Positive electrode active material, electrically conductive slurry and secondary battery

Abstract

The present invention relates to the technical field of secondary batteries, and provides a positive electrode active material, an electrically conductive slurry and a secondary battery. By adding lithium-rich manganese-based material particles to lithium manganese iron phosphate particles and controlling the proportion of an Li2MnO3 phase in the lithium-rich manganese-based material to be less than 0.5, the cycling performance and stability of a secondary battery having the positive electrode active material are improved.

Description

Cathode active material, conductive paste and secondary battery

[0001] This application claims priority to the Chinese patent application No. 202410726252.6 filed on June 5, 2024 in the China Patent Office, the whole content of the above application is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of secondary batteries, in particular to a cathode active material, a conductive paste and a secondary battery. BACKGROUND

[0003] The cathode material has an important influence on the performance of lithium ion batteries and is an important factor for improving the performance of batteries. Lithium manganese iron phosphate (LMFP) is a new generation of cathode material for lithium ion batteries, which has an olivine structure, high working voltage, high energy density and good safety. However, due to the dissolution of iron and Mn and the immaturity of the material synthesis process, the cycle performance of the material is generally poor, which limits the current application scenarios of the material. SUMMARY

[0004] In the related art, in order to improve the cycle performance, the current mainstream method is to add lithium-rich lithium iron phosphate (LFO), which can improve the cycle performance of LMFP material, but the improvement is not large. According to experience, adding more than 2% of LFO material can effectively improve the cycle performance of LMFP material, but after adding more than 2% of LFO, the battery produces a lot of gas, and the negative electrode interface appears serious gas spots, resulting in less than expected cycle improvement effect.

[0005] The present application provides a cathode active material, a conductive paste and a secondary battery, which can improve the cycle performance of the battery and has good safety performance.

[0006] In a first aspect, an embodiment of the present application provides a cathode active material, comprising lithium manganese iron phosphate particles and lithium-rich manganese-based material particles, the chemical formula of the lithium-rich manganese-based material particles is yLi2MnO3·(1-y)LiMO2, wherein 0

[0007] The second aspect of the present application provides a conductive paste, comprising a conductive agent, a binder, a dispersant and the cathode active material.

[0008] The third aspect of the present application provides a secondary battery, comprising a negative electrode, a separator, an electrolyte and a positive electrode, the positive electrode comprises a current collector and a coating layer arranged on at least one side of the current collector, the coating layer comprises the cathode active material or the conductive paste. ADVANTAGEOUS EFFECTS

[0009] In the embodiments of the present application, by adding the lithium-rich manganese-based material particles into the lithium manganese iron phosphate particles, and limiting the proportion of Li2MnO3 phase in the lithium-rich manganese-based material to be less than 0.5, the cycle performance and stability performance of the secondary battery with the positive electrode active material are improved. Embodiments of the present application

[0010] The first aspect of the present application provides a positive electrode active material, which comprises uniformly distributed lithium manganese iron phosphate particles and lithium-rich manganese-based material particles, the mass percentage of the lithium-rich manganese-based material particles in the positive electrode active material is 1% to 50%; the chemical formula of the lithium-rich manganese-based material particles is yLi2MnO3·(1-y)LiMO2, wherein 0

[0011] It can be understood that the positive electrode active material is used to provide active lithium ions for the lithium ion battery, and the active lithium ions migrate between the positive electrode and the negative electrode of the battery, so as to realize the charging and discharging of the battery. Lithium manganese iron phosphate is a new generation of positive electrode material for lithium battery, which has a high working voltage, can greatly improve the energy density of the battery, and has high safety, but has the problem of unsatisfactory cycle performance. In the related art, in order to improve the cycle performance, the mainstream method at present is to add lithium-rich lithium iron phosphate (LFO material), so as to improve the cycle performance of lithium manganese iron phosphate (LMFP material), but the improvement is not large. According to experience, more than 2% of LFO material needs to be added to effectively improve the cycle performance of LMFP material, but after more than 2% of LFO is added, the battery produces a large amount of gas, and the interface of the negative electrode sheet appears serious gas spots, which leads to the cycle improvement effect not as expected.

[0012] In view of the above problems in the prior art, the inventors have found that the addition of lithium-rich manganese-based material particles to lithium iron manganese phosphate particles, and limiting the proportion of Li2MnO3 phase in the lithium-rich manganese-based material to less than 0.5, can improve the cycle performance and stability of a secondary battery having the positive electrode active material. It should be noted that the inventors have also found through experiments that the proportion of Li2MnO3 in the lithium-rich manganese-based material is one of the key factors affecting the cycle performance and stability of the secondary battery. When the proportion of Li2MnO3 phase in the lithium-rich manganese-based material is greater than 0.5, the phase change of the positive electrode active material is severe in the later cycle stage, and the cycle performance is actually reduced. When the proportion of Li2MnO3 phase in the lithium-rich manganese-based material is less than 0.5, the structure of the lithium-rich manganese-based material is more stable during the cycle process, thereby enabling the secondary battery to have better cycle performance and stability. Specifically, 0 < y ≤ 0.3; or, 0.2 ≤ y ≤ 0.4; or, 0.3 < y ≤ 0.5.

[0013] In some embodiments of the present application, the mass percentage of the lithium-rich manganese-based material particles in the positive electrode active material is 1% to 50%, i.e., the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 1% to 50%. For example, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 1% to 15%. For another example, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 15% to 30%. For yet another example, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 30% to 50%.

[0014] It can be understood that increasing the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material can increase the compaction density of the positive electrode material, which is beneficial to providing the volumetric energy density of the battery. For example, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 1% to 15%, and the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material can be specifically but not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%.

[0015] In some other embodiments of the present application, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 15% to 30%, and the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material can be specifically but not limited to 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 15%, 26%, 27%, 28%, 29%, 30%.

[0016] In some embodiments of the present application, the mass percentage of the lithium-rich manganese-based material particles to the positive active material is 30% to 50%, and specifically can be, but is not limited to, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%.

[0017] In some embodiments of the present application, the mass percentage of the lithium-rich manganese-based material particles in the positive active material is 30% to 40%, or 35% to 45%, or 40% to 50%.

[0018] In some embodiments of the present application, the particle size of the lithium iron manganese phosphate particles is smaller than that of the lithium-rich manganese-based material particles. This structure is conducive to further improving the compaction density of the positive active material. Specifically, the D50 ratio of the lithium iron manganese phosphate particles to the lithium-rich manganese-based material particles is 0.05 to 0.25. It can be understood that controlling the D50 ratio of the lithium iron manganese phosphate particles to the lithium-rich manganese-based material particles can achieve a good gradation of particles of different sizes, so that the lithium iron manganese phosphate particles and the lithium-rich manganese-based particles can be better stacked together, the voids between the particles are more uniform, and the cycle performance is the best. Specifically, the D50 ratio of the lithium iron manganese phosphate particles to the lithium-rich manganese-based material particles can be, but is not limited to, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, or 0.25.

[0019] Specifically, the D50 of the lithium iron manganese phosphate particles is 0.4 μm to 1.2 μm. It can be understood that if the particle size of the lithium iron manganese phosphate is too small, for example, less than 0.4 μm, it will cause problems in the process of slurry coating, and the coated pole piece may crack. If the particle size of the lithium iron manganese phosphate is too large, for example, greater than 1.2 μm, it cannot form an optimal stacking effect with the lithium-rich manganese-based particles, which can easily lead to undesirable battery performance.

[0020] Specifically, the specific surface area of the lithium iron manganese phosphate particles is 16 m 2 / g to 26 m 2 / g. It can be understood that if the specific surface area of the lithium iron manganese phosphate particles is too small, for example, less than 16 m 2 / g, it cannot form an optimal stacking effect with the lithium-rich manganese-based particles, which can affect the specific capacity. If the specific surface area is too large, the stability of the slurry is poor, and problems such as pole piece cracking occur in the coating process.

[0021] Specifically, the D50 of the lithium-rich manganese-based material particles is 4 μm ~ 10 μm. It can be understood that if the particle size of the lithium-rich manganese-based particles is too small, for example, less than 4 μm, the slurry coating process will be problematic, and the coated pole piece will crack. If the particle size of the lithium-rich manganese-based particles is too large, for example, greater than 10 μm, the optimal packing effect between the lithium-rich manganese-based particles and the lithium manganese iron phosphate particles cannot be formed, which can easily lead to undesirable battery performance.

[0022] Specifically, the specific surface area of the lithium-rich manganese-based material particles is 0.3 m 2 / g ~ 2 m 2 / g. It can be understood that if the specific surface area of the lithium-rich manganese-based material particles is too small, for example, less than 0.3 m 2 / g, the optimal packing effect between the lithium-rich manganese-based material particles and the lithium manganese iron phosphate particles cannot be formed, which can affect the capacity development. If the specific surface area of the lithium-rich manganese-based material particles is too large, for example, greater than 2 m 2 / g, the slurry stability is poor, and the coating process is problematic, such as pole piece cracking.

[0023] In some embodiments of the present application, the positive electrode active material is composed of the lithium manganese iron phosphate particles and the lithium-rich manganese-based material particles, that is, the positive electrode active material only includes the lithium manganese iron phosphate particles and the lithium-rich manganese-based material particles. This embodiment increases the content of the lithium manganese iron phosphate particles in the positive electrode active material, and a higher content of the lithium manganese iron phosphate particles can ensure that the positive electrode material has a higher working voltage and safety performance. In addition, the positive electrode active material only includes two components, which is conducive to simplifying the process flow and improving the preparation efficiency.

[0024] In some embodiments of the present application, the lithium manganese iron phosphate material includes one or more of materials with a chemical formula of Li a M b (PO4) c , wherein M is Fe 1-x-z Mn x D zwherein a, b, c represent the molar amount of Li, M and PO4 in the material, respectively, and 1-x-z, x, z represent the molar amount of Fe, Mn and metal element D in M, respectively. In the lithium manganese iron phosphate material, the ratio a / c of the molar amount of Li to the molar amount of P is 0.95-1.15, for example, it can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, and a value between any two of the above values; the ratio b / c of the molar amount of M to the molar amount of P is 0.90-1.15, for example, it can be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, and a value between any two of the above values; the ratio a / b of the molar amount of Li to the molar amount of M is 1.01-1.10, for example, it can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, and a value between any two of the above values. In some embodiments of the present application, in M, D is selected from one or more of Mg, Ti, V, Ni, Co, Al, Nb, Y, Mo, Sr, La, Zr. The lithium manganese iron phosphate can be prepared according to the preparation method of lithium manganese iron phosphate in the art, specifically, the corresponding ion sources (lithium source, iron source, manganese source, D source, phosphorus source) can be weighed according to the molar ratio of each element, mixed and calcined to obtain the lithium manganese iron phosphate.

[0025] It can be understood that the molar ratio of different elements in the lithium manganese iron phosphate material has a significant influence on the primary particle morphology, particle size and electrochemical performance of the material. If the molar amount of Li element is too low, the specific capacity of the material will decrease significantly; if the molar amount of Li element is too high, the sintering and fusion between particles will be inhibited, resulting in excessive refinement of the material, which affects the processing performance. In addition, appropriate element doping can improve the electronic conductivity and ion diffusion rate of the lithium manganese iron phosphate material. In this embodiment, a / c (i.e. Li / P) is 0.95-1.10, b / c (i.e. M / P) is 0.90-1.15, a / b (i.e. Li / M) = 1.01-1.10, and element doping can improve the conductivity of lithium iron phosphate.

[0026] The second aspect of the present application provides a conductive slurry, which comprises a conductive agent, a binder, a dispersant and the positive active material. Exemplarily, in the conductive slurry, the positive active material: the conductive agent: the binder: the dispersant is (96.7%~97.1%): (0.7%~1.1%): (1.8%~2.2%): (0.1%~0.3%) in terms of mass percentage.

[0027] The positive active material is used to provide active lithium ions for the lithium ion battery. It can be understood that if the proportion of the active material is too low, for example, less than 96.7%, the overall energy density of the battery is low, which affects the actual application effect; if the proportion of the active material is too high, for example, greater than 97.1%, the proportion of other components is reduced, which affects the processing performance and the rate performance of the battery.

[0028] The conductive agent is mainly used to provide conductivity for the positive electrode, which can improve the conductivity of the positive electrode.

[0029] The conductive agent is a conductive material known in the art that can be used in the positive active material layer. The conductive agent can be selected from any conductive material as long as it does not cause chemical changes. Exemplarily, the conductive agent is selected from one or more of carbon nanotubes, carbon black and graphene.

[0030] The binder is mainly used to firmly bond the positive active material, the conductive agent and the conductive substrate (such as the current collector). The material of the binder is not limited, and the binder is selected from one or more 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) and sodium alginate.

[0031] The dispersant is used to control the viscosity change of the positive slurry. Exemplarily, the dispersant is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol and polyester substances. It can be understood that if the proportion of the lithium-rich manganese-based material in the positive slurry is too high, the viscosity of the slurry will rise too fast, which is not convenient for use. The present application controls the viscosity change of the slurry by adding the dispersant, thereby avoiding the problem of too fast viscosity rise of the slurry.

[0032] Of course, in some other embodiments of the present application, the conductive slurry can also not include a dispersant. Exemplarily, the conductive slurry comprises a conductive agent, a binder and the positive active material; the positive active material: the conductive agent: the binder is (96.7%~97.1%): (0.7%~1.1%): (1.8%~2.2%) in terms of mass percentage.

[0033] It is understood that the positive electrode tab includes a current collector and a coating layer (also referred to as a positive electrode material layer) disposed on at least one surface of the current collector. The positive electrode material layer includes the conductive agent, the binder, the dispersing agent, and the positive electrode active material. In some embodiments, the material of the positive electrode current collector can be any commonly used conductive metal material in the art, including but not limited to aluminum foil, platinum foil, or palladium foil, without limitation.

[0034] Specifically, the preparation of the positive electrode material layer in the present application can be mixing the battery positive electrode material, the conductive agent, the binder, the dispersing agent, and the solvent to form a positive electrode slurry, and then coating and drying the positive electrode slurry to obtain the positive electrode material layer. When preparing the positive electrode slurry, the binder can be first mixed with the solvent, stirred thoroughly, and then the conductive agent and the dispersing agent are added, stirred, and then the battery positive electrode material is added, stirred, and then sieved to obtain the positive electrode slurry. It should be noted that the preparation process of the positive electrode slurry and the positive electrode material layer does not belong to the main improvement points of the present application, and is not limited herein.

[0035] In some embodiments of the present application, the compaction density of the conductive slurry is 2.1 g / cm 3 2.8 g / cm 3 .

[0036] In a third aspect, embodiments of the present application provide a secondary battery, which includes a negative electrode, a separator, an electrolyte, and a positive electrode, the positive electrode including a current collector and a coating layer disposed on at least one side of the current collector. It should be noted that the secondary battery includes but is not limited to a button cell, a soft pack battery, a square lithium ion battery, a cylindrical lithium ion battery, and the like. The secondary battery includes the positive electrode active material or the conductive slurry as described in any of the preceding embodiments.

[0037] In the present application, the negative electrode of the secondary battery can be any negative electrode known in the art. In embodiments of the present application, the negative electrode can include one or more of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The carbon-based negative electrode can include graphite, hard carbon, soft carbon, graphene, etc.; the silicon-based negative electrode can include silicon, silicon-carbon, silicon-oxygen, silicon-metal compounds, or a mixture of such silicon-containing materials and non-silicon-containing materials such as graphite; the tin-based negative electrode can include tin, tin-carbon, tin-oxygen, tin-metal compounds, or a mixture of such tin-containing materials and non-tin-containing materials such as graphite; and the lithium negative electrode can include metallic lithium or lithium alloys. The lithium alloy can be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. In some embodiments of the present application, the current collector of the negative electrode is copper foil, the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon, silicon suboxide, tin and its oxides, and antimony and its oxides; the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR); and the conductive agent includes one or more of acetylene black, ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon, and graphene. In the present application, the negative electrode can be prepared by any method known in the art.

[0038] In the present application, the separator of the secondary battery can be any separator known to those skilled in the art, for example, the separator can be one or more of polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass fiber felt, or ultra-fine glass fiber paper.

[0039] In the present application, the electrolyte solution of the secondary battery includes a solution of an electrolyte lithium salt in a nonaqueous solvent. In the present application, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorosilicate (Li2SiF6), lithium tetraphenylborate (LiB(C6H5)4), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl4), lithium fluorocarbon sulfonate (LiC(SO2CF3)3), LiCH3SO3, LiN(SO2CF3)2, and LiN(SO2C2F5)2. In some embodiments of the present application, the nonaqueous solvent includes one or more of a chain acid ester and a cyclic acid ester. In some embodiments of the present application, the chain acid ester includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), and dipropyl carbonate (DPC). In some embodiments of the present application, the chain acid ester includes a chain organic ester containing fluorine, sulfur, or an unsaturated bond. In some embodiments of the present application, the cyclic acid ester includes one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), and a sulfolactone. In some embodiments of the present application, the cyclic acid ester includes a cyclic organic ester containing fluorine, sulfur, or an unsaturated bond. In some embodiments of the present application, the nonaqueous solvent includes one or more of a chain ether and a cyclic ether solution. In some embodiments of the present application, the cyclic ether includes one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), and 4-methyl-1,3-dioxolane (4-MeDOL). In some embodiments of the present application, the cyclic ether includes a cyclic organic ether containing fluorine, sulfur, or an unsaturated bond. In some embodiments of the present application, the chain ether includes one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), and diethylene glycol dimethyl ether (DG). In some embodiments of the present application, the chain ether includes a chain organic ether containing fluorine, sulfur, or an unsaturated bond. In the present application, the concentration of the electrolyte lithium salt in the electrolyte solution is 0.1 mol / L to 15 mol / L. In some embodiments of the present application, the concentration of the electrolyte lithium salt is 1 mol / L to 10 mol / L.

[0040] The technical solutions and technical effects of the present application are described in detail below through specific examples. The following examples are only some of the examples of the present application, and do not specifically limit the present application.

[0041] Example 1

[0042] lithium manganese iron phosphate and lithium-rich manganese-based material are added into a mixer for mixing, wherein the lithium manganese iron phosphate has a chemical formula of Li 1.05 Mn 0.6 Fe 0.4 PO4, D50 is 0.8 μm, and specific surface area is 21 m 2 / g; the lithium-rich manganese-based material has a chemical formula of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2, material D50 is 7 μm, and specific surface area is 1 m 2 / g, and the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 10%, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain a battery positive electrode active material.

[0043] A slurry is prepared according to a mass ratio of battery positive electrode active material: conductive agent: binder: dispersant of 96.9:0.9:2.0:0.2 in N-methyl pyrrolidone, wherein the conductive agent is carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and drying and pressing are performed to obtain a positive electrode sheet, and the compaction density is 2.3 g / cm 3 , and an electric core is prepared by using the prepared positive electrode sheet, a separator, and a negative electrode sheet, and the electric core is packaged, liquid injected, and capacity distributed to prepare a battery.

[0044] Example 2

[0045] lithium manganese iron phosphate and lithium-rich manganese-based material are added into a mixer for mixing, wherein the lithium manganese iron phosphate has a chemical formula of Li 1.05 Mn 0.6 Fe 0.4 PO4, D50 is 0.8 μm, and specific surface area is 21 m 2 / g; the lithium-rich manganese-based material has a chemical formula of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2, material D50 is 7 μm, and specific surface area is 1 m 2 / g, and the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 20%, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain a battery positive electrode active material.

[0046] A slurry is prepared according to a mass ratio of battery positive electrode active material: conductive agent: binder: dispersant of 96.9:0.9:2.0:0.2 in N-methyl pyrrolidone, wherein the conductive agent is carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and drying and pressing are performed to obtain a positive electrode sheet, and the compaction density is 2.3 g / cm 3The prepared positive electrode sheet, a separator, and a negative electrode sheet are used to prepare a battery cell, and the battery cell is packaged, injected with electrolyte, and tested for capacity to prepare a battery.

[0047] Example 3

[0048] Lithium manganese iron phosphate and a lithium-rich manganese-based material are mixed in a mixer, wherein the lithium manganese iron phosphate has a chemical formula of Li 1.05 Mn 0.6 Fe 0.4 PO4, a D50 of 0.8 μm, and a specific surface area of 21 m 2 / g; the lithium-rich manganese-based material has a chemical formula of 0.3Li2MnO3·0.7Li Ni 0.5 Mn 0.5 O2, a material D50 of 7 μm, and a specific surface area of 1 m 2 / g, and the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 30%, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain a battery positive electrode active material.

[0049] A slurry is prepared by dispersing a battery positive electrode active material, a conductive agent, a binder, and a dispersant in N-methyl pyrrolidone at a mass ratio of 96.9:0.9:2.0:0.2, wherein the conductive agent is a carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and drying and pressing are performed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 The prepared positive electrode sheet, a separator, and a negative electrode sheet are used to prepare a battery cell, and the battery cell is packaged, injected with electrolyte, and tested for capacity to prepare a battery.

[0050] Example 4

[0051] Lithium manganese iron phosphate and a lithium-rich manganese-based material are mixed in a mixer, wherein the lithium manganese iron phosphate has a chemical formula of Li 1.05 Mn 0.6 Fe 0.4 PO4, a D50 of 0.8 μm, and a specific surface area of 21 m 2 / g; the lithium-rich manganese-based material has a chemical formula of 0.3Li2MnO3·0.7Li Ni 0.5 Mn 0.5 O2, a material D50 of 7 μm, and a specific surface area of 1 m 2 / g, and the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 40%, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain a battery positive electrode active material.

[0052] A slurry was prepared by dispersing battery cathode active material: conductive agent: binder: dispersant in a mass ratio of 96.9: 0.9: 2.0: 0.2 in N-methyl pyrrolidone, wherein the conductive agent is carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry was coated on the surface of a carbon-coated aluminum foil, and then dried and pressed to obtain a cathode electrode sheet, and the compaction density was 2.3 g / cm 3 The prepared cathode electrode sheet, a separator, and an anode electrode sheet were used to prepare a battery cell, and the battery cell was packaged, injected with electrolyte, and subjected to capacity distribution to obtain a battery.

[0053] Example 5

[0054] Lithium manganese iron phosphate and a lithium-rich manganese-based material were mixed in a mixer, wherein the chemical formula of the lithium manganese iron phosphate was Li 1.05 Mn 0.6 Fe 0.4 PO4, the D50 was 0.8 μm, and the specific surface area was 21 m 2 / g; the chemical formula of the lithium-rich manganese-based material was 0.3Li2MnO3·0.7Li Ni 0.5 Mn 0.5 O2, the material D50 was 7 μm, and the specific surface area was 1 m 2 / g, and the mass percentage of the lithium-rich manganese-based material particles to the cathode active material was 50%, and mechanical mixing was performed at a speed of 35 rpm for 6 h to obtain a battery cathode active material.

[0055] A slurry was prepared by dispersing battery cathode active material: conductive agent: binder: dispersant in a mass ratio of 96.9: 0.9: 2.0: 0.2 in N-methyl pyrrolidone, wherein the conductive agent is carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry was coated on the surface of a carbon-coated aluminum foil, and then dried and pressed to obtain a cathode electrode sheet, and the compaction density was 2.3 g / cm 3 The prepared cathode electrode sheet, a separator, and an anode electrode sheet were used to prepare a battery cell, and the battery cell was packaged, injected with electrolyte, and subjected to capacity distribution to obtain a battery.

[0056] Example 6

[0057] Lithium manganese iron phosphate and a lithium-rich manganese-based material were mixed in a mixer, wherein the chemical formula of the lithium manganese iron phosphate was Li 1.05 Mn 0.6 Fe 0.4 PO4, the D50 was 0.8 μm, and the specific surface area was 21 m 2 / g; the chemical formula of the lithium-rich manganese-based material was 0.3Li2MnO3·0.7Li Ni 0.5 Mn 0.5 O2, the material D50 was 7 μm, and the specific surface area was 1 m2 / g, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 30%, mechanically mixed at a speed of 35 rpm for 6 h to obtain a battery positive electrode active material.

[0058] A slurry is prepared by dispersing the battery positive electrode active material, the conductive agent, the binder and the dispersant in N-methyl pyrrolidone at a mass ratio of 96.9:0.9:2.0:0.2, wherein the conductive agent is carbon nanotubes, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and then dried and pressed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 The positive electrode sheet obtained is combined with a separator and a negative electrode sheet to obtain an electric core, and the electric core is packaged, injected with electrolyte, and subjected to capacity distribution to obtain a battery.

[0059] Example 7

[0060] Lithium manganese iron phosphate and lithium-rich manganese-based material are mixed in a mixer, wherein the chemical formula of the lithium manganese iron phosphate is Li 1.05 Mn 0.6 Fe 0.4 PO4, the D50 is 0.8 μm, and the specific surface area is 21 m 2 / g; the chemical formula of the lithium-rich manganese-based material is 0.2Li2MnO3·0.8LiNi 0.5 Mn 0.5 O2, the material D50 is 7 μm, and the specific surface area is 1 m 2 / g, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 30%, mechanically mixed at a speed of 35 rpm for 6 h to obtain a battery positive electrode active material.

[0061] A slurry is prepared by dispersing the battery positive electrode active material, the conductive agent, the binder and the dispersant in N-methyl pyrrolidone at a mass ratio of 96.9:0.9:2.0:0.2, wherein the conductive agent is carbon nanotubes, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and then dried and pressed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 The positive electrode sheet obtained is combined with a separator and a negative electrode sheet to obtain an electric core, and the electric core is packaged, injected with electrolyte, and subjected to capacity distribution to obtain a battery.

[0062] Example 8

[0063] Lithium manganese iron phosphate and lithium-rich manganese-based material are mixed in a mixer, wherein the chemical formula of the lithium manganese iron phosphate is Li 1.05 Mn 0.6 Fe 0.4 PO4, the D50 is 0.8 μm, and the specific surface area is 21 m2 / g; the chemical formula of the lithium-rich manganese-based material is 0.4Li2MnO3·0.6LiNi 0.5 Mn 0.5 O2, the material D50 is 7 μm, and the specific surface area is 1 m 2 / g, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 30%, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain the battery positive electrode active material.

[0064] A slurry is prepared by dispersing the battery positive electrode active material, the conductive agent, the binder, and the dispersant in N-methyl pyrrolidone at a mass ratio of 96.9:0.9:2.0:0.2, wherein the conductive agent is a carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and drying and pressing are performed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 The positive electrode sheet obtained is combined with a separator and a negative electrode sheet to obtain an electric core, and the electric core is packaged, injected with electrolyte, and subjected to capacity distribution to obtain a battery.

[0065] Comparative Example 1

[0066] Manganese iron lithium phosphate is added to a mixer and mixed, wherein the chemical formula of the manganese iron lithium phosphate is Li 1.05 Mn 0.6 Fe 0.4 PO4, the D50 is 0.8 μm, and the specific surface area is 21 m 2 / g, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain the battery positive electrode active material.

[0067] A slurry is prepared by dispersing the battery positive electrode active material, the conductive agent, the binder, and the dispersant in N-methyl pyrrolidone at a mass ratio of 96.9:0.9:2.0:0.2, wherein the conductive agent is a carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and drying and pressing are performed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 The positive electrode sheet obtained is combined with a separator and a negative electrode sheet to obtain an electric core, and the electric core is packaged, injected with electrolyte, and subjected to capacity distribution to obtain a battery.

[0068] Comparative Example 2

[0069] Manganese iron lithium phosphate and a lithium-rich manganese-based material are added to a mixer and mixed, wherein the chemical formula of the manganese iron lithium phosphate is Li 1.05 Mn 0.6 Fe 0.4 PO4, the D50 is 0.8 μm, and the specific surface area is 21 m 2 / g; the chemical formula of the lithium-rich manganese-based material is 0.8Li2MnO3·0.2LiMnO2, the material D50 is 7 μm, and the specific surface area is 1 m 2 / g, the mass percentage of the lithium-rich manganese-based material particles to the positive electrode active material is 30%, and mechanical mixing is performed at a speed of 35 rpm for 6 h to obtain the battery positive electrode active material.

[0070] A slurry is prepared by dispersing the battery positive electrode active material, the conductive agent, the binder, and the dispersant in N-methyl pyrrolidone at a mass ratio of 96.9:0.9:2.0:0.2, wherein the conductive agent is a carbon nanotube, the binder is polyvinylidene fluoride, and the dispersant is polyvinylpyrrolidone, and the solid content of the slurry is 60%. The slurry is coated on the surface of a carbon-coated aluminum foil, and drying and pressing are performed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.3 g / cm 3 The prepared positive electrode sheet, a separator, and a negative electrode sheet are used to prepare a battery cell, and the battery cell is packaged, liquid injected, and capacity distributed to prepare a battery.

[0071] The batteries of Examples 1 to 8 and Comparative Examples 1 and 2 are subjected to electrochemical performance testing, and the test results are shown in Table 1.

[0072] 25℃ cycle number: in a 25℃ constant temperature box, 1) stand for 30 min; 2) 1C constant current and constant voltage charging to 4.2V, and the cutoff current is 0.05C; 3) stand for 30 min; 4) 1C constant current discharging to 2.5V; 5) repeat steps 1) to 4) until the capacity retention rate is 80%, and the cycle number is recorded.

[0073] EOL positive electrode sheet discharge gram capacity / BOL positive electrode sheet discharge gram capacity test: the positive electrode sheet of an EOL battery (cycle capacity retention rate is 80%) and the positive electrode sheet of a BOL battery (new battery) are taken respectively, the coating layer on one side of the positive electrode sheet is wiped off with NMP respectively, and then the positive electrode sheets are assembled into button cells respectively, and the 25℃ 0.1C gram capacity of each button cell is tested, and the ratio of the two is the test result.

[0074] Table 1

[0075] Experimental group 25℃ cycle number EOL positive electrode sheet discharge gram capacity / BOL positive electrode sheet discharge gram capacity Example 1 700 97.5% Example 2 1000 97.3% Example 3 3500 97.6% Example 4 3900 98.1% Example 5 4300 97.4% Example 6 3300 96.8% Example 7 3400 96.9% Example 8 3600 97.4% Comparative Example 1 2300 97.0% Comparative Example 2 2500 92.1%

[0076] As can be seen from Examples 1 to 8 and Comparative Example 1, the addition of 10% to 50% of the lithium-rich manganese-based material to the lithium manganese iron phosphate-based positive electrode active material can significantly improve the cycle performance of the secondary battery, and at the same time, the secondary battery has good stability. As can be seen from Examples 3, 6 to 8, with the increase of the content of Li2MnO3 (i.e. the increase of the value of y) in the lithium-rich manganese-based material, the cycle performance of the secondary battery increases, but the stability of the secondary battery first increases and then decreases. As can be seen from Examples 1 to 5 and Comparative Example 2, with the increase of the lithium-rich manganese-based material in the positive electrode active material, the cycle performance of the secondary battery increases, but the stability of the secondary battery first increases and then decreases. When the mass ratio of the lithium-rich manganese-based material to the positive electrode active material is between 30% and 50%, and the value of y is between 0.1 and 0.4, the cycle performance and stability of the secondary battery prepared therefrom are more excellent.

[0077] The above has described the embodiments of the present application in detail, and the principles and implementation manners of the present application have been described by applying specific examples. The above description of the embodiments is only used to help understand the method of the present application and its core idea; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges can be changed, and the above description of the content of the present application should not be understood as a limitation of the present application.

Claims

1. A positive electrode active material, wherein, The positive electrode active material comprises lithium iron manganese phosphate particles and lithium-rich manganese-based material particles, the chemical formula of the lithium-rich manganese-based material particles is yLi2MnO3·(1-y)LiMO2, wherein 0 2. The positive electrode active material according to claim 1, wherein The mass percentage of the lithium-rich manganese-based material particles in the positive electrode active material is 1% to 50%.

3. The positive electrode active material according to claim 2, wherein The mass percentage of the lithium-rich manganese-based material particles in the positive electrode active material is 1% to 10%, or 10% to 30%, or 30% to 50%.

4. The positive electrode active material according to claim 2, wherein The mass percentage of the lithium-rich manganese-based material particles in the positive electrode active material is 30% to 40%, or 35% to 45%, or 40% to 50%.

5. The positive electrode active material according to claim 1, wherein 0＜y≤0.3。 6. The positive electrode active material according to claim 1, wherein 0.2≤y≤0.4。 7. The positive electrode active material according to claim 1, wherein 0.3＜y≤0.5。 8. The positive electrode active material according to claim 1, wherein The particle size of the lithium iron manganese phosphate particles is smaller than that of the lithium-rich manganese-based material particles.

9. The positive electrode active material according to claim 1, wherein The D50 ratio of the lithium iron manganese phosphate particles to the lithium-rich manganese-based material particles is 0.05 to 0.

25.

10. The positive electrode active material according to claim 1, wherein The D50 of the lithium iron manganese phosphate particles is 0.4 μm to 1.2 μm.

11. The positive electrode active material according to claim 1, wherein The specific surface area of the lithium manganese iron phosphate particles is 16 m 2 / g ~ 26 m 2 / g.

12. The positive electrode active material according to claim 1, wherein The D50 of the lithium-rich manganese-based material particles is 4 μm to 10 μm.

13. The positive electrode active material according to claim 1, wherein The specific surface area of the lithium-rich manganese-based material particles is 0.3 m 2 / g ~ 2 m 2 / g.

14. The positive electrode active material according to claim 1, wherein The positive electrode active material is composed of the lithium iron manganese phosphate particles and the lithium-rich manganese-based material particles.

15. The positive electrode active material according to claim 1, wherein The chemical formula of the lithium manganese iron phosphate material is Li a M b (PO4) c ; wherein the chemical formula of M is Fe 1-x-z Mn x D z , and a / c is 0.95-1.15, b / c is 0.90-1.15, a / b is 1.01-1.10, and D is one or more of Mg, Ti, V, Ni, Co, Al, Nb, Y, Mo, Sr, La, Zr, B, and the like.

16. An electroconductive paste, wherein, The positive electrode active material comprises a conductive agent, a binder, and the positive electrode active material according to any one of claims 1 to 5.

17. The conductive paste of claim 16, wherein, The conductive slurry further comprises a dispersant, and the mass percentage of the dispersant in the conductive slurry is 0.1% to 0.3%. And / or, the conductive slurry further comprises a dispersant, and the dispersant is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, and polyester substances.

18. The conductive paste of claim 16, wherein, The mass percentage of the positive electrode active material in the conductive slurry is 96.7% to 97.1%. And / or, the mass percentage of the conductive agent in the conductive slurry is 0.7% to 1.1%. And / or, the mass percentage of the binder in the conductive slurry is 1.8% to 2.2%.

19. The conductive paste of claim 16, wherein, The conductive agent is selected from one or more of carbon nanotubes, carbon black, and graphene. And / or, the binder is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, butadiene-styrene rubber, polyacrylonitrile, polyimide, polyacrylic acid, polyacrylate, polyolefin, sodium carboxymethyl cellulose, and sodium alginate. and / or the green density of the conductive paste is 2.1 g / cm 3 2.8 g / cm 3 .

20. A secondary battery wherein, The secondary battery comprises a negative electrode, a separator, an electrolyte, and a positive electrode, the positive electrode comprises a current collector and a coating layer arranged on at least one side of the current collector, and the coating layer comprises the positive electrode active material according to any one of claims 1 to 15 or the conductive slurry according to any one of claims 16 to 19.