Energy-storage cell

Abstract

According to a first aspect of the disclosure, there is provided an energy-storage cell comprising: an anode; a cathode; a first solid-state electrolyte having a melting temperature above 300°C; and a second solid-state electrolyte having a melting temperature below 300°C; wherein the first solid-state electrolyte is configured to isolate the anode and cathode from one another; and wherein the second solid-state electrolyte is disposed at least partially between the cathode active material and the first solid-state electrolyte.

Description

[0001] Energy-storage cell

[0002] Field of the invention

[0003] The present disclosure relates to energy-storage cell technology, and more specifically to solid-state battery cell technology.

[0004] Background

[0005] Currently, lithium-ion batteries face significant limitations such as low energy and power densities, safety risks due to flammable liquid electrolytes, poor performance in cold temperatures and low affordability. Hence, there is a pressing need for improved batteries, especially improved solid-state batteries, to alleviate the problems associated with known lithium-ion batteries that concomitantly hinder the widespread adoption of electric vehicles (EVs).

[0006] It cannot be overemphasized that currently available lithium-ion cells have reached their performance limit due to the use of flammable liquid electrolytes. Moreover, lithium-ion batteries require expensive electronic protection circuitry (such as a battery management system, BMS) and cooling systems during pack assembly for electric vehicles, in order to mitigate the thermal runaway problem associated with flammable liquid electrolytes; this contributes significantly to the four-fold decrease in energy density at the pack level.

[0007] Finding an electrolyte that overcomes these problems is therefore a significant area of interest in battery research and development. One alternative is "solid-state cells", in which the flammable liquid electrolyte is replaced with a solid-state electrolyte.

[0008] Various inorganic solid-state electrolytes (ISSEs) that exhibit excellent roomtemperature ionic conductivity have emerged over the past decade. However, there are major hurdles in realizing all-solid-state cells (ASSCs) suitable for practical widespread usage. Challenges remain with existing fabrication protocols, and there are numerous issues with scaling existing technology beyond proof-of-concept examples that have been demonstrated in a lab. As a result, SSCs employing ISSEs have not yet been commercialised.

[0009] Extensive literature exists detailing the attempts that are being made to fabricate SSCs that can operate at room temperatures. Some existing solutions employ compression cells or solution-based processing routes. However, major challenges exist with scaling these processes, and the cells produced tend to fail quickly due to the degradation of the interfaces between the various components of the cell.

[0010] In particular, during the operation of known SSCs at room temperature, the typical expansion and contraction of the cathode or anode active materials tend to lead to interfacial voids and cell failure concomitantly. Currently, even with significant static pressures (2 < P < 700 MPa), the interfaces still rapidly degrade leading to failure as the cells operate at room temperature.

[0011] Some attempts to address this issue that are currently under investigation, globally, involve adding liquid (though flammable) or gel polymer electrolytes to the solid-state cells, in an attempt to improve room -temperature performance over time. Cells produced in this manner may be referred to as "quasi-solid-state battery cells". However, present examples of such cells do not perform well due to the low transference number of the quasi-solid-state electrolyte. Also, the use of metallic anodes like lithium or sodium for solid-state cells is very challenging due to the formation of dendrites. Sometimes, the dendrites propagate through sintered ceramic membranes regardless of their density.

[0012] There are solid-state batteries that are known operate at elevated temperatures in excess of 350° C. Such temperatures are required to provide practical ionic conductivity within the sodium P"-alumina ceramic membranes typically used in sodium-sulphur or zebra-type batteries. Apart from the low energy density of such batteries, the high operating temperature had raised safety issues and requires higher- cost materials for the cell housing and complex power management systems, limiting the use of this technology to large stationary installations or military applications.

[0013] There is a need, therefore, for an improved design of energy-storage cell that provides good performance while avoiding the issues associated with present solid and liquid electrolytes.

[0014] Summary of the invention

[0015] According to a first aspect of the disclosure, there is provided an energy-storage cell comprising: an anode; a cathode; a first solid-state electrolyte having a melting temperature above 300 °C; and a second solid-state electrolyte having a melting temperature below 300 °C; wherein the first solid-state electrolyte is configured to isolate the anode and cathode from one another; and wherein the second solid-state electrolyte is disposed at least partially between the cathode and the first solid-state electrolyte.

[0016] Isolating the anode from the cathode is vital in order for an energy-storage cell to operate, since otherwise electrical short circuiting will occur. Traditionally, a separator such as a porous polymer film is used to electrically isolate the anode from the cathode, while the porosity allows ions to cross the separator, via the liquid organic electrolyte, thereby facilitating charge and discharge of the energy-storage cell. However, a traditional separator will not function well (if at all) in higher temperature environments, and in particular when one or more of the electrodes (such as the anode) may be in a molten state. If one or more of the electrodes melts, then a porous isolator will not be able to effectively maintain separation between the anode and the cathode.

[0017] According to the present disclosure, the first solid-state electrolyte (SSE) acts in a similar way to a traditional polymeric separator, by electrically isolating the anode from the cathode. However, the first SSE does not need to be porous in order to facilitate the passage of ions, since the first SSE is an ionic conductor. This allows for the first SSE to isolate the anode and the cathode from one another, both electrically and physically, while facilitating the conduction of ions between the cathode and the anode during charging and discharging of the energy-storage cell.

[0018] The performance of energy-storage cells that use solid-state electrolytes typically degrade rapidly during use. This is because during charge and discharge the active materials of the energy-storage cell typically change in size, thereby causing separations in the interfacial bonds between the various components. These interfacial separations reduce the ionic as well as the electronic conductivity of the battery cell, thereby degrading the performance. The inclusion of the second SSE addresses this problem in the present disclosure.

[0019] The second SSE is disposed between the cathode and the first SSE, thereby facilitating ionic conductivity between the cathode and the first SSE. In a solid state (i.e., at temperatures below the melting point of the second SSE), the second SSE facilitates ionic conductivity. However, the second SSE has a relatively low melting temperature, and as such the second SSE can be melted while the first SSE constantly remains solid. In a molten state, the second SSE can heal any interfacial separations that may have occurred between the second SSE and the first SSE, and also between the second SSE and any other components disposed on the cathode side of the first SSE (for example, the cathode and / or cathode active material). The ionic conductivity of the second SSE may also increase when it is at least partially molten, thereby improving the performance of the energy-storage cell.

[0020] In an embodiment there is provided an energy-storage cell wherein the anode is metallic. Metallic anodes typically offer higher energy densities compared to non- metallic anodes, leading to more efficient energy storage. Furthermore, metallic anodes can be melted during operation, either constantly or periodically, in order to remove any dendrites that may form during use. Melting the metallic anode can also heal any interfacial separations that may occur between the anode and the first SSE.

[0021] In an embodiment there is provided an energy-storage cell wherein the anode comprises lithium or sodium. The SSE materials have good lithium- or sodium-ion conductivity, thereby facilitating the transport of ions during charge and discharge of the energy-storage cell.

[0022] In an embodiment there is provided an energy-storage cell wherein the anode comprises an alloy of lithium or an alloy of sodium. Using alloys of lithium or sodium can enhance the mechanical stability and reduce the dendrite formation, which is a common issue with pure metal anodes.

[0023] In an embodiment there is provided an energy-storage cell wherein the first solid-state electrolyte comprises an electrolyte material that can be densified by sintering. An electrolyte material has high ionic conductivity, facilitating good performance of the energy-storage cell. Densifying the first solid-state electrolyte by sintering can significantly improve its mechanical strength and structural integrity. This process reduces porosity and creates a more uniform and compact material, which can enhance the durability and longevity of the energy-storage cell. Additionally, a denser electrolyte can provide better ionic conductivity and reduce the risk of short circuits, leading to improved overall performance and safety of the cell.

[0024] In an embodiment there is provided an energy-storage cell wherein the first solid-state electrolyte comprises one or more of: garnet, a perovskite, a NASICON, or their respective derivatives. Materials like garnets, perovskites, and NASICONs are known for their high ionic conductivity at room temperature and stability, which can improve the efficiency and safety of the cell. Furthermore, each of these materials have a high melting point and good mechanical properties, thereby improving the mechanical durability of the cell. In an embodiment there is provided an energy-storage cell wherein the second solid- state electrolyte comprises one or more of: a ternary halide, an antiperovskite, or their respective derivatives. Ternary halides and anti perovskites can offer good ionic conductivity at room temperature and at their relatively low melting points. The good ionic conductivity facilitates good performance of the cell, while the low melting point is beneficial for the self-healing properties of the second SSE discussed above.

[0025] In an embodiment there is provided an energy-storage cell wherein the second electrolyte has a melting point of at least 25 °C. A melting point of at least 25 °C ensures that the second electrolyte remains solid at room temperature but can melt to heal defects during operation, maintaining cell integrity.

[0026] In an embodiment there is provided an energy-storage cell wherein the cathode comprises one or more of: a lithium-based insertion electrode, a sodium-based insertion electrode, or a conversion electrode. Insertion and conversion electrodes provide high capacity and stability, enhancing the overall performance of the cell.

[0027] In an embodiment there is provided an energy-storage cell comprising a lithium-based insertion cathode, the lithium-based insertion cathode comprising one or more of: LiNio.5Coo.2Mno.3O2, xLizMnOs (l-x)LiMO2, LiFeP04, LiCoPO4, LisV2(PO4)3, or their respective derivatives; wherein M is Mn, Ni, Co, Cr, or Fe. These particular compounds are known for their high capacity, stability, and good cycling performance, which are crucial for efficient energy storage.

[0028] In an embodiment there is provided an energy-storage cell comprising a sodium-based insertion cathode, the sodium-based insertion cathode comprises one or more of: NaNii / sFei / sMni / sC , NaFePC , NaVPC F, NasV2(PO4)2F3, or their respective derivatives. These compounds offer good electrochemical performance and are more abundant and may be less expensive than lithium, making the cells easier to produce and more cost- effective.

[0029] In an embodiment there is provided an energy-storage cell wherein the conversion cathode comprises MXV, wherein: M is a metal, X is selected from the group consisting of chlorine or fluorine, and y is an integer. Conversion cathodes can provide higher capacities than traditional insertion cathodes, leading to improved energy density. In an embodiment there is provided an energy-storage cell further comprising a third solid-state electrolyte, the third solid-state electrolyte being disposed, at least partially, between the cathode (and / or cathode active material) and the first solid-state electrolyte. Introducing a third solid-state electrolyte can further enhance the roomtemperature ionic conductivity and stability of the cell, improving the overall performance.

[0030] In an embodiment there is provided an energy-storage cell wherein the third solid- state electrolyte has a melting point of at least 200 °C, and optionally above 300 °C. A higher melting point for the third solid-state electrolyte improves the stability at elevated temperatures, contributing to the safety and reliability of the cell.

[0031] In an embodiment there is provided an energy-storage cell wherein the third solid- state electrolyte has a melting point which is at least 10 °C higher than the melting point of the second solid-state electrolyte. A higher melting point for the third solid- state electrolyte improves the stability at elevated temperatures, contributing to the safety and reliability of the cell.

[0032] In an embodiment there is provided an energy-storage cell wherein the third solid- state electrolyte has a higher room-temperature ionic conductivity than the second solid-state electrolyte. Higher room-temperature ionic conductivity can reduce internal resistance, improving the efficiency and power output of the cell.

[0033] In an embodiment there is provided an energy-storage cell wherein the third solid- state electrolyte comprises: argyrodite, LISICON-like, ternary halide, antiperovskite. Such compounds are known for their high ionic conductivity and stability, which can enhance the overall performance of the cell.

[0034] In an embodiment there is provided an energy-storage cell wherein the ternary halide comprises one or more of: A3MIX6 wherein X is an anion, A is an alkali metal, and Ml is a trivalent cation; A2M2X4 wherein X is an anion, A is an alkali metal, and M2 is a divalent metal; A2M3X6 wherein X is an anion, A is an alkali metal, and M3 is a tetravalent metal; AsM'i-zM'zXe wherein M' and M" are trivalent cations, divalent metals, or tetravalent metals, and z is an integer; or As-zM'i-zM'zXe wherein M' and M" are trivalent cations, divalent metals, or tetravalent metals, and z is an integer. These ternary halide compositions can offer tailored properties for improved ionic conductivity and stability, optimizing the cell's performance. According to a second aspect of the present disclosure, there is provided a battery comprising two or more of the cells according to any preceding claim. Combining multiple cells can increase the overall capacity and power output, making the battery suitable for larger applications. As some of the components of the cell melt (at least partially), either constantly or intermittently, the battery of this disclosure may be referred to as a "solid-molten-state battery" (SMSB) instead of solid-state battery (SSB); and the cell may be referred to as a "solid-molten-state battery cell" (or SMSB cell) instead of solid-state battery cell.

[0035] According to a third aspect of the present disclosure, there is provided method of use of a battery according to the second aspect and / or one or more cells according to the first aspect, in an electrically powered device wherein, optionally, the electrically powered device is an electric vehicle. The ability to use these cells in electric vehicles and other devices highlights their versatility and potential for widespread application.

[0036] In an embodiment there is provided a method of use of a battery wherein the anode becomes at least partially molten, constantly or periodically, during operation of the cell or battery. A partially molten anode can improve contact with the first SSE, reducing internal resistance and enhancing performance. Furthermore, at least partially melting an anode facilitates the removal of dendrites that may form during operation of the battery when the anode is in a solid state.

[0037] In an embodiment there is provided a method of use of a battery wherein the second solid-state electrolyte becomes at lest partially molten during operation of the cell or battery. The self-healing property of the second SSE, which is based on the second SSE being at least partially molten, ensures continuous operation and longevity of the cell by healing any voids that form during use.

[0038] According to a fourth aspect of the present disclosure, there is provided an electrically powered device or system, comprising one or more cells according to the first aspect and / or one or more batteries according to the second aspect. Integrating these advanced cells into devices or systems instead of more traditional energy-storage cells can significantly improve their energy efficiency, reliability, and performance.

[0039] Brief description of the drawings

[0040] There now follows a brief description of embodiments of the present disclosure, by way of non-limiting examples, with reference made to the following figures in which: Figure 1 illustrates an example of an energy-storage cell according to the present disclosure;

[0041] Figure 2 illustrates the energy-storage cell shown in figure 1, wherein the second solid-state electrolyte has at least partially melted;

[0042] Figure 3 illustrates a further example of an energy-storage cell according to the present disclosure;

[0043] Figure 4 illustrates a cross section through an encapsulated cathode, as illustrated in figure 3; and

[0044] Figure 5 illustrates a further example of an energy-storage cell according to the present disclosure.

[0045] Detailed description

[0046] In order to address the issues identified with existing battery cell technologies discussed above, the present invention provides a novel solid-state energy-storage cell. By using solid-state electrolytes (SSE), many of the issues associated with traditional liquid-electrolyte storage cell designs (including flammability, thermal runaway, poor ionic transport, limited operating temperature ranges) can be avoided. Furthermore, the SMSB cell design, using a SSE with a low melting temperature, as discussed in more detail below, can mitigate issues with existing solid-state energy storage designs including limited lifespan, low energy and power densities and poor interfaces.

[0047] Figure 1 illustrates an energy-storage cell 100 according to the present disclosure. The energy-storage cell 100 comprises an anode 101. During discharge of an energystorage cell 100, the anode 101 releases electrons into an attached electrical circuit. During charging, the anode 101 receives electrons from an attached electrical circuit. The anode 101 may be of any suitable material, however in some examples the anode 101 may comprise a metal. Metallic anode 101s offer high energy densities compared to non-metallic anode 101s, leading to more efficient energy storage. In some examples, the anode 101 may comprise lithium or sodium metal. In other examples, the anode 101 may comprise a lithium alloy or a sodium alloy. Alloys may be beneficial in improving performance, and in resisting dendrite formation.

[0048] The energy-storage cell 100 further comprises a cathode 102. During discharge of an energy-storage cell 100, the cathode 102 receives electrons from an attached electrical circuit. During charging, the cathode 102 releases electrons into an attached electrical circuit. In some examples, the cathode 102 may comprise a lithium- or sodium-based insertion or conversion cathode 102. In some examples, a sodium-based insertion cathode 102 may comprise one or more of: NaNii / sFei / sMni / sOz, NaFePC , NaVPC F, Na3V2(PO4)2F3, or their respective derivatives. These compounds offer good electrochemical performance and are more abundant and may be less expensive than lithium-based alternatives, making the cells easier to produce and more cost-effective.

[0049] In some examples, a conversion cathode 102 may comprise MXV, wherein: M is a metal, X is selected from the group consisting of chlorine or fluorine, and y is an integer. Conversion cathodes can provide higher capacities than traditional insertion cathodes, leading to improved energy density.

[0050] In the illustrated example, the cathode is included in the form of particles of cathode active material (CAM) 102. By being formed as a plurality of particles, instead of a monolithic cathode, the CAM 102 can be spread more evenly through the energystorage cell 100 thereby minimising the distance that ions need to travel during charge and discharge of the energy-storage cell 100. In the present disclosure, the terms "cathode", "cathode active material", and "CAM" may be used interchangeably.

[0051] In the illustrated example, the CAM 102 particles each comprise a thin surface coating. Such a coating helps to improve the chemical stability of the material, to allow processing without degrading in air. In some examples, the coating is ionically and electrically conductive, thereby to facilitate the conduction of electrons without significantly inhibiting the passage of ions into and out of the CAM particles. The coating may comprise any suitable material, including carbon.

[0052] The energy-storage cell 100 further comprises a first SSE 103 configured to isolate the anode 101 and cathode active material 102 from one another. Isolating the anode 101 and cathode active material 102 from each other, both physically and electrically, is vital in order to ensure that internal short circuiting of the energy-storage cell 100 does not occur. The first SSE 103 is configured to isolate the anode 101 and cathode active material 102 from each other, but also to conduct charge carrying ions between the anode 101 and the cathode active material 102 during charge and discharge of the energy-storage cell 100.

[0053] The first SSE 103 is substantially electrically insulating, thereby to electrically isolate the anode 101 and the cathode active material 102 from each other, but it must also be an ionic conductor for the charge carrying ions used in the energy-storage cell 100 (for example, lithium or sodium ions). Furthermore, according to the present disclosure, the first SSE 103 has a melting point of at least 300 °C. The "melting point" is understood be to be the melting point at atmospheric pressure. Any suitable measurement method known in the art may be used to determine the melting point. Having a high melting point is important for the first SSE 103 to be able to isolate the anode 101 and the cathode active material 102 from each other, even when operating at elevated temperatures.

[0054] The first SSE 103 comprising a high melting point material may be particularly beneficial in examples where one or more components of the energy-storage cell 100 may be at least partially molten. As noted above, constantly or periodically melting the anode 101 metal may be beneficial in removing dendrites that can form during charge and discharge cycles. As noted above, the anode 101 and cathode active material 102 must be physically and electrically isolated from each other for the energy-storage cell 100 to operate. Thus, by comprising a high melting point material, the first SSE 103 can ensure that this isolation is maintained even when the anode 101 is at least partially molten.

[0055] Any suitable material may be used for the first SSE 103. In some examples, the first SSE 103 may be a high-melting point ISSE such as garnet (Li6.4La3Zn.4Tao.6O12), perovskite (Lio.34Lao.56Ti03), Nasicon-like (Lii.3Alo.3Tii.7(P04)3), or their derivatives, or any suitable SSE that can be densified by sintering. Such materials have good ionic conductivity, are substantially electrically insulating, and can be sintered to have good mechanical properties thereby ensuring that the energy-storage cell 100 is physically strong and durable.

[0056] The energy-storage cell 100 further comprises a second SSE 104. The second SSE 104 is disposed on the cathode side of the first SSE 103 at least partially between the cathode active material 102 and the first SSE 103. The second SSE 104 is configured to facilitate the transport of ions between the cathode active material 102 and the first SSE 103.

[0057] The second SSE 104 has a melting point below 300 °C. In some examples, the second SSE 104 has a melting point of 25 °C to 295 °C, such as from 100 °C to 290 °C, in particular from 140 °C to 285 °C. In some examples, the first SSE 103 has a melting point of at least 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 225, or 250 °C. In some examples, the second SSE 104 has a melting point of up to 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 265, 270, 275, 280, 285, 290, 295, or 300 °C.

[0058] As discussed previously, a major challenge with existing solid-state energy-storage cell 100s is maintaining a good interfacial connection between the solid-state electrolyte and the electrode active materials. In the present disclosure, this issue is overcome by the inclusion of the second SSE 104. The second SSE 104 is disposed between the first SSE 103 and the cathode active material 102, thereby facilitating ionic conductivity between the cathode active material 102 and the first SSE 103. The second SSE 104 is able to conduct ions in a solid state, and thus the energy-storage cell 100 may be charged and discharged while the second SSE 104 is in a solid state. During charge and discharge cycles, the dimensions of the various components including the cathode active material 102 will typically change. In existing solid-state energy-storage cells, this causes the interfacial connection between the cathode active material 102 and the solid-state electrolyte to break down, inhibiting ionic conductivity and causing the solid- state cell to fail quickly. However, as noted above, the second SSE 104 of the present disclosure has a low melting temperature, which allows for the second SSE 104 to be periodically melted.

[0059] Figure 2 illustrates an example of an energy-storage cell 100 wherein the second SSE 104 is in a molten state. As illustrated in the example, when in an at least partially molten state, the second SSE 104 is able to flow and to thereby heal any interfacial separations that may have been formed, which were inhibiting ionic conductivity. Such interfacial separations may form between the second SSE 104 and any other components, such as the cathode active material 102 and / or first SSE 103. Interfacial separations, or voids, may also form between other components in use, such as between the cathode active material 102 and the first SSE 103. Thus, any such interfacial separations that may occur during operation of the energy-storage cell 100 can be healed and ionic conductivity restored by at least partially melting the second SSE 104.

[0060] In some examples, the second SSE 104 is able to conduct charge-carrying ions in a molten state, and so when molten the second SSE 104 is still able to facilitate conduction of the charge carrying ions between the cathode active material 102 and the first SSE 103. Thus, in such examples, the energy-storage cell 100 can still be charged or discharged (i.e., can operate normally) during this process. In some examples, an energy-storage cell 100 according to the present disclosure may be periodically thermally cycled in order to melt the second SSE 104 and to thereby restore any lost ionic conductivity. In some examples, a similar thermal cycle may be applied to the anode 101 in order to at least partially melt the anode 101, thereby to heal any separations or dendrites that may have occurred between the anode 101 and the first SSE 103.

[0061] The second SSE 104 may comprise any suitable material. In some examples, the second SSE 104 comprises an inorganic solid-state electrolyte. Examples of suitable materials for the second SSE 104 include ternary halides (such as NaAICk, LiAICk), antiperovskites (such as LisOCI, NasOCI), and their respective derivatives.

[0062] In some examples, the cathode containing portion of the energy-storage cell 100 may be referred to as the "cathode" or alternatively as the "cathode composite". The term cathode composite may refer to a combination of materials disposed on the cathode side of the first SSE 103, and which are isolated from the anode 101 by the first SSE 103. The cathode composite according to the present disclosure comprises at least the cathode active material 102 (which may be in the form of CAM particles) and the second SSE 104. As discussed below, the cathode composite may comprise further components. For simplicity, the term cathode composite may be used, however it should be understood that this term simply refers to the combination of components arranged on the cathode side of the first SSE 103. The cathode composite may not necessarily be a single composite material, but rather a combination of components that act together to facilitate the function of the cathode in an energy-storage cell 100 according to the present disclosure.

[0063] In the illustrated example, the energy-storage cell 100 further comprises a positive current collector 106. The positive current collector 106 is an electrically conductive component that is configured to facilitate the movement of electrons into, and out of, the cathode composite during discharging and charging of the energy-storage cell 100. The positive current collector 106 is in electrical contact with the cathode composite. The positive current collector 106 may comprise any suitable material, including aluminium foil.

[0064] In the illustrated examples, the positive current collector 106 is electrically connected to a positive tab 107. The positive tab 107 is configured for connection with an external electrical circuit in order to facilitate charge, or discharge, of the energy-storage cell 100. In the illustrated example, the energy-storage cell 100 further comprises a negative current collector 108. The negative current collector 108 is an electrically conductive component that is configured to facilitate the movement of electrons out of, and in to, the anode 101 during discharging and charging of the energy-storage cell 100. The negative current collector 108 is in electrical contact with the anode 101. The negative current collector 108 may comprise any suitable material, including copper.

[0065] In the illustrated examples, the negative current collector 108 is electrically connected to a negative tab 107. The negative tab 107 is configured for connection with an external electrical circuit in order to facilitate charge, or discharge, of the energystorage cell 100.

[0066] In the illustrated examples, the cathode composite further comprises one or more conductive additive 105. The conductive additive 105 comprises particles of an electrically conductive material that may be included in the cathode composite in order to increase the electrical conductivity of the cathode composite. Increasing the electrical conductivity of the cathode composite can improve the efficiency of the energy-storage cell 100, by reducing internal resistance and by facilitating the conduction of electrons between the CAM particles and the positive current collector 106.

[0067] In some examples, the ionic conductivity of the cathode composite may be improved by including a third SSE that has a higher ionic conductivity than the second SSE 104. The third SSE (not shown in the illustrations) has a higher ionic conductivity than the second SSE 104 but also a higher melting point than the second SSE 104. This means that the third SSE may be unable to melt and thus heal any interfacial voids that may form during operation of the energy-storage cell 100. However, by including the third SSE in place of some of the second SSE 104, the ionic conductivity of the carbon composite may be improved, particularly the room-temperature ionic conductivity, while maintaining the beneficial healing properties of the second SSE 104.

[0068] In some examples, the third SSE has a melting point of at least 200 °C. In some examples, the third SSE has a melting point of at least 300 °C. In some examples, the third SSE has a melting point of at least 10 °C higher than the melting point of the second SSE 104. In some examples, the third SSE has a melting point of at least 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 225, or 250 °C higher than the melting point of the second SSE 104. In some examples, by having an elevated melting point, the third SSE may be able to improve the ionic conductivity of the cathode composite and may also be able to improve the structural stability of the cathode composite.

[0069] In some examples, the third SSE may comprise any suitable material. In some examples, the third SSE may comprise an inorganic solid-state electrolyte. Suitable materials include:

[0070] A3MIX6 where X is an anion, A is an alkali metal, and Ml is a trivalent cation;

[0071] A2M2X4 where X is an anion, A is an alkali metal, and M2 is a divalent metal;

[0072] A2M3X6 where X is an anion, A is an alkali metal, and M3 is a tetravalent metal;

[0073] AsM'i-zM'zXe where M' and M" are trivalent cations, divalent metals, or tetravalent metals, and z is an integer; and

[0074] A3-ZM'I-ZM"ZX6 wherein M' and M" are trivalent cations, divalent metals, or tetravalent metals, and z is an integer.

[0075] In some examples, X is a halide, such as chloride, bromide or iodide. In some examples, A is lithium or sodium. In some examples, X is chloride and / or A is lithium.

[0076] In some examples, the third SSE may comprise a ternary halide. In some examples, the third SSE may comprise A3MIX6. In some examples, Ml is a trivalent cation selected from indium, yttrium, lanthanum, ytterbium and zirconium. In some examples, the third SSE may comprise LisInCle.

[0077] Figure 3 illustrates a further example of an example of an energy-storage cell 200 according to the present disclosure. In the illustrated example, the energy-storage cell 200 comprises a plurality of encapsulated cathodes 202 and a plurality of anodes 201. In some examples, the plurality of anodes 201 may be isolated from one another whereas in others the anodes 201 may be continuous.

[0078] Figure 4 illustrates a cross section through an encapsulated cathode 202. In the illustrated example, the encapsulated cathode 202 has an outer surface comprising the first SSE 203. The cathode composite is disposed inside the outer surface, and the encapsulated cathode 202 further comprises a positive current collector 205 that is in electrical contact with the cathode composite. As with the previously described examples, the cathode composite comprises the cathode active material (which may be in the form of coated particles) and the second SSE. Optionally, the cathode composite may further comprise conductive additives and a third SSE. The encapsulated cathodes 202 allows for the various components of the cathode composite to be contained and isolated from the anode(s) 201, even in examples where one or more components of the cathode composite may be at least partially molten. Furthermore, by substantially encapsulating the cathode composite, the anode 201 can be isolated from the cathode composite even in examples where the anode 201 may become at least partially molten.

[0079] In some examples, the outer surface of the encapsulated cathode 202 may be formed entirely from the first SSE 203. In other examples, the outer surface may comprise one or more additional materials. In some examples, the outer surface may comprise the first SSE 203 only in areas where ionic conductivity is needed in order to facilitate charge and discharge of the energy-storage cell 200. For example, at the top and bottom of the cell illustrated in figure 3, there is no adjacent anode 201. The anode 201 is instead disposed between the adjacent encapsulated cathodes 202. Therefore, the top and bottom of the encapsulated cathodes 202 may not need to be ionically conductive. In some examples, the top and / or the bottom of the encapsulated cathodes 202 may be formed of a material other than the first SSE 203. This may facilitate easier assembly of the encapsulated cathodes 202, since materials other than the first SSE 203 may be easier to use in order to seal the encapsulated cathodes 202.

[0080] In the illustrated example, the energy-storage cell 200 is contained within a housing. The housing may comprise any suitable material.

[0081] Figure 5 illustrates a cross-section through a further example of an energy-storage cell 300 according to the present disclosure. In the illustrated example, the first SSE 303 is formed into crucible-like shapes. These shapes are configured such that they can be stacked, as shown in figure 5, although this is merely one example of a suitable shape. In some examples, the first SSE 303 may be formed into substantially identical shapes, in other examples each layer may comprise a different shape. The first SSE 303 may be formed into such shapes through any suitable method, for example hot pressing, spark-plasma sintering, or 3D printing.

[0082] The energy-storage cell 300 illustrated in figure 5 is formed by stacking the shaped first SSE 303 components, with alternating layers of anode 301 and cathode composite disposed between the first SSE 303 layers. The alternating layers of anode 301 and cathode composite may each then be sealed with a suitable sealant 311. Current collectors and tabs (not shown) are also added, such that the energy-storage cell 300 may be connected to an external electrical circuit in order to charge or discharge the energy-storage cell 300.

[0083] An energy-storage cell 300 as illustrated in figure 5 may be simple and easy to assemble, thereby reducing the cost and complexity of manufacturing.

[0084] Although the invention has been described in considerable detail in language specific to structural features, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features described. Rather, the specific features are disclosed as exemplary forms of implementing the claimed invention.

[0085] Stated otherwise, it is to be understood that the phrases and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. Therefore, while exemplary illustrative embodiments of the invention have been described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention.

Claims

Claims1. An energy-storage cell comprising: an anode; a cathode; a first solid-state electrolyte having a melting temperature above 300 °C; and a second solid-state electrolyte having a melting temperature below 300 °C; wherein the first solid-state electrolyte is configured to isolate the anode and cathode from one another; wherein the second solid-state electrolyte is disposed at least partially between the cathode and the first solid-state electrolyte; and the cell further comprising a third solid-state electrolyte, the third solid-state electrolyte being disposed, at least partially, between the cathode and the first solid- state electrolyte.

2. The cell of claim 1, wherein the anode is metallic.

3. The cell of claim 2, wherein the anode comprises lithium or sodium.

4. The cell of claim 3, wherein the anode comprises an alloy of lithium or an alloy of sodium.

5. The cell according to any preceding claim, wherein the first solid-state electrolyte comprises an electrolyte material that can be densified by sintering.

6. The cell of any preceding claim, wherein the first solid-state electrolyte comprises one or more of: garnet, a perovskite, a NASICON, or their respective derivatives.

7. The cell of any preceding claim, wherein the second solid-state electrolyte comprises one or more of: a ternary halide, an antiperovskite, or their respective derivatives.

8. The cell of any preceding claim, wherein the second solid-state electrolyte has a melting point of at least 25 °C.

9. The cell of any preceding claim, wherein the cathode comprises one or more of: a lithium-based insertion material, a sodium-based insertion material, or a conversion material.

10. The cell of claim 9, wherein the lithium-based insertion material comprises one or more of: LiNio.5Coo.2Mno.3O2, xLizMnOs (l-x)LiMO2, LiFeP04, LiCoPO4, LisV2(PO4)3, or their respective derivatives; wherein M is Mn, Ni, Co, Cr, or Fe.

11. The cell of claims 9 or 10, wherein the sodium-based insertion cathode material comprises one or more of: NaNii / 3Fei / 3Mni / 3O2, NaFeP04, NaVP04F, NasV2(PO4)2F3, or their respective derivatives.

12. The cell of any of claims 9 to 11, wherein the conversion cathode comprises MXV, wherein : M is a metal, X is selected from the group consisting of chlorine or fluorine, and y is an integer.

13. The cell of any preceding claim, wherein the third solid-state electrolyte has a melting point of at least 200 °C, and optionally above 300 °C.

14. The cell of any preceding claim, wherein the third solid-state electrolyte has a melting point which is at least 10 °C higher than the melting point of the second solid- state electrolyte.

15. The cell according to any preceding claim, wherein the third solid-state electrolyte has a higher ionic conductivity than the second solid-state electrolyte.

16. The cell according to any preceding claim, wherein the third solid-state electrolyte comprises: argyrodite, LISICON-like, ternary halide, or antiperovskite.

17. The cell according to claim 16, wherein the ternary halide comprises one or more of:A3MIX6 wherein X is an anion, A is an alkali metal, and Ml is a trivalent cation; A2M2X4 wherein X is an anion, A is an alkali metal, and M2 is a divalent metal;A2M3X6 wherein X is an anion, A is an alkali metal, and M3 is a tetravalent metal;AsM'i-zM'zXe wherein M' and M" are trivalent cations, divalent metals, or tetravalent metals, and z is an integer; orAs-zM'i-zM'zXe wherein M' and M" are trivalent cations, divalent metals, or tetravalent metals, and z is an integer.

18. An energy-storage cell comprising: an anode; a cathode; a first solid-state electrolyte having a melting temperature above 300 °C; and a second solid-state electrolyte having a melting temperature below 300 °C; wherein the first solid-state electrolyte is configured to isolate the anode and cathode from one another; and wherein the second solid-state electrolyte is disposed at least partially between the cathode and the first solid-state electrolyte.

19. A battery comprising two or more of the cells according to any preceding claim.

20. A method of use of the battery according to claim 19, or the cells of any of claims 1 to 18, in an electrically powered device wherein, optionally, the electrically powered device is an electric vehicle.

21. A method according to claim 20, wherein the anode becomes at least partially molten during operation of the cell or battery.

22. A method according to claims 20 or 21, wherein the second solid-state electrolyte becomes at least partially molten during operation of the cell or battery.

23. An electrically powered device or system, comprising one or more cells according to any of claims 1 to 18, and / or one or more batteries according to claim 19.

Images