Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a positive electrode material. The secondary battery satisfies the following conditions: I200 / I1≥0.62, wherein I200 represents the intensity of an oxidation peak of the H2-H3 phase transition of the positive electrode material in the dQ / dV graph after the secondary battery is subjected to 200 charge-discharge cycles at 1C at a constant temperature of 60°C, and I1 represents the intensity of the oxidation peak of the H2-H3 phase transition of the positive electrode material in the dQ / dV graph after the secondary battery is subjected to 1 charge-discharge cycle at 1C at a constant temperature of 60°C. As the reversibility of the H2-H3 phase transition of the positive electrode material in the dQ / dV graph satisfies relational expression I200 / I1≥0.62 after the secondary battery is subjected to 200 charge-discharge cycles at 1C at a constant temperature of 60°C, it is proved that the positive electrode material has stable cycling performance, thereby making the secondary battery have good cycling stability.

Description

Secondary battery and power-consuming device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 7, 2023, with application number 202311160440.9 and invention name “A Secondary Battery and Electrical Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of battery materials, and in particular to a secondary battery and an electrical device. Background Art

[0003] During the charging process of high-nickel ternary cathode materials, when the voltage is greater than 4.1V, an H2-H3 phase transition occurs, accompanied by a sudden contraction of the unit cell along the c-axis, resulting in a large volume change and the generation of microstress. This induces the appearance of microcracks in subsequent cycles and deteriorates the cycling performance. The capacity decay during the charge and discharge process of high-nickel ternary cathode materials is related to the gradual disappearance of the H3 phase. By achieving better reversibility of the H2-H3 phase transition, lattice collapse can be effectively suppressed. The higher the amount of lithium depletion, the lower the reversibility of the H2-H3 phase transition during charge and discharge. The rapid deterioration of the cycling performance and the short lifespan of high-capacity power batteries are one of the bottlenecks in the current mass production and commercialization.

[0004] Summary of the Invention

[0005] The object of the present invention is to improve the cycle stability and energy density of a secondary battery.

[0006] The inventors of the present invention found that the reversible degree of H2-H3 phase transition of the positive electrode material in the dQ / dV spectrum after the secondary battery was subjected to 1C charge and discharge cycles for 200 weeks at a constant temperature of 60°C was 200 When / I1≥0.62, the secondary battery has excellent cycle performance.

[0007] In one aspect of the present application, a secondary battery is provided, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode material, and wherein the secondary battery satisfies the following conditions:

[0008] I 200 / I1≥0.62,

[0009] Among them, I 200 I1 represents the H2-H3 phase change oxidation peak intensity of the positive electrode material in the dQ / dV spectrum of the secondary battery after 200 cycles of 1C charge and discharge at a constant temperature of 60°C, and I2 represents the H2-H3 phase change oxidation peak intensity of the positive electrode material in the dQ / dV spectrum of the secondary battery after 1 week of 1C charge and discharge at a constant temperature of 60°C.

[0010] As an embodiment of the present application, the positive electrode material includes secondary particles, and the positive electrode material satisfies at least one of the following conditions:

[0011] a. D of the positive electrode material v50 5~18μm;

[0012] b. D of the positive electrode material n10 0.5~10μm;

[0013] c. The BET of the positive electrode material is 0.1 to 1.0 m 2 / g;

[0014] Among them, D v50 D is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%, n10 is the particle size corresponding to when the cumulative distribution percentage of the positive electrode material reaches 10%, and BET is the specific surface area of ​​the positive electrode material.

[0015] As an embodiment of the present application, the positive electrode material includes single crystal particles or quasi-single crystal particles, and the positive electrode material satisfies at least one of the following conditions:

[0016] a1. D of the positive electrode material v50 1~6μm;

[0017] b2. D of the positive electrode material n10 0.4~3μm;

[0018] c3. The BET of the positive electrode material is 0.5m 2 / g~2.0m 2 / g;

[0019] Among them, D v50 D is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%, n10 is the particle size corresponding to when the cumulative distribution percentage of the positive electrode material reaches 10%, and BET is the specific surface area of ​​the positive electrode material.

[0020] As an embodiment of the present application, the positive electrode material includes a ternary material, and the ternary material includes a chemical formula of Li x Ni y Co z M k Me p O r A ma compound wherein 0.95≤x≤1.05, 0.5≤y≤1, 0≤z≤1, 0≤k≤1, 0≤p≤0.1, 1≤r≤2, 0≤m≤2, m+r≤2; M is selected from Mn and / or Al; Me is selected from at least one of Zr, Zn, Ce, B, Mg, Mo, V, Ti, Sr, Sb, Y, W, Nb, La, Al or Ba; and A is selected from at least one of N, F, S or Cl.

[0021] As an implementation scheme of the present application, a coating layer is provided on the surface of the ternary material, and the coating elements in the coating layer include at least one of Zr, P, Ce, B, Mg, Mo, V, Ti, Sr, Sb, Y, W, Nb, La, Ba, and Co.

[0022] As an embodiment of the present application, the coating layer includes a coating material, and the coating material includes at least one of an oxide, a hydroxide, an oxyhydroxide, a fluoride or a corresponding salt of the coating element.

[0023] As an embodiment of the present application, the coating material includes at least one of vanadium pentoxide, barium oxide, titanium dioxide, boron fluoride, magnesium fluoride, phosphorus pentafluoride, magnesium phosphate, barium phosphate, and lithium vanadium phosphate.

[0024] As an embodiment of the present application, based on the mass of the positive electrode material, the mass content of the coating layer in the positive electrode material is 100 ppm to 18000 ppm.

[0025] As an embodiment of the present application, the residual lithium on the surface of the positive electrode material has a content of Li2CO3 less than 3000 ppm and a content of LiOH less than 5000 ppm.

[0026] In another aspect, an electric device including the secondary battery is provided.

[0027] One of the above technical solutions has the following advantages or beneficial effects:

[0028] This application tests the reversibility of the H2-H3 phase transition of the positive electrode material in the dQ / dV spectrum of the secondary battery under specific conditions (I 200 / I1), when the secondary battery undergoes 200 cycles of 1C charge and discharge at a constant temperature of 60℃, the reversibility of the H2-H3 phase transition of the positive electrode material in the dQ / dV spectrum meets I 200 When / I1≥0.62, it indicates that the positive electrode material has excellent stability performance, and the secondary battery prepared from the positive electrode material has excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is a differential capacity curve spectrum of a secondary battery according to Example 1 of the present application, referred to as a dQ / dV spectrum. DETAILED DESCRIPTION

[0030] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments and drawings, but the embodiments do not limit the present invention in any form.

[0031] An embodiment of the present application provides a secondary battery, the secondary battery including a positive electrode plate, the positive electrode plate including a positive electrode material, and the secondary battery meeting the following conditions:

[0032] I 200 / I1≥0.62,

[0033] Among them, I 200 I1 represents the H2-H3 phase change oxidation peak intensity of the positive electrode material in the dQ / dV spectrum of the secondary battery after 200 cycles of 1C charge and discharge at a constant temperature of 60°C, and I2 represents the H2-H3 phase change oxidation peak intensity of the positive electrode material in the dQ / dV spectrum of the secondary battery after 1 week of 1C charge and discharge at a constant temperature of 60°C.

[0034] This application tests the reversibility of the H2-H3 phase transition of the positive electrode material in the dQ / dV spectrum after the secondary battery is cycled under specific conditions. When the secondary battery undergoes 200 cycles of 1C charge and discharge at a constant temperature of 60°C, the reversibility of the H2-H3 phase transition of the positive electrode material in the dQ / dV spectrum meets the requirements of I 200 When / I1≥0.62, the positive electrode material has stable cycle performance, so that the secondary battery has excellent cycle stability.

[0035] In the present application, the dQ / dV spectrum of the secondary battery can be obtained by testing in the Xinwei test cabinet. In the dQ / dV spectrum of the secondary battery, when the voltage is greater than 4.1V, a pair of oxidation / reduction peaks will appear, which correspond to the transformation of the H2-H3 phase of the positive electrode material. During the charge and discharge cycle of the positive electrode material, the H3 phase will gradually disappear, and the irreversibility of the H2-H3 phase change will increase, resulting in the capacity decay of the positive electrode material, the collapse of the lattice structure, and the deterioration of the cycle performance. The ratio of the H2-H3 phase change oxidation / reduction peak intensity of the positive electrode material after the cycle to the initial H2-H3 phase change oxidation / reduction peak intensity (i.e., I 200 / I1) is within a certain range, indicating that the H2-H3 phase transition reversibility of the positive electrode material during charge and discharge is high and the lattice structure of the positive electrode material is more stable, thereby making the secondary battery have a longer cycle life.

[0036] In some embodiments of the present application, I 200 / I1≤1.0. When I 200 / I1 in this range can further improve the reversibility of H2-H3 phase transition during the charge and discharge process of the positive electrode material, making the overall performance of the secondary battery better. 200 The value of / I1 can be in the range of one or any two of 0.62, 0.68, 0.73, 0.79, 0.85, 0.91, 0.96, and 1.0.

[0037] In some embodiments of the present application, I 200 / I1<0.98. When I 200 When / I1 is within this range, the lattice stability of the positive electrode material can be enhanced, further improving the overall performance of the secondary battery.

[0038] In some embodiments of the present application, 0.77≤I 200 / I1<0.98. When I 200 / I1 Within this range, the irreversibility of the H2-H3 phase transition of the positive electrode material is reduced, further improving the overall performance of the secondary battery.

[0039] In some embodiments of the present application, the positive electrode material includes secondary particles.

[0040] In some embodiments of the present application, the D of the positive electrode material v50 The D of the positive electrode material is 5 to 18 μm; for example, it can be 5 μm, 8 μm, 12 μm, 15 μm, 18 μm, or any two of them. v50 Within the above range, the positive electrode material can still have good adsorption and adhesion properties even within a relatively small suitable specific surface area range. When mixing to form the positive electrode slurry, less auxiliary materials can be used to meet the relatively strong adsorption performance of the positive electrode material with the binder and conductive agent, which is beneficial to improving the energy density of the battery.

[0041] In some embodiments of the present application, the D of the positive electrode material n10 The D of the positive electrode material is 0.5 to 10 μm; for example, it can be 0.5 μm, 1.5 μm, 2.8 μm, 3.5 μm, 5 μm, 7 μm, 8 μm, 10 μm or any two of them. n10 Within the above range, the positive electrode material has a suitable specific surface area, which is beneficial to the chemical performance of the battery.

[0042] In some embodiments of the present application, the BET of the positive electrode material is 0.1 to 1.0 m 2 / g, and can further be 0.3 to 0.7 m 2 / g; for example, it can be 0.1m 2 / g, 0.3m 2 / g, 0.5m2 / g, 0.7m 2 / g, 0.9m 2 / g, 1.0m 2 When the specific surface area of ​​the positive electrode material is within the above-mentioned suitable range, the contact area between the electrolyte and the positive electrode material can be reduced, which is beneficial for suppressing side reactions, avoiding electrolyte corrosion and destruction of the crystal structure of the positive electrode material, thereby aggravating the cycle attenuation of the prepared battery, and further improving the cycle stability of the battery.

[0043] Among them, D v50 D is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%, n10 is the particle size corresponding to when the cumulative distribution percentage of the positive electrode material reaches 10%, and BET is the specific surface area of ​​the positive electrode material.

[0044] In some embodiments of the present application, the positive electrode material includes single crystal particles or single crystal-like particles.

[0045] In some embodiments of the present application, when the positive electrode material is a single crystal particle or a quasi-single crystal particle, the D of the positive electrode material is v50 The D of the positive electrode material is 1 to 6 μm; for example, it can be 1 μm, 3 μm, 5 μm, 6 μm or any two of them. v50 Within the above range, the positive electrode material can have a suitable specific surface area, thereby improving the electrochemical performance of the battery.

[0046] In some embodiments of the present application, when the positive electrode material is a single crystal particle or a quasi-single crystal particle, the D of the positive electrode material is n10 The D of the positive electrode material is 0.4 to 3 μm; for example, it can be 0.4 μm, 0.8 μm, 1.2 μm, 2.0 μm, 2.5 μm, 3.0 μm or any two of them. n10 Within the above range, the positive electrode material can have a suitable specific surface area, thereby improving the electrochemical performance of the battery.

[0047] In some embodiments of the present application, when the cathode material is a single crystal particle or a quasi-single crystal particle, the BET of the cathode material is 0.5m 2 / g~2.0m 2 / g; for example, it can be 0.5m 2 / g, 0.8m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2When the BET value of the positive electrode material is within the above range, the surface and internal crystal structure of the positive electrode material are more complete, and the contact area with the electrolyte is smaller, which is beneficial to enhance the stability of the positive electrode material crystal structure and further improve the cycle life of the battery.

[0048] Among them, D v50 D is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%, n10 is the particle size corresponding to when the cumulative distribution percentage of the positive electrode material reaches 10%, and BET is the specific surface area of ​​the positive electrode material.

[0049] In some embodiments of the present application, the positive electrode material includes a ternary material, and the ternary material includes a chemical formula of Li x Ni y Co z M k Me p O r A m A compound, 0.95≤x≤1.05, 0.5≤y≤1, 0≤z≤1, 0≤k≤1, 0≤p≤0.1, 1≤r≤5, 0≤m≤2, m+r≤2; M is selected from Mn and / or Al; the Me is selected from at least one of Zr, Zn, Ce, B, Mg, Mo, V, Ti, Sr, Sb, Y, W, Nb, La, Al, and Ba; A is selected from at least one of N, F, S, and Cl.

[0050] In some embodiments of the present application, Me is a doping element.

[0051] In some embodiments of the present application, in the chemical formula of the ternary material, y may further satisfy 0.60≤y≤0.95, further satisfying 0.70≤y≤0.90; and / or z further satisfies 0≤z≤0.15, further satisfying 0.05≤z≤0.15; and / or k further satisfies 0≤k≤0.2, further satisfying 0.05≤k≤0.2; and / or p further satisfies 0≤p≤0.03, further satisfying 0≤p≤0.025.

[0052] In some embodiments of the present application, the Me element may further be selected from at least one of Al, Ti, Zr, Sr, Ba, Mg, Nb, W, and Y. Doping elements are electrochemically inert, exhibiting minimal changes in their chemical valence during lithium ion insertion and extraction. Furthermore, these doping elements can enhance the reversibility of the H2-H3 phase transition during the charge and discharge process of the positive electrode material, resulting in a more stable crystal structure and improved cycling performance. In this application, the weight percentage of the doping element in the positive electrode material may range from 200 ppm to 9000 ppm.

[0053] In some embodiments of the present application, a coating layer is provided on the surface of the ternary material, and the coating element in the coating layer includes at least one of Zr, P, Ce, B, Mg, Mo, V, Ti, Sr, Sb, Y, W, Nb, La, Ba, and Co. Based on the mass of the positive electrode material, the mass content of the coating layer in the positive electrode material is 100 ppm to 18,000 ppm, and can further be 300 ppm to 12,000 ppm.

[0054] In some embodiments of the present application, the coating layer includes a coating material, and the coating material includes an oxide, hydroxide, oxyhydroxide, fluoride, or corresponding salt of the coating element. For example, the coating material includes at least one of vanadium pentoxide, barium oxide, titanium dioxide, boron fluoride, magnesium fluoride, phosphorus pentafluoride, magnesium phosphate, barium phosphate, and lithium vanadium phosphate.

[0055] By providing a coating layer on the surface of the positive electrode material, the surface can be effectively passivated, isolating the electrolyte, reducing the amount of residual lithium on the surface, inhibiting the reaction between the positive electrode material and the electrolyte, and improving the cycling performance of the positive electrode material. This is because in the actual production process of ternary materials, the raw lithium salt used may be impure and have a low melting point. It will melt, decompose, and volatilize at relatively low temperatures. Therefore, during the preparation of ternary materials, excess lithium salt is added to compensate for the lithium loss caused by the sintering process. The surface of the ternary material contains active oxygen anions, which react with CO2 and H2O in the air to form carbonate ions. Simultaneously, lithium ions migrate from the bulk to the surface and form Li2CO3 on the surface of the ternary material. This process is accompanied by deoxidation of the ternary material surface, forming a structurally distorted surface oxide layer. Furthermore, the excessive amount of lithium salt in the synthesis of ternary materials results in the excess lithium salt primarily producing lithium oxide after high-temperature calcination. This reacts with CO2 and H2O in the air to form LiOH and Li2CO3, which remain on the surface of the ternary material, resulting in a high pH value. And during the charge and discharge process, the Li2CO3 remaining on the surface of the ternary material will decompose to produce CO2. Since the CO2 gas will cause a pressure difference with the temperature difference (especially when a thermal reaction occurs during the reaction process), it aggravates the flatulence of the secondary battery and worsens the cycle performance of the secondary battery. Therefore, providing a coating layer on the surface of the positive electrode material can reduce the content of residual lithium (such as LiOH, Li2CO3, etc.) on the surface of the positive electrode material to a certain extent, thereby achieving the purpose of improving the cycle performance of the lithium-ion battery. In addition, providing a coating layer on the surface of the positive electrode material can also reduce the probability of side reactions due to direct contact between the positive electrode material and the electrolyte, thereby reducing the amount of oxygen released by the positive electrode material in order to balance the charge during the charge and discharge process and the risk of crystal structure collapse caused by this.

[0056] In some embodiments of the present application, the residual lithium on the surface of the positive electrode material has a content of Li2CO3 less than 3000 ppm and a content of LiOH less than 5000 ppm. The residual lithium on the surface of the positive electrode material can be measured by referring to the general principle of potentiometric titration of chemical reagents in GB / T 9736-2008.

[0057] In the present application, the above-mentioned positive electrode material can be prepared by conventional methods in the art. The positive electrode material is prepared by a method comprising the following steps:

[0058] S1. A nickel source, a cobalt source, a manganese and / or aluminum source are configured into a mixed salt solution, and a positive electrode material precursor is prepared by a coprecipitation reaction, wherein the pH value of the coprecipitation reaction is 7.5 to 8.5;

[0059] S2. The cathode material precursor prepared in step S1, the lithium source, the optional Me source and / or the A source are mixed uniformly, and then placed in an atmosphere furnace at 800-900°C for 10-15h. The oxygen flux in the atmosphere furnace during the sintering process is 5-30L / min to obtain a ternary material;

[0060] S3. After mixing the ternary material obtained in step S2 and the coating agent, place it in an atmosphere furnace at 400-500°C and sinter for 3-8 hours. During the sintering process, the oxygen flux in the atmosphere furnace is 20-40 L / min to obtain the positive electrode material.

[0061] The reversibility of the H2-H3 phase transition of the positive electrode material during the charge and discharge process of a secondary battery is mainly determined by the control of processes related to oxygen binding, such as the doping and coating elements of the positive electrode material, the precursor preparation process, and the powder sintering process. By adjusting the pH during the precursor synthesis process to improve the adhesion of hydroxide ions, the sintering temperature, sintering time, and oxygen flow rate during the sintering process, etc., the reversibility of the H2-H3 phase transition corresponding to the positive electrode material in the dQ / dV spectrum of the secondary battery prepared from the positive electrode material after 200 cycles of 1C charge and discharge at a constant temperature of 60°C is controlled to be 0.62≤I 200 / I1, which can ensure the high reversibility of the H2-H3 phase transition during the charge and discharge process of the positive electrode material, thereby ensuring that the crystal structure of the positive electrode material is relatively complete and has good structural stability. The crystal is not prone to collapse during the process of lithium ion insertion and extraction, which is beneficial to extending the cycle life of the battery and improving the energy density of the battery.

[0062] In some embodiments, the ratio of the oxygen flux in step S2 to the oxygen flux in step S3 is 1:(1.5-3). The oxygen flux in the sintering process can make the element doping and coating of the positive electrode material more excellent, and can make the positive electrode material lattice more stable. Controlling the ratio of the oxygen flux within the above range is beneficial to the uniformity of element doping, improving the lattice stability, and also conducive to a denser coating layer and a more thorough conversion of the coating, further improving the stability of the positive electrode material and the cycle performance of the secondary battery.

[0063] In some embodiments, the nickel source can be selected from one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate and nickel acetate; the cobalt source can be selected from one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate and cobalt acetate; the manganese source can be selected from one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate and manganese acetate; the lithium source can be selected from one or more of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3) and lithium nitrate (LiNO3); the Me source can be selected from one or more of oxides, nitric acid compounds, carbonate compounds, hydroxide compounds and acetic acid compounds containing Me element; the A source can be selected according to actual needs, for example, selected from one or more of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium bromide, lithium bromide, hydrogen bromide, ammonium iodide, lithium iodide, hydrogen iodide, hydrogen sulfide, lithium sulfide and ammonium sulfide.

[0064] The secondary battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator separated between the positive electrode sheet and the negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer arranged on at least one surface of the positive electrode collector, and the positive electrode active material layer includes the above-mentioned positive electrode material.

[0065] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material can be any of various materials suitable for use in lithium-ion batteries. For example, it can include, but is not limited to, one or more combinations of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. The graphite can be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from a combination of one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys. The type of the negative electrode current collector is not specifically limited and can be selected based on actual needs. For example, the negative electrode current collector can be copper foil, carbon-coated copper foil, or a polymer conductive film, with copper foil being preferred.

[0066] In the secondary battery of the present application, the isolation membrane can be any material suitable for lithium-ion battery isolation membranes in the art, for example, it can include but is not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber, etc., one or more combinations thereof.

[0067] In the secondary battery of the present application, the electrolyte can be any electrolyte suitable for lithium-ion batteries in the art. For example, the electrolyte generally includes an electrolyte and a solvent. The electrolyte generally includes a lithium salt, etc. More specifically, the lithium salt can be an inorganic lithium salt and / or an organic lithium salt, etc., and specifically can include but is not limited to a combination of one or more of LiPF6, LiBF4, LiN(SO2F)2 (abbreviated as LiFSI), LiN(CF3SO2)2 (abbreviated as LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (abbreviated as LiBOB), and LiBF2C2O4 (abbreviated as LiDFOB). For another example, the concentration of the electrolyte can be between 0.8 mol / L and 1.5 mol / L. The solvent can be any solvent suitable for lithium-ion battery electrolytes in the art. The solvent of the electrolyte is generally a non-aqueous solvent, preferably an organic solvent, and specifically includes but is not limited to ethylene carbonate, propylene carbonate, butylene carbonate, pentyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, etc., or a combination of one or more of their halogenated derivatives.

[0068] The method for preparing the secondary battery should be known to those skilled in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet can each be a layer, so that they can be cut into a target size and stacked in sequence, and can also be wound to a target size to form a battery, and can be further combined with an electrolyte to form a lithium secondary battery.

[0069] An embodiment of the present application further provides an electric device comprising the secondary battery, wherein the secondary battery serves as a power source for the electric device.

[0070] The present application provides the following examples to facilitate understanding of the present application. These examples are not intended to limit the scope of the claims.

[0071] Example 1

[0072] This embodiment provides a positive electrode material, which is prepared according to a method comprising the following steps:

[0073] S1. Add nickel source (nickel sulfate), cobalt source (cobalt sulfate), and manganese source (manganese sulfate) into water at a molar ratio of 8:1:1 to prepare a 1 mol / L mixed salt solution. Use 1 mol / L ammonia water to adjust the pH value of the mixed salt solution to 8.0. After 100 hours of hydroxide coprecipitation reaction, the cathode material precursor (nickel cobalt manganese hydroxide Ni) was prepared. 0.80 Co 0.10 Mn 0.10 (OH)2);

[0074] S2. The cathode material precursor prepared in step S1, the lithium source (LiOH·H2O), and the optional Me source (aluminum oxide) were mixed uniformly, placed in an atmosphere furnace with an oxygen flux of 18 L / min, and sintered for the first time at 900°C for 12 h. After cooling and grinding, the ternary material was obtained;

[0075] S3. After uniformly mixing the ternary material obtained in step S2 with the coating agent (alumina), the mixture was placed in an atmosphere furnace with an oxygen flux of 36 L / min and subjected to a second sintering at 450°C for 5 h. The mixture was crushed and sieved to obtain the positive electrode material (NCM811).

[0076] Examples 2 to 7

[0077] The preparation method is the same as that of Example 1, except that the type and content of the Me source or coating agent are adjusted.

[0078] Examples 8 to 10

[0079] The preparation method is the same as that of Example 1, except that the ratios of the nickel source, the cobalt source, and the manganese source are adjusted, and the type and content of the Me source or the coating agent are adjusted.

[0080] Examples 11 to 14

[0081] The preparation method is the same as that of Example 1, except that the crushing power and sieve mesh number of the positive electrode material are adjusted to obtain positive electrode materials with different particle size distributions.

[0082] Examples 15 to 19

[0083] The preparation method is the same as that of Example 10, except that the pH value of the mixed solution, the first sintering temperature and the second sintering temperature are adjusted to control the obtained positive electrode material to be secondary particles.

[0084] Examples 20 to 22

[0085] The preparation method is the same as that of Example 1, except that the pH value of the mixed solution is adjusted.

[0086] Comparative Example 1

[0087] The preparation method is the same as that of Example 1, except that the Me source is not added in step 2, and the type and content of the coating agent are adjusted.

[0088] Comparative Example 2

[0089] The preparation method is the same as that of Example 1, except that the type and content of the Me source are adjusted, and no coating agent is added in step 3.

[0090] Comparative Example 3

[0091] The preparation method is the same as that of Example 1, except that the types and contents of the Me source and the coating agent are adjusted, and in step 3, the oxygen flux of the atmosphere furnace is 10 L / min.

[0092] The relevant parameters of the positive electrode materials of other embodiments and comparative examples are detailed in Table 1.

[0093] In this application, the particle size of the primary particles of the positive electrode material (D v50 、D n10 ) was obtained by the following test method: the particle size distribution was measured using a laser diffraction particle size distribution measuring instrument according to the particle size distribution laser diffraction method (specific reference GB / T19077-2016).

[0094] The specific surface area of ​​the positive electrode material was measured using a specific surface area meter, with reference to GB / T19587-2004, using the N2 adsorption method.

[0095] The residual lithium (Li2CO3, LiOH) content on the surface of the positive electrode material is obtained by referring to the general rules of the chemical reagent potentiometric titration method "GB / T9736-2008".

[0096] Table 1 Parameters of positive electrode materials of Examples and Comparative Examples

[0097] The performance of secondary batteries using the positive electrode materials prepared in the above examples and comparative examples was tested. The battery preparation process, test method, and results are as follows:

[0098] Preparation of positive electrode sheet

[0099] The positive electrode materials, binder polyvinylidene fluoride, and conductive agent acetylene black prepared in the above examples and comparative examples were respectively mixed in a mass ratio of 96:3:1, N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of an aluminum foil with a thickness of 16 μm; the electrode sheet coated with the positive electrode slurry was dried in an oven at 100°C to 130°C, cold pressed, and cut to obtain a positive electrode sheet.

[0100] Preparation of negative electrode sheet

[0101] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the binder styrene-butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 95.7:0.8:2.5:1, and deionized water was added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on both sides of a copper foil with a thickness of 8 μm; the coated electrode was dried in an oven at 70°C to 100°C, cold pressed, and cut to obtain a negative electrode sheet.

[0102] Secondary battery assembly

[0103] The positive electrode sheet, separator (12μm thick polypropylene separator), and negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role. Then, after being wound into a square bare battery, an aluminum-plastic film is placed in it. After being baked at 85°C to remove water, the corresponding non-aqueous electrolyte is injected (the electrolyte is a LiPF6 solution with a concentration of 1 mol / L, and the solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 30:30:40), sealed, and after standing, hot and cold pressing, formation, clamping, capacity separation and other processes, the finished battery is obtained.

[0104] The cycle life and discharge capacity of the secondary battery are tested according to the following method:

[0105] 1. Cycling performance: At a constant temperature of 45°C, charge to 4.2V or 4.4V at 1C at 2.8-4.2V (Examples 8-10 and Examples 15-19) or 2.8-4.4V (Examples 1-7, Examples 11-14, Examples 20-22 and Comparative Examples 1-3), then charge at a constant voltage at 4.2V or 4.4V to a current ≤ 0.05C, let stand for 10 minutes, then discharge at 1C to a voltage of 2.8V, let stand for 10 minutes, and record the capacity as D n (n = 0, 1, 2 ...), repeat the previous process until the capacity decays to 80% of the initial capacity (D0), and record the number of cycles of the lithium-ion battery;

[0106] 2. Discharge capacity (mAh / g): At a constant temperature of 25°C, charge the battery to 4.2 V or 4.4 V at 1 / 3C at 2.8-4.2 V (Examples 8-10 and 15-19) or 2.8-4.4 V (Examples 1-7, Examples 11-14, Examples 20-21, and Comparative Examples 1-3), then charge the battery at a constant voltage of 4.2 V or 4.4 V to a current of ≤0.05C, let stand for 5 minutes, and then discharge the battery to 2.8 V at 1 / 3C. Record the battery capacity (in mAh / g).

[0107] 3.I 200 / I1 measurement: Under a constant temperature environment of 60℃, in the voltage range of 2.8~4.4V, charge to 4.4V at 1C, then charge at constant voltage at 4.4V to a current ≤0.05C, let it stand for 10min, then discharge to 2.8V at 1C, let it stand for 10min, repeat the previous process until 200 cycles, and then process the recorded charge and discharge parameter capacity and voltage data, and subtract the voltage and charge data of the nth data point from the voltage and charge data of the n+1th data point to obtain a dV and dQ data. All data are processed in turn to obtain a series of dV and dQ data, and then use dQ / dV as the vertical axis and voltage as the horizontal axis to obtain a standard dQ / dV spectrum. After 1 cycle, the H2-H3 phase change oxidation peak intensity in the dQ / dV spectrum is I1, and after 200 cycles, the H2-H3 phase change oxidation peak intensity in the dQ / dV spectrum is I 200 , then calculate I 200 / I1, the test results are shown in Table 2.

[0108] The test results are shown in Table 2.

[0109] Table 2 Performance test results of secondary batteries of Examples and Comparative Examples

[0110] From the above results, it can be seen that when the secondary battery undergoes 200 cycles of 1C charge and discharge, the reversible phase change degree of the positive electrode material in the dQ / dV spectrum is 200 When / I1≥0.62, the secondary battery has an excellent cycle life. In addition, it can be seen from the data of Examples 20 to 22 that I 200 The larger the value of / I1, the better. When its value is 1, the cycle performance of the secondary battery drops to 880 cycles.

[0111] The above steps are merely intended to facilitate understanding of the method, structure, and core concept of this application. Persons skilled in the art will appreciate that improvements and modifications may be made to this application without departing from the principles of this application, and such improvements and modifications are also within the scope of protection of the claims of this application.

Claims

1. A secondary battery, wherein: The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode material, and the secondary battery satisfies the following conditions: 200 / I1≥0.62, Among them, I 200 I1 represents the H2-H3 phase change oxidation peak intensity of the positive electrode material in the dQ / dV spectrum after the secondary battery has undergone 1C charge and discharge cycles for 200 weeks at a constant temperature of 60°C. I2 represents the H2-H3 phase change oxidation peak intensity of the positive electrode material in the dQ / dV spectrum after the secondary battery has undergone 1C charge and discharge cycles for 1 week at a constant temperature of 60°C.

2. The secondary battery according to claim 1, wherein The positive electrode material includes secondary particles, and the positive electrode material satisfies at least one of the following conditions: a. D of the positive electrode material v50 5~18μm; b. D of the positive electrode material n10 0.5~10μm; c. The BET of the positive electrode material is 0.1 to 1.0 m 2 / g; Among them, D v50 is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%, D n10 is the particle size corresponding to when the cumulative distribution percentage of the positive electrode material reaches 10%, and BET is the specific surface area of ​​the positive electrode material.

3. The secondary battery according to claim 1, wherein The positive electrode material includes single crystal particles or quasi-single crystal particles, and the positive electrode material satisfies at least one of the following conditions: a1. D of the positive electrode material v50 1~6μm; b2. D of the positive electrode material n10 0.4~3μm; c3, the BET of the positive electrode material is 0.5m 2 / g~2.0m 2 / g; Among them, D v50 is the particle size corresponding to when the cumulative volume distribution percentage of the positive electrode material reaches 50%, D n10 is the particle size corresponding to when the cumulative distribution percentage of the positive electrode material reaches 10%, and BET is the specific surface area of ​​the positive electrode material.

4. The secondary battery according to claim 1, wherein The positive electrode material includes a ternary material, wherein the ternary material includes a chemical formula of Li x Ni y Co z M k Me p O r A m A compound, 0.95≤x≤1.05, 0.5≤y≤1, 0≤z≤1, 0≤k≤1, 0≤p≤0.1, 1≤r≤2, 0≤m≤2, m+r≤2; M is selected from Mn and / or Al; Me is selected from at least one of Zr, Zn, Ce, B, Mg, Mo, V, Ti, Sr, Sb, Y, W, Nb, La, Al, and Ba; A is selected from at least one of N, F, S, and Cl.

5. The secondary battery according to claim 4, characterized in that: A coating layer is provided on the surface of the ternary material, and the coating element in the coating layer includes at least one of Zr, P, Ce, B, Mg, Mo, V, Ti, Sr, Sb, Y, W, Nb, La, Ba, and Co.

6. The secondary battery according to claim 5, wherein The coating layer includes a coating material, and the coating material includes at least one of an oxide, a hydroxide, an oxyhydroxide, a fluoride or a corresponding salt of the coating element.

7. The secondary battery according to claim 5, wherein Based on the mass of the positive electrode material, the mass content of the coating layer in the positive electrode material is 100 ppm to 18000 ppm.

8. The secondary battery according to claim 1, wherein The residual lithium on the surface of the positive electrode material includes Li2CO3<3000ppm and LiOH<5000ppm.

9. The secondary battery according to claim 6, wherein The coating material includes at least one of vanadium pentoxide, barium oxide, titanium dioxide, boron fluoride, magnesium fluoride, phosphorus pentafluoride, magnesium phosphate, barium phosphate, and lithium vanadium phosphate.

10. An electrical device, wherein: The electric device comprises the secondary battery according to any one of claims 1 to 9.

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