram of the system according an example embodiment of the invention, during charging of the battery. The dashed lines indicate signalling connections, solid bold lines indicate the flow of coolant, and lines with alternating dashes and dots indicate electrical power flow. Figure 3 shows a simplified block diagram of the switch component used in the example embodiment of the invention illustrated in Figures 2a and 2b. The dashed lines indicate signalling connections and solid bold lines indicate the flow of coolant. Figure 4 shows a flowchart of an example process used in an example embodiment of the invention, to determine the control of the switch component illustrated in Figure 3. Detailed Description of the Invention The present invention provides a method and system for controlling battery temperature, the battery system comprising a battery and a power controller for controlling charge and / or discharge of the battery, and the method comprising transferring thermal energy from the power controller to the battery. This invention allows waste heat from the power controller to be used to raise the temperature of the battery if this is below the optimal operating temperature, without requiring any additional discharge of the battery to generate heat; because the system uses heat from the power controller that would otherwise have been waste, the power requirements to operate the power controller do not change. This improves the efficiency of the battery discharge and reduces the size and weight of the system since no additional components such as a dedicated heating element or resistor are required for heat generation. The system and method of this invention also warms the battery more efficiently than conventional methods. For example, a conventional warming method for a battery in an electric vehicle (EV) uses the heating, ventilation, and air conditioning (HVAC) system of the vehicle to warm the battery, or may use the motor and drivetrain to warm the battery. For example, US11130384 describes a heating and cooling system that recycles heat from the drive train of an EV as part of the heater for the cabin of the vehicle. US11325445 discloses a similar mechanism which uses waste heat from the drive train of an EV to warm the passenger compartment. However, these systems do not use waste heat from the power controller to warm the batteries. US20220216535 and JP2021128821 disclose the use of a dedicated component to generate heat for warming a battery, in both cases a motor, but do not describe using a power controller to provide heat to a battery. These previous approaches requires additional energy and are slow to heat up the battery. Thus, during heating power is passed through the power controller and the heat they produce is wasted. The method of the invention begins to use the generated heat immediately, while conventional mechanisms that use heat from a load, such as the HVAC system described above or the systems described below which use the drivetrain of an electric vehicle, require time for the heat to be generated. This minimises the time the battery is operating at non-optimal temperatures (and thus reduced efficiency) and therefore minimises the chance of permanent damage to the battery while increasing the power transfer and speed of charge and discharge of the system as a whole. If the configuration of the control software of the power controller allows, the power controller may be designed with a dedicated warming mode during charging which warms the power controller and therefore the coolant in the heat sink without beginning a full charging session. This allows the battery to be pre-heated prior to charging beginning, meaning that the battery will be at the optimum temperature. During charging, the power controller would continue to produce waste heat as usual, as previously described. Conventionally, this would require an additional large resistor, but in a system according to the invention no additional components are required. A similar method could be used during discharging to raise the battery to an optimal temperature with a minimal initial current draw from the battery. The system could be used in any battery-powered device, but is especially beneficial in situations where the battery may be subject to low temperatures, such as devices used outside. It could be especially beneficial to electric vehicles (EVs) or a grid scale storage battery, since these are commonly used and stored outside and users commonly wish to charge them rapidly; warming the battery to an optimum temperature will improve the safety and efficiency of rapid charging battery systems. Battery System Generally, the present invention relates to a battery system comprising a first heat exchanger in thermal communication with the power controller and a second heat exchanger in thermal communication with the battery, wherein the first and second heat exchangers are in thermal communication and the battery system is configured to transfer thermal energy from the first heat exchanger to the second heat exchanger. In an aspect of the invention, there is provided a battery system for controlling battery temperature, the battery system comprising: a battery, a power controller for controlling and / or conditioning power charged or discharged from the battery, a first heat exchanger in thermal communication with the power controller, and a second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication and the battery system is configured to transfer thermal energy from the first heat exchanger to the second heat exchanger. The battery system is for use in a method of controlling battery temperature, as described below. The description of the method is also applicable to the battery system. Battery The battery system comprises a battery. The battery is generally connectable to a load or a source of power. The battery is typically connectable to the load / source by a power connector. The battery may be separably connected to the load or source of power, by a separable connection. The battery is typically in electrical communication with the power controller, such that the power controller can control and / or condition power charged or discharged from the battery. The electrical communication may be a signalling connection and / or a power transfer connection. The battery system may comprise two or more batteries. The two or more batteries may be the same or different. The battery may comprise one or more cells, which may have the same or different chemical properties. The battery may also comprise any other electrical storage device which would benefit from being warmed to an optimum temperature. A battery typically has an optimal temperature range, which is the temperature range at which the battery performs most efficiently. Outside of this optimal range, the battery performance is limited. The optimal temperature range may be the temperature range at which the battery has its highest specific capacity, its lowest internal resistance, or its highest coulomb efficiency. The optimal temperature range may also be the temperature range at which the battery has the best long term capacity retention, such as long term capacity retention at high charge rate. For example, the optimal temperature range may be the temperature range over which the battery has over 90% of its peak capacity. Preferably, the optimal temperature range is the temperature range over which the battery has over 90% of its peak capacity at a C-rate of 10C or more, such as 20C or more. The optimal temperature range may be the temperature range over which the battery has a capacity retention of at least 80% at 5C maintained over at least 1,000 cycles. Preferably, the optimal temperature range may be the temperature range over which the battery has a capacity retention of at least 80% at 10C maintained over at least 1,000 cycles. The optimal battery temperature range may be 12 °C or more, preferably 20 °C or more, yet more preferably from 25 to 45 °C, even more preferably from 30 to 40 °C. Where two or more batteries are present, the optimal battery temperature range of the two batteries may be the same or different. The optimal temperature range is often different to the ambient temperature, so the battery is not normally within the optimal temperature range. Therefore, the temperature of the battery needs to be controlled to bring it inside the optimal temperature range. Although the battery may heat itself during charging or discharging, but this ‘internal’ heating is inefficient. The internal heating requires a large amount of the batteries stored energy to produce heat, so the battery capacity is depleted more quickly, and the usable capacity of the battery is deceased. This internal heating is also slow, so requires discharging or charging of the battery for a prolonged period at non-optimal temperatures. This may reduce the long term performance of the battery. Standalone heaters may also be used to heat the battery. However, a standalone heater requires additional components to be included in the battery system, which may only be used for a small portion of the batteries lifetime. This increase the bill of materials and complexity of the battery system. The standalone heater also needs to be powered by an external power source or by the battery itself. The present invention uses the thermal energy generated by the power controller to control the temperature of the battery. The battery is charged or discharged using the power controller, and thermal energy from the power controller generated during charging or discharging is transferred to the battery. As a result, the battery is able to be heated to its optimal temperature without the need for a separate battery heater, and without relying on only internal heating of the battery. As a result, the battery can be controlled at its optimal operating temperature quickly and efficiently. The thermal energy may be provided to any component of the battery, such as the working electrode, counter electrode, or electrolyte. Preferably thermal energy is transferred to the working electrode of the battery. Thermal energy is transferred to the battery using the heat exchangers. The battery is in thermal communication with the second heat exchanger. The battery is typically in communication with the power controller, such that the power controller controls and / or conditions power charged or discharged from the battery. In some embodiments, the battery is in communication with the temperature controller, such that the temperature controller can control the temperature of the battery. The battery of the battery system is a battery comprising an electrochemical cell. The electrochemical cell typically has a working electrode active material comprising a metal oxide, preferably a niobium oxide or a niobium metal oxide. Alternatively, the electrochemical cell may have a working electrode active material comprising particles of graphite, silicon, SiOx (where x is from 0 to 2), or LTO. The working electrode may be an anode or cathode during a discharge step. Typically, the working electrode is the anode during a discharge step. The electrochemical cell typically further comprises a counter electrode and an electrolyte. The electrochemical cell may also comprise a separator and a current collector. The counter electrode may be an anode or cathode during a discharge step. The counter electrode is typically the cathode during a discharge step. The electrochemical cell may be a lithium-ion cell. Where there is a plurality of cells, these may be provided in series or parallel, or a mixture of cells in series and in parallel. The battery may comprise any number of cells and may be made up of one or more subbatteries. The battery may be a modular system such that sub-batteries are replaceable. The electrochemical cell may have a capacity retention of at least 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% at 10C maintained over at least 50, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,200, 1,500, 1,800, or 2,000 cycles. The electrochemical cell may have a capacity retention of at least 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% at 20C maintained over at least 50, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,200, 1,500, 1,800, or 2,000 cycles. In some embodiments, the maximum operable discharge rate is 3C or more, where the capacity retention is at least 70% over 1,000 cycles, preferably 5 C or more, where the capacity retention is at least 70% over 1,000 cycles, more preferably 10 C or more where the capacity retention is at least 70% over 1,000 cycles. In some embodiments, the maximum operable discharge rate is 3C or more, where the capacity retention is at least 80% over 1,000 cycles, preferably 5 C or more, where the capacity retention is at least 80% over 1,000 cycles, more preferably 10 C or more where the capacity retention is at least 80% over 1,000 cycles. In some embodiments, the maximum operable discharge rate is 3C or more, where the capacity retention is at least 90% over 1,000 cycles, preferably 5 C or more, where the capacity retention is at least 90% over 1,000 cycles, more preferably 10 C or more where the capacity retention is at least 90% over 1,000 cycles. The electrochemical cell may be regarded as fully charged when the voltage passes a threshold value. For example, an electrochemical cell comprising a lithium metal anode and a niobium tungsten oxide cathode may be regarded as fully charged when the voltage rises above a practicable level, such as where the voltage rises above 2.0 V against Li / Li+, such as above 2.25 V or above 2.5 V. The electrochemical cell may be regarded as fully discharged when the voltage passes a threshold value. For example, an electrochemical cell comprising a lithium metal anode and a niobium tungsten oxide cathode may be regarded as fully discharged when the voltage drops below a practicable level, such as where the voltage drops below 1.5 V against Li / Li+, such as below 1.25 V or below 1.0 V. The battery may have an energy density of 100 Wh / L or more, preferably 150 Wh / L or more, more preferably 200 Wh / L or more. The battery may be a battery as described in WO 2021 / 074406 or WO 2019 / 234248, the contents of which are incorporated herein by reference in their entirety. Working Electrode The working electrode may be an anode or cathode during a discharge step, for example in a lithium ion battery. Preferably, the working electrode is the anode during a discharge step. The working electrode is electrically conductive, and is electrically connectable to a counter electrode, for example within an electrochemical cell. In some embodiments, the working electrode comprises a niobium oxide or a niobium metal oxide. The niobium oxide may be selected from Nb20s polymorphs, NbO2, Nb20a or combinations thereof. The niobium metal oxide may be a compound (for example, having a crystalline structure) of a niobium oxide and an additional metal oxide. Suitable niobium metal oxides include niobium tungsten oxide (for example NbieWsOss or NbisWwCM, a titanium niobium oxide (for example TiNb2O?), a niobium molybdenum oxide (for example Nb2Mo3Oi4), or combinations thereof. Suitable niobium tungsten oxides include Nb^WOaa, Nb26W4O?7, Nbi4W3O44, NbieWsOss, NbisWsOsg, Nb2WOs, NbisWieOgs, Nb22W2oOns, NbsWgO47, Nb54Ws2O38i, Nb2oW3iOi43, Nb4W70si, or Nb2Wi50so or combinations thereof. In some embodiments, the working electrode comprises a niobium metal oxide material having a molar ratio of Nb2O5 to WO3 from 6:1 to 1:15. Preferably, the molar ratio of NbsOs to WO3 in the working electrode is from 8:5 to 11:20. More preferably, the molar ratio of Nb20s to WO3 in the working electrode is 8:5 or 9:16. In some embodiments the working electrode active material comprises NbieWsOss, NbisWsOeg, Nb2WOs, NbisWieOgs, or Nb22W2oOns, or combinations thereof. Preferably the working electrode comprises NbieWsOss or NbisWieOgs, or combinations thereof. In some embodiments, the working electrode comprises graphite, Si, SiOx (where x is typically from 0 to 2), LTO, or a mixture thereof. In some embodiments, the working electrode consists essentially of graphite Si, SiOx (where x is typically from 0 to 2), or lithium titanate (LTO). Preferably, the working electrode comprise these compounds (e.g. graphite) in particulate form. The working electrode may comprise a mixture of niobium tungsten oxide and an additional active material. The additional active material may be an additional metal oxide. For example, the working electrode may comprise a mixture of niobium tungsten oxide and an additional active material selected from lithium titanate (LTO; Li^isO^), titanium niobium oxides (for example TiNbzO?), titanium tantalum oxides (for example TiTa2O?), tantalum molybdenum oxides (for example TasWgCM and niobium molybdenum oxides (for example Nb2Mo3Oi4). The working electrode may comprise a mixture of niobium tungsten oxide and LTO. The additional active material may be graphite. The working electrode may comprise a mixture of niobium tungsten oxide and graphite. Preferably, the working electrode consists essentially of niobium tungsten oxide and an additional active material. For example, the working electrode consists essentially of a mixture of niobium tungsten oxide and LTO. Alternatively, the working electrode may consist essentially of a mixture of niobium tungsten oxide and graphite. Typically, the working electrode does not have a porous or hierarchical structure. For example, the electrode material may have a specific surface area of less than 20 m2 g’1, less than 10 m2 g’1, less than 5 m2 g’1, less than 3 m2 g’1, less than 2 m2g'1 or less than 1 m2g’1. The specific surface area of the electrode material may be known, or it may be determined using standard techniques such as N2 adsorption isotherm analysis and Brunauer-Emmett-Teller (BET) theory. Alternatively, the working electrode may have a porous structure. For example, the working electrode may have a specific surface area of at least 50 m2g’1, at least 60 m2 g’1, 70 m2 g’1, 80 m2 g’1, 90 m2g'1, 100 m2 g’1, 150 m2 g’1, 200 m2 g’1, 300 m2 g-1, or 400 m2 g’1. The working electrode may have a pore volume of of at least 0.1 cm3 g’1, at least 0.2 cm3 g1, at least 0.4 cm3g’1, at least 0.5 cm3g~1, at least 0.7 cm3g~1, at least 0.8 cm3 g~1, at least 0.9 cm3 g-1, at least 1.0 cm3 g-1, at least 1.5 cm3 g-1 or at least 2.0 cm3 g-1. The pore volume of the electrode material may be known, or it may be determined using standard techniques such as N2 adsorption isotherm analysis and Barrett-Joyner-Halenda (BJH) theory. The porous working electrode may have an average pore size (largest cross section) of at least 1 nm, at least 5 nm, at least, 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm or at least 100 nm. The porous working electrode may have a macroporous structure. Thus, the porous working electrode may contain pores having a largest cross section of at least 200 nm, at least 500 nm, at least 1 pm, or at least 5 pm. The pore size of the electrode material may be known, or it may be determined using standard techniques such as scanning electron microscopy (SEM). The working electrode may additionally comprise porous carbon, such as porous reduced graphene oxide. Electrodes comprising porous carbon are generally light and conductive, and can provide large pore volumes, which can allow rapid transport of lithium ions and electrons to the active materials. They may also increase the electrochemical capacity of the working device. The working electrode may additionally comprise reduced graphene oxide, Ketjen black or Super P carbon. Alternatively, the working electrode may have a hierarchical structure. For example, the working electrode may additionally comprise hierarchical reduced graphene oxide (rGO). Preferably, the working electrode comprise a niobium tungsten oxide in particulate form. The average diameter of the niobium tungsten oxide particles of the working electrode may be known, or it may be determined using standard techniques such as SEM. The niobium tungsten oxide particles of the working electrode may have an average primary particle diameter of at least 1 pm. The primary particle diameter is the diameter of the individual crystallite. It is the smallest identifiable subdivision in a particulate system. For example, the niobium tungsten oxide particles have an average primary particle diameter of at least 2 pm, 3 pm, 4 pm, 5 pm or 10 pm, such as from 2 to 100 pm, preferably from 5 to 50 pm, more preferably from 10 to 20 pm. The individual niobium tungsten oxide particles may agglomerate to form secondary particles. Typically, the niobium tungsten oxide particles have an average agglomerate (secondary) particle diameter of at least 5 pm. More preferably, the niobium tungsten oxides have an average agglomerate particle diameter of at least 10 pm, 15 pm, 20 pm, 25 pm or 30 pm, such as from 10 to 200 pm, preferably from 20 to 100 pm, more preferably from 30 to 50 pm. Where present, the additional active material may be in particulate form. The diameter of the additional active material particles may be known, or it may be determined using standard techniques such as SEM. Preferably, the additional active material particles have an average primary particle diameter of 1 pm or less. For example, the additional active material particles have an average primary particle diameter of 800 nm or less, 750 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less or 150 nm or less. Electrodes comprising a mixture of niobium tungsten oxide and an additional active material having particle sizes within the ranges described above can be charged and discharged at very high C-rates and at very high charge densities. To improve conductivity at the working electrode, a conductive carbon material (e.g., carbon black, graphite, nanoparticulate carbon powder, carbon fiber and / or carbon nanotubes) is typically admixed with the working electrode material. Alternatively, the conductive carbon material may be coated onto the working electrode material. In one embodiment, the working electrode comprises porous carbon, such as porous reduced graphene oxide, which may wrap the larger niobium oxides particles. Typically, the working electrode contains 1-5% by weight of binders. The working electrode may be admixed with a binder. Some examples of binders include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR and co-polymers thereof. The working electrode is typically fixed to a current collector, such as a copper or aluminum collector, which may be in the form of a plate. In a specific embodiment the working electrode comprising a particulate niobium tungsten oxide using a standard electrode configuration of 8:1:1 active material / carbon / binderwith a 2-3 mgcm2 loading of active material and a 1.27 cm2 electrode area against a lithium counter electrode and using 1.0 M LiPFe in ethylene carbonate / dimethyl carbonate as electrolyte. Counter Electrode The electrochemical cell typically comprises a counter electrode. The counter electrode may be an anode or cathode during a discharge step, for example in a lithium ion battery. Preferably the counter electrode is the cathode during a discharge step. In addition to the working electrode, an electrochemical cell comprises a counter electrode and an electrolyte, and optionally a separator, such as a microporous polyethylene film, between the working electrode and counter electrode. Suitable materials for the counter electrode include lithium-containing or lithium-intercalated material, such as a lithium metal oxide, wherein the metal may be a transition metal such as Co, Fe, Ni, V, or Mn, or combination thereof. Some examples of counter electrode materials include lithium cobalt oxide (LiCoO2) lithium nickel manganese cobalt oxide (NMC, LiNiMnCoO2, e.g., LiNi0.6Co0.2Mn0.2O2), lithium vanadium fluorophosphate (UVPO4F), lithium nickel cobalt aluminium oxide (NCA, LiNiCoAh), lithium iron phosphate (LFP, LiFePO4) and manganese-based spinels (e.g. LiMn2O4). In one embodiment, the counter electrode is substantially free of binders. In an alternative embodiment, the counter electrode is admixed with a binder or adhesive. Some examples of binders or adhesives include PVDF, PTFE, CMC, PAA, PMMA, PEO, SBR and co-polymers thereof. The counter electrode may be fixed to a current collecting substrate, such as an aluminium plate. Electrolyte The electrochemical cell typically comprises an electrolyte. The electrolyte facilitates ion transport between the cathode and anode. The electrolyte comprises lithium salts, such as lithium (bis(trifluoromethane)sulfonimide (LiTFSI), LiPFe, UBF4, UCIO4, lithium triflate (LiTF), or lithium bis(oxalate)borate (LiBOB). The electrolyte may be a liquid electrolyte, such as a liquid at ambient temperature, for example at 25°C. The electrolyte may be a non-aqueous electrolyte. The electrolyte may comprise a polar aprotic solvent, such a cyclic or linear carbonate, such as ethylene carbonate, dimethyl carbonate, or ethyl methyl carbonate. Suitable solvents include carbonate solvents. For example propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), chloroethylene carbonate, fluorocarbonate solvents (e.g., fluoroethylene carbonate and trifluoromethyl propylene carbonate), as well as the dialkylcarbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Suitable solvents also include sulfone solvents. For example methyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, methyl isopropyl sulfone (MiPS), propyl sulfone, butyl sulfone, tetramethylene sulfone (sulfolane), phenyl vinyl sulfone, allyl methyl sulfone, methyl vinyl sulfone, divinyl sulfone (vinyl sulfone), di phenyl sulfone (phenyl sulfone), dibenzyl sulfone (benzyl sulfone), vinylene sulfone, butadiene sulfone, 4-methoxyphenyl methyl sulfone, 4-chlorophenyl methyl sulfone, 2-chlorophenyl methyl sulfone, 3,4-dichlorophenyl methyl sulfone, 4-(methylsulfonyl)toluene, 2-(methylsulfonyl) ethanol, 4-bromophenyl methyl sulfone, 2-bromophenyl methyl sulfone, 4-fluorophenyl methyl sulfone, 2-fluorophenyl methyl sulfone, 4-aminophenyl methyl sulfone, a sultone (e.g., 1,3-propanesultone), and sulfone solvents containing ether groups (e.g., 2-methoxyethyl(methyl)sulfone and 2-methoxyethoxyethyl(ethyl)sulfone). Suitable solvents also include silicon-containing solvents such as a siloxane or silane. For example, hexamethyldisiloxane (HMDS), 1,3-divinyltetramethyldisiloxane, the polysiloxanes, and polysiloxane-polyoxyalkylene derivatives. Some examples of silane solvents include methoxytrimethy Isilane, ethoxytrimethy Isilane, dimethoxydimethylsilane, methyltrimethoxysilane, and 2-(ethoxy)ethoxytrimethylsilane. Typically, an additive may be included in the electrolyte to improve performance. For example vinylene carbonate (VC), vinyl ethylene carbonate, allyl ethyl carbonate, t-butylene carbonate, vinyl acetate, divinyl adipate, acrylic acid nitrile, 2-vinyl pyridine, maleic anhydride, methyl cinnamate, ethylene carbonate, halogenated ethylene carbonate, a-bromo-y- butyrolactone, methyl chloroformate, 1,3-propanesultone, ethylene sulfite (ES), propylene sulfite (PS), vinyl ethylene sulfite (VES), fluoroethylene sulfite (FES), 12-crown-4 ether, carbon dioxide (CO2), sulfur dioxide (SO2), and sulfur trioxide (SO3). The electrochemical cell may also include a separator, such as a solid porous membrane positioned between the working and counter electrodes. The solid porous membrane may partially or completely replace the liquid electrolyte. The solid porous membrane may comprise a polymer (e.g., polyethylene, polypropylene, or copolymer thereof) or an inorganic material, such as a transition metal oxide (e.g., titania, zirconia, yttria, hafnia, or niobia) or main group metal oxide, such as silicon oxide, which can be in the form of glass fiber. The solid non-porous membrane may comprise a lithium-ion conductor. For example, LLZO (garnet family), LSPO (LISICON family), LGPS (thio-LISICON family), U\TP / U\GP (NASICON family), LLTO (perovskite family) and phosphide / sulfide glass ceramics. Power Controller The battery system comprises a power controller. The power controller is for controlling and / or conditioning power charged or discharged from the battery. The power controller may be in electrical communication with the battery, such as signalling communication or power transfer connection. The power controller may also be in electrical communication with a load (during battery discharging) or the source of power (during battery charging). The power controller may be connected in series or in parallel with the battery. The power controller may be connected in series between the battery and a load, or between the battery and a charger. The battery system may comprise two or more power controllers. The two or more power controllers may be the same or different, and may have the same or different connectivity in the battery system . In embodiments comprising two or more batteries, each battery may have a corresponding power controller. The power controller is typically in electrical communication with the battery. The power controller may also be referred to as “power electronics”. Generally, the power controller generates thermal energy during operation. The power controller controls and / or conditions power charged or discharged from the battery, and produces thermal energy as a result of controlling and / or conditioning power charged or discharged from the battery. The thermal energy may be generated from any component of the power controller. Typically, the switches (for example, transistors and gate drivers) generate thermal energy. Thermal energy from the power controller is transferred to the battery using the heat exchangers. The power controller is in thermal communication with the first heat exchanger. The power controller is in communication with the battery, such that the power controller can control and / or condition power charged or discharged from the battery. In some embodiments, the power controller is also in communication with the temperature controller, such that the temperature controller can monitor the temperature of the power controller. The power controller is for controlling and / or conditioning power charged or discharged from the battery. The power controller may include power electronics circuits and power conditioning circuits. The power controller may comprise a means of measuring and / or storing battery status data. Any suitable means of measuring the status data may be used, such as sensors (e.g., voltmeter, ammeter, ohmmeter, thermistor, thermocouple, high input impedance ohmmeter). The power controller may comprise a means of processing and / or storing battery status data. For example, the power controller may comprise a chip for -post processing status data. The power controller may comprise a means of sending and / or receiving battery status data (e.g., for sending and / or receiving battery status data to / from a remote system (such as the cloud)). Typically, the power controller controls the rate of discharge and / or charge of the battery. The power controller may adjust the rate of charge or discharge of the battery in response to status data obtained from the battery. Typically, the power controller conditions power discharged from the battery and / or conditions power used to charge the battery. In some embodiments separate power controller is used for the power input and the power output. In other embodiments the same power controller is used for both the power input and the power output, and preferably the power controller is bidirectional. The power controller may include a semi-conductor chip, an integrated circuit, a logic circuit or a microprocessor circuit. Typically, the power controller comprise a switch. Suitable switches include transistors, such as insulated-gate bipolar transistors, field effect transistors and high-electron-mobility transistors. The switch may also include a relay. The power controller may include a gate driver. Suitable gate drives typically include a level shifter and an amplifier. The gate driver may be used to switch power switches, such as transistors. The power controller may include a surge protector, frequency corrector or voltage corrector. The power conditioning typically smooths or decreases variability in the power. The power controller may include an inverter (i.e. which changes direct current (DC) to alternating current (AC)) or converter (i.e. AC to DC, or DC to DC). Suitable inverters or converters are known in the art. Typically, a DC-DC converter is comprised in the power controller. Suitable DC-DC converters are known in the art, such as buck, boost, or a buckboost converter. Suitable AC-AC converters are known in the art, such as transformers. DC power (e.g. from a DC fast charger) may be passed through a power controller. The power controller may carry out appropriate power conditioning, converting the voltage received as appropriate and accordingly may incorporate or be connected to a boost, buck, or buck-boost DC-DC converter in order to carry out power conditioning. AC power (e.g. from a domestic power supply) may be passed through an AC / DC power controller to charge the battery. The AC / DC power controller carries out any required conversion and power conditioning. The components of the power controller may be disposed on a printed circuit board. The power controller may also adjust the discharge rate (or charge rate) of individual or groups of electrochemical cells comprised in the battery, thereby balancing the electrochemical cells in the battery. The power controller may also process data about the state of charge (e.g. voltage) of individual or groups of electrochemical cells comprised in the battery. This data may then be used by the power controller to balance the cells in the battery, which reduces the amount of overvoltage or undervoltage of any individual cell, which in turn reduces potential damage to the cells. The power controller may further comprise a battery management system (BMS). The BMS is typically in electronic communication with the battery. The BMS typically controls the discharge and charging individual or groups of electrochemical cells, the balancing of the cells, and measures data about the cells. The BMS may include similar components as the power controller, as described herein. Heat Exchangers The system comprises a first heat exchanger in thermal communication with the power controller, and a second heat exchanger in thermal communication with the battery. A heat exchanger is a component which permits the transfer of thermal energy between one body and another body. Where there is a temperature difference across the heat exchanger, thermal energy is transferred down the temperature gradient, from the “hot side” to the “cold side”. For example, the heat exchanger may transfer thermal energy between a power controller (hot side) and a heat transfer fluid (cold side), or may transfer thermal energy from a heat transfer fluid (hot side) to the surroundings (cold side), or may transfer thermal energy from a heat transfer fluid (hot side) to a battery (cold side). Each of the heat exchangers may be of any suitable configuration. For example, the heat exchangers may be a finned tube heat exchanger, a shell and tube heat exchanger, a plate heat exchanger, a shell and plate heat exchanger, or a direct contact heat exchanger. Each of the heat exchangers typically include a thermally conductive interface which comprises any suitable material having high thermal conductivity. Preferably, the thermally conductive interface comprises a metal, such as aluminium, copper, steel, nickel, Inconel, or cupronickel. The thermally conductive interface may comprise protrusions, such as fins, which transfer thermal energy to the heat transfer fluid. The protrusions increase the surface area of the interface contacting the heat transfer fluid. The second heat exchanger may be a passive heat exchanger or an active heat exchanger. The first heat exchanger is in thermal communication with the power controller. The first heat exchanger may be in thermal communication with two or more power controllers, where the two or more power controllers are the same or different. The system may comprise two or more first heat exchangers, where the two or more first heat exchangers are in thermal communication with two or more power controllers. The first heat exchange is typically arranged to receive thermal energy from the components of the power controller which generated thermal energy. Typically, the first heat exchanger is arranged to receive thermal energy from switching components (for example, transistors (MOSFETs) or gate drivers). The thermal energy received from the power controller may be transferred to a heat transfer fluid. Any heat exchanger able to receive thermal energy from the power controller is suitable. Typically, the first heat exchanger comprises a thermally conductive interface between a heat transfer fluid and the power controller, such as switching components (e.g., transistors (such as MOSFETs) or gate drivers). The thermally conductive interface is preferably located adjacent to the power controller, such as the switching components. The thermally conductive interface may be thermally conductive and have a large surface area. The second heat exchanger is in thermal communication with the battery. The second heat exchanger may be in thermal communication with two or more batteries, where the two or more batteries may be the same or different. The system may comprise two or more second heat exchangers, where the two or more second heat exchangers are in thermal communication with two or more batteries. The second heat exchange is typically arranged to provide thermal energy to the components of the battery which require thermal energy to reach their optimal operating temperature. Typically, the second heat exchanger is arranged to provide thermal energy to the working electrode or counter electrode. Preferably the second heat exchanger is arranged to provide thermal energy to the working electrode. For example, where the battery comprises a lithium cathode, the thermally conductive interface is adjacent to the lithium cathode. Where the battery comprises a graphite anode, the thermally conductive interface is adjacent to the graphite anode. Any heat exchanger able to transfer thermal energy to the battery is suitable. Typically, the second heat exchanger comprises a thermally conductive interface between a heat transfer fluid and the battery, such as working electrode and / or counter electrode. The thermally conductive interface is preferably located adjacent to the working electrode and / or counter electrode, such as the working electrode. The thermally conductive interface may be thermally conductive and have a high surface area. In some embodiments, the system comprises a third heat exchanger in thermal communication with the first and / or second heat exchangers. The third heat exchanger may be in thermal communication with the first heat exchanger. Alternatively, the third heat exchanger may be in thermal communication with the second heat exchanger. Preferably, the third heat exchanger is in thermal communication with the first and second heat exchangers. Typically, the third heat exchanger is in thermal communication with the first and second heat exchangers, wherein the battery system is configured to transfer thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger simultaneously and / or sequentially with transferring thermal energy from the first heat exchanger to the second heat exchanger, preferably wherein the third heat exchanger is for dissipating thermal energy to the environment The system transfers thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger simultaneously and / or sequentially with transferring thermal energy from the first heat exchanger to the second heat exchanger. As a result, the third heat exchanger may be used to remove thermal energy from the battery system. The third heat exchanger may be used to reduce the temperature of the power controller or the battery. Where thermal energy is transferred from the first heat exchanger and / or the second heat exchanger to the third heat exchanger simultaneously with transferring thermal energy from the first heat exchanger to the second heat exchanger, this means that a first portion of thermal energy is being transferred to from the first heat exchanger to the second heat exchanger, and at the same time a second portion of the thermal energy is being transferred to from the first and / or second heat exchanger to the third heat exchanger. Where thermal energy is transferred from the first heat exchanger and / or the second heat exchanger to the third heat exchanger sequentially with transferring thermal energy from the first heat exchanger to the second heat exchanger, this means that at a first time period thermal energy is being transferred from the first heat exchanger to the second heat exchanger, and over a sequential second time period a second portion of the thermal energy is being transferred to from the first and / or second heat exchanger to the third heat exchanger. Where the third heat exchanger is in thermal communication with the first heat exchanger, the third heat exchanger may be used to take thermal energy away from the first heat exchanger. As a result, the third heat exchanger may be used to reduce the temperature of the power controller. Where the third heat exchanger is in thermal communication with the second heat exchanger, the third heat exchanger may be used to take thermal energy away from the second heat exchanger. As a result, the third heat exchanger may be used to reduce the temperature of the battery. Preferably, the third heat exchanger is for dissipating thermal energy to the environment. In other words, the third heat exchanger dissipates thermal energy to the surroundings, such as surrounding air. Any heat exchanger suitable to dissipate thermal energy to the environment is suitable. Typically, the third heat exchanger comprises a thermally conductive interface between a heat transfer fluid and a heat sink. The heat sink may be thermally conductive and have a high surface area. The heat sink is configured to transfer thermal energy to the environment (e.g., surrounding air). The environment is typically any thermal mass outside of the battery system, such as the surrounding air or an external liquid (e.g., water or coolant). The third heat exchanger may comprise protrusions, such as fins, which transfer thermal energy to the environment (e.g., surrounding air). The protrusions increase the surface area of the interface contacting the air. The third heat exchanger may comprise a radiator. The third heat exchanger may comprise a vent. The third heat exchanger may be a passive heat exchanger or an active heat exchanger. An active heat exchanger may include a fan to increase the flow of air over the heat exchanger. The system may comprise an additional fourth heat exchanger and / or fifth heat exchanger, and / or sixth heat exchanger. The fourth, fifth and / or sixth heat exchangers may be in thermal communication with a further component of the system, other than the power controller or battery, or an extraneous component. For example, the fourth, fifth and / or sixth heat exchangers may be in thermal communication with the cabin heating circuit (e.g., HVAC system) of an EV. Thermal Communication The first and the second heat exchangers are in thermal communication. In some embodiments, the first and / or the second heat exchangers are in thermal communication with a third heat exchanger. Thermal communication refers to any connection between two bodies which allows for the transfer of thermal energy. For example, thermal communication includes connection by a thermally conductive material, a heat transfer fluid, or a combination thereof. Thermal communication may be provided by any suitable means, using conductive heat transfer, convective heat transfer and / or radiative heat transfer. The thermal communication may be active, where external power is used to drive the heat transfer, or passive, where external power is not used to drive the heat transfer. Preferably, thermal communication is provided by using a heat transfer fluid in fluidic communication and thermal communication with the heat exchangers. The heat transfer fluid may be pumped between the heat exchangers. The heat transfer fluid may be provided in a fluid circulation system, which is in fluidic communication with the heat exchangers. The heat transfer fluid may be a gas. The gas may be air. The air may be provided in a network of ducts, wherein the ducts transport the air between the heat exchangers. Preferably the heat transfer fluid is a liquid. The liquid may be water, ethylene glycol, or a combination thereof. In some embodiments, the heat transfer fluid is a refrigerant. Any suitable refrigerant may be used, such as CH2F2, CH2FCF3 or a combination thereof. The refrigerant may be present as a liquid or gas. The liquid or gas may be provided in a network of pipes, wherein the pipes transport the fluid between the heat exchangers. The pipes typically form a continuous loop, where the liquid or gas flow continuously through the pipes. In some embodiments, different heat transfer fluids may be used in different heat exchangers. For example, a first heat transfer fluid may be used in the first heat exchanger, and a second heat transfer fluid may be used in the second heat exchanger. In some embodiments, a third heat transfer fluid may be used in the third heat exchanger. The first heat transfer fluid and second heat transfer fluids may be in thermal communication using an intermediate heat exchanger. In some embodiments, the third heat transfer fluid may be in thermal communication with the first and / or second heat transfer fluids using an intermediate heat exchanger. Temperature Controller In some embodiments, the battery system further comprises a temperature controller. The temperature controller is for adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger, to control the battery temperature. The temperature controller is a controller which is configured to control the battery temperature. In some embodiments, the temperature controller is for adjusting the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, to control the battery temperature. In some such embodiments, the temperature controller comprises a battery sensor for obtaining status data from the battery. Preferably, the status data is battery temperature, battery internal resistance, battery voltage or a combination thereof. Preferably, the battery sensor is a current sensor, voltage sensor, temperature sensor, or a combination thereof. The temperature controller typically adjusts the rate of thermal energy transfer by controlling the distribution of thermal energy between the heat exchangers. The distribution may be controlled using any suitable means, such as a switch, manifold and / or value. In addition or alternatively, the temperature controller may adjust the rate of thermal energy transfer by controlling the flow rate of heat transfer fluid between the heat exchangers. The flow rate of heat transfer fluid may be controlled using any suitable means, such as by adjusting a valve, manifold, or by adjusting the flow rate of a pump for the heat transfer fluid. For example, the temperature controller may comprise a valve for adjustably distributing the heat transfer fluid between the heat exchangers, to adjust the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger and / or the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, where present, to control the battery temperature. The temperature controller may adjustably distribute heat transfer fluid between the heat exchangers. Typically, the controller adjusts the flow rate of heat transfer fluid from the first heat exchanger to the second heat exchanger. Where a third heat exchanger is present, the controller adjusts the flow rate of heat transfer fluid of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger. The temperature controller may monitor the rate of heat transfer between each of the heat exchangers. For example, the temperature controller may monitor the temperature of the heat transfer fluid and / or the flow rate of the heat transfer fluid. The temperature controller can then determine the rate of thermal energy transfer. Preferably, the temperature controller comprises a temperature sensor for monitoring the temperature of a heat transfer fluid. Preferably, the temperature controller comprises a flow sensor for measuring the flow rate of the heat transfer fluid. The temperature controller is described in more detail in the temperature control section below. Method of Controlling Battery Temperature Generally, the invention relates to a method of controlling battery temperature in a battery system, the method comprising transferring thermal energy from a power controller to a battery. The method comprises transferring thermal energy from a power controller to a first heat exchanger, transferring thermal energy from the first heat exchanger to a second heat exchanger, and transferring thermal energy from the second heat exchanger to a battery. In an aspect of the invention, there is provided a method of controlling battery temperature in a battery system, the battery system comprising: a battery, a power controller for controlling and / or conditioning power charged or discharged from the battery, a first heat exchanger in thermal communication with the power controller, and a second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication; the method comprising: transferring thermal energy from the power controller to the first heat exchanger, transferring thermal energy from the first heat exchanger to the second heat exchanger, and transferring thermal energy from the second heat exchanger to the battery. The method of controlling battery temperature uses a battery system, as described above. The description of the battery system, as well as the battery, power controller, heat exchangers, thermal communication and temperature controller are equally applicable to the method of controlling battery temperature. The method may be a computer-implemented method. Any or all steps of the method may be computer-implemented. For example, the temperature control step and / or the rate adjustment step may be computer-implemented. The method comprises a step of transferring thermal energy from the power controller to the first heat exchanger. This may be known as the “cooling step”. During use, the power controller generates thermal energy as a result of its operation. This results in a temperature difference between the power controller (hot) side of the heat exchanger and the opposite (cold) side of the heat exchanger. The cooling step reduces the thermal energy stored in the power controller, and so reduces the temperature of the power controller. In some embodiments, the first heat exchanger transfers the thermal energy to a heat transfer fluid, and so increase the temperature of the heat transfer fluid. The heat transfer fluid is heated by the first heat exchanger, to receive thermal energy from the power controller. The heat transfer fluid may transport the thermal energy away from the cold side of the heat exchanger, thus retaining the temperatures difference between the hot and cold side. The method comprises a step of transferring thermal energy from the first heat exchanger to the second heat exchanger. This may be known as the “heat transfer step”. The heat transfer step transfers the thermal energy from the power controller (first heat exchanger) to the battery (second heat exchanger). Typically, there is a temperature difference between the power controller (first heat exchanger) to the battery (second heat exchanger), and so heat is transferred towards the battery. In some embodiments, heat transfer fluid transports thermal energy from the first heat exchanger to the second heat exchanger. For example, a ‘hot’ heat transfer fluid flows from the first heat exchanger to the second heat exchanger, to transfer thermal energy from the first heat exchanger to the second heat exchanger. Typically, a ‘cold’ heat transfer fluid flows returns from the second heat exchanger to the first heat exchanger. Hot refers to the heat transfer fluid which has been heated by the first heat exchanger, to receive thermal energy from the power controller. Cold refer to the heat transfer fluid which has been cooled by the second heat exchanger, to provide thermal energy to the battery. The method comprises a step of transferring thermal energy from the second heat exchanger to the battery. This may be known as the “heating step”. During use, the battery may be colder than the second heat exchanger. This results in a temperature difference between the battery (cold) side of the system and the opposite (hot) side of the system. The heating step increases the thermal energy stored in battery, and so increase the temperature of the battery. In some embodiments, the second heat exchanger transfers the thermal energy from a heat transfer fluid to the battery, and so decreases the temperature of the heat transfer fluid. The heat transfer fluid is cooled by the second heat exchanger, to provide thermal energy to the battery. The heat transfer fluid may transport the thermal energy away to the hot side of the second exchanger, thus retaining the temperatures difference between the hot and cold side. In some embodiments, the battery system further comprises a third heat exchanger in thermal communication with the first and / or second heat exchangers. The third heat exchanger is as described above. Preferably, the third heat exchanger dissipates thermal energy to the environment. In such embodiments, the method further comprise a step of transferring thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger. The transfer of thermal energy to the third heat exchanger is simultaneous and / or sequential with transferring thermal energy from the first heat exchanger to the second heat exchanger. The third heat exchanger may be used to remove thermal energy from the battery system. As such, the third heat exchanger may be used to reduce the temperature of the power controller and / or the battery. For example, if the power controller is producing more thermal energy than is required to heat the battery to its optimal temperature and / or the power controller is at a temperature above its optimal temperature, then the excess thermal energy may be transferred to the third heat exchanger. In addition or alternatively, if the battery is at a temperature above its optimal temperature, thermal energy may be transferred from the second heat exchanger (battery) to the third heat exchanger, to reduce the temperature of the battery. The transfer of heat is as described above for the first and second heat exchangers. The system may comprise an additional fourth heat exchanger and / or fifth heat exchanger, and / or sixth heat exchanger, in thermal communication with the first and / or second heat exchangers, and where present a third heat exchanger. The fourth, fifth and / or sixth heat exchangers may be in thermal communication with a further component of the system, other than the power controller or battery, or an extraneous component, to heat or cool such components. For example, the fourth, fifth and / or sixth heat exchangers may be in thermal communication with the cabin heating circuit (e.g., HVAC) of an EV. Temperature Control In general, the method controls the temperature of the battery, by transferring thermal energy from the power controller to the battery. The temperature of the battery is changed as a result of the thermal energy transferred from the power controller. In a preferred embodiment, the battery system comprises a temperature controller, and the method comprises a step of adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger using the temperature controller, to control the battery temperature. This may be referred to as a “temperature control step”. If the battery temperature is below its optimal temperature, then the temperature controller adjusts (e.g., increases) the rate of thermal energy transfer from the first heat exchanger (power controller) to the second heat exchanger (battery) to increase the temperature of the battery. If the battery temperature is above its optimal temperature, then the temperature controller adjusts (e.g., decreases) the rate of thermal energy transfer from the first heat exchanger (power controller) to the second heat exchanger (battery) to decreases the temperature of the battery. If the battery temperature is within its optimal temperature range, the temperature controller adjusts or maintains the rate of thermal energy transfer from the first heat exchanger (power controller) to the second heat exchanger (battery) to maintain the temperature of the battery. In some embodiments, where a third heat exchanger is present, the method further comprises adjusting the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger using the temperature controller, to control the battery temperature. If the battery temperature is above its optimal temperature, then the temperature controller adjusts (e.g., increases) the rate of thermal energy transfer from the first heat exchanger (power controller) and / or the second heat exchanger (battery) to the third heat exchanger, to decrease the temperature of the power controller and / or the battery. As a result, less thermal energy is in the battery system, so the total amount of thermal energy available to transfer to the battery is decreased. If the battery temperature is below its optimal temperature, then the temperature controller adjusts (e.g., decreases) the rate of thermal energy transfer from the first heat exchanger (power controller) and / or the second heat exchanger (battery) to the third heat exchanger, to increase the temperature of the power controller and / or the battery. As a result, more thermal energy remains in the battery system, so the total amount of thermal energy available to transfer to the battery is increased. If the battery temperature is within its optimal temperature range, the temperature controller adjusts or maintains the rate of thermal energy transfer from the first heat exchanger (power controller) and / or the second heat exchanger (battery) to the third heat exchanger to maintain the temperature of the battery. Preferably, the temperature controller receives status data obtained from the battery, and the temperature controller adjusts the rate of thermal energy transfer in response to the status data. In some embodiments, the temperature controller compares status data obtained from the battery to a target range, and the temperature controller adjusts the rate of thermal energy transfer in response to the comparison of the status data to the target range, such that subsequent status data from the battery is maintained within the target range or is moved into the target range. Preferably, the status data is battery temperature and the target range is a target temperature range. The target temperature range may be 12 °C or more, such as 20 °C or more, from 25 to 50 °C, or from 30 to 45 °C. The target temperature may depend on the type of battery used. In some embodiments, the temperature controller compares status data obtained from the battery to previous status data obtained from the battery, to determine a change in the status data over time and / or rate of change in the status data over time, and the temperature controller adjusts the rate of thermal energy transfer in response to the change and / or rate of change in the status data over time. In some embodiments the temperature controller compares the change in the status data to a target range, and adjusts the rate of thermal energy transfer to control the battery temperature, such that subsequent status data from the battery is maintained within the target range or is moved into the target range. Preferably, the target range is a target change in temperature. The target change in temperature is from 5 to 30 °C, preferably from 10 to 25 °C, yet more preferably from 15 to 20 °C. The target change in temperature may depend on the starting temperature of the battery and the type of battery used. In some embodiments the temperature controller compares the rate of change in the status data to a target range, and adjusts the rate of thermal energy transfer to control the battery temperature, such that subsequent status data from the battery is maintained within the target range or is moved into the target range. Preferably, the target range is a target rate of change in temperature. The target rate of change in temperature is from 1 to 10 °C / min, preferably from 2 to 8 °C / min, yet more preferably from 3 to 7 °C / min. The target rate of change in temperature is preferably about 5 °C / min. In some embodiments, the target range changes depending on the discharge or charge rate of the battery, or the subsequent discharge or charge rate of the battery. If the battery is discharging or charging at a first C-rate range the target range may be a first target range, and if the battery is discharging or charging at second C-rate range the target range may be a second target range. If the subsequent discharge or charge rate is a first C-rate range the target range may be a first target range, and if the battery is discharging or charging at a second C-rate range the target range may be a second target range. For example, if the first C-rate range is from OC to 3C, the first target range may be a temperature range of 12 °C or more, and if the second C-rate range is from 3C to 20C, the second target range may be a temperature range of 20 °C or more. Preferably, if the first C-rate range is from OC to 3C, the first target range may be a temperature range of from 20 to 45 °C, and if the second C-rate range is from 3C to 20C, the second target range may be a temperature range of from 30 to 45 °C. In addition or alternatively, if the first C-rate range is from 0C to 3C, the first target range may be a rate of change in temperature of 2 °C / min to 5 C / min, and if the second C-rate range is from 3C to 20C, the second target range may be a rate of change in temperature of 5 °C / min to 10 °C / min. In some embodiments, the target range is a combination of target ranges, such as a target temperature range and a target rate of change in temperature range. For example, the target ranges may be a temperature range of from 20 to 45 °C and a rate of change in temperature of 2 °C / min to 5 C / min. The combination of target ranges may be the combination of any of the target ranges described herein. The temperature controller may compare one or more types of status data obtained from the battery. Preferably the temperature controller compares two or more types of status data obtained from the battery, such as three or more, four or more, or five or more types of status data. The status data may include battery temperature, battery internal resistance, battery voltage, battery current, battery capacity, battery state of charge, or a combination thereof. Preferably the status data includes battery temperature, battery voltage and battery current. The status data may be obtained directly from the battery, or may be obtained from the battery management system (BMS) or the power controller. In some embodiments, the temperature controller additionally receives status data from the power controller, and the temperature controller adjusts the rate of thermal energy transfer in response to the status data. In some embodiments, the temperature controller compares status data obtained from the power controller to a target range, and the temperature controller adjusts the rate of thermal energy transfer in response to the comparison of the status data to the target range, such that subsequent status data from the power controller is maintained within the target range or is moved into the target range. Preferably, the status data is the temperature of the power controller. In such embodiments, the target range is a target temperature range of the power controller. The target temperature range may be 20 °C or more, preferably 30 °C or more, yet more preferably from 30 to 100 °C, even more preferably from 40 to 80 °C, most preferably 50 to 60 °C. The target temperature may depend on the type of power controller used or the components present in the power controller. The status data may be obtained using a suitable sensor. For example, battery temperature may be obtained using a temperature sensor, battery internal resistance may be obtained using an ohmmeter, battery voltage may be obtained using a voltmeter, and battery current may be obtained using an ammeter. Battery capacity and battery state of charge may be measured by column counting or by using battery voltage. The status data may be post-processed. The status data may be post-processed in the battery system, such as in the temperature controller. Alternatively, the status data may be off-loaded from the battery system to a remote system (e.g., the cloud) and post-processed remotely. The battery system is typically connected to a secured local host, to allow for the status data to be off-loaded from the battery system to a remote system. The status data may be off-loaded continuously, or the status data may be off-loaded in data packages at regular intervals. The status data may be post-processed by combining and / or comparing the data against status data from other battery systems. The status data may be post-processed using machine learning. The status data or post-processed data may be used for battery system optimisation and / or battery system prognostics. The temperature controller may use post-processed status data (where the status data may be is post-processed locally or remotely) to adjust the rate of thermal energy transfer to control the battery temperature. Charge and Discharge Rate Control The method of controlling temperature of the battery may occur when the battery is charging or discharging, or when the battery is not charging or discharging. In embodiments, where the battery is not charging or discharging, the battery is typically charged or discharged sequentially, such as before or after, operation of the method of temperature control. Typically, the method of controlling the battery occurs simultaneously and / or sequentially with charging or discharging the battery. Preferably, the method of controlling the battery occurs simultaneously with charging or discharging the battery. Although the power controller is for controlling and / or conditioning power charged or discharged from the battery, the battery may not be charging or discharging during operation of the method of the invention as described herein. The method of controlling battery temperature may transfer thermal energy from the power controller to the batteries when the battery is not charging or discharging. For example, the method of controlling the battery may occur sequentially with charging or discharging the battery. In some such embodiments, the power controller may have residual thermal energy from previous charging and / or discharging of the battery, and the residual thermal energy is transferred to the battery. In some embodiments, the power controller may be generating thermal energy as a result of controlling and / or conditioning power not charged or discharged from the battery, such as power from an external power source or from another component of the system. In one embodiment, the power controller may generate thermal energy by interaction with an external charger. This may be known as a “pre-heating step”. In some embodiments, the method comprises simultaneously and / or sequentially charging or discharging the battery at a C-rate of 3C or more, such as 5C or more, 10C or more, or 20C or more. Preferably, the method comprises simultaneously charging or discharging the battery at a C-rate of 3C or more, such as 5C or more, 10C or more, or 20C or more. The power controller may also adjust the rate of charge or discharge of the battery. The power controller may adjust the rate of charge or discharge of the battery in response to status data obtained from the battery. In some embodiments, the method further comprises adjusting the rate of charging or discharging using the power controller, wherein the power controller receives status data obtained from the battery, and the power controller adjusts the rate of charging or discharging in response to the status data. This may be known as the “rate adjustment” step. Typically, the rate adjustment step involves reviewing status data from the battery and / or the power controller and adjusting the rate in response to the status data. Generally, the controller compares the status data against a target range, and determines if the discharge rate should be increased or decreased. If the data is inside the target range the rate of discharge is increased or maintained, and if the data is outside of the acceptable range the rate of discharge is decreased. The power controller may signal to the battery to increase or decrease the rate of discharge. The status data may be the same as described above, in relation to the temperature control step. The target range and analysis of the status data may be the same as described above, in relation to the temperature control step. Preferably, the temperature control step and the rate adjustment step are carried out simultaneously. Typically, status data obtained from the battery is compared to a target range, and the temperature controller adjusts the rate of thermal energy transfer in response to comparison of the status data to the target range, and the power controller adjusts the rate of charge or discharge in response to comparison of the status data to the target range. The status data is preferably battery temperature, and the target range is preferably a temperature range. Where the temperature control step and the rate adjustment step are carried out simultaneously, the temperature control step is given preference over the rate adjustment step. In other words, if the battery status data is outside of the target range the system may preferentially use the temperature controller to bring the battery status data inside the target range. The rate adjustment step may only be used to bring the battery status data inside the target range if the temperature controller cannot bring the battery status data inside the target range. Use In a third aspect, there is provided a use of the battery system of the second aspect for controlling the temperature of a battery at a temperature of 12 °C or more, such as 20 °C or more, from 25 to 50 °C, or from 30 to 45 °C. In a further aspect there is provided a use of the battery system of the second aspect in a mobile charging device, a static charging device, or an electric vehicle. An electric vehicle (EV) may include road vehicle, such as an automobile, moped or truck; a rail vehicle, such as a train or a tram; an electric bicycle (e-bike), a drone, an electric aircraft, and an electric or hybrid boat. Preferably the use of the is in a mobile charging device or a static charging device. A mobile charging device may be a power pack, an emergency power supply, an EV charging device. The mobile charging device is preferably an off-grid device. The mobile charging device is typically adapted for transport. For example, the mobile charging device may be mountable to a transport means, such as an air, land or water based transport means, such as a drone, plane, helicopter, truck, car, train, boat. A static charging device may be a storage battery, such as a grid scale storage battery. A static charging device is typically ground mounted and immobile. The static charging device is preferably an off-grid device. The use of the device of may be for charging batteries in power tools such as powered drills or saws; garden tools such as lawnmowers or grass trimmers; home appliances such as toothbrushes or hairdryers; medical devices such as automated surgical robots or pacemakers, or mobile computing devices such as cameras, laptops, tablets and mobile phones. Preferably the use of the device of the second aspect is for charging mobile computing devices such as laptops, tablets, cameras and mobile phones. The use of the device of the second aspect may also be for charging an uninterrupted power supply (UPS) or a power grid management system. Definitions The following common definitions are used herein, as determined by the relevant context. The term “nominal rate” refers to the actual charge or discharge rate without reference to the capacity of the cell. The term “C-rate” has its common meaning as known in the art, referring to a normalized charge or discharge rate obtained by dividing the total discharge capacity of the cell (Ah) by a total period of time of 1 hour (h). A C-rate may be denoted in terms of “3C”, to mean a C-rate of 3, which refers to a full charge (empty to full) in 20 minutes. Other Preferences Each and every compatible combination of the embodiments described above is explicitly disclosed herein, as if each and every combination was individually and explicitly recited. Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. “and / or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and / or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein. Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described. Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described above. Examples The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention. ln Figures 1,2, and 3, dashed lines indicate signalling connections, solid lines indicate the flow of coolant, and lines with alternating dashes and dots indicate electrical power flow. Power controller Figure 1 shows a block diagram of a known system, comprising a power controller

[11] electrically connected to a battery pack

[12] , which is in turn electrically connected to a load

[13] such that it transfers electrical power to the load

[13] to power its operations. For example, where the system is part of an EV the load

[13] may be the drive train of the vehicle. Since during operation the power controller

[11] produces heat due to inevitable inefficiencies, there is also a cooling system associated with the power controller

[11] comprising a heat exchanger

[14] which facilitates heat exchange between the power controller

[11] and a coolant such as liquid water mixed with a substance to lower its freezing point, such as glycerol. This coolant circulates through a coolant circulation system between the heat exchanger

[14] and a vent

[15] which allows it to transfer heat to the system’s surroundings, for example into the cabin of a vehicle if this system is incorporated into the heating system of the vehicle or into the ambient air surrounding a battery-powered device. Part of the load

[13] also generates heat as part of its operation. This may be a part of the load

[13] designed specifically for generating heat to warm the battery

[12] , such as a dedicated resistor, or the heat may be a by product due to inevitable inefficiencies such as friction within the drive train of a vehicle or internal resistance of components. In the system of Figure 1, this heat is passed back to the battery heater

[16] , typically also via a coolant such as that used to remove heat from the power controller

[11] , This system has inefficiencies, since heat from the power controller

[11] may be wasted as it is transferred to the surroundings, and the batteries

[12] cannot be warmed unless either power is wasted to power a dedicated heating component

[16] for the battery

[12] or the load

[13] is given time to warm up, during which time the battery

[12] is operating at a suboptimal temperature. Figure 2a shows an example block diagram of a system according to the invention, where the battery is discharging to a load

[23] , This system comprises power controller

[21] in electrical connection to a battery

[22] , which is in turn in electrical connection with a load

[23] to supply power for the operation of the load

[23] , There is also an electrical connection between the battery

[22] and the power controller

[21] so that the battery

[22] can supply power for the operation of the power controller

[21] , In addition or alternatively, the power controller may be connect in series between the battery and the load (e.g., where the power controller is an inverter or a charger). The system includes a first heat exchanger

[24] associated with the power controller

[21] which facilitates heat transfer between the power controller

[21] and a heat transfer fluid (e.g., coolant). This may, for example, circulate heat transfer fluid in pipes adjacent the MOSFET switches within the power controller circuitry

[21] , since these are the component that generally produces the most heat. There is also a second heat exchanger

[26] associated with the battery

[22] (a “battery heater”). For example, this may take the form of a mechanism for circulating warmed liquid coolant around battery cells. In another example, it may be a fan which blows warm air over the cells that comprise the battery

[22] , There is also a third heat exchanger

[25] which distributes heat from the heat transfer fluid to the surroundings. This may take the form of a vent. The system includes a fluid circulation system (see solid arrows) connecting the first

[24] , second

[26] and third

[25] heat exchangers. This fluid circulation system allows for thermal communication between the first

[24] , second

[26] and third

[25] heat exchangers. The system of the invention also includes a temperature controller, in the form of a switch

[28] , in the fluid circulation system. The temperature controller

[28] allows heat transfer fluid from the first heat exchanger

[24] to be directed either to the third heat exchanger

[25] or to the second heat exchanger

[26] , The temperature controller

[28] is also connected to a temperature sensor

[27] associated with the battery

[22] , which detects the temperature of the battery

[22] and is used as input to the determination made by the switch

[28] as to where the heat transfer fluid is directed. A more detailed view of the internal working of the temperature controller

[28] is shown in Figure 3. Figure 2b shows the same or a similar system to Figure 2a, with the same components. However, Figure 2b shows the system when the battery

[22] is being charged from a source

[29] . Accordingly, the load

[23] has been replaced with a power source (e.g., charger)

[29] and the power flow has been reversed. In this embodiment, power is supplied to the power controller

[21] for their operation from the charger

[29] , not from the battery

[22] as in Figure 2a. However, the coolant circulation system operates in the same way and the same temperature controller

[28] can be used. Since the power controller

[21] in this system is powered from the charger

[29] , there may be a mode whereby the power controller

[21] is actively heated using power from the charger, or as a result of the power controller’s work in charging the battery, to drive warmed coolant to the battery heater

[26] before charging begins. Where the power controller

[21] is actively heated using power from the charger, this means that the battery temperature can be raised before charging begins without requiring an additional heating element for the battery. Figure 3 shows the internal workings of an example temperature controller

[28] , As previously described with reference to Figure 2, the temperature controller

[28] is in thermal communication with the first heat exchanger

[24] , the third heat exchanger

[25] , and the second heat exchanger

[26] using a heat transfer fluid. The temperature controller

[28] is also in communication with a temperature sensor

[27] associated with the battery

[22] , The temperature sensor

[27] provides temperature data from the battery

[22] , The temperature controller

[28] comprises an input for the heat transfer fluid from the first heat exchanger

[24] , outputs for the heat transfer fluid to the third heat exchanger

[25] and the second heat exchanger

[26] , and a switching mechanism

[32] . The switching mechanism may be a valve that allows liquid coolant from the first heat exchanger

[24] to flow down one output pipe or the other or may be a manifold with a movable flap in an air duct that allows heated air to flow down one output pipe or the other. When the switching mechanism

[32] is arranged to allow heat transfer fluid to flow to the second heat exchanger

[26] , this is known as Position 1 and when it is arranged to allow heat transfer fluid to flow to the third heat exchanger

[25] this is known as Position 2. The switching mechanism

[32] is connected to a switch controller

[31] , which receives input from the temperature sensor

[27] and determines the position of the switching mechanism

[32] , The switch controller compares the temperature data from the battery

[22] to a target range. If the temperature of the battery is below the target range, then the switch controller moves the switching mechanism towards position 1. If the temperature of the battery is above the target range, then the switch controller moves the switching mechanism towards position 2. Figure 4 shows an example process followed by the switch controller

[31] in the temperature controller

[28] to determine whether the heat transfer fluid should flow down the outlet to the second heat exchangers

[26] or the first heat exchanger

[25] , The same procedure could be used regardless of whether the system is in discharge mode, as shown in Figure 2a, or charge mode, as shown in Figure 2b. For simplicity, it is described herein with reference to discharging. At Step S41, the switch controller

[31] receives temperature data from the temperature sensor

[27] , This may occur periodically at long or short intervals, and the intervals may vary depending on the usage conditions of the battery

[22] , For example, when the system is first powered on and the battery temperature is likely to be changing rapidly as it begins to discharge, the temperature sensor

[27] may transmit data to the switch controller

[31] more frequently than it does when the system has been running for some time and is likely to have stabilised. At Step S42, the switch controller

[31] compares the received temperature data to a target temperature range. For example, if during manufacture it is determined that the specific chemistry of the battery

[22] means it will operate most efficiently at 25 to 35°C, this may be stored in the switch controller

[31] as the target temperature range. If the switch controller

[31] determines that the temperature of the battery

[22] is below the target temperature range for optimal operation, the process follows the branch to Step S4Y1. The switch controller

[31] directs the switching mechanism

[32] within the switch to either stay in Position 1 or move to Position 1, meaning that the heated fluid flows from the first heat exchanger (at the power controller) to the second heat exchanger (at the battery). When the heated fluid

[21] reaches the second heat exchanger

[26] , it transfers thermal energy to the battery, and in turn warms the battery

[22] and cools the heat transfer fluid. The cooled heat transfer fluid can then flow on to the third heat exchanger

[25] , In an alternative embodiment the cooled heat transfer fluid may flow directly back to the second heat exchanger. In either embodiment, the heat transfer fluid is returned to the second heat exchanger

[24] , re-heated and re-circulated. If at Step S42 the switch controller

[31] determined that the temperature of the battery

[22] was not below the target temperature for optimal operation (i.e., within the target temperature range or above the target temperature range) the process goes to Step S4YN1. The switch controller

[31] directs the switching mechanism to either stay in Position 2 or move to Position 2, meaning that the heated heat transfer fluid flows directly to the third heat exchanger

[25] , It is then able to use the third heat exchanger

[25] to remove heat from the system into the surroundings before flowing back to the first heat exchanger

[24] , This process is repeated while the load is drawing power from the battery

[22] or the source is charging the battery

[22] , References A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein. Electric Vehicle Range Testing: AAA proprietary research into the effect of ambient temperature and HVAC use on driving range and MPGe, American Automobile Association, February 2019 US11130384 US11325445 US20220216535 JP2021128821

Claims

1. A method of controlling battery temperature in a battery system, the battery system comprising:a battery,a power controller for controlling and / or conditioning power charged or discharged from the battery,a first heat exchanger in thermal communication with the power controller, anda second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication;the method comprising:transferring thermal energy from the power controller to the first heat exchanger,transferring thermal energy from the first heat exchanger to the second heat exchanger, andtransferring thermal energy from the second heat exchanger to the battery.

2. The method of claim 1 wherein the battery system further comprises a temperature controller, and the method further comprises:adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger using the temperature controller, to control the battery temperature.

3. The method of claims 2 wherein the battery system further comprises a third heat exchanger in thermal communication with the first and / or second heat exchangers, and the method further comprises:transferring thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, wherein transferring thermal energy to the third heat exchanger is simultaneous and / or sequential with transferring thermal energy from the first heat exchanger to the second heat exchanger.

4. The method of claim 3 wherein the third heat exchanger dissipates thermal energy to the environment.

5. The method of claim 3 or 4 wherein the method further comprises:adjusting the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger using the temperature controller, to control the battery temperature.

6. The method of claims 2 to 5 wherein the temperature controller receives status data obtained from the battery, and the temperature controller adjusts the rate of thermal energy transfer in response to the status data.

7. The method of claim 6 wherein the temperature controller compares status data obtained from the battery to previous status data obtained from the battery, to determine a change in the status data over time and / or a rate of change in the status data over time, and the temperature controller adjusts the rate of thermal energy transfer in response to the change and / or rate of change in the status data over time.

8. The method of claim 6 or 7 wherein the status data is battery temperature, battery internal resistance, battery voltage, battery current, battery capacity, battery state of charge, or a combination thereof.

9. The method of claims 6 to 8 wherein the temperature controller compares status data, the change in the status data over time and / or the rate of change in the status data over time to a target range, and adjusts the rate of thermal energy transfer to control the battery temperature, such that subsequent status data from the battery is maintained within the target range or is moved into the target range.

10. The method of claim 9 wherein the target range changes depending on the discharge or charge rate of the battery, or the subsequent discharge or charge rate of the battery.

11. The method of claim 9 or 10 wherein the status data is battery temperature and the target range is a target temperature range, and preferably the target temperature range is 12 °C or more, such as 20 °C or more, from 25 to 50 °C, or from 30 to 45 °C.

12. The method of claim 1 to 11 further comprising simultaneously and / or sequentially charging or discharging the battery at a C-rate of 3C or more, such as 5C or more, 10C or more, or 20C or more.

13. The method of claim 12 further comprising adjusting the rate of charging or discharging using the power controller, wherein the power controller receives status data obtained from the battery, and the power controller adjusts the rate of charging or discharging in response to the status data.

14. The method of claim 13 wherein the power controller compares the status data to a target range, and adjusts the rate of charging or discharging, such that subsequent status data from the battery is maintained within the target range or is moved into the target range, preferably wherein the status data is battery temperature and the target range is a target temperature range.

15. A battery system for controlling battery temperature, the battery system comprising: a battery,a power controller for controlling and / or conditioning power charged or discharged from the battery,a first heat exchanger in thermal communication with the power controller, anda second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication and the battery system is configured to transfer thermal energy from the first heat exchanger to the second heat exchanger.

16. The battery system of claim 15 further comprising a temperature controller for adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger, to control the battery temperature.

17. The battery system of claim 16 further comprising a third heat exchanger in thermal communication with the first and second heat exchangers, wherein the battery system is configured to transfer thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger simultaneously and / or sequentially with transferring thermal energy from the first heat exchanger to the second heat exchanger, preferably wherein the third heat exchanger is for dissipating thermal energy to the environment.

18. The battery system of claim 17 wherein the temperature controller is for adjusting the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, to control the battery temperature.

19. The battery system of claims 16 to 18 wherein the temperature controller comprises a battery sensor for obtaining status data from the battery, preferably wherein the sensor is for obtaining status data which is battery temperature, battery internal resistance, battery voltage or a combination thereof, more preferably wherein the sensor is a current sensor, voltage sensor, temperature sensor, or a combination thereof.

20. The battery system of claim 15 to 19, further comprising a heat transfer fluid in fluidic communication and thermal communication with the heat exchangers.

21. The battery system of claim 20 wherein the temperature controller comprises a valve for adjustably distributing the heat transfer fluid between the heat exchangers, to adjust the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger, and / orthe rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, where present, to control the battery temperature.

22. A battery system of claims 15 to 21 wherein the first heat exchanger comprises a thermally conductive interface between the heat transfer fluid and the power controller, and / or the second heat exchanger comprise a thermally conductive interface between the heat transfer fluid and a cathode and / or an anode of the battery.

23. A battery system of claims 15 to 22 wherein the battery comprises a working electrode comprising a niobium oxide or a niobium metal oxide.

24. A battery system of claims 15 to 23 wherein the power controller comprises a transistor, such as a metal-oxide-semiconductor field-effect transistor.

25. Use of the battery system of claims 15 to 24 for controlling the temperature of a battery at a temperature of 12 °C or more, such as 20 °C or more, from 25 to 50 °C, or from 30 to 45 °C.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS41ClaimsLD1. A method of controlling battery temperature in a battery system, the battery system comprising:a battery,a power controller for controlling and / or conditioning power charged or discharged from the battery,a temperature controller,a first heat exchanger in thermal communication with the power controller, anda second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication; the method comprising:transferring thermal energy from the power controller to the first heat exchanger, transferring thermal energy from the first heat exchanger to the second heat exchanger, transferring thermal energy from the second heat exchanger to the battery, adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger using the temperature controller, to control the battery temperature, wherein the temperature controller receives status data obtained from the battery, and the temperature controller adjusts the rate of thermal energy transfer in response to the status data, wherein the temperature controller compares status data, the change in the status data overtime and / or the rate of change in the status data overtime to a target range, and adjusts the rate of thermal energy transfer to control the battery temperature, such that subsequent status data from the battery is maintained within the target range or is moved into the target range, andsimultaneously charging the battery from a source or discharging the battery to a load using the power controller.

2. The method of claim 1 wherein the battery system further comprises a third heat exchanger in thermal communication with the first and / or second heat exchangers, and the method further comprises:transferring thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, wherein transferring thermal energy to the third heat exchanger is simultaneous or sequential with transferring thermal energy from the first heat exchanger to the second heat exchanger.

3. The method of claim 2 wherein the third heat exchanger dissipates thermal energy to the environment.

4. The method of claim 2 or 3 wherein the method further comprises:adjusting the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger using the temperature controller, to control the battery temperature.

5. The method of claims 1 to 4 wherein the temperature controller compares status data obtained from the battery to previous status data obtained from the battery, to determine a change in the status data over time and / or a rate of change in the status data over time, and the temperature controller adjusts the rate of thermal energy transfer in response to the change and / or rate of change in the status data over time.

6. The method of claims 1 to 5 wherein the status data is battery temperature, battery internal resistance, battery voltage, battery current, battery capacity, battery state of charge, or a combination thereof.

7. The method of claims 1 to 6 wherein the target range changes depending on the discharge or charge rate of the battery, or the subsequent discharge or charge rate of the battery.

8. The method of claims 1 to 7 wherein the status data is battery temperature and the target range is a target temperature range of 12 °C or more, such as 20 °C or more, from 25 to 50 °C, or from 30 to 45 °C.LDCM9. The method of claims 1 to 8 further comprising simultaneously charging or discharging the battery at a C-rate of 3C or more, such as 5C or more, 10C or more, or 20C or more.

10. The method of claim 9 further comprising adjusting the rate of charging or discharging using the power controller, wherein the power controller receives status data obtained from the battery, and the power controller adjusts the rate of charging or discharging in response to the status data.

11. The method of claim 10 wherein the power controller compares the status data to a target range, and adjusts the rate of charging or discharging, such that subsequent status data from the battery is maintained within the target range or is moved into the target range.

12. The method of claim 11 wherein the status data is battery temperature and the target range is a target temperature range.

13. A battery system for controlling battery temperature, the battery system comprising: a battery, a power controller for controlling and / or conditioning power charged or discharged from the battery,a first heat exchanger in thermal communication with the power controller, anda second heat exchanger in thermal communication with the battery, wherein the first and the second heat exchangers are in thermal communication and the battery system is configured to transfer thermal energy from the first heat exchanger to the second heat exchanger,a temperature controller for adjusting the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger, to control the battery temperature during charging or discharging of the battery, wherein:the temperature controller is for receiving status data obtained from the battery, and the temperature controller is for adjusting the rate of thermal energy transfer in response to the status data; andthe temperature controller compares status data, the change in the status data over time and / or the rate of change in the status data over time to a target range, and adjusts the rate of thermal energy transfer to control the battery temperature, such that subsequent status data from the battery is maintained within the target range or is moved into the target range.

14. The battery system of claim 13 further comprising a third heat exchanger in thermal communication with the first and second heat exchangers, wherein the battery system is configured to transfer thermal energy from the first heat exchanger and / or the second heat exchanger to the third heat exchanger simultaneously or sequentially with transferring thermal energy from the first heat exchanger to the second heat exchanger.LDCM15. The battery system of claim 14, wherein the third heat exchanger is for dissipating thermal energy to the environment.

16. The battery system of claim 14 or 15 wherein the temperature controller is for adjusting the rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, to control the battery temperature.

17. The battery system of claims 13 to 16 wherein the temperature controller comprises a battery sensor for obtaining status data from the battery, wherein the status data is battery temperature, battery internal resistance, battery voltage or a combination thereof.

18. The battery system of claims 13 to 16, wherein the temperature controller comprises a battery sensor for obtaining status data from the battery, wherein the sensor is a current sensor, voltage sensor, temperature sensor, or a combination thereof.

19. The battery system of claim 13 to 18, further comprising a heat transfer fluid in fluidic communication and thermal communication with the heat exchangers.

20. The battery system of claim 19 wherein the temperature controller comprises a valve for adjustably distributing the heat transfer fluid between the heat exchangers, to adjust the rate of thermal energy transfer from the first heat exchanger to the second heat exchanger, and / orthe rate of thermal energy transfer from the first heat exchanger and / or the second heat exchanger to the third heat exchanger, where present, to control the battery temperature.CMCM CM21. A battery system of claims 13 to 20 wherein the first heat exchanger comprises a thermally conductive interface between the heat transfer fluid and the power controller, and / or the second heat exchanger comprise a thermally conductive interface between the heat transfer fluid and a cathode and / or an anode of the battery.

22. A battery system of claims 13 to 21 wherein the battery comprises a working electrode comprising a niobium oxide or a niobium metal oxide.

23. A battery system of claims 13 to 22 wherein the power controller comprises a transistor, such as a metal-oxide-semiconductor field-effect transistor.

24. Use of the battery system of claims 13 to 23 for controlling the temperature of a battery at a temperature of 12 °C or more, such as 20 °C or more, from 25 to 50 °C, or from 30 to 45 °C.

Images