A positive electrode composite material and preparation method thereof, a positive electrode sheet and a battery

Abstract

This application provides a positive electrode composite material and its preparation method, a positive electrode sheet, and a battery. The positive electrode composite material includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes a ternary material and a hydrophobic group, and the hydrophobic group is chemically bonded to the ternary material. Under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.05. By introducing hydrophobic groups onto the ternary material, this application can improve the technical problem of poor electrochemical stability caused by the large difference in the sensitivity of different positive electrode active materials to moisture in the positive electrode composite material.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a positive electrode composite material and its preparation method, a positive electrode sheet, and a battery. Background Art

[0002] In recent years, with the rapid development of new energy technologies, the research and development of power batteries has also been booming, with a growing focus on the development of high-energy-density battery materials. New materials composed of lithium manganese iron phosphate (LMFP) and ternary (NCM) materials can further improve energy density, and the two materials complement each other. On the one hand, NCM materials can improve the inherent conductivity deficiency of LMFP materials; on the other hand, the introduction of LMFP materials can improve the thermal stability of NCM materials. Therefore, materials composed of LMFP and NCM materials have become a promising emerging cathode material for lithium-ion batteries.

[0003] Because LMFP and NCM materials have different sensitivities to moisture, their moisture requirements differ when used individually. However, when LMFP and NCM materials are used in combination, the different moisture sensitivities lead to a decrease in the consistency between the two materials, thereby affecting the electrochemical stability of the composite material and consequently impacting the battery's cycle and storage performance. Summary of the Invention

[0004] The embodiments of the present invention provide a positive electrode composite material and its preparation method, a positive electrode sheet and a battery, which can improve the technical problem of poor electrochemical stability caused by the large difference in the sensitivity of different positive electrode active materials to moisture in the positive electrode composite material.

[0005] In a first aspect, embodiments of the present invention provide a positive electrode composite material, including a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material includes a ternary material and a hydrophobic group, and the hydrophobic group is connected to the ternary material by a chemical bond;

[0006] Under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.05.

[0007] In some embodiments, the hydrophobic group comprises at least one of a hydrocarbon group, a fatty acid group, an aromatic group, and a halogenated hydrocarbon group.

[0008] In some embodiments, the hydrophobic group is selected from oleic acid groups.

[0009] In some embodiments, the mass fraction of the hydrophobic group in the first positive electrode active material ranges from 0.5% to 5%.

[0010] In some embodiments, the positive electrode composite material further includes a conductive agent and a binder; in the positive electrode composite material, the sum of the mass fractions of the first positive electrode active material and the second positive electrode active material ranges from 94.5% to 97%, the mass fraction of the conductive agent ranges from 1.5% to 3%, and the mass fraction of the binder ranges from 1.5% to 2.5%.

[0011] In some embodiments, the ternary material includes nickel-cobalt-manganese material, and the second positive electrode active material includes lithium manganese iron phosphate material.

[0012] Secondly, embodiments of the present invention provide a method for preparing a positive electrode composite material, comprising:

[0013] Hydrophobic groups are formed on a ternary material to obtain a first positive electrode active material, wherein the hydrophobic groups are chemically bonded to the ternary material; and

[0014] At least the first positive electrode active material and the second positive electrode active material are mixed to obtain a positive electrode composite material; wherein, under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.05.

[0015] In some embodiments, the step of forming hydrophobic groups on the ternary material to obtain the first positive electrode active material includes:

[0016] Nickel, cobalt, and manganese sources are mixed and dissolved in a preset ratio to obtain a mixed salt solution. A precipitant is added to the mixed salt solution, and the mixture is stirred evenly at a first preset temperature. During stirring, a complexing agent is added to the mixed solution. After standing, the solution is washed and impurities are removed to obtain a ternary material precursor. At least one of the nickel, cobalt, and manganese sources is chemically bonded with a hydrophobic group.

[0017] The ternary material precursor is dried at a second preset temperature and then calcined at a third preset temperature to obtain the first positive electrode active material.

[0018] The nickel source is selected from nickel oleate, the cobalt source is selected from cobalt nitrate, and the manganese source is selected from cobalt sulfate; the mass fraction of the nickel source ranges from 50% to 80%, the mass fraction of the cobalt source ranges from 10% to 20%, and the mass fraction of the manganese source ranges from 10% to 30%.

[0019] Thirdly, embodiments of the present invention provide a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active layer located on at least one side of the positive current collector, the material of the positive active layer comprising the positive electrode composite material described above.

[0020] Fourthly, embodiments of the present invention provide a battery comprising the positive electrode sheet described above.

[0021] This invention provides a positive electrode composite material, its preparation method, a positive electrode sheet, and a battery. By introducing hydrophobic groups into a ternary material, a first positive electrode active material is obtained, making the sensitivity of the first and second positive electrode active materials to moisture more consistent. This ensures that the chemical activity of the first and second positive electrode active materials remains consistent in the same environment, thereby improving the electrochemical stability of the positive electrode composite material. When the positive electrode composite material is used in the positive electrode sheet of a battery, it can improve the cycle and storage performance of the battery cell. Therefore, this application can improve the technical problem of poor electrochemical stability caused by the large difference in the sensitivity of different positive electrode active materials to moisture in the positive electrode composite material. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating a method for preparing a positive electrode composite material according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the structure of a positive electrode sheet provided in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of another positive electrode sheet provided in an embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of the structure of a battery provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention. In the present invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0028] Layered NCM materials are more sensitive to moisture than LMFP materials, and are more prone to chemical reactions upon contact with water, such as the formation of hydroxides, which can affect the material's performance and the battery's electrochemical performance, potentially leading to capacity decay and reduced cycle life. Furthermore, high-nickel NCM materials, with their higher nickel content, are more susceptible to safety risks such as thermal runaway. LMFP materials, on the other hand, have an olivine structure, which is relatively stable and less sensitive to moisture than NCM materials. Therefore, the thermal stability of a composite material formed by combining NCM and LMFP materials can be improved.

[0029] However, due to the inconsistent sensitivity of NCM and LMFP materials to moisture, the degree of side reactions of the two materials will differ in the same environment. When using composite materials of NCM and LMFP materials for a long time, the deviation between the chemical activities of the two materials will become larger and larger, resulting in a decrease in the electrochemical stability of the composite material, that is, the loss of the composite advantage.

[0030] To address the aforementioned technical problems, this application provides a positive electrode composite material, a method for preparing the same, a positive electrode sheet, and a battery, as described in the following embodiments.

[0031] This application provides a positive electrode composite material, which includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes a ternary material and a hydrophobic group, and the hydrophobic group is connected to the ternary material by a chemical bond.

[0032] Under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.05.

[0033] In some embodiments, the sensitivity of a substance to water can be assessed using the weight change method. Specifically, the weight change of a substance under different humidity conditions is measured to determine its sensitivity to moisture. When a substance is exposed to an environment containing a certain amount of moisture, it absorbs or adsorbs moisture, resulting in an increase in weight. By monitoring the weight change, the substance's ability to absorb moisture and its sensitivity can be assessed.

[0034] In some embodiments, the method for determining the rate of change of weight includes the following steps.

[0035] (1) Dry the substance to be tested at a certain temperature to constant weight to remove any moisture that may be present inside it and ensure the consistency of the initial state.

[0036] (2) Set different humidity environments: Use humidity control equipment, such as constant temperature and humidity chamber, to set different relative humidity levels, such as 10%, 30%, 50%, 70%, etc.

[0037] (3) Place the samples and weigh them: Place the dried samples in different humidity environments. After a certain period of time (such as 24 hours or 48 hours), take out the samples and weigh them quickly. Record the weight of the samples under each humidity condition.

[0038] (4) Calculate the weight change rate: Calculate the weight change rate based on the weight change of the sample under different humidity conditions. Weight change rate = (weight after moisture absorption - initial weight) / initial weight × 100%.

[0039] It is understood that the weight change rate A of the first positive electrode active material and the weight change rate B of the second positive electrode active material can be measured by the weight change rate measurement method described above, and the ratio of A to B (A / B) satisfies 0.95≤A / B≤1.05.

[0040] This application embodiment introduces hydrophobic groups into a ternary material to obtain a first positive electrode active material. This makes the sensitivity of the first and second positive electrode active materials to moisture more consistent, thereby ensuring that their chemical activities remain consistent in the same environment. This improves the electrochemical stability of the positive electrode composite material. When the positive electrode composite material is used in the positive electrode sheet of a battery, it can improve the cycle life and storage performance of the battery cell.

[0041] In some embodiments, the hydrophobic group comprises at least one of a hydrocarbon group, a fatty acid group, an aromatic group, and a halohydrocarbon group, but is not limited thereto. By introducing these types of hydrophobic groups into the ternary material, the sensitivity of the first positive electrode active material to moisture can be reduced, making the sensitivity of the first positive electrode active material and the second positive electrode active material to moisture comparable, without having a negative impact on the ternary material.

[0042] In one specific embodiment, the hydrophobic group is selected from the oleic acid group. Of course, in other specific embodiments, the hydrophobic group can also be selected from other hydrophobic groups; the embodiments of this application use the oleic acid group as an example for illustration.

[0043] In some embodiments, hydrophobic groups can be introduced into the raw materials of the ternary material (e.g., nickel source, cobalt source, and manganese source) so that the prepared ternary material contains hydrophobic groups.

[0044] In some embodiments, the hydrophobic group and the raw material of the ternary material are directly bonded by chemical bonds. For example, when the hydrophobic group is an oleic acid group, the nickel source of the ternary material can be selected from nickel oleate ((C 17 H 33 COO)2Ni) gives the nickel source a hydrophobic group.

[0045] It is understood that the chemical bonds described in the embodiments of this application include, but are not limited to, covalent bonds.

[0046] It should be noted that the hydrophobic groups in the embodiments of this application can also be bonded to the ternary material through intermediate linking groups.

[0047] In some embodiments, the mass fraction of hydrophobic groups in the first positive electrode active material ranges from 0.5% to 5%. For example, the mass fraction of hydrophobic groups in the first positive electrode active material is 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. By controlling the content of hydrophobic groups within the range of 0.5% to 5%, the sensitivity of the ternary material to moisture can be reduced within a suitable range, making the sensitivity of the first and second positive electrode active materials to moisture more consistent.

[0048] In some embodiments, the ternary material includes nickel-cobalt-manganese material, and the second positive electrode active material includes lithium manganese iron phosphate material. In this case, the ternary material is abbreviated as NCM, and the second positive electrode active material is abbreviated as LMFP.

[0049] Of course, in the embodiments of this application, the metal elements in the ternary material are not limited to the combination of nickel, cobalt, and manganese, and the metal elements in the second positive electrode active material are not limited to the combination of manganese, iron, and lithium. The embodiments of this application only use NCM and LMFP as examples for illustration.

[0050] In some embodiments, the positive electrode composite material further includes a conductive agent and a binder. In the positive electrode composite material, the sum of the mass fractions of the first positive electrode active material and the second positive electrode active material ranges from 94.5% to 97%, the mass fraction of the conductive agent ranges from 1.5% to 3%, and the mass fraction of the binder ranges from 1.5% to 2.5%.

[0051] For example, in the positive electrode composite material, the sum of the mass fractions of the first positive electrode active material and the second positive electrode active material is 94.5%, 95%, 95.5%, 96%, 96.5%, or 97%; the mass fraction of the conductive agent is 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%; and the mass fraction of the binder is 1.5%, 1.8%, 2%, 2.2%, or 2.5%.

[0052] In some embodiments, the positive electrode composite material further includes a solvent selected from, but not limited to, N-methyl-2-pyrrolidone (NMP).

[0053] like Figure 1 As shown, this application provides a method for preparing the positive electrode composite material described in the foregoing embodiments, the preparation method including steps S101 and S102.

[0054] S101: Hydrophobic groups are formed on the ternary material to obtain the first positive electrode active material. The hydrophobic groups are connected to the ternary material by chemical bonds.

[0055] Specifically, step S101 includes the following steps:

[0056] Nickel, cobalt, and manganese sources are mixed and dissolved in a preset ratio to obtain a mixed salt solution. A precipitant is added to the mixed salt solution, and the mixture is stirred evenly at a first preset temperature. During stirring, a complexing agent is slowly added dropwise to the mixed solution. After standing, the solution is washed and impurities are removed to obtain a ternary material precursor. At least one of the nickel, cobalt, and manganese sources is chemically bonded with a hydrophobic group.

[0057] The ternary material precursor is dried at a second preset temperature and then calcined at a third preset temperature to obtain the first positive electrode active material.

[0058] In one specific embodiment, the nickel source is selected from nickel oleate, the cobalt source is selected from cobalt nitrate, and the manganese source is selected from cobalt sulfate. Furthermore, the mass fraction of the nickel source ranges from 50% to 80%, the mass fraction of the cobalt source ranges from 10% to 20%, and the mass fraction of the manganese source ranges from 10% to 30%, and the sum of the mass fractions of the nickel source, cobalt source, and manganese source is 100%.

[0059] In one specific embodiment, nickel oleate, cobalt nitrate, and manganese sulfate are dissolved in deionized water according to the stoichiometric ratio of the target ternary material to prepare a mixed salt solution, and the concentration of the mixed salt solution is controlled between 0.5 mol / L and 2.0 mol / L.

[0060] For example, the concentration of the mixed salt solution is 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2.0 mol / L.

[0061] In one specific embodiment, the precipitant is selected from sodium hydroxide solution, and the concentration of sodium hydroxide solution ranges from 5 mol / L to 10 mol / L.

[0062] For example, the concentration of sodium hydroxide solution is 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L.

[0063] In one specific embodiment, the complexing agent is selected from ammonia water, and the concentration of ammonia water is from 2 mol / L to 6 mol / L.

[0064] For example, the concentration of ammonia water is 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, or 6 mol / L.

[0065] In one specific embodiment, the first preset temperature ranges from 50°C to 90°C.

[0066] For example, the first preset temperature is 50℃, 60℃, 70℃, 80℃ or 90℃.

[0067] In one specific embodiment, the second preset temperature ranges from 80°C to 120°C, and the third preset temperature ranges from 700°C to 1000°C.

[0068] For example, the second preset temperature is 80℃, 90℃, 100℃, 110℃ or 120℃, and the third preset temperature is 700℃, 800℃, 900℃ or 1000℃.

[0069] In one specific embodiment, the calcination time ranges from 5 hours to 15 hours.

[0070] For example, the calcination time is 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours.

[0071] It should be noted that the ternary material in the first positive electrode active material formed by calcination has a specific crystal structure, and the obtained first positive electrode active material can also be preserved after crushing and screening.

[0072] In one specific embodiment, step S101 includes the following steps:

[0073] Nickel oleate, cobalt nitrate, and manganese sulfate were dissolved in deionized water according to the stoichiometric ratio of the target ternary material to prepare a mixed salt solution. The concentration of the mixed salt solution was controlled between 0.5 mol / L and 2.0 mol / L.

[0074] While stirring, slowly add a sodium hydroxide solution with a concentration ranging from 5 mol / L to 10 mol / L to the mixed salt solution, and control the pH value of the mixed salt solution between 10 and 13.

[0075] The mixed salt solution was stirred at 300 to 600 rpm at 50 to 90 ℃, while ammonia solution with a concentration range of 2 mol / L to 6 mol / L was slowly added dropwise to the mixed salt solution to carry out a precipitation reaction.

[0076] Let the solution stand for 12 to 16 hours to promote further growth and crystallization of the precipitated particles;

[0077] The precipitate was repeatedly washed with deionized water to remove impurity ions, yielding a ternary material precursor; and

[0078] The ternary material precursor was dried at 80℃~120℃ to obtain precursor powder;

[0079] The dried precursor powder is placed in a high-temperature furnace and calcined at a temperature of 700℃ to 1000℃ for 5 to 15 hours to form a first positive electrode active material with a specific crystal structure.

[0080] In some embodiments, the mass fraction of hydrophobic groups in the first positive electrode active material ranges from 0.5% to 5%. For example, the mass fraction of hydrophobic groups in the first positive electrode active material is 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0081] Understandably, the content of hydrophobic groups on ternary materials can be controlled by adjusting the ratio of nickel oleate.

[0082] S102: At least a first positive electrode active material and a second positive electrode active material are mixed to obtain a positive electrode composite material; wherein, under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.05.

[0083] Specifically, the weight change rate of the first positive electrode active material and the second positive electrode active material can be obtained by the aforementioned method for measuring the weight change rate, which will not be repeated here.

[0084] In some embodiments, the second positive electrode active material may be selected from positive electrode active materials containing at least two metal elements selected from manganese, iron and lithium.

[0085] In one specific embodiment, the second positive electrode active material is selected from lithium manganese iron phosphate (LMFP).

[0086] The combined use of ternary cathode materials (NCM) and lithium manganese iron phosphate (LMFP) materials can effectively improve energy density. Furthermore, NCM materials can address the inherent conductivity deficiency of LMFP materials, while LMFP materials can enhance the thermal stability of NCM materials. Therefore, using a composite material of a first and second positive electrode active material to fabricate the positive electrode sheet is beneficial for improving the battery's energy density, electrochemical stability, and thermal stability, thereby enhancing its cycle life and storage performance.

[0087] Specifically, in step S102, the process of mixing at least the first positive electrode active material and the second positive electrode active material to obtain the positive electrode composite material includes the following steps:

[0088] The first positive electrode active material, the second positive electrode active material, the conductive agent, and the binder are dispersed in a solvent and stirred evenly to obtain a slurry of positive electrode composite material.

[0089] In some embodiments, the solvent is selected from NMP.

[0090] In some embodiments, in the positive electrode composite material, the sum of the mass fractions of the first positive electrode active material and the second positive electrode active material ranges from 94.5% to 97%, the mass fraction of the conductive agent ranges from 1.5% to 3%, and the mass fraction of the binder ranges from 1.5% to 2.5%.

[0091] For example, in the positive electrode composite material, the sum of the mass fractions of the first positive electrode active material and the second positive electrode active material is 94.5%, 95%, 95.5%, 96%, 96.5%, or 97%; the mass fraction of the conductive agent is 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%; and the mass fraction of the binder is 1.5%, 1.8%, 2%, 2.2%, or 2.5%.

[0092] In some embodiments, a positive electrode sheet can be obtained by coating a positive electrode composite material slurry onto at least one side of a positive electrode current collector and then performing processes such as drying and cold pressing.

[0093] It is understood that the positive electrode composite material provided in the embodiments of this application can be applied to the positive electrode sheet of a battery.

[0094] In this embodiment, by introducing hydrophobic groups into the ternary material, a first positive electrode active material is obtained. This makes the sensitivity of the first and second positive electrode active materials to moisture more consistent, thereby ensuring that the chemical activity of the first and second positive electrode active materials remains consistent in the same environment, thus improving the electrochemical stability of the positive electrode composite material. When the positive electrode composite material is applied to the positive electrode sheet of a battery, it can improve the cycle and storage performance of the battery cell.

[0095] like Figure 2 and Figure 3 As shown, this application embodiment also provides a positive electrode 1, which includes a positive current collector 2 and a positive active layer 3 located on at least one side of the positive current collector 2. The material of the positive active layer 3 includes the positive electrode composite material described in the foregoing embodiment.

[0096] In some embodiments, a mixture slurry formed from the positive electrode composite material described in the foregoing embodiments is coated on the surface of the positive electrode current collector 2, and then dried and rolled to form the positive electrode sheet 1.

[0097] In some embodiments, the material of the positive current collector 2 may be a metal, such as aluminum or copper, but is not limited thereto.

[0098] In some embodiments, the positive electrode current collector 2 may be a sheet-like structure having two opposing surfaces, and at least one side of the positive electrode current collector 2 is coated with a positive electrode composite material. For example, such as Figure 2 As shown, a positive electrode composite material can be coated on one surface of the positive electrode current collector 2 to form a positive electrode active layer 3, or, as... Figure 3 As shown, positive electrode composite material is coated on both opposite surfaces of the positive electrode current collector 2 to form a positive electrode active layer 3.

[0099] In some embodiments, the areal density of the positive electrode active layer 3 on one side is 210 g / m². 2 ~230g / m 2 When the areal density is within the above-mentioned range, the battery has good range. When the areal density is too low, the battery capacity is too small, resulting in insufficient range; when the areal density is too high, there are problems with dynamics and the manufacturing cost increases.

[0100] In this embodiment, since the material of the positive active layer 3 on the positive electrode 1 includes the aforementioned positive composite material, and the first positive active material and the second positive active material in the positive composite material have very similar sensitivity to moisture, the chemical activity of the first positive active material and the second positive active material in the positive active layer 3 remains consistent in the same environment. This is beneficial to improving the electrochemical stability of the positive electrode 1, and thus can improve the cycle and storage performance of the battery cell using the positive electrode 1.

[0101] like Figure 4 As shown, this application embodiment also provides a battery 4, which includes a battery casing 5 and an electrolyte (not shown in the figure), a negative electrode 6, a separator 7 and the positive electrode 1 described in the foregoing embodiment located inside the battery casing 5.

[0102] The battery casing 5 has a receiving cavity 8, in which the negative electrode 6, separator 7, and positive electrode 1 are sequentially stacked, and the electrolyte is contained within the receiving cavity 8. The battery casing 5 can be made of metal, such as steel or aluminum.

[0103] In some embodiments, the negative electrode sheet 6 includes a negative electrode current collector and a negative electrode material coated on the negative electrode current collector. The negative electrode material may include graphite, a conductive agent, a binder, etc. The negative electrode sheet is formed by coating a mixture slurry of the negative electrode material onto the surface of the negative electrode current collector, and then drying and rolling it.

[0104] In some embodiments, battery 4 is a lithium-ion battery, but is not limited thereto.

[0105] In some embodiments, the assembly steps of battery 4 include: cutting, die-cutting, slitting, etc., of the vacuum-dried positive electrode 1, negative electrode 6, and separator 7, and then injecting electrolyte under high temperature and negative pressure to assemble them into a square aluminum-cased battery.

[0106] This application also provides Examples 1, 1 Comparative Example, and 2 to test the battery performance, specifically testing the battery's cycle performance. The batteries provided in Examples 1, 1 Comparative Example, and 2 have the same structure and are the batteries described in the preceding examples, differing only in the ratio (A / B) of the weight change rate A of the first positive electrode active material and the weight change rate B of the second positive electrode active material in the positive electrode sheet.

[0107] Specifically, in the batteries provided in Example 1, Comparative Example 1 and Comparative Example 2, the first positive electrode active material in the positive electrode sheet is an NCM material containing hydrophobic groups, and the second positive electrode active material in the positive electrode sheet is an LMFP material.

[0108] It should be noted that the hydrophobic groups in the first positive electrode active materials of Example 1, Comparative Example 1 and Comparative Example 2 are the same hydrophobic groups, only the content of the hydrophobic groups is different.

[0109] Specifically, the content of hydrophobic groups in the first positive electrode active material in Example 1 is 2.7 wt%, the content of hydrophobic groups in the first positive electrode active material in Comparative Example 1 is 0.3 wt%, and the content of hydrophobic groups in the first positive electrode active material in Comparative Example 2 is 5.9 wt%.

[0110] The weight change rates of the positive electrode active materials in Example 1, Comparative Example 1, and Comparative Example 2 were measured using the weight change rate determination method described above, as shown below:

[0111] In Example 1, the weight change rate A of the NCM material containing hydrophobic groups in the positive electrode is 0.35%, and the weight change rate B of the LMFP material in the positive electrode is 0.36%.

[0112] In Comparative Example 1, the weight change rate A of the NCM material containing hydrophobic groups in the positive electrode sheet was 0.43%, and the weight change rate B of the LMFP material in the positive electrode sheet was 0.36%.

[0113] In Comparative Example 2, the weight change rate A of the NCM material containing hydrophobic groups in the positive electrode was 0.21%, and the weight change rate B of the LMFP material in the positive electrode was 0.36%.

[0114] The testing method for cycle performance is as follows:

[0115] The batteries provided in Example 1, Comparative Example 1, and Comparative Example 2 were placed at 25°C for 1 hour, then charged to 4.2V with a constant current and constant voltage of 1C and a cutoff current of 0.05C. After that, they were placed for 30 minutes and then placed at 2.5V with a constant current of 1C. The stability of the materials was evaluated by the cycle capacity retention rate after 500 cycles. The test results are shown in Table 1.

[0116] Table 1

[0117] Example 1 Comparative Example 1 Comparative Example 2 A 0.35％ 0.43％ 0.21％ B 0.36％ 0.36％ 0.36％ Mixing ratio (A / B) 0.98 1.20 0.60 Cyclic performance 93.70％ 91.80％ 92.60％

[0118] As shown in Table 1, the ratio (A / B) of the weight change rate A of the first positive electrode active material and the weight change rate B of the second positive electrode active material in Example 1 meets the requirement of 0.95≤A / B≤1.05. However, the content of hydrophobic groups in the first positive electrode active material in Comparative Example 1 is too low, and the content of hydrophobic groups in the first positive electrode active material in Comparative Example 2 is too high, resulting in the ratio (A / B) of the weight change rate A of the first positive electrode active material and the weight change rate B of the second positive electrode active material in both Comparative Example 1 and Comparative Example 2 not meeting the requirement of 0.95≤A / B≤1.05.

[0119] As shown in Table 1, the battery exhibits the best cycle performance when the weight change rate A of the first positive electrode active material (NCM material containing hydrophobic groups) and the weight change rate B of the second positive electrode active material (LMFP material) satisfy the requirement of 0.95 ≤ A / B ≤ 1.05. Furthermore, the battery's cycle performance deteriorates when the NCM material's sensitivity to moisture is too high or too low. This is because, regardless of whether the NCM material's sensitivity to moisture is too high or too low, partial redox reactions occur in the presence of water, leading to changes in the crystal structure of either the NCM or LMFP material, thus affecting the lithium-ion insertion and extraction capabilities. When the NCM and LMFP materials suffer different degrees of damage due to redox reactions, lithium-ion insertion and extraction will favor the material with less damage. From a material level perspective, one type of material (such as LMFP material) undergoes deep charge and discharge, while another type of material (such as NCM material) undergoes shallow charge and discharge. As the number of cycles increases, this differentiated charge and discharge phenomenon becomes more pronounced, leading to a decrease in the electrochemical stability of the material and further deterioration of the battery's cycle performance.

[0120] Therefore, the introduction of hydrophobic groups can improve the hydrophobicity of materials, making them more stable in humid environments; appropriate introduction of hydrophobic groups can improve the conductivity and stability of materials; by regulating the moisture sensitivity of NCM materials and LMFP materials to keep them at a comparable level, electrochemical stability can be improved, which is beneficial to improving the cycle performance of batteries.

[0121] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A positive electrode composite material, characterized in that, It includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes a ternary material and a hydrophobic group, and the hydrophobic group is connected to the ternary material by a chemical bond. The ternary material includes nickel-cobalt-manganese material, the second positive electrode active material includes lithium manganese iron phosphate material, the mass fraction of the hydrophobic group in the first positive electrode active material is in the range of 0.5% to 5%, and under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.

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2. The positive electrode composite material according to claim 1, characterized in that, The hydrophobic group comprises at least one of a hydrocarbon group, a fatty acid group, an aromatic group, and a halogenated hydrocarbon group.

3. The positive electrode composite material according to claim 2, characterized in that, The hydrophobic group is selected from oleic acid groups.

4. The positive electrode composite material according to claim 1, characterized in that, The positive electrode composite material also includes a conductive agent and a binder; In the positive electrode composite material, the sum of the mass fractions of the first positive electrode active material and the second positive electrode active material ranges from 94.5% to 97%, the mass fraction of the conductive agent ranges from 1.5% to 3%, and the mass fraction of the binder ranges from 1.5% to 2.5%.

5. A method for preparing a positive electrode composite material, characterized in that, include: Hydrophobic groups are formed on a ternary material to obtain a first positive electrode active material, wherein the hydrophobic groups are chemically bonded to the ternary material; the ternary material includes nickel-cobalt-manganese materials, and the mass fraction of the hydrophobic groups in the first positive electrode active material ranges from 0.5% to 5%; and At least the first positive electrode active material and the second positive electrode active material are mixed to obtain a positive electrode composite material; wherein, the second positive electrode active material includes lithium manganese iron phosphate material, and under the same humidity environment, the ratio of the weight change rate of the first positive electrode active material to the weight change rate of the second positive electrode active material is greater than or equal to 0.95 and less than or equal to 1.

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6. The method for preparing the positive electrode composite material according to claim 5, characterized in that, The step of forming hydrophobic groups on the ternary material to obtain the first positive electrode active material includes: Nickel, cobalt, and manganese sources are mixed and dissolved in a preset ratio to obtain a mixed salt solution. A precipitant is added to the mixed salt solution, and the mixture is stirred evenly at a first preset temperature. During stirring, a complexing agent is added to the mixed solution. After standing, the solution is washed and impurities are removed to obtain a ternary material precursor. At least one of the nickel, cobalt, and manganese sources is chemically bonded to the hydrophobic group. The ternary material precursor is dried at a second preset temperature and then calcined at a third preset temperature to obtain the first positive electrode active material. The nickel source is selected from nickel oleate, the cobalt source is selected from cobalt nitrate, and the manganese source is selected from cobalt sulfate; the mass fraction of the nickel source ranges from 50% to 80%, the mass fraction of the cobalt source ranges from 10% to 20%, and the mass fraction of the manganese source ranges from 10% to 30%.

7. A positive electrode sheet, characterized in that, It includes a positive current collector and a positive active layer located on at least one side of the positive current collector, wherein the material of the positive active layer includes the positive composite material as described in any one of claims 1 to 4.

8. A battery, characterized in that, Includes the positive electrode sheet as described in claim 7.

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