A composite cathode material, a preparation method thereof, a secondary battery, a battery module, a battery pack, and an electric device

Abstract

The present application provides a composite positive electrode material, a preparation method thereof, a secondary battery, a battery module, a battery pack, and a power utilization device. The composite positive electrode material comprises a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide, the coating layer being a carbon-complexed lithium iron manganese vanadium phosphate material, the general formula of the lithium iron manganese vanadium phosphate material being shown as Formula I, LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, wherein M2 is selected from one or more of Ni, Co, Ti, Al. The carbon-complexed lithium iron manganese vanadium phosphate material at least partially coating the lithium-containing metal oxide composite positive electrode material can improve the cycle performance, storage performance, and safety performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a composite cathode material, a preparation method thereof, a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] In recent years, the application range of secondary batteries is more and more extensive, and in particular, secondary batteries have been widely applied to energy storage power supply systems such as hydroelectric, thermal, wind and solar power stations, and to many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] With the increasing demand for the endurance and safety of power utilization devices, secondary batteries are required to have more excellent comprehensive performance including capacity performance, safety performance and cycle performance. The cathode material has an important influence on the electrochemical performance of the battery, such as the specific capacity. However, while the new generation of cathode materials bring about an increase in battery capacity, they are often accompanied by a decrease in cycle performance and safety performance. Therefore, the existing cathode materials still need to be improved. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, one object of the present application is to provide a composite cathode material to further improve the cycle performance, storage performance and safety performance of the battery.

[0005] A first aspect of the present application provides a composite cathode material, comprising: a lithium-containing metal oxide and a coating layer provided on at least a part of the lithium-containing metal oxide, the coating layer being a carbon-composite lithium iron manganese vanadium phosphate material, the general formula of the lithium iron manganese vanadium phosphate material being shown as Formula I,

[0006] LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I

[0007] wherein 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and wherein M2 is selected from one or more of Ni, Co, Ti and Al.

[0008] The composite cathode material prepared by coating the lithium-containing metal oxide with the carbon-composite lithium iron manganese vanadium phosphate material can improve the cycle capacity retention rate of the battery at room temperature and high temperature, reduce the unit capacity gas volume of the battery at high temperature, i.e., improve the cycle performance, storage performance and safety performance of the battery, and at the same time, the coating of the coating layer will not significantly reduce the capacity performance of the battery, so that the battery with the composite cathode material as the cathode still has excellent capacity performance and initial efficiency.

[0009] In any embodiment, the coating content is 0.1% to 10% by mass, based on the total mass of the composite cathode material. Composite cathode materials with appropriate coating amounts can yield batteries that combine high capacity performance, excellent cycle performance, storage performance, and safety performance.

[0010] In any embodiment, the carbon mass fraction in the coating layer is 0.01% to 25%, based on the total mass of the coating layer. An appropriate mass of carbon results in a coating layer with low powder resistivity, high material stability, and high conductivity, which is beneficial for maintaining the high capacity performance of the battery.

[0011] In any embodiment, the powder resistivity of the composite cathode material is 1000–5500 Ω·cm. When the powder resistivity of the composite cathode material is within this range, the composite cathode material exhibits better stability and superior conductivity, which is beneficial for maintaining and improving the capacity performance of the battery.

[0012] In any embodiment, the average particle size Dv50 of the composite cathode material is 8–12 μm. If the particle size of the composite cathode material is too large, it is detrimental to lithium-ion insertion and extraction; if the particle size is too small, the material is prone to aggregation. A suitable average particle size range allows the battery to exhibit excellent electrochemical and cycle performance.

[0013] In any embodiment, the general formula for lithium-containing metal oxides is shown in Formula II.

[0014] Li 1.05-a2 M1 a2 (Ni b2 Co c2 Mn d2 ) 1-e2 Q e2 O2, Formula II

[0015] In the formula, 0≤a2≤0.1, 0.7≤b2≤0.96, 0.03≤c2≤0.2, 0.01≤d2≤0.2, 0≤e2≤0.05; where M1 is selected from one or more of the alkali metal elements Na, K, Rb, and Cs, and Q is selected from one or more of Al, Mg, Zr, Ti, W, Y, B, Co, Nb, Mo, Sb, and Sr.

[0016] Lithium-containing metal oxides are high-nickel metal oxides, which have high energy density, enabling batteries to have high capacity and power performance.

[0017] A second aspect of this application provides a method for preparing a composite cathode material, comprising the following steps:

[0018] A first mixture containing lithium, iron, manganese, vanadium, phosphorus, and carbon sources is subjected to a first sintering treatment to prepare a carbon-composite lithium iron manganese vanadium phosphate material.

[0019] A second mixture containing a lithium source and a nickel-cobalt-manganese precursor is subjected to a second sintering treatment, wherein the molar ratio of lithium in the lithium source to the total amount of nickel, cobalt and manganese in the nickel-cobalt-manganese precursor is 0.95 to 1.05, to prepare a lithium-containing metal oxide.

[0020] The carbon-composite lithium iron manganese vanadium phosphate material is subjected to a third sintering treatment with the lithium-containing metal oxide to obtain a composite cathode material.

[0021] The composite cathode material includes a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide. The coating layer is a carbon-composite lithium iron manganese vanadium phosphate material, and the general formula of the lithium iron manganese vanadium phosphate material is shown in Formula I.

[0022] LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I

[0023] Wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and M2 is selected from one or more of Ni, Co, Ti, and Al.

[0024] The composite cathode material prepared by the above method, which is a carbon composite lithium iron manganese vanadium phosphate material, is at least partially coated with lithium-containing metal oxides, which can improve the cycle performance, storage performance and safety performance of the battery, and the capacity performance of the battery has a high retention rate and can even be further improved.

[0025] In any embodiment, during the third sintering process, the mass ratio of the lithium-containing metal oxide to the carbon-composite lithium iron manganese vanadium phosphate material is 9:1 to 999:1. A suitable coating amount can balance the battery's high capacity performance with excellent cycle performance, storage performance, and safety performance.

[0026] In any embodiment, during the first sintering process, the molar ratio of vanadium in the vanadium source to iron in the iron source is 0.5:8 to 4:1. Controlling the molar ratio of vanadium to iron can improve the battery's cycle performance, storage performance, and safety performance while maintaining its high-rate performance.

[0027] In any embodiment, the mass ratio of carbon in the carbon source to the lithium iron manganese vanadium phosphate material is 1:9999 to 1:4. A suitable mass of carbon results in low powder resistivity in the carbon-composite lithium iron manganese vanadium phosphate material, which helps maintain the high capacity performance of the cathode material.

[0028] In any embodiment, the sintering temperature of the first sintering treatment is 650℃~800℃, and the sintering time of the first sintering treatment is 10~20h. Controlling the temperature and time of the first sintering treatment within a suitable range is beneficial for preparing carbon composite lithium iron manganese vanadium phosphate materials with low powder resistivity and suitable average particle size Dv50, enabling them to effectively coat lithium-containing metal oxides, thereby improving the cycle performance, storage performance and safety performance of the battery.

[0029] In any embodiment, the first mixture further comprises one or more of a nickel source, a cobalt source, a titanium source, and an aluminum source, wherein the nickel source, cobalt source, titanium source, and aluminum source are respectively selected from one or more oxides, hydroxides, carbonates, and phosphates containing nickel, cobalt, titanium, and aluminum. Doping with the above elements can improve the stability of the coating layer, thereby optimizing the cycle performance, storage performance, and safety performance of the battery.

[0030] In any embodiment, the iron source is selected from one or more of ferric oxide and magnetite; the manganese source is selected from one or more of manganese dioxide and manganese tetroxide; the vanadium source is selected from one or more of vanadium trioxide and vanadium pentoxide; the phosphorus source is selected from one or more of ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate; and the carbon source is selected from one or more of carbon black, citric acid, polyethylene glycol, sucrose, and glucose.

[0031] In any embodiment, the second mixture further includes an alkali metal compound, the alkali metal compound comprising 0–5.5% by mass, based on the total mass of the second mixture. Alkali metal doping of lithium-containing metal oxides optimizes lithium-ion diffusion efficiency, thereby improving the battery's rate performance, cycle performance, storage performance, and first-time efficiency.

[0032] A third aspect of this application provides a secondary battery, including a positive electrode, a separator, a negative electrode, and an electrolyte. The positive electrode comprises a composite positive electrode material as described in any embodiment of the first aspect. This battery exhibits good cycle performance, storage performance, and safety performance.

[0033] A fourth aspect of this application provides a battery module including the secondary battery of the third aspect. This battery module exhibits good cycle performance, storage performance, and safety performance.

[0034] The fifth aspect of this application provides a battery pack comprising a four-sided battery module. This battery pack exhibits good cycle performance, storage performance, and safety performance.

[0035] A sixth aspect of this application provides an electrical device, comprising at least one of the secondary battery of the third aspect, the battery module of the fourth aspect, and the battery pack of the fifth aspect. This electrical device has good battery life and safety.

[0036] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0037] Figure 1 This is a SEM image of the composite cathode material prepared in Example 1 of the present invention.

[0038] Figure 2 The graph shows the 25°C cycle performance test of a secondary battery made from the composite cathode material prepared in Example 1 of this invention.

[0039] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0040] Figure 4 yes Figure 3 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0041] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0042] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0043] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0044] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0045] Explanation of reference numerals in the attached figures:

[0046] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0047] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the adhesive, preparation method, electrode, battery, and power device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0048] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0050] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0051] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0053] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0054] High-nickel lithium-containing metal oxides are commonly used as cathode materials in existing technologies to improve battery capacity. However, due to the high surface defects and high content of strong oxidizing transition metals such as Ni, Co, and Mn in these oxides, side reactions with the electrolyte are severe. This leads to easy damage to the contact interface structure, causing transition metals like Ni, Mn, and Co to dissolve and deposit on the anode, increasing internal resistance and resulting in severe capacity degradation and reduced cycle performance. Furthermore, the surface structure of high-nickel lithium-containing metal oxides is highly unstable under electrolyte catalysis, easily releasing oxygen and exotherm when subjected to pressure or high temperatures, which can easily lead to thermal runaway and, in severe cases, safety accidents. While conventional coating treatments can improve cycle performance and safety to some extent, the improvement is limited and insufficient to meet market demands for next-generation batteries.

[0055] [Composite cathode material]

[0056] Based on this, this application proposes a composite cathode material, comprising: a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide, wherein the coating layer is a carbon-composite lithium iron manganese vanadium phosphate material, and the general formula of the lithium iron manganese vanadium phosphate material is shown in Formula I, LiFe a1 Mn b1 V c1 M2d1 PO4, Formula I

[0057] Wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and M2 is selected from one or more of Ni, Co, Ti, and Al.

[0058] In some embodiments, the carbon-composite lithium iron manganese vanadium phosphate material is a composite material comprising carbon and lithium iron manganese vanadium phosphate. It is understood that carbon and lithium iron manganese vanadium phosphate can be composited in any manner, such as physical mixing or chemical composites. Specifically, carbon and lithium iron manganese vanadium phosphate can be composited through methods such as stirring, grinding, ultrasonication, in-situ growth, grafting, and coating.

[0059] In some embodiments, 0 < d2 ≤ 0.01, and the carbon-composite lithium iron manganese vanadium phosphate material includes one or more of Ni, Co, Ti, and Al.

[0060] Lithium iron manganese vanadium phosphate (LiFeMP) materials possess advantages such as good stability, high potential, and high rate capability. Using it as a coating layer can protect the surface of lithium-containing metal oxides, improving the stability of the surface of the lithium-containing metal oxides and the interface between them and the electrolyte. Composite cathode materials prepared by coating lithium-containing metal oxides with carbon-composite LiFeMP materials can improve the battery's cycle capacity retention at both room temperature and high temperature, and reduce the gas production volume per unit capacity at high temperatures. In other words, it improves the battery's cycle performance, storage performance, and safety performance. Simultaneously, the coating layer does not significantly reduce the battery's capacity performance; batteries using composite cathode materials as the cathode still exhibit excellent capacity performance and first-day coin cell efficiency.

[0061] In some embodiments, the coating layer has a mass content of 0.1% to 10%, based on the total mass of the composite cathode material. In some embodiments, the coating layer has a mass content of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9%.

[0062] Excessive coating content leads to insufficient lithium-containing metal oxide content, resulting in reduced battery capacity. Conversely, insufficient coating content prevents effective coating of carbon-composite lithium iron manganese vanadium phosphate materials, hindering improvements in cycle and storage performance. A suitable coating amount balances battery capacity, cycle, and storage performance, further enhancing cycle, storage, and safety while maintaining or even improving capacity and first-time coin-time efficiency.

[0063] In some embodiments, the carbon mass fraction in the coating layer is 0.01% to 25%, based on the total mass of the coating layer. In some embodiments, the carbon mass fraction in the coating layer may be selected from 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%.

[0064] In some embodiments, a carbon content analyzer is used to test the mass content of carbon in the carbon-composite lithium iron manganese vanadium phosphate material. In this paper, the mass content of carbon in the carbon-composite lithium iron manganese vanadium phosphate material can be adjusted by changing the mass of the carbon source added during the preparation of the carbon-composite lithium iron manganese vanadium phosphate material.

[0065] Excessive carbon content in the coating layer can reduce the proportion of lithium iron phosphate (LFP) in carbon-composite lithium iron phosphate (LFP) materials, hindering the utilization of LFP's high stability and voltage platform. Conversely, insufficient carbon content leads to low conductivity, impairing electron transport. Controlling the carbon content within a suitable range in carbon-composite oxide particles of LFP materials allows for uniform carbon composite formation, resulting in LFP materials with uniform particle size distribution and high carbon dispersion. This results in a coating layer with suitable powder resistivity, facilitating lithium-ion insertion / extraction. Even with the addition of a coating layer, battery capacity and initial efficiency can be maintained or improved, without performance degradation due to the coating layer.

[0066] In some embodiments, the powder resistivity of the composite cathode material is 1000–5500 Ω·cm. In some embodiments, the powder resistivity of the composite cathode material is 1100 Ω·cm, 1500 Ω·cm, 2000 Ω·cm, 2500 Ω·cm, 3000 Ω·cm, 3500 Ω·cm, 4000 Ω·cm, 4500 Ω·cm, 5000 Ω·cm, or 5500 Ω·cm.

[0067] In this paper, the term "powder resistivity" refers to a parameter used to characterize the electrical conductivity of the material itself, which is different from the resistivity of the electrode. Typically, powder resistivity is measured using a testing instrument such as a four-probe analyzer, according to GB / T 30835-2014, "Carbon Composite Lithium Iron Phosphate Cathode Materials for Lithium-ion Batteries".

[0068] When the resistivity of the composite cathode material powder is within this range, the composite cathode material has better stability and superior conductivity, which is beneficial for maintaining and improving the capacity performance of the battery.

[0069] In some embodiments, the average particle size Dv50 of the composite cathode material is 8–12 μm. In some embodiments, the average particle size Dv50 of the composite cathode material is 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, or 12 μm.

[0070] In this document, the average particle size Dv50 has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%. It can be determined using methods and instruments known in the art. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0071] If the particle size of the composite cathode material is too large, it will hinder the insertion and extraction of lithium ions. If the particle size of the composite cathode material is too small, the material will easily aggregate. When the average particle size of the composite cathode material is within a suitable range, the battery can exhibit excellent electrochemical performance and cycle performance.

[0072] In some embodiments, the general formula of lithium-containing metal oxides is shown in Formula II.

[0073] Li 1.05-a2 M1 a2 (Ni b2 Co c2 Mn d2 ) 1-e2 Q e2 O2, Formula II

[0074] In the formula, 0≤a2≤0.1, 0.7≤b2≤0.96, 0.03≤c2≤0.2, 0.01≤d2≤0.2, 0≤e2≤0.05; where M1 is selected from one or more of the alkali metal elements Na, K, Rb, and Cs, and Q is selected from one or more of Al, Mg, Zr, Ti, W, Y, B, Co, Nb, Mo, Sb, and Sr.

[0075] In some embodiments, 0 < a1 ≤ 0.1. During the preparation of lithium-containing metal oxides, alkali metal doping is achieved by adding carbonates, sulfates, chlorides, or oxides of Na, K, Rb, and Cs and co-sintering them. Alkali metal doping of lithium-containing metal oxides can improve lithium-ion diffusion efficiency, thereby maintaining the battery's high capacity and high rate performance.

[0076] In some embodiments, 0 < e1 ≤ 0.05. During the preparation of lithium-containing metal oxides, oxides, hydroxides, carbonates, or phosphates of Al, Mg, Zr, Ti, W, Y, B, Co, Nb, Mo, Sb, and Sr are added and co-sintered to achieve transition metal doping. Transition metal doping can improve the structural stability of lithium-containing metal oxides, stabilize the structural framework, and thus improve the cycle performance and high-rate performance of the battery.

[0077] Lithium-containing metal oxides have a high nickel content and high energy density, which enables batteries to have high capacity and power performance.

[0078] In one embodiment of this application, a method for preparing a composite cathode material is provided, comprising the following steps:

[0079] A first mixture containing lithium, iron, manganese, vanadium, phosphorus, and carbon sources is subjected to a first sintering treatment to prepare a carbon-composite lithium iron manganese vanadium phosphate material.

[0080] A second mixture containing a lithium source and a nickel-cobalt-manganese precursor is subjected to a second sintering treatment, wherein the molar ratio of lithium in the lithium source to the total amount of nickel, cobalt and manganese in the nickel-cobalt-manganese precursor is 0.95 to 1.05, thereby preparing a lithium-containing metal oxide.

[0081] A composite cathode material is obtained by subjecting a carbon-composite lithium iron manganese vanadium phosphate material to a third sintering process with a lithium-containing metal oxide.

[0082] The composite cathode material includes a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide. The coating layer is a carbon-composite lithium iron manganese vanadium phosphate material, and the general formula of lithium iron manganese vanadium phosphate material is shown in Formula I.

[0083] LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I

[0084] Wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and M2 is selected from one or more of Ni, Co, Ti, and Al.

[0085] In some embodiments, the sintering temperature of the third sintering treatment is 100–400°C.

[0086] In some embodiments, the sintering time for the third sintering treatment is 2 to 8 hours.

[0087] In some embodiments, the third sintering process is carried out in a reducing atmosphere, which is nitrogen or argon.

[0088] The composite cathode material prepared by the above method, which is a carbon composite lithium iron manganese vanadium phosphate material, is at least partially coated with lithium-containing metal oxides, which can improve the cycle performance, storage performance and safety performance of the battery, and the capacity performance of the battery has excellent retention rate and can even be further improved.

[0089] In some embodiments, during the third sintering process, the mass ratio of lithium-containing metal oxide to carbon-composite lithium iron manganese vanadium phosphate material is 9:1 to 999:1.

[0090] If the content of lithium-containing metal oxides is too low, it is difficult to maintain the high capacity performance of the battery. If the content of carbon composite lithium iron manganese vanadium phosphate is too low, it cannot effectively coat the lithium-containing metal oxides, and the improvement of cycle performance, storage performance and safety performance is limited.

[0091] Appropriate coating can balance the battery's high capacity performance with excellent cycle performance, storage performance and safety performance.

[0092] In some embodiments, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, and lithium acetate. In some embodiments, the iron source is one or two of ferric oxide and magnetite. In some embodiments, the manganese source is one or two of manganese dioxide and manganese tetroxide. In some embodiments, the vanadium source is one or two of vanadium trioxide and vanadium pentoxide. In some embodiments, the phosphorus source is one or more of ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate. In some embodiments, the carbon source is one or more of carbon black, citric acid, polyethylene glycol, sucrose, and glucose.

[0093] In some embodiments, a lithium source, an iron source, a manganese source, a vanadium source, a phosphorus source, and a carbon source are mixed, wherein the molar mass ratio of lithium metal in the lithium source to the total molar mass ratio of iron, manganese, and vanadium in the iron, manganese, and vanadium sources is 0.95 to 1.05.

[0094] In some embodiments, a first mixture comprising a lithium source, an iron source, a manganese source, a vanadium source, a phosphorus source, and a carbon source is refined by a sand mill and then subjected to a first sintering treatment after spray drying.

[0095] Carbon-composite lithium iron manganese vanadium phosphate (LiFePO4) materials can improve the cycle performance, storage performance, and safety performance of batteries. The carbon-composite LiFePO4 materials incorporate carbon elements, resulting in low powder resistivity. This eliminates the need for carbon doping post-processing in composite cathode materials using it as a coating layer, resolving the adverse effects of conventional carbon coating post-processing. Furthermore, this can improve the stability of cathode composite materials and reduce manufacturing costs.

[0096] In some embodiments, the molar ratio of vanadium in the vanadium source to iron in the iron source is 0.5:8 to 4:1. In some embodiments, the molar ratio of vanadium in the vanadium source to iron in the iron source is 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, or 3:1.

[0097] A high molar ratio of vanadium to iron results in excellent rate performance, but reduces battery stability. Conversely, a low molar ratio improves stability but decreases rate performance. Controlling the molar ratio of vanadium to iron allows for a balance between rate performance, cycle life, and storage performance.

[0098] In some embodiments, the mass ratio of carbon in the carbon source to the lithium iron manganese vanadium phosphate material is 1:9999 to 1:4. In some embodiments, the mass content of carbon in the carbon-composite lithium iron manganese vanadium phosphate material can be selected from 1:999, 1:99, 1:9, 1:8, 1:7, 1:6, and 1:5.

[0099] In some embodiments, the sintering temperature of the first sintering treatment is 650°C to 800°C, and the sintering time of the first sintering treatment is 10 to 20 hours.

[0100] In some embodiments, the first sintering process is performed under a reducing atmosphere. In some embodiments, the first sintering process is performed under a nitrogen or argon atmosphere.

[0101] Controlling the sintering time of the first sintering treatment can control the nucleation and growth process of carbon-composite lithium iron manganese vanadium phosphate materials. Too short a reaction time or too low a reaction temperature can easily lead to incomplete nucleation and growth of the carbon-composite lithium iron manganese vanadium phosphate materials, resulting in poor crystallinity. Too long a reaction time or too high a reaction temperature can easily cause the carbon-composite lithium iron manganese vanadium phosphate materials to continue growing after nucleation, resulting in excessively large particle sizes.

[0102] Controlling the temperature and time of the first sintering treatment within a suitable range is beneficial for preparing lithium iron manganese vanadium phosphate materials with low powder resistivity, suitable average particle size Dv50, and suitability as a coating layer.

[0103] In some embodiments, the first mixture further comprises one or more of a nickel source, a cobalt source, a titanium source, and an aluminum source, wherein the nickel source, cobalt source, titanium source, and aluminum source are selected from one or more oxides, hydroxides, carbonates, and phosphates containing nickel, cobalt, titanium, and aluminum. Doping with nickel, cobalt, titanium, and aluminum improves the stability of the carbon-composite lithium iron manganese vanadium phosphate material, further enhancing the battery's cycle performance, storage performance, and safety performance.

[0104] In some embodiments, the sintering temperature of the second sintering treatment is 600–900°C, and the sintering time is 10–20 h.

[0105] In some embodiments, the second mixture further includes an alkali metal compound, the alkali metal compound comprising 0 to 5.5% by mass based on the total mass of the second mixture.

[0106] In some embodiments, the alkali metal compound is a carbonate, sulfate, chloride, or oxide of Na, K, Rb, or Cs.

[0107] The second mixture includes alkali metal compounds to achieve alkali metal doping of lithium-containing metal oxides, thereby improving the lithium-ion diffusion efficiency of the cathode material, thus optimizing the rate performance of the battery and also improving the first-time efficiency of the battery.

[0108] In one embodiment of this application, a secondary battery is provided.

[0109] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0110] [Positive electrode plate]

[0111] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the composite positive electrode material of the first aspect of this application.

[0112] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0113] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0115] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as composite positive electrode material, conductive agent, binder and any other components, in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0117] [Negative electrode plate]

[0118] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0119] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0121] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0122] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0124] In some embodiments, the negative electrode sheet of a full cell can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then drying, cold pressing and other processes to obtain the negative electrode sheet of the full cell.

[0125] [Electrolytes]

[0126] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0127] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0128] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0129] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0130] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0131] [Isolation membrane]

[0132] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0133] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0134] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0135] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0136] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0137] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0138] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0139] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0140] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0141] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0142] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0143] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0144] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0145] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0146] Figure 8This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0147] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0148] Example

[0149] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0150] Example 1

[0151] Preparation of composite cathode materials:

[0152] 1) Preparation of carbon-composite lithium iron manganese vanadium phosphate materials

[0153] First sintering treatment: Lithium carbonate, ferric oxide, manganese dioxide, vanadium trioxide, and ammonium dihydrogen phosphate are mixed in a molar ratio of 1:0.5:0.4:0.2:2. Sucrose is added at 5% of the mass of the mixture, and a certain amount of water is added to make the solid content 40%. The mixture is ground into a fine powder by a sand mill and then mixed evenly in a mixing tank. The evenly mixed slurry is then spray-dried to obtain a mixed powder. The material is then placed in a kiln for sintering at a temperature of 700℃ for 10 hours in a nitrogen atmosphere. The sintering yields a carbon composite lithium iron manganese vanadium phosphate material.

[0154] 2) Preparation of lithium-containing metal oxides

[0155] Second sintering process: Lithium hydroxide and cathode material precursor Ni are sintered together. 0.8 Co 0.1 Mn 0.1 (OH)2 and alumina were mixed evenly in a plow mixer at a molar ratio of 1.05:0.99:0.01. The mixture was then placed in a kiln for sintering at a temperature of 750℃ for 15 hours in an oxygen atmosphere. After cooling, lithium-containing metal oxides were obtained by mechanical crushing.

[0156] 3) Preparation of composite cathode materials

[0157] The third sintering process involves uniformly mixing lithium-containing metal oxides and carbon-composite lithium iron manganese vanadium phosphate materials at a mass ratio of 95:5, and sintering them at 300°C for 5 hours under a nitrogen atmosphere to obtain the composite cathode material.

[0158] Fabrication of button cells:

[0159] 1) Preparation of positive electrode sheet

[0160] Composite cathode material, polyvinylidene fluoride (PVDF), and acetylene black were added to the solvent N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a cathode sheet. The coating amount was 0.01 g / cm³. 2 The compacted density is 3.5 g / cm³. 3 .

[0161] 2) Preparation of negative electrode sheet

[0162] A 0.5mm lithium metal sheet was used as the negative electrode.

[0163] 3) Preparation of electrolyte

[0164] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above mixed solution to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0165] 4) Preparation of the separating membrane

[0166] The separator membrane was purchased from Cellgard, model number Cellgard 2400.

[0167] 5) Assembly of button cells

[0168] The positive electrode, negative electrode, separator, and electrolyte prepared above are assembled into a CR2032 coin cell in a coin cell box.

[0169] Preparation of full cells:

[0170] 1) Preparation of positive electrode sheet

[0171] Composite cathode material, polyvinylidene fluoride (PVDF), and acetylene black were added to the solvent N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a cathode sheet. The coating amount was 0.01 g / cm³. 2 The compacted density is 3.5 g / cm³. 3 .

[0172] 2) Preparation of negative electrode sheet

[0173] Artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1. The mixture was then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet. The coating amount was 0.015 g / cm³. 2 The compacted density is 1.6 g / cm³. 3 .

[0174] 3) Preparation of electrolyte

[0175] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above mixed solution to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0176] 4) Preparation of the separating membrane

[0177] PE porous polymer film is used as the separator.

[0178] 5) Preparation of full cells

[0179] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. The resulting cells are then wound to obtain a bare cell. The bare cell is placed in outer packaging, electrolyte is injected, and the cell is sealed to obtain a full cell (hereinafter referred to as "full cell"). The full cell has dimensions of 90mm × 30mm × 60mm (length × width × height) and a cell margin of 91.0%. The batteries in Examples 2-24 are prepared using methods similar to those in Example 1.

[0180] In Examples 2-5, the mass fraction of carbon in the carbon-composite lithium iron manganese vanadium phosphate material was adjusted by changing the mass fraction of sucrose added in the first sintering treatment. In Examples 6-9, the temperature of the first sintering treatment was adjusted. In Examples 10-13, the time of the first sintering treatment was adjusted. In Examples 14-17, the mass fraction of the coating layer was adjusted. In Examples 18-21, the molar ratio of vanadium in the vanadium source to iron in the iron source in the first sintering treatment was adjusted. The specific parameters are shown in Figure 1.

[0181] In Example 22, sodium carbonate, lithium hydroxide, sodium carbonate, and the cathode material precursor Ni were added during the second sintering process. 0.8 Co 0.1 Mn 0.1 The molar ratio of (OH)2 to alumina is 1.03:0.02:0.99:0.01.

[0182] In Example 23, during the first sintering treatment, alumina, lithium carbonate, alumina, ferric oxide, manganese dioxide, vanadium trioxide, and ammonium dihydrogen phosphate were added in a molar ratio of 1:0.002:0.5:0.4:0.2:1.

[0183] In Example 24, the cathode material precursor added during the second sintering process is Ni. 0.92 Co 0.06 Mn 0.02 (OH)2.

[0184] In Comparative Example 1, the cathode material is a lithium-containing metal oxide without a coating layer;

[0185] The coating material in Comparative Example 2 is a carbon-composite lithium iron manganese phosphate material, and the specific parameters are shown in Table 1.

[0186] In addition, the carbon composite iron manganese vanadium phosphate materials and batteries obtained in Examples 1 to 24 and Comparative Examples 1 and 2 were subjected to performance tests, and the test results are shown in Table 1.

[0187] The testing method is as follows:

[0188] 1. Performance test of carbon-complexed iron manganese vanadium phosphate material

[0189] 1) Particle size testing of carbon-composite iron-manganese-vanadium phosphate materials

[0190] Particle size distribution was determined using a Malvern Mastersizer 2000E laser particle size analyzer, in accordance with GB / T 19077-2016, laser diffraction method.

[0191] 2) Powder resistivity of carbon-composite iron manganese vanadium phosphate materials

[0192] The carbon-composite iron-manganese-vanadium phosphate material powder was dried, an appropriate amount of powder was weighed, and then the powder resistivity of the sample was determined using a powder resistivity tester, specifically a ST2722 digital four-probe instrument, according to GB / T 30835-2014 "Carbon-composite lithium iron phosphate cathode material for lithium-ion batteries".

[0193] 3) Carbon content testing of carbon-composite iron-manganese-vanadium phosphate materials

[0194] The carbon content analyzer, model HCS-140, was used to test the carbon content in the powder according to the determination of total carbon and sulfur content in steel using the infrared absorption method after combustion in a high-frequency induction furnace (conventional method) GBT20123-2006.

[0195] 2. Morphology characterization of the composite cathode material

[0196] The surface morphology of the composite cathode material was characterized using a field emission scanning electron microscope (Sigma300) from ZEISS GmbH, Germany.

[0197] 3. Performance test of the battery

[0198] 1) Initial capacity and first-efficiency test of button cells

[0199] Between 2.8 and 4.3V, the coin cell is charged at 0.1C to 4.3V, then charged at a constant voltage at 4.3V until the current is ≤0.05mA. After resting for 2 minutes, the charged capacity is recorded as C0. Then, it is discharged at 0.1C to 2.8V; the discharged capacity at this point is the initial specific capacity, recorded as D0. The first efficiency is calculated as D0 / C0*100%.

[0200] 2) Full cell capacity retention rate at 25℃

[0201] At 25°C, the battery is charged to 4.25V with a constant current of 1C, then charged at a constant voltage of 4.25V until the current drops to 0.05C, and finally discharged to 2.8V with a constant current of 1C. This yields the initial discharge capacity (Cdl). This charge-discharge cycle is repeated until the 300th cycle, yielding the discharge capacity after n cycles, denoted as Cdn. Capacity retention = Discharge capacity after n cycles (Cdn) / Initial discharge capacity (Cdl).

[0202] 3) Full cell capacity retention rate at 45℃

[0203] At 45℃, the battery is charged to 4.25V with a constant current of 1C, then charged at a constant voltage of 4.25V until the current drops to 0.05C, and finally discharged to 2.8V with a constant current of 1C. This yields the initial discharge specific capacity (Cdl). This charge-discharge cycle is repeated until the 300th cycle, yielding the discharge specific capacity after n cycles, denoted as Cdn. Capacity retention = Discharge specific capacity after n cycles (Cdn) / Initial discharge specific capacity (Cdl).

[0204] 4) Gas production test of the entire battery at 70°C

[0205] Full cells at 100% State of Charge (SOC) were stored at 70°C. The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. Every 48 hours of storage, the full cells were removed, allowed to stand for 1 hour, and then OCV and IMP were tested. After cooling to room temperature, the cell volume was measured using the displacement method. The displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion from the dial readings, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3In the process, the weight F2 of the battery cell at this moment is measured, and the buoyant force F_buoyancy on the battery cell is F1-F2. Then, according to Archimedes' principle, F_buoyancy = ρgV 排 The cell volume V = (F1 - F2) / ρg was calculated.

[0206] After each volume test, the battery cell is recharged with a constant current of 1C to 4.25V, and then charged with a constant voltage of 4.25V until the current drops to 0.05C. After the recharge is completed, the cell is put into the furnace for further testing.

[0207] After 30 days of storage, the cell volume is measured, and the increase in cell volume after storage is calculated relative to the cell volume before storage, i.e., the gas production. The gas production / cell capacity gives the gas production volume per unit capacity.

[0208] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0209]

[0210]

[0211] The morphology of the composite cathode material was measured using scanning electron microscopy (SEM). The results are shown in [Figure number missing]. Figure 1 As can be seen from the contrast in the image, the Li2FeMn alloy prepared in Example 1... 0.4 V 0.4 The composite cathode material with PO4@C as the coating layer has a uniform particle size at the micron level, with a uniform particle distribution and no agglomeration. The 25℃ cycle performance test curve of the battery assembled using it as the cathode material is shown in [reference needed]. Figure 2 This is used to calculate the battery's cycle capacity retention rate.

[0212] As can be seen from the comparison of Examples 1-24 and Comparative Example 1, the composite cathode material provided in this application includes: a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide. The coating layer is a carbon-composite lithium iron manganese vanadium phosphate material, and the general formula of lithium iron manganese vanadium phosphate material is shown in Formula I.

[0213] LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I

[0214] Wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and M2 is selected from one or more of Ni, Co, Ti, and Al.

[0215] Composite cathode materials prepared by coating lithium-containing metal oxides with carbon-composite iron-manganese-vanadium lithium phosphate materials can improve the cycle capacity retention rate of batteries at room temperature and high temperature, and reduce the gas production volume per unit capacity of batteries at high temperature. In other words, they can improve the cycle performance, storage performance and safety performance of batteries. At the same time, the coating layer does not significantly reduce the capacity performance of batteries. Batteries using composite cathode materials as cathodes still have excellent capacity performance and first-time coin-count efficiency.

[0216] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, compared with the traditional lithium iron manganese phosphate coating layer, the coating layer of this application can further improve the battery's toroidal performance, storage performance and safety performance. At the same time, the coating layer can also increase the battery's specific capacity.

[0217] As can be seen from Examples 1 and 14-17, the mass content of the coating layer is 0.1% to 10%. Based on the total mass of the composite cathode material, the composite cathode material can maintain or even improve the battery's capacity performance and first-time coin cell efficiency while further improving the battery's cycle performance, storage performance and safety performance.

[0218] As can be seen from Examples 1 to 5, the mass fraction of carbon in the coating layer is 0.01% to 25%. Based on the total mass of the coating layer, the coating layer has a suitable powder resistivity, which makes it easy to achieve lithium ion insertion and extraction. Even with the addition of the coating layer, the capacity performance and first efficiency of the battery can be further maintained or improved, and the battery performance will not deteriorate due to the addition of the coating layer.

[0219] As can be seen from the comparison of Examples 1-5 and Comparative Example 3, the powder resistivity of the composite cathode material is 1000-5500 Ω·cm. The low powder resistivity of the composite cathode material indicates higher material stability and conductivity, which helps to maintain and improve battery capacity.

[0220] As can be seen from Examples 1, 6-13, the average particle size D50 of the composite cathode material is 8-12 μm. When it can be selected as 8-10 μm, the composite cathode material can exhibit excellent electrochemical performance and cycle performance.

[0221] As can be seen from Examples 1, 18-21, when the molar ratio of vanadium in the vanadium source to iron in the iron source is 0.5:8 to 4:1, the composite cathode material can maintain or even improve the battery's capacity performance and first-time coin-count efficiency while further improving the battery's cycle performance, storage performance and safety performance.

[0222] As can be seen from Examples 1 and 23, doping aluminum into carbon-composite lithium iron manganese vanadium phosphate materials can further improve the stability of the coating layer, thereby improving the cycle performance of the battery at high temperatures.

[0223] As can be seen from Examples 1 and 22, the lithium-containing metal oxide, after being doped with alkali metals, improves the battery's first coin efficiency, cycle performance, and storage performance.

[0224] As can be seen from Examples 1 and 24, using carbon-composite lithium iron manganese vanadium phosphate material as a coating layer is suitable for lithium-containing metal oxides with different nickel, cobalt and manganese contents. Adjusting the nickel, cobalt and manganese ratio helps to adjust the battery's capacity performance and first-time coin-count efficiency.

Claims

1. A composite cathode material, characterized in that, The composite cathode material comprises: a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide, wherein the coating layer is a carbon-composite lithium iron manganese vanadium phosphate material, and the general formula of the lithium iron manganese vanadium phosphate material is shown in Formula I. LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I Wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and M2 is selected from one or more of Ni, Co, Ti, and Al; The carbon mass fraction in the coating layer is 0.01% to 25%, based on the total mass of the coating layer.

2. The composite cathode material according to claim 1, characterized in that, The mass content of the coating layer is 0.1% to 10%, based on the total mass of the composite cathode material.

3. The composite cathode material according to claim 1 or 2, characterized in that, The resistivity of the composite cathode material is 1000~5500 Ω·cm.

4. The composite cathode material according to any one of claims 1 to 3, characterized in that, The average particle size Dv50 of the composite cathode material is 8~12 μm.

5. The composite cathode material according to any one of claims 1 to 4, characterized in that, The general formula of the lithium-containing metal oxide is shown in Formula II. Li 1.05-a2 M1 a2 (Ni b2 Co c2 Mn d2 ) 1-e2 Q e2 O2, Formula II In the formula, 0≤a2≤0.1, 0.7≤b2≤0.96, 0.03≤c2≤0.2, 0.01≤d2≤0.2, 0≤e2≤0.05; where M1 is selected from one or more of the alkali metal elements Na, K, Rb, and Cs, and Q is selected from one or more of Al, Mg, Zr, Ti, W, Y, B, Co, Nb, Mo, Sb, and Sr.

6. A method for preparing a composite cathode material, characterized in that, Includes the following steps: A first mixture containing lithium, iron, manganese, vanadium, phosphorus, and carbon sources is subjected to a first sintering treatment to prepare a carbon-composite lithium iron manganese vanadium phosphate material. A second mixture containing a lithium source and a nickel-cobalt-manganese precursor is subjected to a second sintering treatment, wherein the molar ratio of lithium in the lithium source to the total amount of nickel, cobalt and manganese in the nickel-cobalt-manganese precursor is 0.95 to 1.05, to prepare a lithium-containing metal oxide. The carbon-composite lithium iron manganese vanadium phosphate material is subjected to a third sintering treatment with the lithium-containing metal oxide to obtain a composite cathode material. The composite cathode material includes a lithium-containing metal oxide and a coating layer disposed on at least a portion of the lithium-containing metal oxide. The coating layer is a carbon-composite lithium iron manganese vanadium phosphate material, and the general formula of the lithium iron manganese vanadium phosphate material is shown in Formula I. LiFe a1 Mn b1 V c1 M2 d1 PO4, Formula I Wherein, 0.1≤a1≤0.8, 0.1≤b1≤0.45, 0.07≤c1≤0.3, 0≤d1≤0.01, and M2 is selected from one or more of Ni, Co, Ti, and Al.

7. The method for preparing the composite cathode material according to claim 6, characterized in that, In the third sintering process, the mass ratio of the lithium-containing metal oxide to the carbon-composite lithium iron manganese vanadium phosphate material is 9:1 to 999:

1.

8. The method for preparing the composite cathode material according to claim 6 or 7, characterized in that, In the first sintering process, the molar ratio of vanadium in the vanadium source to iron in the iron source is 0.5:8 to 4:

1.

9. The method for preparing the composite cathode material according to any one of claims 6 to 8, characterized in that, The mass ratio of carbon in the carbon source to the mass of the lithium iron manganese vanadium phosphate material is 1:9999~1:

4.

10. The method for preparing the composite cathode material according to any one of claims 6 to 9, characterized in that, The sintering temperature of the first sintering treatment is 650℃~800℃, or the sintering time of the first sintering treatment is 10~20 h.

11. The method for preparing the composite cathode material according to any one of claims 6 to 10, characterized in that, The first mixture also contains one or more of a nickel source, a cobalt source, a titanium source, and an aluminum source, wherein the nickel source, cobalt source, titanium source, and aluminum source are selected from one or more of oxides, hydroxides, carbonates, and phosphates containing nickel, cobalt, titanium, and aluminum.

12. The method for preparing the composite cathode material according to any one of claims 6 to 11, characterized in that, The iron source is selected from one or more of ferric oxide and iron(II) oxide; the manganese source is selected from one or more of manganese dioxide and manganese(II) oxide; the vanadium source is selected from one or more of vanadium(II) oxide and vanadium(II) pentoxide; the phosphorus source is selected from one or more of ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate; and the carbon source is selected from one or more of carbon black, citric acid, polyethylene glycol, sucrose, and glucose.

13. The method for preparing the composite cathode material according to any one of claims 6 to 12, characterized in that, It also includes the following steps: The second mixture also includes an alkali metal compound, the alkali metal compound having a mass content of 0 to 5.5% based on the total mass of the second mixture.

14. A secondary battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode comprises the composite positive electrode material according to any one of claims 1 to 5.

15. A battery module, characterized in that, Includes the secondary battery as described in claim 14.

16. A battery pack, characterized in that, Includes the battery module as described in claim 15.

17. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery of claim 14, the battery module of claim 15, or the battery pack of claim 16.

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