Positive electrode sheet, secondary battery, and electric device

Abstract

The present application relates to the technical field of electrochemistry, and specifically discloses a positive electrode sheet, a secondary battery, and an electric device. A positive electrode active material of the positive electrode sheet in the present application comprises a manganese-containing phosphate material. The positive electrode sheet satisfies the following relational expression: 0.08≤(A×H) / IAl≤27, wherein A is the content of manganese in the positive electrode active material, H is the growth rate of hydrogen ion content when the positive electrode sheet is immersed in a mixed solution, and IAl is the difference between the peak intensities of aluminum element characteristic peaks in an XPS spectrum when XPS analysis is performed on the positive electrode sheet at different depths. By comprehensively controlling the content of manganese in the positive electrode active material, the hydrogen ion growth characteristics of the positive electrode sheet, and the Al peak intensities at different depths of the electrode sheet, the present application significantly mitigates the gas generation problem of the secondary battery comprising the positive electrode sheet, and achieves low increase rate of internal resistance of the battery after cycling.

Description

A positive electrode, a secondary battery, and an electrical device.

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411449883.4, filed on October 17, 2024, entitled "A Positive Electrode, a Secondary Battery, and an Electrical Device", the entire contents of which are incorporated herein by reference; this application also claims priority to Chinese Patent Application No. 202411936439.5, filed on October 17, 2024, entitled "A Positive Electrode, a Secondary Battery, and an Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a positive electrode, a secondary battery, and an electrical device. Background Technology

[0004] Lithium manganese iron phosphate (LMFP) cathode materials have attracted widespread attention in the fields of electric vehicles and portable electronic devices due to their high energy density. Compared with lithium iron phosphate (LFP), LMFP improves the theoretical energy density of the battery by introducing manganese, thus enabling the battery to have a longer driving range.

[0005] However, the increased manganese content leads to manganese leaching problems, especially at high temperatures where the leaching of manganese ions may be exacerbated. Manganese leaching not only causes gas to be generated inside the battery, increasing the risk of battery swelling, but it also forms deposits. These deposits increase the battery's internal resistance, reducing its charge / discharge efficiency and lifespan.

[0006] Therefore, there is a need to provide a positive electrode that can improve gas generation and reduce internal resistance. Summary of the Invention

[0007] The purpose of this application is to overcome the shortcomings of the existing technology and provide a positive electrode, a secondary battery and an electrical device. By comprehensively controlling the manganese content in the positive electrode active material, the hydrogen ion growth characteristics of the positive electrode, and the peak intensity of Al at different depths of the electrode, the gas generation problem of the secondary battery containing the positive electrode is greatly improved, and the internal resistance growth rate of the battery is low after cycling.

[0008] To achieve the above objectives, in a first aspect of this application, this application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material, and the positive active material includes a manganese-containing phosphate material;

[0009] The positive electrode plate satisfies the following relationship: 0.08≤(A×h) / I Al ≤27;

[0010] Where A is the molar content of manganese in the transition metal element in the positive electrode active material, in mol%.

[0011] H represents the hydrogen ion content growth rate of the positive electrode sheet after immersion in the mixed solution at 60°C from T1h to T2h, where T2-T1 = 72 and T1 > 0; the mixed solution contains organic solvent and lithium salt, and the unit of H is %;

[0012] I Al =I2-I1, where I1 is the peak intensity of the aluminum characteristic peak in the XPS image when the surface of the positive electrode is analyzed by X-ray photoelectron spectroscopy (XPS); I2 is the peak intensity of the aluminum characteristic peak in the XPS image after etching the positive electrode at a depth of 50 nm and then performing XPS analysis; I1, I2 and I Al The unit for all values ​​is counts / s.

[0013] As an optional implementation of this application, the positive electrode sheet satisfies the following relationship: 0.16≤(A×h) / I Al ≤4.5.

[0014] As an optional implementation of this application, the range of A is 50–95 mol%.

[0015] As a further optional embodiment of this application, the range of A is 55–85 mol%.

[0016] As an optional implementation of this application, the range of H is 12% to 42%.

[0017] As a further optional implementation of this application, the range of H is 15% to 35%.

[0018] As an optional implementation of this application, the I Al The range is 100 to 9000 counts / s.

[0019] As a further optional implementation of this application, the I Al The range is 600 to 7000 counts / s.

[0020] As an optional implementation of this application, the range of I1 is 100 to 12800 counts / s.

[0021] As an optional implementation of this application, the positive electrode active material includes lithium manganese iron phosphate materials.

[0022] As an optional embodiment of this application, the average particle size of the lithium manganese iron phosphate material is 30-400 nm.

[0023] As an optional embodiment of this application, the mixed solution includes ethylene carbonate, methyl ethyl carbonate and lithium perchlorate, wherein the volume ratio of ethylene carbonate to methyl ethyl carbonate is 3:7, and the molar concentration of lithium perchlorate in the mixed solution is 1 mol / L.

[0024] In a second aspect, this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is the aforementioned positive electrode.

[0025] In a third aspect, this application provides an electrical device including the aforementioned secondary battery.

[0026] The beneficial effects of this application are as follows:

[0027] This application develops a positive electrode, a secondary battery, and an electrical device. By comprehensively controlling the manganese content in the positive electrode active material, the hydrogen ion growth characteristics of the positive electrode, and the Al peak intensity at different depths of the electrode, the gas generation problem of the secondary battery containing this positive electrode is greatly improved, and the battery exhibits a low internal resistance growth rate after cycling. Attached Figure Description

[0028] Figure 1 is an XPS image of the positive electrode sheet of Example 6. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0031] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0032] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0033] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0034] Positive electrode sheet

[0035] This application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material, and the positive active material includes a manganese-containing phosphate material;

[0036] The positive electrode plate satisfies the following relationship:

[0037] 0.08≤(A×H) / I Al ≤27;

[0038] Where A is the molar content of manganese in the transition metal element in the positive electrode active material, in mol%.

[0039] H represents the hydrogen ion content growth rate of the positive electrode sheet after immersion in the mixed solution at 60°C from T1h to T2h, where T2-T1 = 72 and T1 > 0; the mixed solution contains organic solvent and lithium salt, and the unit of H is %;

[0040] I Al =I2-I1, where I1 is the peak intensity of the aluminum characteristic peak in the XPS image when the surface of the positive electrode is subjected to XPS analysis; I2 is the peak intensity of the aluminum characteristic peak in the XPS image after etching the positive electrode at a depth of 50 nm and then performing XPS analysis; I1, I2 and I Al The unit for all values ​​is counts / s.

[0041] This application significantly improves the gas generation problem of secondary batteries containing the positive electrode by comprehensively controlling the manganese content in the positive electrode active material, the hydrogen ion growth rate of the positive electrode sheet, and the Al peak intensity at different depths of the positive electrode sheet. Furthermore, the battery exhibits a low internal resistance growth rate after cycling.

[0042] This study found that the presence of a certain amount of aluminum (Al) in the positive electrode helps to improve gas generation within the battery. During the first charge of the battery, Al in the positive electrode participates in the chemical reaction earlier than manganese (Mn), promoting the formation of a solid electrolyte interphase (CEI) film on the surface of the positive electrode. The rapid formation of the CEI film effectively protects the positive electrode before manganese dissolves, thereby greatly reducing side reactions between the positive electrode active material and the electrolyte, and reducing the generation of gas inside the battery. However, the Al content in the surface layer of the positive electrode (mainly the CEI film) should not be too high. Al located in the surface layer of the positive electrode may dissolve into the negative electrode and participate in the formation of the negative electrode solid electrolyte interphase (SEI) film. Excessive Al content may lead to an increase in the film impedance of the negative electrode SEI film, thereby increasing the internal resistance of the battery.

[0043] In XPS analysis, the positions of characteristic peaks of elements are primarily determined by binding energy. The positions of these peaks are generally related to the element type, valence state, structure, and testing environment. For the positive electrode of this application, the characteristic peaks of aluminum typically appear in XPS spectra with binding energies between 60 and 90 eV. The peak intensity of the aluminum characteristic peak in the XPS spectra reflects the relative content of Al at that position. Al To address the difference in peak intensity of the Al peak at different etching depths on the positive electrode, this application adjusts the I... Al The size of the value, that is, controlling the content distribution of Al at different depths of the positive electrode, thereby improving the gas generation phenomenon of the battery and keeping the battery with low internal resistance.

[0044] H represents the hydrogen ion content growth rate of the positive electrode sheet during immersion in a mixed solution containing lithium perchlorate. When the positive electrode sheet is immersed in a mixed solution containing lithium salt, an interfacial reaction occurs between the positive electrode active material and the mixed solution, generating hydrogen ions. A higher hydrogen ion content growth rate during immersion indicates a higher degree of interfacial reaction. The degree of particle passivation of the positive electrode active material is a crucial factor affecting the aforementioned reaction degree; therefore, the hydrogen ion growth rate in this application reflects, to some extent, the degree of particle passivation of the positive electrode active material. By controlling the value of H, the passivation degree can be adjusted, and the oxidative properties of the positive electrode active material can be reduced through passivation, thereby protecting the positive electrode sheet, reducing manganese dissolution, improving battery gas production, and lowering the battery's internal resistance. However, the H value should not be too low, as an excessively low H value may indicate excessive passivation, leading to obstructed electron transport within the positive electrode sheet and increased battery internal resistance.

[0045] The H value is related to various factors, such as the particle structure and coating of the positive electrode active material, the additive composition of the battery electrolyte, and the doping elements and their content in the positive electrode active material. In other words, the content of Al and Mn in the positive electrode sheet both affect the H value. Therefore, this application comprehensively controls the manganese content in the positive electrode active material, the hydrogen ion growth rate of the positive electrode sheet, and the Al peak intensity at different depths of the positive electrode sheet. By controlling it to satisfy 0.08 ≤ (A × H) / IAl ≤ 27, the gas generation problem of the secondary battery containing this positive electrode sheet is improved, and the internal resistance growth rate of the battery is low after cycling.

[0046] When(A×H) / I Al When the value is too small, below 0.08, there may be excessive passivation or excessive aluminum content in the surface layer of the positive electrode, leading to an excessively high rate of increase in the battery's internal resistance; when (A×H) / I Al When the value is too high, greater than 27, it may lead to severe gas production in the battery and a high rate of increase in internal resistance.

[0047] For example, in this application, (A×H) / I Al The value can be 0.08, 0.10, 0.15, 0.20, 0.50, 1.0, 2.0, 5.0, 10.0, 15.0, 20.0, 25.0, 25.5, 26.0, 26.5, 26.8, 26.85, 26.90, 26.95, 27.0, or any range formed by any two of the above values.

[0048] In one embodiment, the positive electrode plate satisfies the following relationship: 0.16 ≤ (A × h) / I Al ≤4.5.

[0049] Further research in this application has revealed that when the positive electrode sheet is within the aforementioned preferred range, the overall gas production and internal resistance growth rate of the battery are better.

[0050] In one embodiment, the range of A is 50–95 mol%, for example, A can be 50 mol%, 55 mol%, 60 mol%, 70 mol%, 80 mol%, 90 mol%, or 95 mol%.

[0051] In one preferred embodiment, the range of A is 55–85 mol%.

[0052] In this application, a positive electrode active material with a higher manganese content is preferred, which helps the battery to have a better energy density. However, the A value should not be too high. An excessively high A value will increase the possibility of manganese dissolution, affect the passivation effect of the positive electrode, degrade the battery's gas generation, and also increase the battery's internal resistance.

[0053] This application does not limit the detection method for A. Those skilled in the art can detect the molar content of manganese in phosphate materials using conventional technical means, such as ICP testing.

[0054] For example, A can be detected using the following method:

[0055] The battery was disassembled in its empty state to obtain the positive electrode sheet. After processing, the positive electrode active material powder was obtained. The molar content of manganese in the transition metal elements in the positive electrode active material was obtained by ICP test.

[0056] In one embodiment, the range of H is 12% to 42%, for example, H can be 12%, 15%, 18%, 25%, 30%, 35%, 38%, 40%, or 42%.

[0057] In one preferred embodiment, the range of H is 15% to 35%.

[0058] The H value reflects the passivation degree of the positive electrode active material and is influenced by various factors, such as the particle structure, particle size, coating thickness, coating integrity, and coating amount of the positive electrode active material; the composition of the electrolyte additives, including whether it contains additives that promote film formation and passivation; and the doping elements and their content in the bulk phase of the positive electrode active material. An H value within the aforementioned preferred range indicates that the passivation effect of the positive electrode active material is appropriate, effectively improving gas generation in the battery without causing excessive increases in internal resistance.

[0059] In one embodiment, the mixed solution comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), and lithium perchlorate, wherein the volume ratio of ethylene carbonate to ethyl methyl carbonate is 3:7, and the molar concentration of lithium perchlorate in the mixed solution is 1 mol / L.

[0060] When using the above-mentioned mixed solution, the positive electrode sheet is immersed in the mixed solution. The lithium salt and solvent (EC, EMC) react to form a solvated structure, promoting the interfacial reaction between the solvent and the positive electrode active material. The solvent dehydrogenates to produce hydrogen ions, and the hydrogen ion content in the mixed solution increases with the extension of immersion time. Lithium perchlorate, as a relatively stable lithium salt, helps to make the detection of H value more accurate.

[0061] For example, H can be detected using the following method:

[0062] The battery was disassembled in a fully charged state to obtain the positive electrode sheet in a fully charged state. After being dried at 80℃ for 4 hours, the positive electrode sheet was obtained. The positive electrode sheet was then cut into 7cm×7cm electrode sheets to be tested.

[0063] At a test temperature of 60℃, the electrode to be tested was immersed in 20ml of a mixed solution, which consisted of ethylene carbonate, methyl ethyl carbonate and lithium perchlorate, with a volume ratio of ethylene carbonate to methyl ethyl carbonate of 3:7 and a molar concentration of lithium perchlorate of 1mol / L in the mixed solution.

[0064] When the electrode to be tested is immersed in the mixed solution for 48 hours, the hydrogen ion content in the mixed solution is measured and recorded as H1ppm; when the electrode to be tested is immersed in the mixed solution for another 72 hours, the hydrogen ion content in the mixed solution is measured again and recorded as H2ppm.

[0065] The hydrogen ion content can be tested using acid-base titration.

[0066] The hydrogen ion content growth rate H of the positive electrode immersed in a mixed solution containing high chloric acid is calculated as H = (H2 - H1) / H1 × 100%. The hydrogen ion content of the electrode under test after immersion in the mixed solution for 48 hours is taken as the initial hydrogen ion content, taking into account the process of sufficient wetting of the positive electrode by the mixed solution.

[0067] In one embodiment, the I Al The range is 100 to 9000 counts / s, for example, the I... Al The values ​​can be 100 counts / s, 200 counts / s, 500 counts / s, 1000 counts / s, 3000 counts / s, 5000 counts / s, 8000 counts / s, 8500 counts / s, or 9000 counts / s.

[0068] In one preferred embodiment, the I Al The range is 600 to 7000 counts / s.

[0069] In one embodiment, the range of I1 is 100 to 12800 counts / s.

[0070] I Al A value greater than 0 indicates that Al is more present in the positive electrode active material layer than in the CEI film layer. When I... Al Within the aforementioned preferred range, the distribution of Al is more suitable. Sufficient aluminum elements are present in the positive electrode active material layer at the middle position of the positive electrode sheet (etching depth 50nm), which helps to effectively improve the gas generation of the battery. Furthermore, the aluminum content in the surface layer of the positive electrode sheet (etching depth 0nm) is low, which avoids the deterioration of the battery's internal resistance.

[0071] Since neither I1 nor I2 can be negative, we can deduce that I AlWhen the value of I1 is too low, it means that the value of I2 is very small (the value of I1 is relatively smaller), or the values ​​of I1 and I2 are very close. If the values ​​of I1 and I2 are too small, it indicates that the Al content in the positive electrode is low, and the improvement on the battery gas generation problem is not significant enough; if the values ​​of I1 and I2 are very close, it indicates that the difference in Al content between the middle and surface of the positive electrode is too small, which may lead to a high internal resistance of the battery. When I... Al A value higher than 9000 counts / s means that the Al content (i.e., I2) in the middle of the positive electrode is not less than 9000 counts / s. The overall Al content of the positive electrode is too high, which may lead to a large increase in the internal resistance of the battery during cycling.

[0072] I Al The value can be controlled by adding doping elements during the preparation of the positive electrode active material, or by adding aluminum elements during the preparation of the positive electrode sheet.

[0073] For example, I Al The following methods can be used for detection:

[0074] The battery was disassembled to obtain the positive electrode sheet, which was then dried to obtain the electrode sheet to be tested. XPS analysis was performed on the surface of the electrode sheet and at an etching depth of 50 nm to obtain the difference in peak intensity of the characteristic peaks of aluminum.

[0075] In one embodiment, the positive electrode active material includes lithium manganese iron phosphate materials.

[0076] The lithium manganese iron phosphate materials include at least one of lithium manganese iron phosphate (LMFP), lithium manganese iron phosphate containing doped elements, and lithium manganese iron phosphate containing a coating layer.

[0077] In one embodiment, the average particle size of the lithium manganese iron phosphate material is 30-400 nm.

[0078] Lithium manganese iron phosphate materials can be single particles or aggregates composed of primary particles. When lithium manganese iron phosphate materials are single particles, the average particle size refers to the average particle size of a single particle; when lithium manganese iron phosphate materials are aggregates, the average particle size refers to the average particle size of the primary particles.

[0079] The doping element can be aluminum.

[0080] The coating layer is applied to the surface of the LMFP particles, and the coating layer may be a carbon layer.

[0081] This application does not limit the preparation method of LMFP. Those skilled in the art can prepare LMFP using conventional techniques.

[0082] For example, a method for preparing LMFP may include the following steps:

[0083] Manganese, iron, phosphorus, and lithium sources are mixed in a certain molar ratio and then ground.

[0084] The ground product was spray-dried and then sintered in an atmosphere with an oxygen concentration of less than 150 ppm to obtain LMFP.

[0085] Depending on the requirements, the preparation of LMFP can involve multiple grinding-spray drying-sintering processes. For example, manganese, iron, phosphorus, and lithium sources can be mixed, ground once, spray dried once, and then sintered once in an atmosphere with an oxygen concentration of less than 150 ppm. The product from the first sintering is then ground a second time, spray dried a second time, and sintered a second time in an atmosphere with an oxygen concentration of less than 150 ppm. After post-processing, LMFP is obtained.

[0086] The lithium source may include at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, or lithium acetate.

[0087] The phosphorus source may include at least one of diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate, or lithium phosphate.

[0088] The iron source may include at least one of ferrous oxalate, ferric hydroxide, ferrous hydroxide, ferric phosphate, ferrous phosphate, ferric acetate, ferrous acetate, ferric carbonate, ferrous carbonate, ferric oxide, ferric oxide, or ferric oxalate.

[0089] The manganese source may include at least one of manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, or manganese acetate.

[0090] Ferric manganese phosphate can be used as a source of manganese, iron and phosphorus simultaneously; iron phosphate can be used as a source of both iron and phosphorus simultaneously.

[0091] When LMFP contains doped elements, a certain amount of doped element source can be weighed and mixed with manganese source, iron source, phosphorus source and lithium source, and then ball-milled.

[0092] When the doping element is aluminum, the source of the doping element is an aluminum source. The aluminum source may include at least one of the following: aluminum formate, aluminum acetate, aluminum glycolate, aluminum lactate, aluminum tartrate, aluminum oxalate, aluminum phosphate, aluminum hydrogen phosphate, aluminum dihydrogen phosphate, aluminum carbonate, aluminum oxide, aluminum hydroxide, aluminum fluoride, aluminum chloride, aluminum nitrate, aluminum sulfate, and aluminum bromide.

[0093] When LMFP also contains a coating layer, a certain amount of coating layer raw material can be weighed and mixed with manganese source, iron source, phosphorus source and lithium source, and then ball-milled.

[0094] When the coating layer is a carbon layer, the raw material for the coating layer is a carbon source. The carbon source may include at least one of glucose, sucrose, and polyethylene glycol.

[0095] In one embodiment, the positive electrode active material includes at least one of lithium iron phosphate and lithium nickel cobalt manganese oxide.

[0096] When lithium manganese iron phosphate is combined with other types of cathode materials (such as lithium iron phosphate or lithium nickel cobalt manganese oxide) as the cathode active material, the cathode electrode sheet satisfies 0.08 ≤ (A × H) / I. Al When the temperature is ≤27, the secondary batteries using this positive electrode have lower gas production and lower cycle internal resistance growth rate.

[0097] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also contain conductive agents and binders.

[0098] The conductive agent only needs to have suitable electronic conductivity and not cause adverse chemical changes in the battery; this application does not impose any particular limitation on the type of conductive agent. Specifically, the conductive agent can be at least one of carbon nanotubes, carbon black, or graphene.

[0099] The binder is used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. In this application, the binder can be a conventional choice in the battery field. Specifically, the conductive agent can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), or sodium alginate.

[0100] This application does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0101] In this application, the positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive active material, conductive agent and binder are dispersed in a solvent to form a uniform positive electrode slurry, the positive electrode slurry is coated on the positive current collector, and after drying, rolling and other processes, the positive electrode sheet is obtained.

[0102] Secondary batteries

[0103] One embodiment of this application provides a secondary battery comprising the positive electrode sheet described above.

[0104] In addition to the positive electrode, the electrochemical device also includes a negative electrode, a separator, and an electrolyte.

[0105] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material. Regarding the negative active material, this application embodiment does not specifically limit the type of negative active material, and it can be selected according to actual needs. As an example, the negative active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, or silicon-carbon composites.

[0106] The separator is located between the positive and negative electrode plates, serving to separate them and prevent short circuits caused by contact. The separator can be any material suitable for separators in electrochemical energy storage devices. Specifically, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0107] The electrolyte in this application can be any electrolyte suitable for electrochemical energy storage devices in the art. The electrolyte includes an electrolyte and a solvent, and the electrolyte typically includes a lithium salt.

[0108] Specifically, the lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be 0.5–5 mol / L.

[0109] Specifically, the solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0110] Electrical appliances

[0111] One embodiment of this application provides an electrical device comprising the secondary battery described above.

[0112] The electrical device serves as the power source for the electrical device.

[0113] The term "electrical device" refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or one or more other energy forms, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0114] The present application is further illustrated below with specific embodiments:

[0115] Example 1

[0116] This embodiment provides a lithium-ion battery, and the specific preparation method is as follows:

[0117] (1) Preparation of positive electrode sheet

[0118] S1. According to the molar ratio n(Li):n(Mn+Fe):n(P)=1:1:1 and n(Mn):n(Fe)=75:25, accurately weigh Mn3O4, FePO4 and LiH2PO4 and mix them to obtain a mixture.

[0119] The carbon source (75 wt.% glucose and 25 wt.% polyethylene glycol) and the aluminum source (Al2O3) were weighed and added to the mixture for the first ball milling, the first spraying, and the first sintering to obtain a sintered precursor.

[0120] Wherein: the aluminum source is weighed according to the molar ratio n(Al) / n(Mn) = 6000ppm;

[0121] Among them: the carbon source is weighed at 5 wt.% of the weight of the mixture;

[0122] The conditions for the first ball milling were: 500 rpm, 25℃, 22 h;

[0123] The conditions for the first spray are: spray pressure 0.65 MPa;

[0124] The conditions for the first sintering were: 500℃, 10h;

[0125] S2. Weigh a certain amount of carbon source (75wt.% glucose and 25wt.% polyethylene glycol), mix it with the precursor, and perform a second ball milling, a second spraying, and a second sintering. After crushing, sieving, and removing impurities, obtain lithium manganese iron phosphate material (lithium manganese iron phosphate with a carbon material layer on the surface) with an average particle size of 85.2nm. The lithium manganese iron phosphate material is the positive electrode active material.

[0126] Among them: adjusting the amount of carbon source, controlling the carbon coating amount of lithium manganese iron phosphate (the mass ratio of carbon material to lithium manganese iron phosphate material) to 2.8 wt.%;

[0127] The conditions for the second ball milling were: 500 rpm, 25℃, 22 h;

[0128] The conditions for the second spray were: spray pressure 0.65 MPa;

[0129] The conditions for the second sintering were: 600℃ for 10 hours.

[0130] S3. The positive electrode active material is mixed with binder (PVDF) and conductive agent (SP) in a mass ratio of 96:3:1 and dispersed in NMP to obtain a positive electrode slurry. Then, the mixed positive electrode slurry is uniformly coated on aluminum foil, dried in a vacuum furnace at 100°C, rolled, cut, and baked to obtain a positive electrode sheet.

[0131] (2) Preparation of negative electrode sheet

[0132] The negative electrode active material (artificial graphite), conductive agent (SP), and binder (carboxymethyl cellulose, CMC) are mixed in a mass ratio of 92:4:4 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector (copper foil). The negative electrode current collector coated with the negative electrode slurry is transferred to a vacuum environment in an oven and dried at 100°C. It is then rolled, cut, and baked to obtain the negative electrode sheet.

[0133] (3) Preparation of electrolyte

[0134] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0135] (4) Preparation of the diaphragm

[0136] A polyethylene (PE) diaphragm is used.

[0137] (5) Battery manufacturing

[0138] The prepared positive electrode, separator, and negative electrode are wound to obtain an unfilled bare cell; the bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0139] Examples 2-9, Examples 11-18, and Comparative Examples 1 and 2

[0140] Examples 2-9, Examples 11-18, and Comparative Examples 1 and 2 each provide a lithium-ion battery, the specific preparation method of which is similar to that of Example 1, the difference being in the preparation of the positive electrode sheet:

[0141] The values ​​of n(Mn):n(Fe) and n(Al) / n(Mn) in S1 are shown in Table 1;

[0142] The time for the first ball milling is shown in Table 1;

[0143] In S2, after crushing and sieving, the average particle size of the lithium manganese iron phosphate material is adjusted to meet the requirements shown in Table 1; the amount of carbon source is adjusted to control the carbon coating amount of the lithium manganese iron phosphate material to meet the requirements shown in Table 1; the time of the second ball milling is shown in Table 1.

[0144] For Example 3, step S2 has the following difference: after obtaining the lithium manganese iron phosphate material, the lithium manganese iron phosphate material and lithium iron phosphate are mixed at a mass ratio of 8:2 to obtain the positive electrode active material.

[0145] For Example 15, step S2 also has the following difference: After obtaining the lithium manganese iron phosphate material, the lithium manganese iron phosphate material is combined with the ternary material (LiNi). 0.6 Co 0.2 Mn 0.2 O2) mixed at a mass ratio of 2:8 becomes the positive electrode active material;

[0146] For Example 16, step S2 also has the following difference: After obtaining the lithium manganese iron phosphate material, the lithium manganese iron phosphate material is combined with the ternary material (LiNi). 0.8 Co 0.1 Mn0.1 O2) mixed at a mass ratio of 2:8 is the positive electrode active material.

[0147] Example 10

[0148] Example 10 provides a lithium-ion battery, the specific preparation method of which is similar to that of Example 1, except that the positive electrode sheet is prepared according to the following method:

[0149] According to the molar ratio n(Li):n(Mn+Fe):n(P)=1:1:1 and n(Mn):n(Fe)=56:44, accurately weigh Mn3O4, FePO4 and LiH2PO4 and mix them to obtain a mixture.

[0150] The carbon source (75 wt.% glucose and 25 wt.% polyethylene glycol) and the aluminum source (Al2O3) were weighed and added to the mixture for the first ball milling, the first spraying, and the first sintering to obtain lithium manganese iron phosphate material (lithium manganese iron phosphate with a carbon material layer on the surface) with an average particle size of 210 nm; (without multiple ball milling or multiple sintering), this lithium manganese iron phosphate material is the positive electrode active material;

[0151] Wherein: the aluminum source is weighed according to the molar ratio n(Al) / n(Mn) = 7600ppm;

[0152] Adjust the amount of carbon source to control the carbon coating amount (the mass ratio of carbon material to lithium manganese iron phosphate material) of lithium manganese iron phosphate to 2.0 wt.%.

[0153] The conditions for the first ball milling were: 500 rpm, 25℃, 24h;

[0154] The conditions for the first spray are: spray pressure 0.65 MPa;

[0155] The conditions for the first sintering were: 600℃, 10h;

[0156] Then, the positive electrode active material is mixed with binder (PVDF) and conductive agent (SP) at a mass ratio of 96:3:1 and dispersed in NMP to obtain a positive electrode slurry. Subsequently, the mixed positive electrode slurry is uniformly coated on aluminum foil, dried in a vacuum furnace at 100°C, rolled, cut, and then baked to obtain a positive electrode sheet.

[0157] Comparative Example 3

[0158] Comparative Example 3 provides a lithium-ion battery, the specific preparation method of which is similar to that of Example 1, except that in the preparation of the positive electrode sheet:

[0159] In S1, no aluminum source is added, and the values ​​of n(Mn):n(Fe) are shown in Table 1; the time of the first ball milling is shown in Table 1.

[0160] In S2, after crushing and sieving, the average particle size of the lithium manganese iron phosphate material is adjusted to meet the requirements shown in Table 1; the amount of carbon source is adjusted to control the carbon coating amount of the positive electrode active material to meet the requirements shown in Table 1; the time for the second ball milling is shown in Table 1.

[0161] S3 consists of the following steps:

[0162] S3. The positive electrode active material, binder (PVDF), and conductive agent (SP) are mixed at a mass ratio of 96:3:1 and dispersed in NMP to obtain the first positive electrode slurry; 1.2 wt.% Al2O3 is added to the first positive electrode slurry to obtain the second positive electrode slurry;

[0163] The second positive electrode slurry is evenly coated on aluminum foil, dried in a vacuum furnace at 100°C, rolled, cut, and then baked to obtain the positive electrode sheet.

[0164] The carbon coating content of lithium manganese iron phosphate materials was determined by the following method:

[0165] After being weighed by an electronic balance, the sample enters the combustion reaction cell. Under sufficient oxygen conditions, it is heated at high temperature in a high-frequency furnace, oxidizing carbon into carbon dioxide. This gas is then filtered and dried before entering the corresponding absorption cell, where it absorbs the corresponding infrared radiation spectrum (carbon dioxide 4200nm). The absorption is then converted into a corresponding electrical signal by a detector. This signal is acquired by a computer, linearly corrected, and converted into a value proportional to carbon dioxide. The values ​​from the entire analysis process are then accumulated. After the analysis, this accumulated value is divided by the weighed value and multiplied by the correction factor in the computer to obtain the mass fraction of carbon in the sample, which is the carbon coating amount (in wt.%).

[0166] Table 1

[0167] The A, h, and I of the positive electrode in the lithium-ion batteries prepared in the above embodiments and comparative examples Al The testing was conducted using the following methods, and the test results are shown in Table 2.

[0168] Detection method:

[0169] A: Disassemble the lithium-ion battery in an empty state to obtain the positive electrode sheet. After drying the positive electrode sheet at 80°C for 4 hours, place it in a sintering furnace at 400°C for 4 hours and scrape off the positive electrode active material powder with a ceramic knife.

[0170] Accurately weigh 0.5g of positive electrode active material powder, disperse it in 20ml of water, add 10ml of nitric acid, mix well, and then heat it. After the positive electrode active material powder dissolves, dilute the material with water to 100mL to obtain the test solution.

[0171] ICP testing was performed on the solution to be tested. ICP testing conditions: the selected elemental detection wavelength (Mn wavelength 257.61 nm) was used. Based on the characteristics of the sample and the element to be detected, appropriate ICP instrument operating conditions were set, including a gas flow rate of 0.5 L / min and a power of 1150 W. The Mn content was determined by ICP testing, yielding the molar content of manganese in the positive electrode active material relative to the transition metal elements, which is the value of A (in mol).

[0172] H: First, discharge the lithium-ion battery at a rate of 0.33C; then charge it at a rate of 0.33C to a cutoff voltage of 4.25V and a cutoff current of 0.05C, so that the battery reaches 100% SOC, i.e., fully charged state; disassemble the fully charged battery to obtain the positive electrode sheet in the fully charged state, and dry it at 80℃ for 4 hours to obtain the positive electrode sheet, and cut the positive electrode sheet into a 7cm×7cm electrode sheet to be tested;

[0173] At 60℃, the electrode to be tested was immersed in 20 ml of a mixed solution, which consisted of ethylene carbonate, methyl ethyl carbonate and perchloric acid, with a volume ratio of ethylene carbonate to methyl ethyl carbonate of 3:7 and a molar concentration of lithium perchlorate of 1 mol / L in the mixed solution.

[0174] When the electrode to be tested is immersed in the mixed solution for 48 hours, the hydrogen ion content in the mixed solution is measured and recorded as H1ppm; when the electrode to be tested is immersed in the mixed solution for another 72 hours, the hydrogen ion content in the mixed solution is measured again and recorded as H2ppm.

[0175] The hydrogen ion content (H1, H2) in the mixed solution was detected by the following method:

[0176] Prepare a 0.05 mol / L triethylamine titrant using triethylamine and ethyl methyl carbonate (EMC). Take the mixed solution impregnated with the positive electrode as the test solution, add 10–30 drops of methyl red as an indicator, and add the triethylamine titrant to the test solution containing methyl red. Record the amount of triethylamine titrant used when the test solution turns orange. Then, calculate the hydrogen ion content using the formula:

[0177] Hydrogen ion content = M × V × 20010 / m, where the unit of hydrogen ion content is ppm;

[0178] In the formula: M is the concentration of the triethylamine titrant, in mol / L.

[0179] V represents the volume of titrant consumed by triethylamine, in mL.

[0180] m is the mass of the solution to be tested, in grams.

[0181] 20010 = 20.01 × 10 3 20.01 is the molecular weight of HF. The fully charged positive electrode contains the electrolyte component LiPF6. The positive electrode active material reacts with EC and EMC to dehydrogenate and generates HF in the presence of LiPF6. The amount of HF represents the hydrogen ions.

[0182] Calculate the growth rate of hydrogen ion content H in the positive electrode plate immersed in a mixed solution containing high chloric acid: H = (H2 - H1) / H1 × 100%.

[0183] I Al Disassemble the battery to obtain the positive electrode sheet. After drying the positive electrode sheet at 80℃ for 4 hours, the electrode sheet to be tested is obtained.

[0184] XPS analysis was performed on the surface of the electrode to be tested. The peak intensity of the characteristic peak of aluminum in the obtained XPS image was I1 counts / s.

[0185] After etching the electrode under test at a depth of 50 nm, XPS analysis was performed. The peak intensity of the characteristic peak of aluminum in the obtained XPS image was I2 counts / s.

[0186] The XPS analysis conditions were as follows: a 120W monochromatic Al Kα X-ray source was used; the energy resolution was less than or equal to 0.48 eV; the test beam spot size was 400 micrometers; and the instrument automatically supplemented the test energy range according to the element to be measured. The etching conditions were as follows: Ar ions were used for etching, and the etching depth was controlled to be 50 nm by adjusting the etching rate or etching time.

[0187] After the XPS analysis is completed, the instrument will automatically provide the test results, from which I1 and I2 can be read.

[0188] Calculate I Al =I2-I1, I1, I2 and I Al The unit for all values ​​is counts / s.

[0189] Figure 1 shows the XPS spectrum of the positive electrode sheet of Example 1. The lower line represents the XPS spectrum obtained by XPS analysis of the surface of the electrode sheet under test; the upper line represents the XPS spectrum obtained by XPS analysis after etching the electrode sheet under test at an etching depth of 50 nm. In Figure 1, the characteristic peak of aluminum is located at the binding energy of 84 ± 1 eV.

[0190] Table 2

[0191] The gas generation performance of the positive electrode sheets prepared in the above embodiments and comparative examples, as well as the internal resistance (DCR) growth rate of the lithium-ion batteries prepared in the embodiments and comparative examples, were tested. The specific test methods are as follows, and the test results are shown in Table 3.

[0192] (1) Gas production performance:

[0193] The positive electrode, separator, and negative electrode of each embodiment and comparative example are used to prepare soft-pack batteries through rolling, assembly, drying, and liquid injection processes.

[0194] Set up the special container, electronic scale, one soft-pack battery, wires, bracket and formation device, pour water into the special container until water overflows from the opening of the special container and the soft-pack battery is completely submerged in water.

[0195] Once the overflow stops, zero the electronic scale; proceed with the formation process (formation process: charge to 2.4V at 0.02C, let stand for 10 minutes, discharge to 2V at 0.02C, let stand for 10 minutes, repeat this process three times, then charge to 3.5V at 0.02C, let stand for 10 minutes, then charge to 4.25V at 0.1C). During the formation process, gas is generated inside the soft-pack battery, causing the battery volume to continuously expand, which in turn causes the liquid in the special container to continuously overflow. As a result, the reading on the electronic scale changes simultaneously, and the volume of water that overflows is the volume of gas generated.

[0196] Once the reaction is complete, the reading on the electronic scale is the mass of liquid lost. The density of water is known. Therefore, the gas production rate = mass of liquid lost / density of water, in milliliters (ml).

[0197] The soft-pack battery was subjected to a constant capacity test (charged at a constant current rate of 1 / 3C to 4.25V, and then charged at a constant voltage rate to a current of less than 0.05C, for more than 3 cycles, and the battery capacity was recorded to obtain the actual capacity of the soft-pack battery (in Ah).

[0198] The gas production performance of the positive electrode is evaluated by the gas production per unit capacity of the battery. Gas production per unit capacity = gas production / actual capacity (unit: ml / Ah).

[0199] (2) DCR growth rate:

[0200] The lithium-ion battery was charged to its constant capacity, fully charged to 4.25V at 0.33C, with a constant voltage cutoff current of 0.05C, discharged at 0.33C to adjust the charge to 50% SOC, left to stand for 2 hours, and then discharged at 1C at 50% SOC. The initial internal resistance of the battery was measured to obtain DCR1.

[0201] The lithium-ion battery was placed in a 55°C constant temperature chamber and discharged at a constant current of 0.33C. Then, it was cycled in the constant temperature chamber at a charge / discharge test rate of 1C / 1C and a cycle voltage range of 2.5-4.25V for a total of 300 cycles.

[0202] After 300 cycles, the battery was discharged at 0.33C to adjust the charge to 50% SOC, left to stand for 2 hours, and then discharged at 1C at 50% SOC. The internal resistance of the battery after cycling was tested to obtain DCR2.

[0203] The battery internal resistance test method is as follows: take the voltage at the last second of rest as V0, the voltage after 18 seconds of discharge as V1, and the current during the discharge process as I. DCR = (V0 - V1) / I.

[0204] Calculate the DCR growth rate as (DCR2 - DCR1) / DCR1 × 100%.

[0205] Table 3

[0206] According to the test results in Table 3, the lithium-ion batteries using the positive electrode sheets prepared in the various embodiments of this application all have excellent gas generation performance (gas generation per unit capacity ≤ 24.1 ml / Ah), and the internal resistance growth rate of the lithium-ion batteries after cycling is low (DCR growth rate ≤ 65%).

[0207] As can be seen from Examples 1-6 and Examples 10-11, when the positive electrode further satisfies 0.16≤(A×H) / I Al At a value of ≤4.5, the battery exhibits superior overall performance, with relatively lower gas production and less internal resistance increase.

[0208] As can be seen from Comparative Examples 1 to 3, when the positive electrode exceeds the technical solution of this application, it does not satisfy 0.08≤(A×H) / I Al When the value is ≤27, it is difficult for lithium-ion batteries using this positive electrode to achieve both good gas generation performance and a low internal resistance growth rate.

[0209] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, characterized in that, The positive electrode active material includes a manganese-containing phosphate material; The positive electrode plate satisfies the following relationship: 0.08 < (A x H) / I Al ≤ 27; Where A is the molar content of manganese in the transition metal element in the positive electrode active material, in mol%. H represents the hydrogen ion content growth rate of the positive electrode sheet after immersion in the mixed solution at 60°C from T1h to T2h, where T2-T1 = 72 and T1 > 0; the mixed solution contains organic solvent and lithium salt, and the unit of H is %; I Al I2-I1, wherein I1 is the peak intensity of the aluminum element characteristic peak in the XPS graph when the surface of the positive electrode plate is analyzed by XPS; I2 is the peak intensity of the aluminum element characteristic peak in the XPS graph after the positive electrode plate is etched to a depth of 50 nm and then analyzed by XPS; I1, I2, and I Al are all in counts / s.

2. The positive electrode sheet according to claim 1, characterized by The positive electrode sheet satisfies the following relationship: 0.16 ≤ (A x H) / I Al ≤ 4.

5.

3. The positive electrode sheet according to claim 1 or 2, characterized by The range of A is 50–95 mol%.

4. The positive electrode sheet according to claim 3, wherein The range of A is 55–85 mol%.

5. The positive electrode sheet according to claim 1 or 2, wherein The range of H is 12% to 42%.

6. The positive electrode sheet according to claim 5, wherein The range of H is 15% to 35%.

7. The positive electrode sheet according to claim 1 or 2, wherein The I Al ranges from 100 to 9000 counts / s.

8. The positive electrode sheet according to claim 7, wherein The I Al range is 600-7000 counts / s.

9. The positive electrode sheet according to claim 1 or 2, wherein The range of I1 is 100 to 12800 counts / s.

10. The positive electrode plate of claim 1, wherein, The positive electrode active material includes lithium manganese iron phosphate materials.

11. The positive electrode sheet according to claim 10, wherein The average particle size of the lithium manganese iron phosphate material is 30–400 nm.

12. The positive electrode plate of claim 1, wherein, The mixed solution comprises ethylene carbonate, methyl ethyl carbonate and lithium perchlorate, wherein the volume ratio of ethylene carbonate to methyl ethyl carbonate is 3:7, and the molar concentration of lithium perchlorate in the mixed solution is 1 mol / L.

13. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, characterized by The positive electrode is the positive electrode as described in any one of claims 1 to 12.

14. An electrical device, characterized by Includes the secondary battery as described in claim 13.

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