Secondary battery and electrical device

Abstract

A secondary battery and an electrical device. A positive electrode sheet of the secondary battery contains specific additives, and the number of additives per unit cross-sectional area in an SEM image of the cross section of the positive electrode sheet, the porosity of the positive electrode sheet, and the sheet resistance satisfy a certain relationship, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries, and improving the energy density of secondary batteries.

Description

Secondary battery and power consuming device

[0001] The present application claims priority to the Chinese patent application No. 202411385727.6, filed on September 29, 2024, and entitled "Secondary battery and power consuming device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of battery, in particular to a secondary battery and a power consuming device. BACKGROUND

[0003] Lithium iron phosphate secondary battery has the characteristics of low cost, good cycle performance and high safety, and has been widely used in new energy vehicles and energy storage fields. Currently, there are still several problems in lithium iron phosphate secondary battery, which restrict its further development: (1) after long-term cycle and storage, the loss of active lithium leads to the life of the secondary battery cannot meet the demand of long cycle energy storage project; (2) poor kinetics and low compaction density, which cannot meet the demand of energy density and fast charging performance of the next generation of fast charging power battery. SUMMARY

[0004] The purpose of the present application is to provide a secondary battery and a power consuming device to improve the rate performance and cycle performance of the existing secondary battery.

[0005] To achieve the above purpose, the first aspect of the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive active material layer arranged on at least one side of the current collector, the positive active material layer comprising an additive and a lithium-containing phosphate, the additive comprising a compound with a chemical formula of Li x M1 y1 M2 y2 N1 z1 N2 z2 , wherein M1 and M2 each independently comprise at least one of W, Nb, Ni, Fe, Si, Cu, Al, Ti, La, Zr, Sr, Sb, B, Co, Mn, N1 and N2 each independently comprise at least one of P, F, O, 1≤x≤10, 1≤y1, y2≤10, 1≤z1, z2≤20;

[0006] The positive electrode sheet satisfies: 8≤(N*P) / R≤3000, wherein N is the number of the additive per mm 2 P% is the porosity of the positive electrode sheet, and RΩ is the sheet resistance of the positive electrode sheet.

[0007] As an embodiment of the present application, the additive includes one or more of Li2W2O7, LiNbO3, Li2NiO2, Li5FeO4, Li4SiO4, Li2CuO2, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 .

[0008] As an embodiment of the present application, the positive electrode tab satisfies: 300 ≤ N ≤ 6000.

[0009] As an embodiment of the present application, the positive electrode tab satisfies: 10 ≤ P ≤ 60.

[0010] As an embodiment of the present application, the positive electrode tab satisfies: R ≤ 600.

[0011] As an embodiment of the present application, the positive electrode tab satisfies: N / A ≤ 600, where AN / m is the positive electrode tab adhesion.

[0012] As an embodiment of the present application, the positive electrode tab adhesion AN / m satisfies: 10 ≤ A ≤ 50.

[0013] As an embodiment of the present application, the positive electrode tab satisfies: 3 ≤ N / L ≤ 67, where Lwt% is the weight percentage of lithium-containing phosphates in the positive electrode active material layer.

[0014] As an embodiment of the present application, the weight percentage of lithium-containing phosphates in the positive electrode active material layer Lwt% satisfies: 90 ≤ L ≤ 99.

[0015] As an embodiment of the present application, the positive electrode tab satisfies: N*C ≥ 30*10 3 , where C g / m 2 is the single-sided area density of the positive electrode tab.

[0016] As an embodiment of the present application, the single-sided area density C g / m 2 of the positive electrode tab satisfies: 100 ≤ C ≤ 220.

[0017] As an embodiment of the present application, the positive electrode tab satisfies: N*D ≥ 700, where D g / cm 3 is the compacted density of the positive electrode tab.

[0018] As an embodiment of the present application, the compacted density D g / cm 3 of the positive electrode tab satisfies: 2.4 ≤ D ≤ 2.8.

[0019] In a second aspect of the present application, a kind of electric equipment is provided, and the electric equipment includes the secondary battery of the first aspect of the present application.

[0020] Compared with the prior art, the beneficial effects of the present application are:

[0021] The positive pole piece of the secondary battery described in the present application contains a specific additive, and the number of additives per unit cross-sectional area, the porosity and the membrane resistance of the positive pole piece in the SEM image of the cross section of the positive pole piece meet certain relationships, which improves the high-temperature cycle performance and high-temperature storage performance of the secondary battery, and improves the energy density of the secondary battery. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0023] In the present application, the technical features described in an open manner include both closed technical solutions consisting of listed features and open technical solutions containing listed features.

[0024] In the present application, if no special instructions are given, the numerical range is considered to be continuous and includes the minimum value and the maximum value of the range, as well as every value between the minimum value and the maximum value. Further, when the range refers to an integer, every integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0025] The reagents or instruments used in the present application are not marked with the manufacturer, and are conventional products that can be obtained from the market.

[0026] The embodiments of the present application provide a kind of secondary battery, the secondary battery includes positive pole piece, the positive pole piece includes current collector and the positive pole active material layer of at least one side of the current collector, the positive pole active material layer includes additive and lithium-containing phosphate, the additive includes chemical formula Li x M1 y1 M2 y2 N1 z1 N2 z2The compound, wherein M1 and M2 each independently contain at least one of W, Nb, Ni, Fe, Si, Cu, Al, Ti, La, Zr, Sr, Sb, B, Co, and Mn, and N1 and N2 each independently contain at least one of P, F, and O, and 1≤x≤10, 1≤y1, y2≤10, 1≤z1, z2≤20;

[0027] The positive electrode sheet satisfies: 8 ≤ (N*P) / R ≤ 3000, where N is the number of electrodes per mm. 2 P% represents the amount of additive per unit cross-sectional area in the SEM image of the positive electrode sheet, P% represents the porosity of the positive electrode sheet, and RΩ represents the film resistance of the positive electrode sheet.

[0028] In this application, the number N of additives per unit cross-sectional area refers to the number of additive particles with an average particle size greater than 8 μm contained in a unit area region of the positive electrode sheet. The method for testing the number N of additives per unit cross-sectional area is as follows: After ion cutting the positive electrode sheet, SEM is performed on the electrode cross-section to obtain a 1K magnification SEM image. The result is then calculated using the formula N = n / (h / x*w / x), where n represents the number of additive particles in the 1K magnification SEM image of the positive electrode sheet cross-section; h and w represent the actual measured length and width of the 1K magnification SEM image of the secondary particle cross-section, respectively, in cm; and x represents the actual measured length corresponding to a scale of 10 μm in the 1K magnification SEM image of the secondary particle cross-section, in cm / μm. It should be noted that additives not fully exposed in the SEM image are also included in the calculation of the number N of additives per unit cross-sectional area.

[0029] In some embodiments, M1 comprises at least one of W, Nb, Ni, Fe, Si, Cu, Ti, La, and Zr.

[0030] In some embodiments, M2 comprises at least one of W, Nb, Ni, Fe, Si, Cu, Al, Ti, La, and Zr.

[0031] In some embodiments, y2 = 0.

[0032] In some embodiments, y1 ≤ 4.

[0033] In some embodiments, Z1 ≤ 15.

[0034] In some embodiments, Z2 ≤ 15.

[0035] In some embodiments, Z2 = 0.

[0036] In some embodiments, the additive comprises Li₂W₂O₇, LiNbO₃, Li₂NiO₂, Li₅FeO₄, Li₄SiO₄, Li₂CuO₂, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 One or more of them.

[0037] In some embodiments, the additive comprises Li₂W₂O₇, LiNbO₃, Li₂NiO₂, Li₅FeO₄, and Li. 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 One or more of them.

[0038] In some embodiments, the additive is a particle with an average particle size greater than 8 μm and a loose and porous interior.

[0039] In some embodiments, the positive electrode sheet satisfies: 300 ≤ N ≤ 6000. For example, N can be any one value or a range between any two values ​​from 300, 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, and 6000. In some embodiments, the positive electrode sheet satisfies: 400 ≤ N ≤ 2800. N within the above range can further balance the energy density, high-temperature cycle performance, and high-temperature storage performance of the secondary battery.

[0040] In some embodiments, the positive electrode sheet satisfies: 10 ≤ P ≤ 60. For example, P can be any one or a range between any two values ​​from 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, and 60. In some embodiments, the positive electrode sheet satisfies: 20 ≤ P ≤ 35. P within the above range can further balance the energy density, high-temperature cycle performance, and high-temperature storage performance of the secondary battery. The porosity of the positive electrode sheet can be tested by the hexadecane absorption method, specifically referring to GB / T 33052-2016 Porosity Determination Method.

[0041] In some embodiments, the positive electrode sheet satisfies: R≤600. Exemplarily, R can be any one of 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600 or a range between any two of them. In some embodiments, the positive electrode sheet satisfies: R≤500. The sheet resistance of the positive electrode sheet is tested by the following method: using four-probe method, placing the electrode sheet on the testing device, making its surface flat, adjusting the pressure gauge to fix the testing sample, ensuring that the probe is in good contact with the sample, turning on the testing device, connecting the circuit to introduce current into the sample to be tested, and recording the voltage change, according to Ohm's law, calculating the sheet resistance value of the sample.

[0042] In some embodiments, the positive electrode sheet satisfies: N / A≤600, wherein AN / m is the adhesion of the positive electrode sheet. The adhesion of the positive electrode sheet in this application refers to the adhesion between the positive electrode active material layer and the positive electrode current collector (such as aluminum foil). For example, N / A can be any one of 10, 20, 50, 100, 200, 300, 400, 500, 600 or a range between any two of them. Controlling N / A in the above range can ensure that the positive electrode sheet has high adhesion strength, thereby improving the cycle performance and storage performance of the secondary battery.

[0043] In some embodiments, the adhesion AN / m of the positive electrode sheet satisfies: 10≤A≤50. Exemplarily, the adhesion of the positive electrode sheet can be any one of 10 N / m, 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, 50 N / m or a range between any two of them. The adhesion of the positive electrode sheet is tested by the following method: using a universal tensile testing machine to test the pulling force required to peel off the positive electrode active material layer, with the unit being N / m. The peeling length is 150 mm; the travel speed is 50 mm / min.

[0044] In some embodiments, the positive electrode sheet satisfies: 3≤N / L≤67, wherein Lwt% is the weight percentage content of lithium-containing phosphate in the positive electrode active material layer. Exemplarily, N / L can be any one of 3, 10, 20, 30, 40, 50, 60, 67 or a range between any two of them. Controlling N / L in the above range can increase the content of active material in the positive electrode sheet, thereby increasing the energy density of the battery.

[0045] In some embodiments, the weight percentage content Lwt% of lithium-containing phosphate in the positive electrode active material layer satisfies: 90≤L≤99. Exemplarily, L can be any one of 90, 92, 94, 95, 96, 97, 98, 99 or a range between any two of them.

[0046] In some embodiments, the positive electrode sheet satisfies: N*C≥30*10 3 , where C g / m 2 is the single-sided area density of the positive electrode sheet. Controlling N*C in the above range can improve the fast-charging cycle performance of high-energy-density batteries.

[0047] In some embodiments, the single-sided area density C g / m 2 of the positive electrode sheet satisfies: 100≤C≤220. The test method for the single-sided area density of the positive electrode sheet is as follows: the positive electrode sheet is cut into 10 small discs with an area of 1540.25 mm 2 , and the mass of the small discs is weighed using a high-precision balance. When the positive active material layer is coated on one side, the single-sided area density of the positive electrode sheet is calculated by dividing the mass of the aluminum foil after deduction by the disc area. When the positive active material layer is coated on both sides, the single-sided area density of the positive electrode sheet is calculated by dividing the mass of the aluminum foil after deduction by the disc area and then by 2.

[0048] In some embodiments, the single-sided area density C g / m 2 of the positive electrode sheet satisfies: 120≤C≤200. For example, the single-sided area density of the positive electrode sheet can be any one of 120 g / m 2 , 130 g / m 2 , 140 g / m 2 , 150 g / m 2 , 160 g / m 2 , 170 g / m 2 , 180 g / m 2 , 190 g / m 2 , 200 g / m 2 , or a range between any two of them. In some embodiments, the single-sided area density C g / m 2 of the positive electrode sheet satisfies: 140≤C≤180. Controlling the single-sided area density of the positive electrode sheet in the above range can improve the kinetic performance while maintaining a high energy density of the battery.

[0049] In some embodiments, the positive electrode sheet satisfies: N*D≥700, where D g / cm 3 is the compacted density of the positive electrode sheet. The positive electrode sheet additive has high ion and electron conductivity. Controlling N*D in the above range can reduce the amount of conductive agent in the positive electrode sheet, improve the compacting ability of the positive electrode sheet, and improve the energy density of the battery.

[0050] In some embodiments, the compacted density D g / cm 3Satisfy: 2.4≤D≤2.8. Exemplarily, D can be any one of 2.4, 2.5, 2.6, 2.7, 2.8 or a range between any two of them. Positive electrode tab compacted density = positive electrode tab double surface density / (thickness of positive electrode tab after rolling - thickness of positive electrode current collector).

[0051] In some embodiments, the lithium-containing phosphate comprises a compound of formula Li x Fe y M 1-y PO4; wherein M comprises one or more of Al, Mn, Ni, Co, W, Mo, Ti, 0.8≤x≤1.2, 0≤y≤1.

[0052] In some embodiments, the average particle size of the additive is greater than 8 μm. The additive has high ionic and electronic conductivity and is internally loose and porous, and after being added, can improve the kinetic performance of the positive electrode tab, reduce the internal resistance of the battery, improve the specific capacity of the battery and improve the fast charging cycle life.

[0053] In some embodiments, the weight percentage content of the additive in the positive electrode active material layer is 0.5wt% to 8wt%. Exemplarily, the weight percentage content of the additive in the positive electrode active material layer can be any one of 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt% or a range between any two of them.

[0054] In some embodiments, the preparation process of the positive electrode tab can include steps such as stirring, coating, drying, cold pressing, slitting and cutting. In some embodiments, the preparation of the positive electrode tab comprises: dispersing the positive electrode active material, the additive, the positive electrode conductive agent and the positive electrode binder in N-methyl pyrrolidone (NMP) according to a certain proportion, coating the obtained slurry on an aluminum foil, drying, and then cold pressing and slitting to obtain the positive electrode tab.

[0055] In some embodiments, the secondary battery further comprises a negative electrode tab, the negative electrode tab comprising 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 comprising a negative electrode active material.

[0056] The type of negative electrode active material is not particularly limited and can be selected according to actual needs. For example, the negative electrode active material can be artificial graphite, natural graphite, silicon-carbon composite material, silicon monoxide, hard carbon, lithium metal and lithium titanate, etc.

[0057] The type of negative electrode current collector is also not particularly limited and can be selected according to actual needs. Preferably, copper foil or carbon-coated copper foil, etc. can be used.

[0058] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited and can be selected according to actual needs. The separator can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride film, a spandex film, an aramid film, or a multi-layer composite film modified by coating.

[0059] In some embodiments, the preparation of the secondary battery comprises: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, then winding the stacked sheets into a square bare cell, and then loading the bare cell into a battery shell. After baking at 65-95°C to remove water, the secondary battery is obtained by injecting electrolyte, sealing, standing, hot and cold pressing, formation, clamping, and distribution.

[0060] In some embodiments, the secondary battery can comprise an outer package, which can be a hard shell such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package such as a bag-type soft package. The material of the soft package can be plastic such as one or more of polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

[0061] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0062] In a second aspect of the present application, a power consuming device is provided, which comprises the secondary battery of the first aspect of the present application. The power consuming device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. The vehicle can be a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range extended vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle, a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric plane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, etc. The above devices are not particularly limited in the embodiments of the present application.

[0063] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in conjunction with the embodiments. However, the present application is not limited to these embodiments. The reagents, methods, and equipment used in the present application are conventional reagents, methods, and equipment in the technical field unless otherwise specified.

[0064] Embodiment 1

[0065] Embodiment 1 provides a secondary battery, and the specific preparation process of the secondary battery comprises:

[0066] (1) Preparation of the positive electrode sheet

[0067] The positive electrode active material LiFePO4, the additive Li2NiO2, the conductive agent SP and the binder PVDF were dispersed in N-methyl pyrrolidone (NMP) at a mass ratio of 97:1:1:1, the stirring speed was 2500 rpm, and the stirring time was 24 h, to obtain a uniformly mixed positive electrode slurry. The obtained positive electrode slurry was coated on both sides of an aluminum foil at a surface density of 180 g / m2 (single-sided), dried at 120°C for 5 min, and then roll-pressed at a compaction density of 2.5 g / cm3, to obtain the positive electrode sheet after slitting and cutting. 2 (2) Preparation of the negative electrode sheet 3 The negative electrode active material graphite, the conductive agent SP, the thickening agent CMC and the binder SBR were mixed uniformly at a mass ratio of 97:1:1:1, deionized water was added as a solvent, and the negative electrode slurry was uniformly coated on both sides of the current collector copper foil, and then baked at 120°C, cold-pressed, slitted and cut, to obtain the negative electrode sheet.

[0068] (2) Preparation of the negative electrode sheet

[0069] The negative electrode active material graphite, the conductive agent SP, the thickening agent CMC and the binder SBR were mixed uniformly at a mass ratio of 97:1:1:1, deionized water was added as a solvent, and the negative electrode slurry was uniformly coated on both sides of the current collector copper foil, and then baked at 120°C, cold-pressed, slitted and cut, to obtain the negative electrode sheet.

[0070] (3) Preparation of the electrolyte

[0071] The organic solvent ethylene carbonate and the organic solvent methyl ethyl carbonate were mixed at a mass ratio of 3:7, and then lithium hexafluorophosphate was dissolved in the above organic solvent in an argon atmosphere glove box with a water content of <10 ppm, to obtain the electrolyte, wherein the concentration of lithium hexafluorophosphate was 1M.

[0072] (4) Preparation of the secondary battery

[0073] The positive electrode sheet, the negative electrode sheet and the separator (a polypropylene film with a thickness of 12 μm) were wound into a bare cell, and then placed in an aluminum plastic film, baked, and injected with the electrolyte. After the processes of formation, sealing and capacity distribution, the secondary battery was obtained.

[0074] Example 2

[0075] The preparation method of the secondary battery in Example 2 was basically the same as that in Example 1, except that the mass ratio of the positive electrode active material LiFePO4, the additive Li2NiO2, the conductive agent SP and the binder PVDF in the preparation of the positive electrode sheet was 99:0.5:0.1:0.4, and the stirring speed was 1000 rpm and the stirring time was 12 h.

[0076] Example 3

[0077] The preparation method of the secondary battery described in Example 3 is substantially the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP, and the binder PVDF in the preparation of the positive electrode sheet is 98:1:0.5:0.5, the stirring speed is 1000 rpm, and the stirring time is 12 h.

[0078] Example 4

[0079] The preparation method of the secondary battery described in Example 4 is substantially the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP, and the binder PVDF in the preparation of the positive electrode sheet is 96:2:1:1, the stirring speed is 1500 rpm, and the stirring time is 12 h.

[0080] Example 5

[0081] The preparation method of the secondary battery described in Example 5 is substantially the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP, and the binder PVDF in the preparation of the positive electrode sheet is 95:3:1:1, the stirring speed is 1500 rpm, and the stirring time is 12 h.

[0082] Example 6

[0083] The preparation method of the secondary battery described in Example 6 is substantially the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP, and the binder PVDF in the preparation of the positive electrode sheet is 94:4:1:1, the stirring speed is 2000 rpm, and the stirring time is 18 h.

[0084] Example 7

[0085] The preparation method of the secondary battery described in Example 7 is substantially the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP, and the binder PVDF in the preparation of the positive electrode sheet is 93:5:1:1, the stirring speed is 2000 rpm, and the stirring time is 18 h.

[0086] Example 8

[0087] The preparation method of the secondary battery described in Example 8 is substantially the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP, and the binder PVDF in the preparation of the positive electrode sheet is 90:8:1:1, the stirring speed is 2000 rpm, and the stirring time is 18 h.

[0088] Example 9

[0089] The preparation method of the secondary battery described in Example 9 is basically the same as that in Example 2, except that the additive used in the preparation of the positive electrode is Li2W2O7, with a single-sided surface density of 100 g / m³. 2 The drying temperature is 60℃ and the drying time is 20 minutes.

[0090] Example 10

[0091] The preparation method of the secondary battery described in Example 10 is basically the same as that in Example 2, except that the additive used in the preparation of the positive electrode is Li2W2O7, with a single-sided areal density of 120 g / m². 2 The drying temperature is 60℃ and the drying time is 15 minutes.

[0092] Example 11

[0093] The preparation method of the secondary battery described in Example 11 is basically the same as that in Example 2, except that the additive used in the preparation of the positive electrode is Li2W2O7, with a single-sided surface density of 140 g / m². 2 The drying temperature is 80℃ and the drying time is 10 minutes.

[0094] Example 12

[0095] The preparation method of the secondary battery described in Example 12 is basically the same as that in Example 2, except that the additive used in the preparation of the positive electrode is Li2W2O7, with a single-sided surface density of 160 g / m². 2 The drying temperature is 80℃ and the drying time is 10 minutes.

[0096] Example 13

[0097] The preparation method of the secondary battery described in Example 13 is basically the same as that in Example 2, except that the additive used in the preparation of the positive electrode is Li2W2O7, with a single-sided surface density of 200 g / m³. 2 The drying temperature is 100℃ and the drying time is 15min.

[0098] Example 14

[0099] The preparation method of the secondary battery described in Example 14 is basically the same as that in Example 2, except that the additive used in the preparation of the positive electrode is Li2W2O7, with a single-sided areal density of 220 g / m². 2 The drying temperature is 120℃ and the drying time is 15 minutes.

[0100] Example 15

[0101] The preparation method of the secondary battery described in Example 15 is basically the same as that in Example 2, except that the positive electrode sheet is prepared according to 2.4 g / cm³. 3The compacted density was 2.6 g / cm

[0102] Example 16

[0103] The preparation method of the secondary battery of Example 16 was substantially the same as that of Example 2, except that the compacted density was 2.6 g / cm 3 in the preparation of the positive electrode sheet.

[0104] Example 17

[0105] The preparation method of the secondary battery of Example 17 was substantially the same as that of Example 2, except that the compacted density was 2.7 g / cm 3 in the preparation of the positive electrode sheet.

[0106] Example 18

[0107] The preparation method of the secondary battery of Example 18 was substantially the same as that of Example 2, except that the compacted density was 2.8 g / cm 3 in the preparation of the positive electrode sheet.

[0108] Example 19

[0109] The preparation method of the secondary battery of Example 19 was substantially the same as that of Example 1, except that the additive was Li5FeO4.

[0110] Example 20

[0111] The preparation method of the secondary battery of Example 20 was substantially the same as that of Example 1, except that the additive was LiNbO3.

[0112] Example 21

[0113] The preparation method of the secondary battery of Example 21 was substantially the same as that of Example 1, except that the additive was Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0114] Example 22

[0115] The preparation method of the secondary battery of Example 22 was substantially the same as that of Example 1, except that the additive was Li7La3Zr2O 12 .

[0116] Comparative Example 1

[0117] The preparation method of the secondary battery of Comparative Example 1 is basically the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP and the binder PVDF in the preparation of the positive electrode sheet is 97:0:2:1.

[0118] Comparative Example 2

[0119] The preparation method of the secondary battery of Comparative Example 2 is basically the same as that of Example 1, except that the mass ratio of the positive active material LiFePO4, the additive Li2NiO2, the conductive agent SP and the binder PVDF in the preparation of the positive electrode sheet is 88:10:1:1.

[0120] Comparative Example 3

[0121] The preparation method of the secondary battery of Comparative Example 3 is basically the same as that of Example 1, except that the single surface density of the positive electrode sheet is 350 g / m2 2 , and the rolling is performed at a compacting density of 1.5 g / cm3 3 .

[0122] The physical property parameters of the secondary batteries of Examples 1-22 and Comparative Examples 1-3 are shown in Table 1.

[0123] Table 1

[0124] Table 1 (continued)

[0125] The following performances of the secondary batteries prepared in each example and comparative example were tested, and the specific test results are shown in Table 3.

[0126] (1) Gram capacity: at room temperature, constant current charging to 3.65 V at a current of 0.33 C, then constant voltage charging to a current less than 0.05 C at 3.65 V, standing for 5 min, then discharging to 2.5 V at a current of 0.33 C, to obtain the first discharge gram capacity.

[0127] (2) DCR test: at room temperature, constant current charging to 3.65 V at a current of 1 C, then constant voltage charging to a current less than 0.05 C, standing for 5 min, then discharging at a current of 1 C for 30 min, adjusting the battery to 50% SOC. Discharge the battery at a rate of 5 C for 10 s, and record the voltage drop AV. The battery DCR can be calculated from DCR=AV / 5C.

[0128] (3) Cycle performance test: charge at 4C to 3.65V, then charge at 3.65V to current less than 0.05C, rest for 5min, then discharge at 1C to 2.5V. Repeat the charge-discharge cycle, the capacity retention rate at 1000th cycle = capacity at 1000th cycle / initial capacity x 100%.

[0129] (4) Storage life test: charge at 1C to 3.65V, then charge at 3.65V to current less than 0.05C. Put the full battery in a 60℃ oven, take out the battery every 15 days, and move to room temperature for 2h. Discharge at 1C to 2.5C, rest for 10min, charge at 1C to 3.65V, then charge at 3.65V to current less than 0.05C, rest for 5min, then discharge at 1C to 2.5V to get the recovery capacity.

[0130] Table 3

[0131] From the above examples and comparative examples, by adding a specific additive to the positive electrode sheet, and at the same time, the number of additives per unit cross-sectional area in the SEM image of the cross section of the positive electrode sheet, the porosity of the positive electrode sheet and the membrane resistance meet a certain relationship, the high-temperature cycle performance and high-temperature storage performance of the secondary battery are improved, and the energy density of the secondary battery is improved.

[0132] From Comparative Examples 1-8, when the positive electrode sheet satisfies 20≤P≤35, the discharge gram capacity, high-temperature cycle performance and high-temperature storage performance of the secondary battery can be further balanced.

[0133] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and do not limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet including a current collector and a positive active material layer provided on at least one side of the current collector, the positive active material layer containing an additive and a lithium-containing phosphate, the additive containing a compound of the formula Li x M1 y1 M2 y2 N1 z1 N2 z2 wherein M1 and M2 each independently contain at least one of W, Nb, Ni, Fe, Si, Cu, Al, Ti, La, Zr, Sr, Sb, B, Co, Mn, N1 and N2 each independently contain at least one of P, F, O, 1≤x≤10, 1≤y1, y2≤10, 1≤z1, z2≤20. The positive electrode sheet satisfies: 8 ≤ (N*P) / R ≤ 3000, where N is the number of additives per mm 2 P% is the porosity of the positive electrode sheet, and RΩ is the sheet resistance of the positive electrode sheet.

2. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies at least one of the following characteristics: (1)300≤N≤6000； (2)10≤P≤60； (3)R≤600。 3. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies at least one of the following characteristics: (1)400≤N≤2800； (2)20≤P≤35； (3)R≤500。 4. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies: N / A ≤ 600, wherein AN / m is the positive electrode sheet adhesion.

5. The secondary battery according to claim 4, wherein The positive electrode sheet adhesion AN / m satisfies: 10 ≤ A ≤ 50.

6. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies: 3 ≤ N / L ≤ 67, wherein Lwt% is the weight percentage content of lithium-containing phosphates in the positive electrode active material layer.

7. The secondary battery according to claim 6, wherein The weight percentage content of lithium-containing phosphates in the positive electrode active material layer Lwt% satisfies: 90 ≤ L ≤ 99.

8. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies: N*C ≥ 30*10 3 where C g / m 2 is the single-sided area density of the positive electrode sheet.

9. The secondary battery according to claim 8, wherein The single-sided area density C g / m2 of the positive electrode sheet 2 satisfies: 100 ≤ C ≤ 220.

10. The secondary battery according to claim 8, wherein The single-sided area density Cg / m of the positive electrode sheet 2 satisfies: 120 ≤ C ≤ 200.

11. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies: N*D ≥ 700, where D g / cm 3 is the compacted density of the positive electrode sheet.

12. The secondary battery according to claim 11, wherein The compacted density D of the positive electrode tab is 2.4 to 2.8 g / cm3. 3 satisfies: 2.4 ≤ D ≤ 2.

8.

13. The secondary battery according to claim 1, wherein The M1 comprises at least one of W, Nb, Ni, Fe, Si, Cu, Ti, La, Zr, and / or the M2 comprises at least one of W, Nb, Ni, Fe, Si, Cu, Al, Ti, La, Zr.

14. The secondary battery according to claim 1, wherein The positive electrode sheet satisfies at least one of the following characteristics: 1) The y2 = 0; 2) The y1 ≤ 4; 3) The Z1 ≤ 15; 4) The Z2 ≤ 15; 5) The Z2 = 0.

15. The secondary battery according to claim 1, wherein The additive comprises one or more of Li2W2O7, LiNbO3, Li2NiO2, Li5FeO4, Li4SiO4, Li2CuO2, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 .

16. The secondary battery according to claim 1, wherein The additive comprises one or more of Li2W2O7, LiNbO3, Li2NiO2, Li5FeO4, Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li7La3Zr2O 12 .

17. The secondary battery according to claim 1, wherein The lithium-containing phosphate comprises a chemical formula of Li x Fe y M 1-y PO4; wherein M comprises one or more of Al, Mn, Ni, Co, W, Mo, Ti, 0.8≤x≤1.2, 0≤y≤1.

18. The secondary battery according to claim 1, wherein The average particle size of the additive is greater than 8 μm.

19. The secondary battery of claim 1, wherein, The weight percentage content of the additive in the positive electrode active material layer is 0.5 wt% to 8 wt%.

20. An electrical device, comprising: The electric device comprises the secondary battery of any one of claims 1 to 19.

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