Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector. During charge / discharge of the secondary battery at a rate of 0.1 C between 0% SOC and 100% SOC, the ratio of the change in porosity of a positive electrode sheet to the change rate of lattice parameter c of a positive electrode active material is greater than 0.5 and less than 1.8. Therefore, the problem of micro-cracks between primary particles in the positive electrode active material can be reduced.

Description

Secondary batteries and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202510337925.3, filed on March 20, 2025, entitled "A Secondary Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of secondary battery manufacturing technology, and in particular to a secondary battery and an electrical device. Background Technology

[0003] Currently, energy conservation and emission reduction are key to the sustainable development of the automotive industry. Electric vehicles, due to their energy-saving and environmentally friendly advantages, have become an important part of the automotive industry's sustainable development. Long-range electric vehicles require high-energy-density rechargeable batteries. High-nickel ternary cathode active materials can improve the energy density of rechargeable batteries. However, high-nickel ternary cathode active materials are prone to cracking during charge-discharge cycles. The formation of cracks exposes more reactive surfaces in the high-nickel ternary cathode active material, exacerbating interfacial side reactions between the high-nickel ternary cathode active material and the electrolyte during charge-discharge cycles, thus leading to a decline in the cycle performance of the rechargeable battery. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a secondary battery and an electrical device to solve the problem that microcracks easily appear in the positive electrode active material of existing secondary batteries based on high-nickel ternary positive electrode active materials during charge and discharge cycles, which leads to a decrease in the cycle performance of the secondary battery.

[0005] This application discloses a secondary battery, including a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer including a positive active material; the secondary battery satisfies: Wherein, b1 represents the porosity of the positive electrode sheet when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate; b2 represents the porosity of the positive electrode sheet when the secondary battery is discharged from 100% SOC to 0% SOC at a 0.1C rate; c1 represents the cell c-parameter of the positive electrode active material when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate; and c2 represents the cell c-parameter of the positive electrode active material when the secondary battery is discharged from 100% SOC to 0% SOC at a 0.1C rate.

[0006] Furthermore, in the secondary battery, (c1-c2) / c1 is 1.0% to 3.8%.

[0007] Furthermore, the value of c1 is in within the range of, and / or c2 falls within the range.

[0008] Further, in the secondary battery, b1-b2 is 0.5% to 4.0%.

[0009] Further, b1 falls within the range of 25% to 28%, and / or b2 falls within the range of 23% to 27%.

[0010] Further, in the positive electrode active material, based on all metal elements other than lithium, the molar proportion of Ni is greater than 80%.

[0011] Further, in the secondary battery, the positive electrode active material comprises secondary particles formed by aggregation of primary particles; the secondary particles satisfy: 10≤d·e≤200, wherein d represents the aspect ratio of the primary particles; and e is, in a cross-sectional area of 1 μm 2 of the secondary particle, the number of pores between the primary particles within the region.

[0012] Further, in the secondary battery, the secondary particles satisfy: 24≤d·e≤120.

[0013] Further, the aspect ratio d of the primary particles falls within the range of 1.67 to 8.00.

[0014] Further, in a cross-sectional area of 1 μm 2 of the secondary particle, the number e of pores between the primary particles within the region falls within the range of 6 to 25.

[0015] Further, in the secondary battery, the positive electrode active material comprises a compound having a chemical formula of Li a Ni x Co y Mn z Q p O2, wherein 0.95≤a≤1.15, 0.8≤x≤0.94, 0.04≤y≤0.15, 0.02≤z≤0.06, 0<p≤0.01, and Q comprises at least one of B, Sr, Zn, Al, Ce, Ti, Zr, Sb, W, Y, Nb, Ta and Mo.

[0016] Further, in the secondary battery, the content of Q in the positive electrode active material is 2500 ppm to 8000 ppm.

[0017] Furthermore, in the secondary battery, the particle size Dv50 of the positive electrode active material is 8μm to 16μm, wherein Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material.

[0018] Furthermore, in the aforementioned secondary battery, the compacted density of the positive electrode active material under a pressure of 30 kN is 3.0 g / cm³. 3 ~3.6g / cm 3 .

[0019] This application also proposes an electrical device including the aforementioned secondary battery, which serves as the power supply for the electrical device.

[0020] The positive electrode sheet in the secondary battery provided in this application embodiment includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material. The difference between the porosity of the positive electrode sheet when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate and when it is discharged from 100% SOC to 0% SOC at a 0.1C rate, and the ratio between the change rate of the cell c-parameter of the positive active material when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate and when it is discharged from 100% SOC to 0% SOC at a 0.1C rate, satisfies a value greater than 0.5 and less than 1.8. The difference (b1-b2) between the porosity of the positive electrode sheet when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate and discharged from 100% SOC to 0% SOC at a 0.1C rate reflects the degree of SOC non-uniformity among primary particles in the positive electrode active material during the charge-discharge cycle of the secondary battery. The rate of change (c1-c2) / c1 of the cell c-parameter of the positive electrode active material when charged from 0% SOC to 100% SOC at a 0.1C rate and discharged from 100% SOC to 0% SOC at a 0.1C rate reflects the degree of change of the cell c-parameter of the positive electrode active material during the charge-discharge cycle of the secondary battery.

[0021] This application embodiment limits the ratio between the change in porosity of the positive electrode sheet and the change rate of the cell c-parameter of the positive electrode active material during the charge and discharge process of the secondary battery containing the positive electrode active material to the above-mentioned range. This reduces the drastic changes in cell parameters and the degree of difference in electrochemical reactions among different primary particles in the positive electrode active material during the charge and discharge cycle of the secondary battery. This suppresses the generation of microcracks in the positive electrode active material, thereby avoiding an excessive number of reactive surfaces in the positive electrode active material. It also reduces interfacial side reactions between the positive electrode active material and the electrolyte during the charge and discharge cycle, thus improving the cycle performance of the secondary battery while ensuring a high energy density.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0023] Figure 1 is a schematic diagram of the structure of a secondary particle provided in an embodiment of this application.

[0024] Explanation of reference numerals in the attached figures:

[0025] 10 - Secondary particles, 101 - Primary particles, 102 - Pores. Detailed Implementation

[0026] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The applicant of this application discovered that, during charge-discharge cycling, secondary batteries prepared based on high-nickel ternary cathode active materials experience uneven stress distribution within the primary particles due to the rapid lattice contraction caused by the c-axis phase transition from H2 to H3 in the primary particles. This uneven stress distribution, concentrated at the grain boundaries of the primary particles, easily leads to microcracks. When microcracks form between the grains of the primary particles, they expose more reactive surfaces in the cathode active material, exacerbating the reaction of highly active Ni during charge-discharge cycling. 4+ Interfacial side reactions between the positive electrode and the electrolyte severely damage the layered structure of the positive electrode active material, causing the structure of the positive electrode active material to collapse, reducing the electrochemical contact between primary particles in the positive electrode active material, and causing an increase in the direct current resistance (DCR) of the secondary battery.

[0028] To address the aforementioned problems, this application provides a secondary battery, comprising a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising a positive active material; the secondary battery satisfies:

[0029] Wherein, b1 represents the porosity of the positive electrode sheet when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate; b2 represents the porosity of the positive electrode sheet when the secondary battery is discharged from 100% SOC to 0% SOC at a 0.1C rate; c1 represents the cell c-parameter of the positive electrode active material when the secondary battery is charged from 0% SOC to 100% SOC at a 0.1C rate; and c2 represents the cell c-parameter of the positive electrode active material when the secondary battery is discharged from 100% SOC to 0% SOC at a 0.1C rate.

[0030] In the embodiments of this application, the molar content of Ni in the positive electrode active material accounts for more than 80% of the metal elements other than lithium.

[0031] As shown in Formula 1, (b1-b2) represents the difference in porosity of the positive electrode sheet during the charging and discharging process of the secondary battery at a rate of 0.1C between 100% SOC and 0% SOC; (b1-b2) reflects the degree of change in porosity of the positive electrode sheet during the charging and discharging cycle of the secondary battery, and indirectly reflects the degree of difference in electrochemical reaction of primary particles in the positive electrode active material.

[0032] It should be noted that the porosity of the positive electrode refers to the proportion of the volume of pores in the positive electrode to the total volume of the positive electrode. (c1-c2) / c1 represents the rate of change of the cell c-parameter of the positive electrode active material during the charging and discharging process of the secondary battery at a rate of 0.1C between 100% SOC and 0% SOC; (c1-c2) / c1 reflects the degree of change of the cell c-parameter of the positive electrode active material during the charge and discharge cycle of the secondary battery. The larger the value of (c1-c2) / c1, the greater the change of the c-parameter of the positive electrode active material during the charge and discharge process, indicating a higher degree of H2 to H3 phase transition during the charge and discharge process, and a greater volume change caused by the H2 to H3 phase transition. This leads to a higher degree of stress non-uniformity within the primary particles of the positive electrode active material, and the concentration of stress at the grain boundaries of the primary particles is the direct cause of microcrack formation.

[0033] In this embodiment, during the charging and discharging of the secondary battery at a rate of 0.1C between 100% SOC and 0% SOC, the ratio between the difference in porosity of the positive electrode sheet and the rate of change of the cell c-parameter of the positive electrode active material is limited to a range greater than 0.5 and less than 1.8. This reduces the drastic changes in cell parameters and the differences in electrochemical reactions among different primary particles in the positive electrode active material during the charge-discharge cycle of the secondary battery, thereby suppressing the formation of microcracks in the positive electrode active material and avoiding an excessive number of reactive surfaces in the positive electrode active material. This reduces interfacial side reactions between the positive electrode active material and the electrolyte during the charge-discharge cycle, ensuring a high energy density for the secondary battery while improving its cycle performance.

[0034] Optionally, in some embodiments, the rate of change of the cell c-parameter of the positive electrode active material (c1-c2) / c1 is 1.0% to 3.8%. When the rate of change of the cell c-parameter of the positive electrode active material Δc=(c1-c2) / c1 is limited to 1.0% to 3.8%, the degree of change of the lattice c-parameter of the positive electrode active material during the secondary battery charging process can be reduced to a certain extent, thereby slowing down the stress concentration at the grain boundaries of the primary particles during the secondary battery charging process and reducing the generation of microcracks.

[0035] In some embodiments, the rate of change (c1-c2) / c1 of the cell c-parameter of the positive electrode active material can be a range of one or both of 1.0%, 1.4%, 1.8%, 2.2%, 2.6%, 3.0%, 3.4%, and 3.8%.

[0036] Optionally, in some embodiments, the change in porosity b1-b2 of the positive electrode sheet is 0.5% to 4.0%. When Δb = b1-b2 is limited to 0.5% to 4.0%, the uniformity of the electrochemical reaction rate and reaction degree between different primary particles during the secondary battery charging process can be improved, thereby mitigating the promoting effect of the difference in electrochemical reaction between different primary particles on the formation of intergranular microcracks in primary particles.

[0037] In some embodiments, the variation in porosity of the positive electrode sheet, b1-b2, can be a range of one or any two of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, and 4.0%.

[0038] In some embodiments, b1 is 25% to 28%. For example, it can be a range of 25.0%, 25.5%, 26%, 26.8%, 28%, or any two of these values. In some embodiments, b2 is 23% to 27%. For example, it can be a range of 23%, 24%, 26%, 27%, or any two of these values.

[0039] In some implementations, c1 is For example, it can be... The range of one or both of these values. In some implementations, c2 is... For example, it can be... The range of one or any two of them.

[0040] Optionally, in some embodiments, the positive electrode active material includes secondary particles formed by the aggregation of primary particles, and the secondary particles satisfy: 10 ≤ d·e ≤ 200 (2)

[0041] Where d represents the aspect ratio of the primary particle; e represents the cross-sectional area of ​​the secondary particle when it is 1 μm. 2 The number of pores between particles within a region.

[0042] Referring to Figure 1, a schematic diagram of a secondary particle structure provided in an embodiment of this application is shown. During the preparation of the positive electrode active material, the primary particles 101 aggregate together due to various forces (e.g., intermolecular forces) to form larger agglomerates, which are the secondary particles 10 formed by the aggregation of primary particles 101. The aspect ratio of the primary particles 101 is the ratio of the longest diameter passing through the geometric center of the primary particle 101 to the longest diameter passing through the geometric center of the particle and perpendicular to that longest diameter. The pores 102 between the primary particles 101 refer to the pores 102 formed between the individual primary particles 101 in the cross-section of the secondary particles 10.

[0043] In this embodiment, the cross-sectional area of ​​the secondary particles in the positive electrode active material is 1 μm. 2 The product of the number of pores between primary particles within the region and the aspect ratio of the primary particles is 10–200. In some embodiments, the cross-sectional area of ​​the secondary particles in the positive electrode active material is 1 μm. 2 The product of the number of pores between primary particles and the aspect ratio of the primary particles within the region can be a value within the range of one or both of the following: 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200.

[0044] In this embodiment, the number of pores between primary particles is controlled by adjusting the stirring speed during the co-precipitation synthesis of the nickel-cobalt-manganese precursor and by introducing nitrogen (N2) at a certain flow rate during the reaction. Furthermore, a certain amount of high-oxidation-state dopant is introduced during calcination to influence the growth of the primary particles and control their aspect ratio. By combining these two strategies, the cross-sectional area of ​​the secondary particles in the positive electrode active material is reduced to 1 μm. 2Within the specified region, the product of the number of pores between primary particles and the aspect ratio of the primary particles is limited to the range of 10–200. On the one hand, a suitable aspect ratio of the primary particles ensures that the surface and internal structure of the secondary particles formed by the aggregation of primary particles have high density, and the lithium ion transport distance between the primary particles is moderate, which is beneficial to improving the compressive strength of the secondary particles. On the other hand, a suitable aspect ratio of the primary particles can also make the primary particles slender and highly oriented, which can effectively suppress the formation of microcracks during the charge and discharge cycles of the secondary battery and improve the long-term cycle stability of the secondary battery. On the other hand, the cross-sectional area of ​​the secondary particles is 1 μm. 2 Within a certain range, the number of pores between primary particles in the region can improve the electrolyte wetting effect while ensuring that the secondary particles have a certain compressive strength. In summary, the embodiments of this application use secondary particles with a cross-sectional area of ​​1 μm in the positive electrode active material. 2 By limiting the product of the number of pores between primary particles and the aspect ratio of the primary particles within the region to the range of 10 to 200, the tightness of the bonding between primary particles in the secondary particles, the mechanical strength of the secondary particles, and the wetting effect of the electrolyte can be improved. This results in secondary batteries based on positive electrode active materials having lower polarization and faster lithium-ion transport rates during charge and discharge processes, fewer side reactions between the electrolyte and the positive electrode active material, and consequently, lower internal resistance and improved cycle performance of the secondary battery.

[0045] Optionally, in some embodiments, the secondary particles satisfy: 24≤d·e≤120 (3).

[0046] In this embodiment of the application, the cross-sectional area of ​​the secondary particles in the positive electrode active material is 1 μm. 2 Within the region, the product of the number of pores between primary particles and the aspect ratio of the primary particles is limited to the range of 24 to 120. This can further improve the tightness of the bonding between primary particles in the secondary particles, the mechanical strength of the secondary particles, and the wetting effect of the electrolyte. As a result, the polarization degree of the secondary battery based on the positive electrode active material is further reduced during the charging and discharging process, the lithium-ion transport rate is increased, and the side reactions between the electrolyte and the positive electrode active material are further reduced. Consequently, the internal resistance of the secondary battery is further reduced, and the cycle performance of the secondary battery is further improved.

[0047] In some embodiments, the cross-sectional area of ​​the secondary particles in the positive electrode active material is 1 μm. 2 The product of the number of pores between primary particles and the aspect ratio of the primary particles within the region can be a value within the range of one or both of the following: 24, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120.

[0048] Optionally, in some embodiments, d is 1.67 to 8.00. For example, d can be one of 1.67, 2.58, 3.46, 5.52, 7.00, 8.00 or a range between any two of them. This can further reduce the generation of microcracks in electrode sheets.

[0049] In some embodiments, e is 6 to 25. For example, e can be one of 6, 8, 12, 18, 22, 25 or a range between any two of them. This can improve the wettability of electrode sheets.

[0050] Optionally, in some embodiments, the positive active material in the present application includes a compound of the chemical formula Li a Ni x Co y Mn z Q p O₂, wherein 0.95≤a≤1.15, 0.8≤x≤0.94, 0.04≤y≤0.15, 0.02≤z≤0.06, 0<p≤0.01, and Q comprises at least one of B, Sr, Zn, Al, Ce, Ti, Zr, Sb, W, Y, Nb, Ta and Mo. In this embodiment, Q can be a doping element, which can promote the orientation of primary particles in the positive active material, reduce stress concentration at grain boundaries of the positive active material during charge-discharge cycles, and reduce the degree of change in the unit cell c parameter of the positive active material during charge-discharge cycles, thereby helping to improve the stability of the crystal structure of the positive active material and the cycle performance of the secondary battery.

[0051] Optionally, in some embodiments, the content of Q in the positive active material is 2500 ppm to 8000 ppm.

[0052] In some embodiments, the content of Q in the positive active material is one of 2500 ppm, 3500 ppm, 4500 ppm, 5500 ppm, 6500 ppm, 7500 ppm and 8000 ppm, or a range between any two of them.

[0053] In the embodiments of the present application, limiting the content of Q in the positive active material to 2500 ppm to 8000 ppm can increase the binding energy between Ni, Co, Mn elements at transition metal sites in the crystal structure of the positive active material and oxygen, help reduce oxygen defects in the positive active material, inhibit cation mixing, reduce the first irreversible capacity of the secondary battery, improve the integrity of the layered structure and the stability of the crystal structure of the positive active material, reduce the probability of particle breakage and crystal structure damage of the positive active material, thereby improving the thermodynamic performance of the positive active material, while ensuring that the intrinsic electronic conductivity of the positive active material is at a high level, which is beneficial to improving the cycle performance of the secondary battery.

[0054] Optionally, in some embodiments, the particle size Dv50 of the positive electrode active material is 8 μm to 16 μm, which allows the positive electrode active material to have both high compaction capability and kinetic performance. Here, Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material.

[0055] In some embodiments, the particle size Dv50 of the positive electrode active material can be a range of one or any two of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm and 16 μm.

[0056] Optionally, in some embodiments, the compaction density of the positive electrode active material powder under 30 kN pressure is 3.0 g / cm³. 3 ~3.6g / cm 3 This allows the positive electrode sheet prepared based on the positive electrode active material to have high compaction capability. High compaction capability can improve the energy density of the secondary battery and enhance the ability of the positive electrode active material to resist particle breakage under high compaction conditions. It reduces particle breakage caused by grain boundary stress concentration during rolling and cyclic charging and discharging, thereby improving the cycle performance of the secondary battery. In some embodiments, the powder compaction density of the positive electrode active material under 30 kN pressure can be 3.0 g / cm³. 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 and 3.6g / cm 3 The range of one or any two of them.

[0057] Optionally, in some embodiments, the positive electrode active material further includes a coating material for coating primary and / or secondary particles in the positive electrode active material; the coating material includes an oxide of at least one element selected from Sn, B, P, Zr, and Sr. The coating material in the positive electrode active material can further optimize the internal structure and interfacial stability of the positive electrode active material, making the structure of the positive electrode active material more stable, reducing the stress generated by the H2-H3 phase transition, suppressing the occurrence of interfacial side reactions, and improving the overall performance of the secondary battery.

[0058] Optionally, in one embodiment, the positive electrode further includes a conductive agent and a binder. The conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, carbon fibers, and carbon microspheres. The binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0059] In some embodiments, the positive electrode sheet is prepared as follows: the components used to prepare the positive electrode sheet, such as the positive active material, binder and any other components, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of a positive electrode current collector such as an aluminum foil; after baking, rolling, cutting and slitting, the positive electrode sheet can be obtained.

[0060] The secondary battery provided in this application embodiment also includes a negative electrode, a separator, and an electrolyte.

[0061] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer can be a negative active material used in batteries, and the negative active material includes any one or a combination of at least two of hard carbon, soft carbon, graphite, and silicon suboxide.

[0062] In some embodiments, the negative electrode sheet is prepared as follows: the components used to prepare the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; after baking, rolling, cutting and slitting, the negative electrode sheet can be obtained.

[0063] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid, gel-like, or entirely solid. In some embodiments, the electrolyte is a liquid electrolyte comprising an electrolyte salt and a solvent. The electrolyte salt is a lithium salt, and the solvent includes cyclic ester solvents and chain ester solvents. In some embodiments, the cyclic ester solvent includes at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, fluoroethylene carbonate, and γ-butyrolactone; the chain ester solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and diphenyl carbonate. In some embodiments, the organic solvent includes fluoroethylene carbonate, ethylene carbonate, propylene carbonate, and methyl ethyl carbonate.

[0064] In practical applications, the negative electrode sheet, separator and positive electrode sheet are stacked in sequence and wound to obtain a core. The core is then packaged to obtain a bare cell. After baking, the bare cell is injected with electrolyte, formed, repackaged and sorted to obtain the above-mentioned secondary battery.

[0065] This application also proposes an electrical device, which includes the aforementioned secondary battery, serving as the power supply for the electrical device.

[0066] The above-described electrical equipment embodiment includes the aforementioned secondary battery and achieves the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the secondary battery embodiment.

[0067] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0068] The present application will be described in detail below through embodiments.

[0069] Example 1

[0070] (1) Preparation of positive electrode active material:

[0071] (i) Nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a 2 mol / L mixed transition metal salt solution according to a molar ratio of n(Ni):n(Co):n(Mn) = 83:12:5. Sodium hydroxide was used as a precipitant and ammonia was used as a complexing agent. The mixed transition metal salt solution, precipitant, and complexing agent were contacted and mixed in a solvent to obtain a mixed solution. Nitrogen gas was introduced into the mixed solution and stirred at a stirring speed of 400 r / min and a nitrogen flow rate of 300 mL / min. After co-precipitation, a nickel-cobalt-manganese ternary hydroxide precursor Ni with a certain porosity structure was prepared. 0.83 Co 0.12 Mn 0.05 (OH)2.

[0072] (ii) The nickel-cobalt-manganese ternary hydroxide precursor, lithium source LiOH·H2O, and doping sources Nb2O5 and ZrO2 are added to a high-speed mixer in a molar ratio of 0.995:1.05:0.0025:0.0025 and thoroughly mixed to obtain a mixture. The mixture is then transferred to a tube furnace with an oxygen atmosphere for a first high-temperature calcination to obtain the calcined material. The temperature of the first high-temperature calcination is 730℃ and the duration of the first high-temperature calcination is 10h.

[0073] (iii) The material after the first calcination and boron trioxide are added to a high-speed mixer at a mass ratio of 100:0.05 and mixed evenly. The mixture is then subjected to a second high-temperature calcination to obtain the material after the second calcination. The temperature of the second high-temperature calcination is 450℃ and the duration of the second high-temperature calcination is 8h.

[0074] (iv) After secondary calcination, the material is crushed and sieved to obtain Nb and Zr-doped positive electrode active material with boron coating on the surface; wherein the particle size Dv50 of the positive electrode active material is 8 μm, and the powder compaction density of the positive electrode active material under 30 kN pressure is 3.6 g / cm³. 3 .

[0075] (2) Preparation of the positive electrode sheet:

[0076] The positive electrode active material prepared in step (1) was added to a high-speed vacuum mixer in a mass ratio of 97:2:1:0.2 along with conductive carbon black, polyvinylidene fluoride binder, and fatty alcohol polyoxyethylene ether electrode additive. The mixture was then stirred for 12 hours to obtain a positive electrode slurry with a certain fluidity. The obtained positive electrode slurry was then coated evenly on both sides of the positive electrode current collector aluminum foil using a coating machine. The foil was then dried in an oven at a high temperature of 110°C. The positive electrode sheet was then prepared by processes such as rolling, cutting, and slitting.

[0077] (3) Preparation of negative electrode sheet:

[0078] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and negative electrode thickener sodium carboxymethyl cellulose were added to a high-speed vacuum mixer in a mass ratio of 96:2:1:1 and mixed evenly. Then, deionized water was added as a solvent, and the mixture was stirred for 12 hours to obtain a negative electrode slurry with a certain fluidity. The obtained negative electrode slurry was evenly coated onto the negative electrode current collector copper foil using a coating machine and dried in an oven at a high temperature of 120°C. After rolling, cutting, and slitting, the negative electrode sheet can be prepared.

[0079] (4) Preparation of the separating membrane:

[0080] Polyethylene polymer film was selected as the separator.

[0081] (5) Preparation of electrolyte:

[0082] Ethylene carbonate and dimethyl carbonate were mixed in a volume ratio of 1:1 to obtain an organic solvent. Lithium hexafluorophosphate was then dissolved in the organic solvent to prepare an electrolyte. The concentration of lithium hexafluorophosphate was 1 mol / L.

[0083] (6) Preparation of secondary batteries:

[0084] The positive electrode sheet prepared in step (2), the negative electrode sheet prepared in step (3), and the separator prepared in step (4) are wound in a predetermined order to prepare a bare cell. The bare cell is placed in an outer packaging aluminum-plastic film, baked to remove moisture, and then a certain amount of electrolyte prepared in step (5) is injected. The cell is then vacuum-sealed to prepare a secondary battery.

[0085] Examples 2-4

[0086] The difference between Examples 2-4 and Example 1 is as follows:

[0087] In step (1) (i), the stirring speed is adjusted to 300 r / min, 500 r / min, and 600 r / min, and the flow rate of nitrogen is adjusted to 400 mL / min, 300 mL / min, and 500 mL / min, respectively. In step (ii), the ratios of the nickel-cobalt-manganese ternary hydroxide precursor to the lithium source LiOH·H2O and the doping sources Nb2O5 and ZrO2 are adjusted to 0.995:1.05:0.0015:0.0015, 0.995:1.05:0.0040:0.0040, and 0.995:1.05:0.0015:0.0035, respectively.

[0088] Examples 5-10

[0089] The difference between Examples 5-10 and Example 1 is that:

[0090] In step (1) (ii), the ratios of the nickel-cobalt-manganese ternary hydroxide precursor to the lithium source LiOH·H2O and the doping sources Nb2O5 and ZrO2 are adjusted to 0.995∶1.05∶0.0015∶0.0015, 0.995∶1.05∶0.0040∶0.0040, 0.995∶1.05∶0.0015∶0.0035, 0.995∶1.05∶0.0012∶0.0012, 0.995∶1.05∶0.0035∶0.0035, and 0.995∶1.05∶0.0020∶0.0040.

[0091] Examples 11-13

[0092] The difference between Examples 11-13 and Example 1 is that:

[0093] In step (1) (i), the stirring speed is adjusted to 300 r / min, 500 r / min, and 600 r / min, and the flow rate of nitrogen is 400 mL / min, 300 mL / min, and 500 mL / min, respectively.

[0094] Examples 14-19

[0095] The difference between Examples 14-19 and Example 1 is that:

[0096] In step (1) (i), the flow rates of nitrogen gas are 380 mL / min, 400 mL / min, 350 mL / min, 500 mL / min, 450 mL / min, and 480 mL / min, and the types of dopant sources in step (ii) are adjusted to SrO2 & ZrO2, Sb2O3 & WO3, Sb2O3 & ZrO2, Ta2O5, MoO3, WO3 & TiO2.

[0097] Examples 20-22

[0098] The difference between Examples 20-22 and Example 1 is that in step (1) (i), the molar ratio of n(Ni):n(Co):n(Mn) is adjusted.

[0099] Examples 23-24

[0100] The difference between Examples 23 and 24 and Example 1 is that in step (1) (ii), the molar ratio of the nickel-cobalt-manganese ternary hydroxide precursor to the lithium source LiOH·H2O is adjusted.

[0101] Examples 25-26

[0102] The difference between Examples 25 and 26 and Example 1 is that, in step (1) (iv), the particle size Dv50 of the positive electrode active material is adjusted.

[0103] Example 27

[0104] The difference between Example 27 and Example 1 is that in step (1), the doping source is WO3 and ZrO2; the coating source is ZrO2.

[0105] Example 28

[0106] The difference between Example 28 and Example 27 is that in step (1), the doping source is TiO2 and ZrO2.

[0107] Example 29

[0108] The difference between Example 29 and Example 27 is that in step (1), the doping source is Al2O3 and ZrO2.

[0109] Comparative Example 1

[0110] The difference between Comparative Example 1 and Example 1 is as follows:

[0111] In step (1) (ii), the doping source is MgO, and the ratio of the nickel-cobalt-manganese ternary hydroxide precursor to the lithium source LiOH·H2O and the doping source MgO is 0.995:1.05:0.0025:0.0015; the temperature of the first high-temperature calcination is 780℃.

[0112] Comparative Example 2

[0113] The difference between Comparative Example 2 and Example 1 is that;

[0114] In step (1) (i), the stirring speed is 800 r / min and the nitrogen flow rate is 600 mL / min.

[0115] Test method:

[0116] (1) The aspect ratio d of the primary particle and the cross-sectional area of ​​the secondary particle are 1 μm. 2 Test of the number of pores e between particles within the region:

[0117] Argon ion polishing was used to polish the positive electrode sample. Scanning electron microscopy was used to analyze the micro-morphology of the polished positive electrode active material, obtaining cross-sectional morphology images. The values ​​d and e in the prepared sample morphology images were statistically determined at 10K magnification. The specific method is as follows: d is defined as the ratio of the longest diameter inside a primary particle to the longest diameter perpendicular to it. The ratio of at least 20 primary particles was obtained, and the average value was used to calculate the d value. (Area greater than 150 nm) 2 The area to be included in the pore count is less than 150 nm. 2 The number of pores is not included in the calculation, and the result after statistics is 1μm. 2 The number of pores e between particles within a region.

[0118] (2) Testing of the content and valence state of dopants in the positive electrode active material:

[0119] The content of doped elements in the positive electrode active material was obtained by inductively coupled plasma mass spectrometry (ICP), with reference to the standard: Positive electrode active material: EPA6010D-2018 inductively coupled plasma atomic emission spectrometry.

[0120] (3) Porosity test of the positive electrode sheet during battery charging and discharging process:

[0121] At room temperature of 25°C, the secondary battery was charged at a constant current of 0.1C to the upper limit of the charge / discharge cutoff voltage of 4.2V, and then charged at a constant voltage until the current was less than or equal to 0.05mA. The battery was then adjusted to 100% SOC state, and then left to rest for 2 minutes. The secondary battery was then discharged at a constant current of 0.1C to the lower limit of the charge / discharge cutoff voltage of 2.8V, and then adjusted to 0% SOC state.

[0122] Disassemble secondary batteries with SOC states of 0% and 100% in a drying chamber. Remove the entire positive electrode sheet and place it in a beaker. Pour in an appropriate amount of high-purity anhydrous dimethyl carbonate (DMC). Replace the DMC every 8 hours, repeating this process three times. Then place the beaker in a vacuum chamber within the drying chamber, maintaining a vacuum, and dry for 12 hours. Use the dried positive electrode sheets with 0% and 100% SOC states for porosity testing. The change in porosity Δb during charge and discharge can be measured. Reference standards: GB / T 24533-2019 Graphite-based negative electrode materials for secondary batteries; GB / T 33052-2016 Method for determining porosity: hexadecane absorption method. Gas parameters: 99.999% He, 19.5 psig, 0.14 MPa-0.16 MPa. Standard sphere volume: 2.423204 cm³. 3 Sample cup volume: 3.5 cm³ 3 Sample requirements: area 154.025 mm² 2 The small circular plates are 16mm in diameter, with 25 positive electrode plates and 10 negative electrode plates; the thickness is the average thickness of the 10 small circular plates.

[0123] (4) Test on the change of cell c-parameter of the positive electrode active material during battery charging and discharging:

[0124] At room temperature of 25°C, the secondary battery was charged at a constant current of 0.1C to the upper limit of the charge / discharge cutoff voltage of 4.2V, and then charged at a constant voltage until the current was less than or equal to 0.05mA. The battery was then adjusted to 100% SOC state, and then left to rest for 2 minutes. The secondary battery was then discharged at a constant current of 0.1C to the lower limit of the charge / discharge cutoff voltage of 2.8V, and then adjusted to 0% SOC state.

[0125] In a drying room, secondary batteries with SOC states of 0% and 100% were disassembled with scissors. The entire positive electrode was removed and placed in a beaker. An appropriate amount of high-purity anhydrous dimethyl carbonate (DMC) was added, and the DMC was replaced every 8 hours for three consecutive cleaning cycles. Then, the electrode was placed in a vacuum chamber in the drying room and dried for 12 hours under a vacuum of -0.096 MPa. The dried positive electrode was used as a sample for XRD analysis. A D8 DISCOVER X-ray diffractometer from Brucker AxS (Germany) was used with CuKα rays as the radiation source. The wavelength of the rays was 1.5418 Å. The XRD analysis was performed on the sample at a scanning speed of 5° / min, a test angle range of 10° to 90°, and a step size of 0.02°. The X-ray diffraction pattern was obtained, and the c-parameter of the unit cell was calculated. The rate of change Δc of the c-parameter of the unit cell during the charging process of the positive electrode active material was further calculated.

[0126] (5) Battery cycle performance test:

[0127] Under constant temperature conditions of 45℃, charge the battery at 1C to 4.2V at a voltage of 2.8V to 4.2V, then charge it at 4.2V at a constant voltage until the current is ≤0.05mA. Let it stand for 5 minutes, then discharge it at 1C to 2.8V. Record the capacity as Dn (n=0, 1, 2……). Repeat the above process until the capacity decays to 80% of the initial capacity. Record the number of cycles of the battery.

[0128] (6) High-temperature gas generation test of the battery:

[0129] The secondary battery was fully charged to 4.2V at 1C and then left to stand in a 70℃ constant temperature chamber for 30 days. The volume expansion rate of the secondary battery was obtained by measuring the initial volume and the volume after standing for 30 days using the water displacement method.

[0130] Battery volume expansion rate (%) = (volume after 30 days of standing / initial volume - 1) × 100%.

[0131] (7) Battery thermal stability test:

[0132] After the battery was fully charged to 4.2V at 1C, it was transferred to a humidity-controlled dry room for disassembly and removal of the positive electrode. The separated positive electrode was repeatedly immersed and cleaned in DMC solution three times. Then, a small sample was transferred to a high-pressure crucible in a Differential Scanning Calorimeter (DSC). A small amount of electrolyte was added to fully wet the electrode. The sample was placed in a nitrogen atmosphere and heated from room temperature to 400℃ at a rate of 5℃ / min. The enthalpy curve was then measured to obtain the thermal decomposition temperature and heat release of the positive electrode active material. The thermal stability of the battery was evaluated based on the thermal decomposition temperature and heat release of the positive electrode active material.

[0133] The secondary batteries fabricated in each embodiment were subjected to the above tests, and the test data are shown in Tables 1 and 2.

[0134] Table 1

[0135] Table 2

[0136] According to the test data above, compared with the secondary battery provided in the comparative example, the secondary battery provided in this application embodiment, when charged and discharged at a rate of 0.1C between 0% SOC and 100% SOC, maintains a ratio between the change in porosity of the positive electrode sheet and the change rate of the cell c-parameter of the positive electrode active material that is greater than 0.5 and less than 1.8. This increases the cycle life of the secondary battery from 986 cycles in Comparative Example 1 and 995 cycles in Comparative Example 2 to over 1100 cycles, improving the cycle life by more than 10%. Furthermore, the volume expansion rate after 30 days of storage at 70°C decreases from 15.6% in Comparative Example 1 and 22.1% in Comparative Example 2 to below 10.5%, reducing the volume expansion rate by more than 5%. In addition, the DSC thermal decomposition temperature of the secondary battery provided in this application embodiment is also significantly higher than that of Comparative Example 1 and Comparative Example 2. Therefore, by limiting the ratio between the change in porosity of the positive electrode sheet and the change rate of the cell c-parameter of the positive electrode active material during the charge and discharge process of the secondary battery containing the positive electrode active material to the above-mentioned range, this application can reduce the drastic changes in the cell parameters of the positive electrode active material during the charge and discharge cycle of the secondary battery and the degree of difference in electrochemical reactions among different primary particles in the positive electrode active material. This suppresses the generation of microcracks in the positive electrode active material, thereby avoiding an excessive number of reactive surfaces in the positive electrode active material, reducing interfacial side reactions between the positive electrode active material and the electrolyte during the charge and discharge cycle, improving the cycle life of the secondary battery while ensuring a high energy density, reducing the volume expansion rate of the secondary battery during the charge and discharge process, and improving the structural stability, thermal stability, and cycle stability of the secondary battery.

[0137] The above provides a detailed description of a secondary battery and electrical device provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. 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 this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A secondary battery, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising a positive active material; the secondary battery satisfies: in, b1 represents the porosity of the positive electrode sheet when the secondary battery is charged from 0% SOC to 100% SOC at a rate of 0.1C. b2 represents the porosity of the positive electrode sheet when the secondary battery is discharged from 100% SOC to 0% SOC at a rate of 0.1C. c1 represents the cell c parameter of the positive electrode active material when the secondary battery is charged from 0% SOC to 100% SOC at a rate of 0.1C. c2 represents the cell c parameter of the positive electrode active material when the secondary battery is discharged from 100% SOC to 0% SOC at a rate of 0.1C.

2. The secondary battery according to claim 1, wherein (c1-c2) / c1 is 1.0% to 3.8%.

3. The secondary battery according to claim 2, wherein the value of c1 is within... Within the range, and / or the value of c2 is within... Within the range.

4. The secondary battery according to claim 1, wherein b1-b2 is 0.5% to 4.0%.

5. The secondary battery according to claim 4, wherein the value of b1 is in the range of 25% to 28%, and / or the value of b2 is in the range of 23% to 27%.

6. In the secondary battery according to claim 1, the molar content of Ni in the positive electrode active material, excluding lithium, is greater than 80%.

7. The secondary battery according to claim 1, wherein the positive electrode active material comprises secondary particles formed by the aggregation of primary particles; the secondary particles satisfy: 10≤d·e≤200, in, d represents the aspect ratio of the primary particle; e represents the cross-sectional area of ​​the secondary particle being 1 μm. 2 The number of pores between the primary particles within the region.

8. The secondary battery according to claim 7, wherein the secondary particles satisfy: 24 ≤ d·e ≤ 120.

9. The secondary battery according to claim 7 or 8, wherein the value of d is in the range of 1.67 to 8.

00.

10. The secondary battery according to claim 7 or 8, wherein the value of e is in the range of 6 to 25.

11. The secondary battery according to claim 1, wherein the positive electrode active material comprises Li a Ni x Co y Mn z Q p Compounds of O2, wherein 0.95≤a≤1.15, 0.8≤x≤0.94, 0.04≤y≤0.15, 0.02≤z≤0.06, 0<p≤0.01, and Q includes at least one of B, Sr, Zn, Al, Ce, Ti, Zr, Sb, W, Y, Nb, Ta and Mo.

12. The secondary battery according to claim 11, wherein the content of Q in the positive electrode active material is from 2500 ppm to 8000 ppm.

13. The secondary battery according to claim 1, wherein the particle size Dv50 of the positive electrode active material is 8 μm to 16 μm, wherein, Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the positive electrode active material.

14. The secondary battery according to claim 1, wherein the powder compaction density of the positive electrode active material under 30 kN pressure is 3.0 g / cm³. 3 ~3.6g / cm 3 .

15. An electrical device comprising a secondary battery as claimed in any one of claims 1 to 14, wherein the secondary battery serves as a power supply for the electrical device.

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