Composite positive electrode material, positive plate and lithium ion battery

Abstract

The invention relates to a composite positive electrode material, a positive plate and a lithium ion battery. The composite positive electrode material comprises a lithium battery positive electrode active material, a lithium supplement agent and a sodium battery positive electrode active material, the discharge voltage lower limit V3 of the lithium supplement agent is greater than or equal to the discharge voltage lower limit V1 of the lithium battery positive electrode active material and less than or equal to the charge voltage upper limit V2 of the lithium battery positive electrode active material; the discharge voltage lower limit V5 of the sodium battery positive electrode active material is greater than or equal to V3 and less than or equal to the charge voltage upper limit V4 of the lithium supplement agent. Therefore, after the lithium battery positive electrode active material releases lithium ions, the lithium supplementing agent can timely release the lithium ions to effectively supplement lithium, and when the lithium supplementing agent releases oxygen due to unstable structure caused by deintercalation of certain lithium ions, the sodium battery positive electrode active material can deintercalate sodium ions to inhibit the lithium supplementing agent from releasing oxygen, so that the lithium battery positive electrode active material can effectively supplement lithium. Therefore, the gas production rate of the battery is effectively reduced while the lithium supplement effect of the lithium supplement agent is fully exerted, the cycle life of the battery is prolonged, and the safety risk is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a composite cathode material, a cathode sheet and a lithium-ion battery. Background Art

[0002] During the first charge of a lithium-ion battery, the organic electrolyte will undergo a reductive decomposition reaction on the surface of the negative electrode to form a solid electrolyte interface (SEI) film. This process will irreversibly consume a large amount of active lithium from the positive electrode, resulting in a low initial Coulombic efficiency of the lithium-ion battery, thereby reducing the energy density and capacity of the lithium-ion battery.

[0003] To address the above problems, by pre-inserting a lithium supplement agent into the positive electrode and using the lithium released by the lithium supplement agent to supplement the irreversibly consumed active lithium, the capacity loss of the lithium-ion battery can be compensated to extend the cycle life.

[0004] However, during the lithium supplementation process of the lithium supplement agent, due to the extraction and insertion of a large amount of lithium ions, its structure will become unstable, and a large amount of oxygen will be released, generating oxygen and oxidizing the electrolyte, resulting in serious gas generation during high-temperature standing and cycling of the battery, and further leading to problems such as cycle attenuation and even cycle dives, and there are significant safety hazards. Summary of the Invention

[0005] In view of this, embodiments of the present application provide a composite cathode material, a cathode sheet and a lithium-ion battery to solve at least one problem in the background art.

[0006] In a first aspect, embodiments of the present application provide a composite cathode material, including a lithium-ion battery cathode active material, a lithium supplement agent, and a sodium-ion battery cathode active material;

[0007] The lower discharge voltage limit V3 of the lithium supplement agent is greater than or equal to the lower discharge voltage limit V1 of the lithium-ion battery cathode active material and less than or equal to the upper charge voltage limit V2 of the lithium-ion battery cathode active material;

[0008] The lower discharge voltage limit V5 of the sodium-ion battery cathode active material is greater than or equal to V3 and less than or equal to the upper charge voltage limit V4 of the lithium supplement agent.

[0009] Combined with the first aspect of the present application, in an optional embodiment, V4 is greater than V2; and / or, the upper charge voltage limit V6 of the sodium-ion battery cathode active material is greater than V4.

[0010] Combined with the first aspect of the present application, in an optional embodiment, the ratio of the molar amount of sodium ions that the sodium-ion battery cathode active material can release to the molar amount of lithium ions that the lithium supplement agent can release is greater than or equal to 0.6 and less than or equal to 1.

[0011] Combined with the first aspect of the present application, in an alternative embodiment, the sodium battery cathode active material includes at least one of polyanionic compounds, layered transition metal oxides, and Prussian blue compounds, preferably polyanionic compounds, and more preferably Na3V2(PO4)2F3.

[0012] Combined with the first aspect of the present application, in an alternative embodiment, the lithium supplementing agent includes at least one of Li2NiO2, Li5FeO4, Li2MoO3, Li6CoO4, and Li2O2, preferably Li5FeO4.

[0013] Combined with the first aspect of the present application, in an alternative embodiment, the lithium battery cathode active material includes at least one of ternary cathode materials, lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, and lithium-rich manganese-based materials.

[0014] Combined with the first aspect of the present application, in an alternative embodiment, the mass of the lithium supplementing agent is 0.5% - 4% of the mass of the lithium battery cathode active material; the mass of the sodium battery cathode active material is 1% - 12% of the mass of the lithium battery cathode active material.

[0015] In the second aspect, an embodiment of the present application provides a positive electrode sheet, which includes a current collector and a positive electrode active material layer located on at least one surface of the current collector, and the positive electrode active material layer includes the composite positive electrode material according to any one of the first aspect.

[0016] Combined with the second aspect of the present application, in an alternative embodiment, the positive electrode active material layer further includes a binder and a conductive agent. Based on the total weight of the positive electrode active material layer being 100%, the weight percentage content of the lithium battery cathode active material is 80% - 98%, the weight percentage content of the binder is 1% - 10%, and the weight percentage content of the conductive agent is 0.1% - 5%.

[0017] In the third aspect, an embodiment of the present application provides a lithium ion battery, which includes the positive electrode sheet according to any one of the second aspect.

[0018] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0019] The composite cathode material, cathode sheet and lithium-ion battery provided by the embodiments of the present application, the composite cathode material includes a lithium battery cathode active material, a lithium supplement agent and a sodium battery cathode active material; the lower discharge voltage limit V3 of the lithium supplement agent is greater than or equal to the lower discharge voltage limit V1 of the lithium battery cathode active material and less than or equal to the upper charge voltage limit V2 of the lithium battery cathode active material; the lower discharge voltage limit V5 of the sodium battery cathode active material is greater than or equal to V3 and less than or equal to the upper charge voltage limit V4 of the lithium supplement agent. By setting V3 between V1 and V2, that is, the lower discharge voltage limit of the lithium supplement agent is between the lower discharge voltage limit and the upper charge voltage limit of the lithium battery cathode active material, so that after the lithium battery cathode active material releases lithium ions, the lithium supplement agent can release lithium ions in time for effective lithium supplementation. At the same time, V5 is set between V3 and V4, that is, the lower discharge voltage limit of the sodium battery cathode active material is between the lower discharge voltage limit and the upper charge voltage limit of the lithium supplement agent. In this way, when a certain amount of lithium ions are deintercalated from the lithium supplement agent, resulting in the instability of its structure and the release of oxygen, the sodium battery cathode active material can deintercalate sodium ions, and the positively charged sodium ions can combine with the negatively charged oxygen anions to form sodium oxide to coat the lithium supplement agent, inhibiting the release of oxygen, and thus effectively alleviating the problem of battery gas generation caused by the side reaction of the oxygen released by the lithium supplement agent with the electrolyte; in addition, the sodium ions released by the sodium battery cathode active material can also be evenly distributed with the lithium supplement agent after releasing lithium ions, improving the charge uniformity, further inhibiting the release of oxygen by the lithium supplement agent, thereby effectively reducing the battery gas generation while ensuring that the lithium supplement agent fully exerts the lithium supplementation effect, and further improving the cycle life of the battery and reducing the safety risk.

[0020] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The illustrative embodiments and descriptions thereof of the present application are used to explain the present application, and do not constitute an improper limitation of the present application. In the drawings:

[0022] Figure 1 It is a schematic diagram of the charge and discharge voltage ranges of the lithium battery cathode active material, lithium supplement agent and sodium battery cathode active material in the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following is a detailed description by combining the drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0024] In the following description, numerous specific details are given to provide a more thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application may be practiced without one or more of these details. In other instances, some technical features known to the art are not described in order to avoid obscuring the present application; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0025] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. When used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. The terms "comprising" and / or "including", when used in this specification, identify the presence of the described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. When used herein, the term "and / or" includes any and all combinations of the related listed items.

[0026] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may also have other embodiments.

[0027] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those of the technical and scientific terms in the technical field to which the present application belongs.

[0028] For those not specified with specific technologies or conditions in the following embodiments, they are generally carried out according to the conventional technologies or conditions described in the literature in the art, or according to the conditions recommended in the product specifications and by the manufacturers. The numerical ranges in the following embodiments all include the end point values.

[0029] In the related art, the impact of the active oxygen released by the lithium supplement agent during lithium supplementation on the electrolyte can be reduced by adding additives such as oxygen radical scavengers to the electrolyte. However, such oxygen radical scavenging additives will cause certain consumption before the lithium supplement agent releases oxygen, making it difficult to achieve good results.

[0030] Based on this, the embodiments of the present application provide a composite cathode material, which includes a lithium battery cathode active material, a lithium supplement agent, and a sodium battery cathode active material; the lower discharge voltage limit V3 of the lithium supplement agent is greater than or equal to the lower discharge voltage limit V1 of the lithium battery cathode active material and less than or equal to the upper charge voltage limit V2 of the lithium battery cathode active material; the lower discharge voltage limit V5 of the sodium battery cathode active material is greater than or equal to V3 and less than or equal to the upper charge voltage limit V4 of the lithium supplement agent.

[0031] If the lower discharge voltage limit V3 of the lithium supplementing agent is less than the lower discharge voltage limit V1 of the lithium-ion battery cathode active material, then when the voltage has not reached the voltage at which the lithium-ion battery cathode active material starts to intercalate and deintercalate lithium ions, the voltage at which the lithium supplementing agent starts to deintercalate lithium ions has already been reached. In this way, the lithium supplementing agent releases lithium ions in advance, which not only fails to effectively supplement lithium, but may also affect the normal process of the lithium-ion battery cathode active material releasing lithium ions. If the lower discharge voltage limit V3 of the lithium supplementing agent is greater than the upper charge voltage limit V2 of the lithium-ion battery cathode active material, then after all the lithium in the lithium-ion battery cathode active material is released, the lithium supplementing agent can start to deintercalate lithium ions, and it cannot timely supplement the lithium ions irreversibly consumed during the battery cycle, thus failing to play an effective lithium supplementing role. Therefore, in the embodiments of the present application, as Figure 1 shown, V3 is set between V1 and V2, that is, the lower discharge voltage limit of the lithium supplementing agent is between the lower discharge voltage limit and the upper charge voltage limit of the lithium-ion battery cathode active material. In this way, after the lithium-ion battery cathode active material releases lithium ions, the lithium supplementing agent can timely release lithium ions to effectively supplement lithium. If the lower discharge voltage limit V5 of the sodium-ion battery cathode active material is less than the lower discharge voltage limit V3 of the lithium supplementing agent, then when the voltage has not reached the voltage at which the lithium supplementing agent starts to deintercalate lithium ions, the voltage at which the sodium-ion battery cathode active material deintercalates sodium ions has already been reached. In this way, sodium ions are released in advance, which will inhibit the lithium supplementing effect of the lithium supplementing agent. If the lower discharge voltage limit V5 of the sodium-ion battery cathode active material is greater than the upper charge voltage limit V4 of the lithium supplementing agent, then after all the lithium in the lithium supplementing agent is released, the sodium-ion battery cathode active material can start to deintercalate sodium ions, thus failing to play the role of stabilizing the structure of the lithium supplementing agent and the interface of the lithium supplementing agent to inhibit oxygen release. Therefore, in the embodiments of the present application, as Figure 1 shown, V5 is set between V3 and V4, that is, the lower discharge voltage limit of the sodium-ion battery cathode active material is between the lower discharge voltage limit and the upper charge voltage limit of the lithium supplementing agent. In this way, when the lithium supplementing agent deintercalates a certain amount of lithium ions, resulting in the instability of its structure and the release of oxygen, the sodium-ion battery cathode active material can deintercalate sodium ions. The positively charged sodium ions can combine with the negatively charged oxygen anions to form sodium oxide to coat the lithium supplementing agent, inhibiting oxygen release, and further effectively alleviating the problem of battery gas generation caused by the side reaction between the oxygen released by the lithium supplementing agent and the electrolyte. In addition, the sodium ions released by the sodium-ion battery cathode active material can also evenly distribute charges with the lithium supplementing agent (which can also be called the lithium-deficient state lithium supplementing agent) after releasing lithium ions, improving charge uniformity, further inhibiting the oxygen release of the lithium supplementing agent, thereby effectively reducing the battery gas generation while ensuring that the lithium supplementing agent fully exerts its lithium supplementing effect, and further improving the cycle life of the battery and reducing safety risks.

[0032] In some embodiments, as Figure 1As shown, the upper limit of the charging voltage V4 of the lithium supplement can be greater than the upper limit of the charging voltage V2 of the lithium-ion battery cathode active material. On the basis that V3 is set between V1 and V2, V4 is greater than V2, that is, the upper limit of the charging voltage of the lithium supplement is greater than the upper limit of the charging voltage of the lithium-ion battery cathode active material. In this way, it is possible to avoid the situation where the lithium supplement releases lithium ions almost completely in advance before a large amount or even almost all of the lithium ions in the lithium-ion battery cathode active material are deintercalated. Thus, it can ensure that the lithium supplement can better supplement lithium during the entire process of the lithium-ion battery cathode active material releasing lithium ions, and further improve the cycle life and capacity of the battery.

[0033] In some embodiments, as Figure 1 shown, the upper limit of the charging voltage V6 of the sodium-ion battery cathode active material can be greater than V4. On the basis that V5 is set between V3 and V4, V6 is greater than V4, that is, the upper limit of the charging voltage of the sodium-ion battery cathode active material is greater than the upper limit of the charging voltage of the lithium supplement. In this way, it is possible to avoid the situation where the sodium-ion battery cathode active material releases sodium ions almost completely in advance before a large amount or even almost all of the lithium ions in the lithium supplement are deintercalated, and at the same time avoid the problem that the release of a large amount of sodium ions in advance may affect the effect of the lithium supplement. Thus, it can ensure that the sodium-ion battery cathode active material can better release sodium ions to stabilize the structure and interface of the lithium supplement during the entire process of the lithium supplement supplementing lithium, and further better inhibit the oxygen release of the lithium supplement to further improve the cycle life and safety performance of the battery.

[0034] In the embodiments of the present application, during the cycle of the lithium-ion battery, the lower limit of the discharge voltage (discharge cut-off voltage) of the battery can be less than or equal to the lower limit of the discharge voltage V3 of the lithium supplement, and the upper limit of the charging voltage (charging cut-off voltage) of the battery can be greater than or equal to the lower limit of the discharge voltage V5 of the sodium-ion battery cathode active material. In this way, on the one hand, it can ensure that when the lithium-ion battery is charged to V3, the lithium supplement can release lithium ions for lithium supplementation, and on the other hand, it can ensure that when the lithium-ion battery is charged to V5, the sodium-ion battery cathode active material releases sodium ions to stabilize the structure and interface of the lithium supplement.

[0035] Exemplarily, if V2 is greater than or equal to V5, the charge-discharge voltage range of the battery can be V1 to V2. In this way, during the charging process of the lithium-ion battery, the lower limits of the discharge voltages of both the lithium supplement agent and the sodium battery positive electrode active material can be reached simultaneously, ensuring that the lithium supplement agent can release lithium ions for lithium supplementation, and the sodium battery positive electrode active material releases sodium ions to stabilize the structure and interface of the lithium supplement agent. Further, the charge-discharge voltage range of the battery can be V1 to V4. In this way, during the charging process of the lithium-ion battery, the upper limit of the charging voltage of the lithium supplement agent and the lower limit of the discharge voltage of the sodium battery positive electrode active material can be reached, thereby enabling the lithium supplement agent to release more lithium ions for lithium supplementation. Even further, the charge-discharge voltage range of the battery can be V1 to V6. In this way, during the charging process of the lithium-ion battery, the upper limits of the charging voltages of both the lithium supplement agent and the sodium battery positive electrode active material can be reached simultaneously, thereby enabling the lithium supplement agent to release more lithium ions for lithium supplementation, and at the same time, the sodium battery positive electrode active material can release more sodium ions to better stabilize the structure and interface of the lithium supplement agent. If V2 is less than V5, the charge-discharge voltage range of the battery can be V1 to V4. In this way, during the charging process of the lithium-ion battery, the upper limit of the charging voltage of the lithium supplement agent and the lower limit of the discharge voltage of the sodium battery positive electrode active material can be reached, thereby enabling the lithium supplement agent to release more lithium ions for lithium supplementation, and at the same time, the sodium battery positive electrode active material can release a certain amount of sodium ions to stabilize the structure and interface of the lithium supplement agent. Further, the charge-discharge voltage range of the battery can be V1 to V6. In this way, during the charging process of the lithium-ion battery, the upper limits of the charging voltages of both the lithium supplement agent and the sodium battery positive electrode active material can be reached simultaneously, thereby enabling the lithium supplement agent to release more lithium ions for lithium supplementation, and at the same time, the sodium battery positive electrode active material can release more sodium ions to better stabilize the structure and interface of the lithium supplement agent.

[0036] It can be understood that if one wants to increase the molar amount of sodium ions that can be released by the sodium-based cathode active material, it is necessary to increase the addition amount of the sodium-based cathode active material. When the proportion of the sodium-based cathode active material in the composite cathode material is too high, it will lead to a decrease in the proportion of the lithium-based cathode active material and the lithium supplement agent, which is not conducive to the improvement of the battery capacity and cycle life. If one wants to increase the molar amount of lithium ions that can be released by the lithium supplement agent, it is necessary to increase the addition amount of the lithium supplement agent. When the proportion of the lithium supplement agent in the composite cathode material is too high, the sodium-based cathode active material may not be able to comprehensively protect the structure and interface of the lithium supplement agent, thereby affecting the effect of inhibiting the release of oxygen from the lithium supplement agent. Therefore, in some embodiments, the ratio of the molar amount of sodium ions that can be released by the sodium-based cathode active material to the molar amount of lithium ions that can be released by the lithium supplement agent can be greater than or equal to 0.6 and less than or equal to 1. For example, it can be 0.6, 0.7, 0.8, 0.9, 1, or any value between any two of the above numerical ranges. In this way, the oxygen released by the lithium supplement agent can be fully inhibited by the sodium ions released by the sodium-based cathode active material, so that while better ensuring the lithium supplement effect of the lithium supplement agent, the gas generation of the battery can be better reduced, and the cycle life and safety performance of the battery can be further improved.

[0037] In some embodiments, the mass of the lithium supplement agent can be 0.5% - 4% of the mass of the lithium-based cathode active material. For example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any value between any two of the above numerical ranges. The mass of the sodium-based cathode active material can be 1% - 12% of the mass of the lithium-based cathode active material. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or any value between any two of the above numerical ranges. Controlling the mass of the lithium supplement agent and the sodium-based cathode active material within the above ranges can enable the lithium supplement agent to better supplement the lithium ions irreversibly consumed during the battery cycle, and at the same time, the sodium-based cathode active material can play a more comprehensive protective role on the structure and interface of the lithium supplement agent to inhibit oxygen release. In this way, the capacity performance, cycle performance, and safety performance of the battery can be taken into account.

[0038] In the embodiments of the present application, the lithium-based cathode active material (which can also be referred to as the main cathode active material) can include at least one of ternary cathode materials (specifically, for example, NCM ternary materials, NCA ternary materials, etc.), lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, and lithium-rich manganese-based materials. There are many types of lithium-based cathode active materials applicable to the present application. The above types of lithium-based cathode active materials have different charge and discharge voltage ranges. By selecting appropriate lithium supplement agents and sodium-based cathode active materials to match the charge and discharge voltage ranges of the lithium-based cathode active material, the purpose of effectively supplementing lithium by the lithium supplement agent, inhibiting the release of oxygen from the lithium supplement agent by the sodium-based cathode active material, and thus reducing battery gas generation and improving the battery cycle life can be achieved.

[0039] In the embodiments of the present application, the lithium supplement agent may include at least one of Li2NiO2, Li5FeO4, Li2MoO3, Li6CoO4, and Li2O2. The lithium supplement agents of the above types have a charge-discharge voltage range that matches the charge-discharge voltage range of the lithium-ion battery cathode active material. Thus, it is beneficial to continuously and effectively release lithium ions through the lithium supplement agent for lithium supplementation during the entire charge-discharge process of the lithium-ion battery cathode active material. In a specific embodiment, the lithium supplement agent is lithium-rich lithium ferrate (Li5FeO4). Li5FeO4 has a charge-discharge voltage range that is more matched with the charge-discharge voltage range of the lithium-ion battery cathode active material, and has a more appropriate number of moles of lithium ions. Therefore, it can play a better role in lithium supplementation when combined with the lithium-ion battery cathode active material. In addition, Li5FeO4 is a lithium metal oxide with an anti-fluorite structure and has a very high specific capacity. At a voltage of 2.5V to 4.7V, its theoretical capacity can reach 867 mAh / g. Taking the lithium iron phosphate battery system as an example, when the addition amount of Li5FeO4 in the cathode material is about 2wt%, the energy density of the battery can be increased by about 5%. When the addition amount is increased to about 4%, the cycle life of the battery can be increased by nearly 100%. Therefore, Li5FeO4 is a lithium supplement agent with excellent comprehensive performance.

[0040] In the embodiments of the present application, the sodium-ion battery cathode active material may include at least one of polyanion-type compounds, layered transition metal oxides, and Prussian blue compounds. The sodium-ion battery cathode active materials of the above types have a charge-discharge voltage range that matches the charge-discharge voltage range of the lithium supplement agent. Thus, it is beneficial to deintercalate sodium ions through the sodium-ion battery cathode active material to protect the structural stability and interfacial stability of the lithium supplement agent after deintercalating lithium ions during the entire process of the lithium supplement agent releasing lithium ions for lithium supplementation, thereby inhibiting oxygen release. Specifically, the polyanion-type compound may include, for example, at least one of Na3V2(PO4)2F3, Na3V2(PO4)2O2F, and Na2Fe2(SO4)3. The layered transition metal oxide may include, for example, Na x Mn 1-y Ti y O2 (x = 0.44, 0.66; y = 0.34, 0.56), Na 0.67 [Mn 0.65 Ni 0.15 Co 0.2 O2, Na 0.68 Cu 0.34 Mn 0.66At least one of O2. Prussian blue compounds can include, for example, Na2MnFe(CN)6, etc. In a specific embodiment, the sodium-ion battery cathode active material is sodium fluorophosphate vanadate (Na3V2(PO4)2F3). Na3V2(PO4)2F3 has a relatively high lower limit of discharge voltage, can better match the charge-discharge voltage range of the lithium supplement agent, and Na3V2(PO4)2F3 has a relatively high number of moles of sodium ions.

[0041] Next, taking the lithium iron phosphate system as an example, where the lithium-ion battery cathode active material is LiFePO4 (LFP), the lithium supplement agent is Li5FeO4 (LFO), and the sodium-ion battery cathode active material is Na3V2(PO4)2F3 (NVPF), the technical solution of the present application will be further described.

[0042] The lithium supplement agent Li5FeO4 has two lithium deintercalation voltage platforms, specifically as follows:

[0043] The first lithium deintercalation voltage platform: The lower limit of the discharge voltage V3 of the lithium supplement agent Li5FeO4 is 3.5V - 3.9V. After the voltage reaches V3, the lithium ion deintercalation process is Li5FeO4 → 2Li + + 2e - + Li3FeO4.

[0044] The second lithium deintercalation voltage platform: The upper limit of the charging voltage V4 of the lithium supplement agent Li5FeO4 is 4.0V - 4.5V. After the voltage reaches V4, the lithium ion deintercalation process is Li3FeO4 → nLi + + ne - + O (2+n) / 2 + Li (3-n) FeO (6-x) / 2 ; where the value of n is 1 - 3.

[0045] For the above first de-lithiation voltage platform, it can be satisfied that the lower discharge voltage limit V3 of the lithium supplement agent Li5FeO4 is greater than the lower discharge voltage limit V1 (about 2.5V) of the lithium-ion battery cathode active material LiFePO4, and less than or equal to the upper charge voltage limit V2 (about 3.8V) of the lithium-ion battery cathode active material LiFePO4. When the voltage reaches the first de-lithiation voltage platform, the lithium supplement agent Li5FeO4 begins to de-embed lithium ions. Because the lower discharge voltage limit V3 of the lithium supplement agent Li5FeO4 is relatively close to the upper charge voltage limit V2 of the lithium-ion battery cathode active material LiFePO4, therefore, the addition of the lithium supplement agent Li5FeO4 basically does not affect the de-embedding of lithium ions by the lithium-ion battery cathode active material LiFePO4 itself. The lithium ions released by the lithium-ion battery cathode active material LiFePO4 will partially fill the positions where the lithium ions are de-embedded from the lithium supplement agent Li5FeO4. Therefore, the amount of lithium ions released by the lithium supplement agent Li5FeO4 as a whole will decrease, resulting in limited lithium supplementation effect, and the battery capacity is relatively low under this voltage platform. Before the voltage reaches the second de-lithiation voltage platform, relatively few lithium ions are released by the lithium supplement agent, and the structure of the lithium supplement agent Li5FeO4 is relatively stable. Therefore, less oxygen is released, and the gas generation amount of the battery is also less.

[0046] For the above second de-lithiation voltage platform, it can be satisfied that the upper charge voltage limit V4 of the lithium supplement agent Li5FeO4 is greater than the upper charge voltage limit V2 of the lithium-ion battery cathode active material LiFePO4. Under this de-lithiation voltage platform, the lithium ions in the lithium-ion battery cathode active material LiFePO4 have been basically all de-embedded. At high voltages, a large amount of lithium ions are also de-embedded from the lithium supplement agent Li5FeO4. Due to the rapid de-embedding of lithium ions, it is easy to cause the structural instability of the lithium supplement agent Li5FeO4, thereby releasing oxygen, forming oxygen and oxidizing the electrolyte to cause gas generation problems. At the same time, due to the release of oxygen, the overall structure of the lithium supplement agent Li5FeO4 becomes more unstable, restricting the de-embedding of lithium ions, resulting in a certain limitation in the increase of the battery capacity under this voltage platform.

[0047] The sodium-ion battery cathode active material Na3V2(PO4)2F3 has two de-sodium voltage platforms, which are specifically as follows:

[0048] The first de-sodium voltage platform: The lower discharge voltage limit V5 of the sodium-ion battery cathode active material Na3V2(PO4)2F3 is about 3.7V. After the voltage reaches V5, the de-embedding process of sodium ions is Na3V2(PO4)2F3 → Na + +e - +Na2V2(PO4)2F3.

[0049] The second de-sodium voltage platform: The upper charge voltage limit V6 of the sodium-ion battery cathode active material Na3V2(PO4)2F3 is about 4.3V. After the voltage reaches V6, the de-embedding process of sodium ions is Na2V2(PO4)2F3 → Na+ +e - + Na1V2(PO4)2F3。

[0050] For the above first sodiation voltage plateau, it can be satisfied that the lower discharge voltage limit V5 of the sodium-ion battery cathode active material Na3V2(PO4)2F3 is greater than or equal to the lower discharge voltage limit V3 of the lithium supplement agent Li5FeO4 and less than the upper charge voltage limit V4 of the lithium supplement agent Li5FeO4. Since a certain amount of sodium ions will be released only after the voltage reaches the lower discharge voltage limit V5 (about 3.7 V) of the sodium-ion battery cathode active material Na3V2(PO4)2F3, and the upper charge voltage limit V2 of the lithium-ion battery cathode active material LiFePO4 is about 3.8 V, therefore, the addition of the sodium-ion battery cathode active material basically does not affect the intercalation and deintercalation of lithium ions in the lithium-ion battery cathode active material LiFePO4 itself. In addition, due to the relatively large radius of sodium ions and poor kinetics, sodium ions are more difficult to deintercalate from the cathode system than lithium ions. Since the cathode system will contain a large amount of sodium ions, according to the principle of like charges repelling each other, it can also promote the release of lithium ions. Therefore, by adding the sodium-ion battery cathode active material, the battery capacity under this voltage plateau will be better improved.

[0051] For the above second sodiation voltage plateau, it can be satisfied that the upper charge voltage limit V6 of the sodium-ion battery cathode active material Na3V2(PO4)2F3 is greater than the upper charge voltage limit V4 of the lithium supplement agent Li5FeO4. Under this sodiation voltage plateau, the sodium-ion battery cathode active material Na3V2(PO4)2F3 releases a large amount of sodium ions, and at the same time, a large amount of lithium ions are also deintercalated from the lithium supplement agent Li5FeO4. Since lithium ions are more easily deintercalated from the cathode system than sodium ions, the oxygen and sodium ions released by the lithium supplement agent are likely to combine to form sodium oxide to protect the cathode interface and reduce the interfacial side reactions. Moreover, the relatively large amount of sodium ions accumulated in the battery will also distribute the charge evenly with the lithium supplement agent Li5FeO4 in the lithium-deficient state, improving the overall charge uniformity of the lithium supplement agent Li5FeO4, which is beneficial to stabilizing the structure of the lithium supplement agent and further promoting the release of lithium ions. Therefore, the release of the battery capacity under this plateau will also be further significantly improved.

[0052] As can be seen from the above, in the present application, by adding a certain amount of sodium-based cathode active material to the lithium compensation design system for the positive electrode (i.e., the lithium-ion battery cathode active material + lithium compensation agent system), since the sodium extraction voltage platform of the selected sodium-based cathode active material is relatively high, the addition of the sodium-based cathode active material basically does not affect the insertion and extraction of lithium ions in the cathode active material system. The positively charged sodium ions extracted and inserted by the sodium-based cathode active material at high voltage can combine with the oxygen released by the lithium compensation agent to form sodium oxide coating the lithium compensation agent, thereby inhibiting the release of oxygen and avoiding the side reaction between the formed oxygen and the electrolyte, thus reducing gas generation. In addition, the sodium ions can also evenly distribute the charge with the lithium compensation agent in the lithium-deficient state, improving the overall charge uniformity of the lithium compensation agent, further inhibiting the release of oxygen, and better ensuring the lithium compensation effect of the lithium compensation agent. Therefore, it can improve the cycle life of the battery and at the same time reduce the safety risks caused by gas generation.

[0053] The embodiment of the present application also provides a positive electrode sheet, which includes a current collector and a cathode active material layer located on at least one surface of the current collector, and the cathode active material layer includes the composite cathode material described in any of the above embodiments.

[0054] It should be understood that the beneficial effects of the composite cathode material described in any of the above embodiments are applicable to this positive electrode sheet.

[0055] In some embodiments, the cathode active material layer may further include a binder and a conductive agent. Based on the total weight of the cathode active material layer being 100%, the weight percentage of the lithium-ion battery cathode active material may be 80% - 98%, the weight percentage of the binder may be 1% - 10%, and the weight percentage of the conductive agent may be 0.1% - 5%. Controlling the weight percentages of the lithium-ion battery cathode active material, the binder, and the conductive agent within the above ranges is beneficial to improving the capacity performance, mechanical performance, and conductive performance of the positive electrode sheet.

[0056] Furthermore, in the cathode active material layer, the mass of the lithium compensation agent may be 0.5% - 4% of the mass of the lithium-ion battery cathode active material; the mass of the sodium-based cathode active material may be 1% - 12% of the mass of the lithium-ion battery cathode active material. In this way, the lithium compensation agent can better supplement the lithium ions irreversibly consumed during the battery cycle, and at the same time, the sodium-based cathode active material can comprehensively protect the structure and interface of the lithium compensation agent to inhibit the release of oxygen, so as to better balance the capacity performance, cycle performance, and safety performance of the battery.

[0057] The embodiment of the present application also provides a lithium-ion battery, which includes the positive electrode sheet described in any of the above embodiments.

[0058] It should be understood that the beneficial effects of the positive electrode sheet in the above embodiments are applicable to this battery.

[0059] In some embodiments, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active lithium ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0060] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples.

[0061] The preparation steps of the batteries in each embodiment and comparative example are as follows:

[0062] (1) Preparation of the positive electrode sheet: First, the binder polyvinylidene fluoride (PVDF) and conductive carbon black are mixed in a weight ratio of 2:1, and then together with the lithium-ion battery positive electrode active material, the lithium supplement agent, and the sodium-ion battery positive electrode active material are added to N-methylpyrrolidone (NMP), and stirred under the action of a vacuum mixer to form a uniformly mixed positive electrode slurry; Next, the positive electrode slurry is uniformly coated on the current collector aluminum foil, and after the coated aluminum foil is baked in an oven to remove the solvent, it is then dried in an oven at 120 °C for 8 h; Finally, after rolling and slitting, the positive electrode sheet is obtained. Among them, the types of the lithium-ion battery positive electrode active materials in each embodiment and comparative example and their mass percentages in the positive electrode active material layer, the types of the lithium supplement agents and their mass percentages relative to the lithium-ion battery positive electrode active materials, and the types of the sodium-ion battery positive electrode active materials and their mass percentages relative to the lithium-ion battery positive electrode active materials are shown in Table 1. In each embodiment and comparative example, other preparation conditions are the same except for the types and addition amounts of the lithium-ion battery positive electrode active materials, the lithium supplement agents, and the sodium-ion battery positive electrode active materials.

[0063] (2) Preparation of the negative electrode sheet: First, the negative electrode active material graphite, the thickening agent sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a weight ratio of 97:1:1:1, and deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum mixer; Next, the negative electrode slurry is uniformly coated on a high-strength carbon-coated aluminum foil to obtain a coated electrode sheet; Next, the coated electrode sheet is air-dried at room temperature and then transferred to an oven at 80 °C for drying for 10 h; Finally, after rolling and slitting, the negative electrode sheet is obtained.

[0064] (3) Preparation of electrolyte: In a glove box filled with inert gas (H2O content < 10 ppm, O2 content < 5 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are configured in a mass ratio of 30:70 to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), methylene methanesulfonate (MMDS), and tris(trimethylsilyl) borate (TMSB) are added to the mixed solvent to obtain a 1 mol / L LiPF6 electrolyte. Among them, the proportions of FEC, MMDS, and TMSB in the electrolyte are all 0.5 wt%.

[0065] (4) Preparation of battery: The positive electrode sheet prepared in the above step (1), the separator (PP film with a thickness of 9 microns), and the negative electrode sheet prepared in the above step (2) are stacked in sequence. Ensure that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolation role. After winding, a bare battery core is obtained. The bare battery core is placed in an aluminum-plastic film outer package to obtain a battery core with a capacity of 3 Ah; the electrolyte prepared in the above step (3) is injected into the dried battery core. After encapsulation, standing, and formation, secondary encapsulation, standing, and grading are carried out to complete the preparation of the lithium-ion soft-pack battery.

[0066] It should be noted that the voltage in the formation stage of each example and comparative example in the preparation of the battery reaches the upper limit of the charging voltage V4 of the lithium supplement agent added to the corresponding battery. Because the active lithium is consumed in the formation stage, when the voltage in the formation stage reaches the upper limit of the charging voltage V4 of the lithium supplement agent added to the corresponding battery, it can ensure that the lithium supplement agent can release a large amount of lithium ions for lithium supplementation. Moreover, the sodium-ion battery positive electrode active material can also release a certain amount of sodium ions to form sodium oxide on the surface of the lithium supplement agent to stabilize the interface of the lithium supplement agent and inhibit oxygen release. In this way, through the performance test of the battery, it can be better detected whether the sodium-ion battery positive electrode active material can play a role in stabilizing the structure and interface of the lithium supplement agent and reducing the gas generation of the battery.

[0067] The lithium-ion battery prepared in the above step (4) is subjected to formation gas generation test and high-temperature cycle performance test. The specific tests are as follows:

[0068] (1) Formation gas generation test: Measure the volume of the battery before formation and grading, and record it as M1; measure the volume of the battery after completion of formation, and record it as M2. The formation volume change (M2 - M1) is the formation gas generation amount. Specifically, the drainage method is used to measure the volume of the battery to be tested: Take a container with scales, add water to the container and record the water level scale N1 at this time. Place the battery to be tested in the container and completely submerge it in the water in the container, and record the water level scale N2 at this time. Based on Archimedes' principle, the volume of the liquid displaced by an object in a liquid is equal to the volume of the object itself. Therefore, N2 - N1 is the volume of the battery to be tested.

[0069] (2) High-temperature cycling test: Place the battery in an environment of 45°C and perform charge-discharge cycles at a rate of 1C within the voltage range of X1V to X2V, that is, charge at a constant current of 1C until the upper limit voltage X2V, and then discharge at a constant current of 1C until the lower limit voltage X1V. Record the discharge capacity at this time as the first-cycle discharge capacity. Repeat the above charge-discharge cycles until the discharge capacity drops to 80% of the first-cycle discharge capacity, which is the test termination point, and record the number of cycles. Among them, for the battery with LFP as the lithium-ion battery cathode active material (corresponding to the lithium-ion battery cathode active material in the LFP category in Table 1), the voltage range of the above charge-discharge cycles is 2.8V to 3.7V; for the battery with NCM as the lithium-ion battery cathode active material (corresponding to the lithium-ion battery cathode active material in the NCM category in Table 1), the voltage range of the above charge-discharge cycles is 2.8V to 4.2V.

[0070] The above test results are shown in Table 2.

[0071] Table 1

[0072]

[0073]

[0074] Table 2

[0075] Gas production volume during formation / ml Number of circulation cycles / cycle Example 1 8 4605 Example 2 6 5816 Example 3 5 4980 Example 4 4 4210 Example 5 9 3960 Example 6 7 5608 Example 7 8 2800 Example 8 4 3508 Example 9 11 3109 Example 10 5 3950 Example 11 7 1985 Comparative Example 1 6 1600 Comparative Example 2 4 2986 Comparative Example 3 15 1550 Comparative Example 4 3 2310

[0076] As can be seen from the data in Table 1, lithium-ion battery cathode active materials (which can also be referred to as the main cathode active materials), lithium supplement agents, and sodium-ion battery cathode active materials are added to the cathode sheets of Examples 1 to 11, and it is satisfied that the lower discharge voltage limit V3 of the lithium supplement agent is greater than or equal to the lower discharge voltage limit V1 of the lithium-ion battery cathode active material and less than or equal to the upper charge voltage limit V2 of the lithium-ion battery cathode active material; the lower discharge voltage limit V5 of the sodium-ion battery cathode active material is greater than or equal to V3 and less than or equal to the upper charge voltage limit V4 of the lithium supplement agent. The lithium-ion battery cathode active materials in the batteries of Examples 1 to 6, Examples 8 to 10, and Comparative Examples 2 to 4 are all lithium iron phosphate (LFP), and the lithium-ion battery cathode active materials in the batteries of Example 7, Example 11, and Comparative Example 1 are all NCM ternary materials. As can be seen from the data in Table 2, compared with Comparative Example 3, the formation gas production of the batteries of Examples 1 to 6 and Examples 8 to 10 is significantly reduced, and at the same time, the cycle life of the batteries is significantly increased. The lithium supplement agent is not added to the cathode sheets of the batteries of Comparative Example 2 and Comparative Example 4. Therefore, the formation gas production of the corresponding batteries is at a relatively low level, but the cycle life of the corresponding batteries is lower than that of the batteries of Examples 1 to 6 and Examples 8 to 10. The formation gas production of the batteries of Example 7 and Example 11 is at a similar low level to that of the battery in Comparative Example 1 where the lithium supplement agent is not added to the cathode sheet, and the cycle life of the batteries of Example 7 and Example 11 is significantly improved compared with Comparative Example 1. It can be seen from this that in this application, by adding a lithium supplement agent and a sodium-ion battery cathode active material to the main cathode active material and setting V3 between V1 and V2, that is, the lower discharge voltage limit of the lithium supplement agent is between the lower discharge voltage limit and the upper charge voltage limit of the lithium-ion battery cathode active material, so that after the lithium-ion battery cathode active material releases lithium ions, the lithium supplement agent can release lithium ions in time for effective lithium supplementation. At the same time, V5 is set between V3 and V4, that is, the lower discharge voltage limit of the sodium-ion battery cathode active material is between the lower discharge voltage limit and the upper charge voltage limit of the lithium supplement agent. In this way, when a certain amount of lithium ions are deintercalated from the lithium supplement agent, resulting in its unstable structure and the release of oxygen, the sodium-ion battery cathode active material can deintercalate sodium ions, and the positively charged sodium ions can combine with the negatively charged oxygen anions to form sodium oxide to coat the lithium supplement agent, inhibiting the release of oxygen, and thus effectively alleviating the problem of battery gas production caused by the side reaction of the oxygen released by the lithium supplement agent with the electrolyte; in addition, the sodium ions released by the sodium-ion battery cathode active material can also evenly distribute charges with the lithium-deficient lithium supplement agent, improving the charge uniformity, further inhibiting the release of oxygen by the lithium supplement agent, thereby effectively reducing the battery gas production while ensuring that the lithium supplement agent fully exerts its lithium supplementation effect, and then improving the cycle life of the battery and reducing the safety risk.

[0077] From the comparison of the data of Example 8 and Example 9 in Table 2 with the data of Example 1 to Example 6, it can be seen that the ratio of the molar amount of sodium ions that the sodium-ion battery cathode active material can release to the molar amount of lithium ions that the lithium supplement agent can release in Example 8 is greater than 1, that is, the proportion of the sodium-ion battery cathode active material in the cathode sheet is relatively too high, which will lead to a relatively reduced proportion of the main cathode active material. Therefore, the cycle performance of the battery is reduced compared with Example 1 to Example 6; in Example 9, the ratio of the molar amount of sodium ions that the sodium-ion battery cathode active material can release to the molar amount of lithium ions that the lithium supplement agent can release is less than 0.6, that is, the proportion of the lithium supplement agent in the cathode sheet is relatively too high, and the proportion of the sodium-ion battery cathode active material in the cathode sheet is relatively too low. This will cause the sodium-ion battery cathode active material may not be able to comprehensively protect the structure and interface of the lithium supplement agent, thus affecting the effect of inhibiting the oxygen release of the lithium supplement agent. Therefore, the gas production of the battery increases compared with Example 1 to Example 6, and at the same time, the cycle performance of the battery also decreases compared with Example 1 to Example 6. It can be seen from this that in this application, the ratio of the molar amount of sodium ions that the sodium-ion battery cathode active material can release to the molar amount of lithium ions that the lithium supplement agent can release is greater than or equal to 0.6 and less than or equal to 1, which is a more preferred solution.

[0078] From the comparison of the data of Example 2 and Example 10 in Table 2, it can be seen that the upper limit of the charging voltage V6 of the sodium-ion battery cathode active material in Example 2 is greater than the upper limit of the charging voltage V4 of the lithium supplement agent, while the upper limit of the charging voltage V6 of the sodium-ion battery cathode active material in Example 10 is less than the upper limit of the charging voltage V4 of the lithium supplement agent. The cycle life of the battery in Example 2 is significantly higher than that of the battery in Example 10. This is because the upper limit of the charging voltage of the sodium-ion battery cathode active material is greater than the upper limit of the charging voltage of the lithium supplement agent. In this way, it is possible to avoid the situation that the sodium-ion battery cathode active material releases almost all the sodium ions in advance before a large amount or even almost all of the lithium ions in the lithium supplement agent are deintercalated. Thus, it can ensure that during the entire process of the lithium supplement agent replenishing lithium, the sodium-ion battery cathode active material can better release sodium ions to stabilize the structure and interface of the lithium supplement agent, and further better inhibit the oxygen release of the lithium supplement agent, so as to further improve the cycle life and safety performance of the battery. Therefore, in this application, the upper limit of the charging voltage V6 of the sodium-ion battery cathode active material being greater than the upper limit of the charging voltage V4 of the lithium supplement agent is a more preferred solution.

[0079] It can be seen from the data comparison between Example 7 and Example 11 in Table 2 that the upper limit of the charging voltage V4 of the lithium supplement in Example 7 is greater than the upper limit of the charging voltage V2 of the lithium-ion battery cathode active material, while the upper limit of the charging voltage V4 of the lithium supplement in Example 11 is less than the upper limit of the charging voltage V2 of the lithium-ion battery cathode active material. The number of cycles of the battery in Example 7 is significantly higher than that of the battery in Example 11. This is because the upper limit of the charging voltage of the lithium supplement is greater than the upper limit of the charging voltage of the lithium-ion battery cathode active material. In this way, it is possible to avoid the situation where the lithium supplement releases lithium ions almost completely in advance before a large amount or even almost all of the lithium ions in the lithium-ion battery cathode active material are deintercalated. Thus, it can ensure that the lithium supplement can better supplement lithium during the entire process of the lithium-ion battery cathode active material releasing lithium ions, and further improve the cycle life and capacity of the battery. Therefore, in this application, the upper limit of the charging voltage V4 of the lithium supplement being greater than the upper limit of the charging voltage V2 of the lithium-ion battery cathode active material is a relatively preferred solution.

[0080] It can be seen from the data of Examples 1 to 3 in Table 1 and Table 2 that, under the same type and content of the lithium supplement, as the content of the sodium-ion battery cathode active material increases, the gas production of the battery gradually decreases, and the number of cycles of the battery shows a trend of increasing first and then decreasing. Because when the content of the sodium-ion battery cathode active material is relatively low, the effect of suppressing the oxygen release of the lithium supplement is limited, and thus the effect of suppressing the gas production of the battery is affected, and the lithium supplement effect of the lithium supplement will also be affected. Therefore, the cycle life of the battery will be reduced; while when the content of the sodium-ion battery cathode active material is relatively high, although the effect of suppressing the gas production of the battery is good, it will cause a decrease in the content of the cathode active main material, and thus will also affect the cycle life of the battery. The design of the positive electrode sheet of the battery in Example 2 is relatively more reasonable, which effectively improves the cycle life of the battery while better suppressing the gas production of the battery.

[0081] This application provides a design for suppressing the gas production of the battery caused by the oxygen release of the lithium supplement by blending the sodium-ion battery cathode active material in the lithium supplement system of the positive electrode of the lithium-ion battery. By blending the sodium-ion battery cathode active material in the positive electrode lithium supplement design system, since the lower limit of the discharge voltage of the selected sodium-ion battery cathode active material is relatively high, the sodium-ion battery cathode active material basically does not affect the deintercalation of ions in the lithium-ion battery cathode active material system. Instead, it can release sodium ions at a high voltage. While not affecting the lithium supplement effect, by combining the positively charged sodium ions with the negatively charged oxygen anions, the release of oxygen can be avoided, and sodium oxide is formed to coat the lithium supplement, isolating the side reaction with the electrolyte. Sodium ions can also evenly distribute charges with the lithium-deficient lithium supplement, improving the charge uniformity to reduce oxygen release, ensuring the full play of the lithium supplement effect, reducing the gas production of the battery, and thus being able to improve the cycle life of the battery and reduce the safety risk.

[0082] It should be noted that the composite cathode material embodiments, cathode sheet embodiments, and lithium-ion battery embodiments provided in this application belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.

[0083] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners. Without departing from the scope of the present disclosure, various deformations and changes can also be made on the basis of the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present invention that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A composite cathode material, characterized in that, It includes a lithium-ion battery cathode active material, a lithium supplement agent, and a sodium-ion battery cathode active material; The lower discharge voltage limit V3 of the lithium supplement agent is greater than or equal to the lower discharge voltage limit V1 of the lithium-ion battery cathode active material and less than or equal to the upper charge voltage limit V2 of the lithium-ion battery cathode active material; The lower discharge voltage limit V5 of the sodium-ion battery cathode active material is greater than or equal to V3 and less than or equal to the upper charge voltage limit V4 of the lithium supplement agent.

2. The composite cathode material according to claim 1, wherein V4 is greater than V2; and / or, the upper charge voltage limit V6 of the sodium-ion battery cathode active material is greater than V4.

3. The composite cathode material according to claim 1, wherein The ratio of the molar amount of sodium ions that the sodium-ion battery cathode active material can release to the molar amount of lithium ions that the lithium supplement agent can release is greater than or equal to 0.6 and less than or equal to 1.

4. The composite cathode material according to claim 1, wherein, The sodium-ion battery cathode active material includes at least one of polyanion-type compounds, layered transition metal oxides, Prussian blue compounds, preferably a polyanion-type compound, more preferably Na3V2(PO4)2F3.

5. The composite cathode material according to claim 1, wherein The lithium supplement agent includes at least one of Li2NiO2, Li5FeO4, Li2MoO3, Li6CoO4, Li2O2, preferably Li5FeO4.

6. The composite cathode material according to claim 1, wherein The lithium-ion battery cathode active material includes at least one of ternary cathode materials, lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, and lithium-rich manganese-based materials.

7. The composite cathode material according to any one of claims 1 to 6, characterized in that, The mass of the lithium supplement agent is 0.5% - 4% of the mass of the lithium-ion battery cathode active material; the mass of the sodium-ion battery cathode active material is 1% - 12% of the mass of the lithium-ion battery cathode active material.

8. A positive electrode sheet, characterized in that, The positive electrode sheet includes a current collector and a positive electrode active material layer located on at least one surface of the current collector, and the positive electrode active material layer includes the composite positive electrode material according to any one of claims 1 to 7.

9. The positive electrode sheet according to claim 8, wherein, The positive electrode active material layer further includes a binder and a conductive agent. Based on the total weight of the positive electrode active material layer being 100%, the weight percentage content of the lithium-ion battery cathode active material is 80% - 98%, the weight percentage content of the binder is 1% - 10%, and the weight percentage content of the conductive agent is 0.1% - 5%.

10. A lithium-ion battery, characterized in that, It includes the positive electrode sheet according to claim 8 or 9.

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