Cathode material layer, cathode and lithium-ion battery

Abstract

The present invention discloses a positive electrode material layer, a positive electrode, and a lithium-ion battery. The positive electrode material layer comprises a ternary material layer, a lithium iron manganese phosphate layer, and an aqueous polyurethane-based solid electrolyte layer disposed sequentially away from the active material layer. The positive electrode material layer of the present invention, when applied to a lithium-ion battery, can improve safety while maintaining high energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, in particular to a positive electrode material layer, a positive electrode and a lithium ion battery. Background Art

[0002] In today's society, lithium-ion batteries have gradually become the most important mobile energy source due to their good cycle performance and environmental friendliness. Correspondingly, the safety and energy density of lithium-ion batteries are also receiving increasing attention.

[0003] CN107431234A discloses a battery with high safety and high energy density, comprising a positive electrode, a negative electrode, an electrolyte, and a separator arranged between the positive electrode and the negative electrode, wherein the positive electrode has a 3 mAh / cm 2 The negative electrode comprises a metal and / or metal oxide and carbon as the negative electrode active material, the amount of lithium that can be accepted by the carbon in the negative electrode is less than the amount of lithium that can be released from the positive electrode, and the separator has a thermal contraction coefficient of less than 3% in the electrolyte at the boiling point of the electrolyte. By using a large amount of metal material in the negative electrode active material to increase energy density, this addresses safety concerns when the amount of lithium that can be accepted by the negative electrode carbon material is less than the amount of lithium that can be released by the positive electrode active material.

[0004] CN209515896U discloses a lithium-ion secondary battery, comprising a housing, and a positive electrode active layer, a negative electrode active layer, a separator, a positive electrode side current collector, and an electrolyte layer disposed inside the housing; the positive electrode active layer and the negative electrode active layer are perpendicular to each other; the separator is disposed inside the positive electrode active layer and parallel to the positive electrode active layer; the positive electrode side current collector is disposed outside the positive electrode active layer (1) and parallel to the positive electrode active layer; and the electrolyte layer is disposed between the housing and the positive electrode active layer, the negative electrode active layer, and the separator. Because lithium is used as the negative electrode and the growth direction of lithium dendrites is not directly opposite to the separator, the patent improves the safety of the lithium-ion secondary battery while increasing the energy density.

[0005] However, the side reactions between the positive electrode material and the electrolyte will greatly affect the battery performance, and the safety characteristics of lithium batteries are still an urgent problem that needs to be solved in lithium-ion batteries. Summary of the Invention

[0006] The present invention aims to provide a positive electrode material layer, a positive electrode and a lithium ion battery. The positive electrode material layer of the present invention is applied to a lithium ion battery, which can improve safety performance while ensuring high energy density.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention aims to provide a positive electrode material layer, characterized in that the positive electrode material layer includes an active material layer, and a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer are sequentially arranged in a direction away from the active material layer.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0010] Preferably, the aqueous polyurethane-based solid electrolyte layer accounts for 5-15% of the total thickness of the positive electrode material layer, preferably 7-12%.

[0011] Preferably, the ionic conductivity of the aqueous polyurethane-based solid electrolyte layer is (6.0-7.0)×10 -5 S cm -1 , preferably 6.6×10 -5 S cm -1 .

[0012] Preferably, the aqueous polyurethane-based solid electrolyte layer comprises non-ionic aqueous polyurethane and lithium salt.

[0013] As an embodiment, the lithium salt content in the aqueous polyurethane-based solid electrolyte layer is 10-60 wt.%; it is understandable that there is no special requirement for the lithium salt content, and it is known in the art to adjust the ionic conductivity of the solid electrolyte layer by the lithium salt content.

[0014] Preferably, the active material layer accounts for 60-80% of the total thickness of the positive electrode material layer, for example, 60%, 65%, 72%, 74%, 75%, 77%, 78% or 80%.

[0015] Preferably, the active material layer includes a positive electrode active material.

[0016] Preferably, the active material layer includes a first binder and a first conductive material.

[0017] Preferably, the lithium manganese iron phosphate layer accounts for 10-30% of the total thickness of the positive electrode material layer, for example, 10%, 15%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28% or 30%, etc.

[0018] Preferably, the lithium manganese iron phosphate layer includes lithium manganese iron phosphate.

[0019] Preferably, the chemical formula of the lithium manganese iron phosphate positive electrode material is LiMn x Fe 1-xPO4, wherein x is 0.4-0.6, such as 0.4, 0.45, 0.5, 0.55 or 0.6, etc.

[0020] Preferably, the lithium manganese iron phosphate layer further includes a second binder and a second conductive material, and the second conductive material includes at least one of single-walled carbon nanotubes and VGCF.

[0021] As a preferred technical solution of the method of the present invention, an oily polymer solid electrolyte layer is further provided between the active material layer and the lithium manganese iron phosphate layer.

[0022] The use of an oily polymer solid electrolyte on the surface between the active material layer and the lithium manganese iron phosphate layer can improve the cycle performance of the battery. At the same time, it also solves the moisture process control problem of setting a polymer solid electrolyte layer on the surface of the ternary material and improves the process efficiency.

[0023] Preferably, the oily polymer solid electrolyte layer accounts for 5-15% of the total thickness of the positive electrode material layer.

[0024] Preferably, the ionic conductivity of the oily polymer-based solid electrolyte layer is lower than the ionic conductivity of the aqueous polyurethane-based solid electrolyte layer.

[0025] Preferably, the ionic conductivity of the oily polymer solid electrolyte layer is (5.0-6.0)×10 -5 S cm -1 , preferably 5.6×10 -5 S cm -1 .

[0026] Preferably, the oily polymer solid electrolyte layer comprises a polymer and a lithium salt.

[0027] Preferably, the polymer in the oily polymer-type solid electrolyte includes at least one of PEO and PEG.

[0028] In a second aspect, the present invention provides a positive electrode, comprising a current collector and a positive electrode material layer as described in the first aspect disposed on a surface of the current collector, wherein the active material layer is close to a side of the current collector.

[0029] In a third aspect, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the positive electrode material layer described in the first aspect, or the positive electrode of the lithium-ion battery adopts the positive electrode described in the second aspect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] In the present invention, the battery can be guaranteed to have high energy density and safety performance through the coordination of the positive electrode active material layer, the lithium manganese iron phosphate layer and the aqueous polyurethane-based solid electrolyte layer.

[0032] Furthermore, an oily polymer solid electrolyte layer is provided between the ternary material layer and the lithium manganese iron phosphate layer, which further improves the safety and electrochemical performance of the battery. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0034] In one embodiment, the present invention provides a positive electrode material layer, which includes a positive electrode active material layer, a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer arranged in sequence in a direction away from the positive electrode active material layer.

[0035] Lithium iron manganese phosphate (LMP) is a new phosphate-based cathode material for lithium-ion batteries, formed by doping LMP with a certain proportion of manganese (Mn). The addition of manganese effectively combines the advantages of both iron and manganese. Furthermore, manganese and iron are both located in adjacent groups in the fourth period of the periodic table, sharing similar ionic radii and some chemical properties, so doping does not significantly affect the original structure. Compared to LMP, the high voltage characteristics of manganese give LMP a higher voltage platform, resulting in a higher energy density at the same specific capacity—10%-20% higher than LMP under the same conditions.

[0036] In one embodiment of the present invention, the combination of a positive electrode active material layer, a lithium iron manganese phosphate layer, and an aqueous polyurethane-based solid electrolyte layer can ensure that the battery has high energy density and safety performance. The positive electrode active material layer is beneficial for improving the energy density of the battery; the lithium iron manganese phosphate layer has good safety performance and a higher energy density than lithium iron phosphate. As a positive electrode coating, it not only provides partial capacity to the battery cell, but also improves safety compared to pure ternary battery cells. Polyurethane has a unique soft and hard segment structure, and its molecules are highly designable, allowing it to be prepared into materials with different mechanical properties according to application requirements. The soft segment of polyurethane can dissolve a large amount of lithium salts and has good flexibility, which can provide excellent ion conductivity. At the same time, the presence of a large number of hydrogen bonding groups in the aqueous polyurethane provides the polymer electrolyte with good mechanical properties. The aqueous polyurethane-based solid polymer electrolyte layer exhibits good mechanical strength and thermal stability, further improving the safety performance of the battery cell. Furthermore, polyurethane is water-soluble, and lithium iron manganese phosphate is not sensitive to moisture. A water-based polyurethane-based solid electrolyte layer can be formed on the surface of lithium iron manganese phosphate by a simple method, and the preparation process is excellent in environmental friendliness.

[0037] In one embodiment, the aqueous polyurethane-based solid electrolyte layer accounts for 5-15% of the total thickness of the positive electrode material layer, such as 5%, 6%, 7%, 8%, 10%, 12%, 13% or 15%, etc., preferably 7-12%.

[0038] In one embodiment, the ionic conductivity of the aqueous polyurethane-based solid electrolyte layer is (6.0-7.0)×10 -5 S cm -1 , for example 6.2×10 -5 S cm -1 , 6.5×10 -5 S cm -1 , 6.8×10 -5 S cm -1 or 6.6×10 -5 S cm -1 etc., preferably 6.6×10 -5 S cm -1 .

[0039] In one embodiment, the aqueous polyurethane-based solid electrolyte layer includes non-ionic aqueous polyurethane and a lithium salt.

[0040] In one embodiment, there is no particular limitation on the type of lithium salt in the aqueous polyurethane-based solid electrolyte layer. Without violating the inventive concept of the present application, any known type of lithium salt can be used in the present application. It is only used as an illustrative example, not a limitation on the scope of protection. The lithium salt in the aqueous polyurethane-based solid electrolyte layer includes lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiBF2(C2O4))(LiODFB), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalato)borate (LiB(C2O4)2)(LiBOB), lithium tetrafluorooxalatophosphate (LiPF4(C2O4))(LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl imide) (LITFSI)(LiN(CF3SO2)2), lithium bis(fluorosulfonyl imide) (LiN(FSO2)2)(LIFSI) and combinations thereof. In certain variations, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI)(LiN(CF3SO2)2), lithium bis(fluorosulfonyl imide) (LiN(FSO2)2)(LiFSI), lithium fluoroalkyl phosphonate (LiFAP), lithium phosphate (Li3PO4), and combinations thereof.

[0041] In one embodiment, the lithium salt content in the aqueous polyurethane-based solid electrolyte layer is 10-60 wt.%, for example, 10 wt.%, 15 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, or 60 wt.%, etc. It will be appreciated that there is no particular requirement for the lithium salt content, and adjusting the ionic conductivity of the solid electrolyte layer by the lithium salt content is well known in the art.

[0042] In one embodiment, the positive electrode active material layer accounts for 70-80% of the total thickness of the positive electrode material layer, such as 70%, 72%, 74%, 75%, 77%, 78% or 80%.

[0043] In one embodiment, the active material layer includes a positive electrode active material, and the positive electrode active material is selected from LiM x K y N 1-x-y O2(0≤x≤1,0≤y≤1), Li 1-z Na z Ni x Coy Mn 1-x-y O2(0≤x≤1, 0≤y≤1, 0≤z≤1), Li2Ru 1-y Mn y O3(0≤y≤1),xLi2MnO3·(1-x)LiMO2(0≤x≤0.5),LiMXO4,Li x S(0≤x≤8), M x V2O5(0≤x≤1), MoO 3-x (0≤x≤2) and MS x O y At least one of (0≤x≤2, 0≤y≤2). x K y N 1-x-y In O2, M, K, and N are not independently selected from one of Fe, Mn, Ni, Co, V, Ti, Cu, Zn, Y, Zr, Nb, Mo, Te, Ru, Rh, Sb, Ag, Cd, La, Ta, W, Pt, Au, or Cr. "Not independently selected" means that M, K, and N are different. If M is selected from one element, K and N can only be selected from the remaining elements. In xLi2MnO3·(1-x)LiMO2, M is Ni, Mn, or Co. In LiMXO4, M is Fe, Mn, Ni, Co, V, Ti, or Cr, and X is Si, P, or S. M x In V2O5, M is Ag, Ni or Cu. x O y In the above formula, M is Mo, Fe or W.

[0044] In one embodiment, the positive electrode active material layer further includes a first binder and / or a first conductive material.

[0045] The first binder is used to bond the positive electrode active material, the first conductive material and the current collector together. Specifically, it can include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber and fluororubber, preferably polyvinylidene fluoride.

[0046] In one embodiment, the amount of the positive electrode binder contained in the positive electrode active material layer can be 1wt%-20wt%, for example, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%, 12.5wt%, 15wt%, 16wt%, 18wt% or 20wt%, etc., preferably 1.2wt% to 10wt%.

[0047] The first conductive material is primarily used to assist and improve the conductivity of the secondary battery and is not particularly limited, as long as it is conductive and does not cause chemical changes. Specifically, the first conductive material can include graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives. Carbon black is preferably included for improved conductivity.

[0048] In one embodiment, the amount of the first conductive material included in the positive electrode active material layer can be 1wt%-20wt%, for example, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%, 12.5wt%, 15wt%, 16wt%, 18wt% or 20wt%, etc., preferably 1.2wt%-10wt%.

[0049] In one embodiment, the lithium manganese iron phosphate layer accounts for 10-30% of the total thickness of the positive electrode material layer, such as 10%, 15%, 20%, 26%, 27%, 28% or 30%.

[0050] In one embodiment, the lithium manganese iron phosphate layer includes lithium manganese iron phosphate.

[0051] In one embodiment, the chemical formula of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, wherein x is 0.4-0.6, such as 0.4, 0.45, 0.5, 0.55 or 0.6, etc.

[0052] In one embodiment, the lithium iron phosphate layer further includes a second binder and a second conductive agent.

[0053] The second binder is used to bond the components such as the lithium manganese iron phosphate positive electrode material, the second conductive material and the current collector together. Specifically, it can include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber and fluororubber, preferably polyvinylidene fluoride.

[0054] In one embodiment, the amount of the positive electrode binder contained in the lithium manganese iron phosphate layer can be 1wt%-20wt%, for example, 1wt%, 3wt%, 5wt%, 7wt%, 10wt%, 12.5wt%, 15wt%, 16wt%, 18wt% or 20wt%, etc., preferably 1.2wt% to 10wt%.

[0055] In one embodiment, the second conductive material includes at least one of single-walled carbon nanotubes and VGCF.

[0056] In one embodiment, the amount of the second conductive material included in the positive electrode active material layer may be 1 wt % to 5 wt %, for example, 1 wt %, 3 wt %, or 5 wt %.

[0057] In one embodiment, the positive electrode active material layer is obtained by coating a positive electrode slurry comprising a positive electrode active material and optionally a first binder, a first conductive material, and a solvent, followed by drying and roll pressing.

[0058] In one embodiment, the solvent for forming the positive electrode slurry may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and the amount used may be such that a preferred viscosity is obtained when the positive electrode active material is included and optionally a first binder, a first conductive material, etc. For example, the amount of the positive electrode slurry-forming solvent included in the positive electrode slurry may be such that the concentration of the solids containing the positive electrode active material and optionally a positive electrode binder and a first conductive material is 50 wt% to 95 wt%, such as 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt% or 95 wt%, etc., preferably 70 wt% to 90 wt%.

[0059] In one embodiment, an oily polymer solid electrolyte layer is further provided between the active material layer and the lithium manganese iron phosphate layer.

[0060] In one embodiment, the oily polymer solid electrolyte layer accounts for 5-15% of the total thickness of the positive electrode material layer, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc.

[0061] In one embodiment, the ionic conductivity of the oily polymer-based solid electrolyte layer is lower than the ionic conductivity of the aqueous polyurethane-based solid electrolyte layer.

[0062] In one embodiment, the ionic conductivity of the oily polymer solid electrolyte layer is (5.0-6.0)×10 -5 S cm -1 , preferably 5.6×10-5 S cm -1 .

[0063] In one embodiment, the oily polymer solid electrolyte layer includes a polymer and a lithium salt.

[0064] In the embodiment of the present invention, there is no particular requirement for the type of lithium salt in the oily polymer solid electrolyte. Without violating the inventive concept of the present application, any known type of lithium salt can be used in the present application. The lithium salt in the oily polymer solid electrolyte layer includes lithium hexafluorophosphate (LiPF6); lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiBF2(C2O4)) (LiODFB), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalato)borate (LiB(C2O4)2)(LiBOB), lithium tetrafluorooxalatophosphate (LiPF4(C2O4))(LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl imide) (LITFSI)(LiN(CF3SO2)2), lithium bis(fluorosulfonyl imide) (LiN(FSO2)2)(LIFSI), and combinations thereof. In certain variations, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI)(LiN(CF3SO2)2), lithium bis(fluorosulfonyl imide) (LiN(FSO2)2)(LiFSI), lithium fluoroalkyl phosphonate (LiFAP), lithium phosphate (Li3PO4), and combinations thereof.

[0065] As an embodiment, the lithium salt content in the oily polyurethane-based solid electrolyte layer is 10-60wt.%, for example, 10wt.%, 15wt.%, 20wt.%, 25wt.%, 30wt.%, 35wt.%, 40wt.%, 45wt.%, 50wt.% or 60wt.%, etc.; it can be understood that there is no special requirement for the lithium salt content, and it is known in the art to adjust the ionic conductivity of the solid electrolyte layer by the lithium salt content.

[0066] The type of lithium salt in the oily polymer solid electrolyte layer and the type of lithium salt in the aqueous polyurethane solid electrolyte layer may be the same or different.

[0067] In one embodiment, the polymer in the oily polymer-type solid electrolyte includes at least one of PEO and PEG.

[0068] In another embodiment, the present invention provides a positive electrode, comprising a current collector and the positive electrode material layer as described above disposed on a surface of the current collector, wherein the active material layer is close to a side of the current collector.

[0069] In one embodiment, the present invention provides a method for preparing the above-mentioned positive electrode, the method comprising the following steps:

[0070] S100: coating the positive electrode slurry on the surface of the current collector and drying it once;

[0071] S200: coating the surface of the positive electrode active material layer formed after the primary drying with lithium manganese iron phosphate positive electrode slurry, and performing secondary drying;

[0072] S300: coating the surface of the lithium manganese iron phosphate layer formed after the secondary drying with an aqueous polyurethane-based solid electrolyte layer slurry, drying it three times, and rolling it to obtain a positive electrode.

[0073] In one embodiment, the method further includes applying an oily polymer solid electrolyte slurry and drying the slurry after step S200 and before step S300.

[0074] In another embodiment, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the positive electrode material layer as described above, or the positive electrode in the lithium-ion battery adopts the positive electrode as described above.

[0075] Example 1

[0076] This embodiment provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, and a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer are sequentially arranged in a direction away from the positive electrode active material layer.

[0077] The positive electrode active material layer is composed of 96wt% NCM622, 2wt% super-P and 2wt% PVDF, and the thickness of the positive electrode active material layer accounts for 70% of the total thickness of the positive electrode excluding the aluminum foil;

[0078] The lithium manganese iron phosphate layer is composed of 96wt% LiMn 0.5 Fe 0.5 PO4, 2wt% super-P and 2wt% PVDF. The thickness of the lithium manganese iron phosphate layer accounts for 20% of the total thickness of the positive electrode excluding the aluminum foil.

[0079] The composition of the aqueous polyurethane solid electrolyte layer is 80 wt% aqueous polyurethane and 20 wt% lithium bis(trifluoromethanesulfonyl imide) (LITFSI). The thickness of the aqueous polyurethane solid electrolyte layer accounts for 10% of the total thickness of the positive electrode excluding the aluminum foil. The ionic conductivity of the aqueous polyurethane solid electrolyte layer is 6.6×10 -5 S cm -1 .

[0080] Example 2

[0081] This embodiment provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, and a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer are sequentially arranged in a direction away from the positive electrode active material layer.

[0082] The positive electrode active material layer is composed of 96wt% NCM622, 2wt% super-P and 2wt% PVDF, and the positive electrode active material layer accounts for 70% of the total thickness of the positive electrode excluding the aluminum foil;

[0083] The lithium manganese iron phosphate layer is composed of 96wt% LiMn 0.4 Fe 0.6 PO4, 2wt% super-P and 2wt% PVDF. The lithium manganese iron phosphate layer accounts for 15% of the total thickness of the positive electrode excluding the aluminum foil.

[0084] The aqueous polyurethane solid electrolyte layer comprises 80 wt% of aqueous polyurethane and 20 wt% of lithium perchlorate, and the aqueous polyurethane solid electrolyte layer accounts for 15% of the total thickness of the positive electrode excluding the aluminum foil.

[0085] Example 3

[0086] This embodiment provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, and a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer are sequentially arranged in a direction away from the positive electrode active material layer.

[0087] The positive electrode active material layer is composed of 96 wt% NCM523, 2 wt% conductive carbon black and 2 wt% PVDF, wherein the positive electrode active material layer accounts for 65% of the total thickness of the positive electrode excluding the aluminum foil;

[0088] The lithium manganese iron phosphate layer is composed of 95wt% LiMn 0.4 Fe 0.6 PO4, 2wt% super-P and 3wt% PVDF. The lithium manganese iron phosphate layer accounts for 25% of the total thickness of the positive electrode excluding the aluminum foil.

[0089] The aqueous polyurethane solid electrolyte layer is composed of 80 wt% aqueous polyurethane and 20 wt% lithium hexafluorophosphate, and the aqueous polyurethane solid electrolyte layer accounts for 10% of the total thickness of the positive electrode excluding the aluminum foil.

[0090] Example 4

[0091] This embodiment provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, and an oily polymer solid electrolyte layer, a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer are arranged in sequence along the direction away from the positive electrode active material layer.

[0092] The positive electrode active material layer is composed of 96wt% NCM622, 2wt% super-P and 2wt% PVDF, wherein the positive electrode active material layer accounts for 70% of the total thickness of the positive electrode excluding the aluminum foil;

[0093] The oily polymer solid electrolyte layer comprises 80 wt% PEG and 20 wt% lithium bis(trifluoromethanesulfonyl imide) (LITFSI), and the oily polymer solid electrolyte layer accounts for 10% of the total thickness of the positive electrode excluding the aluminum foil;

[0094] The lithium manganese iron phosphate layer is composed of 96wt% LiMn 0.4 Fe 0.6 PO4, 2wt% super-P and 2wt% PVDF. The lithium manganese iron phosphate layer accounts for 10% of the total thickness of the positive electrode excluding the aluminum foil.

[0095] The aqueous polyurethane solid electrolyte layer comprises 80 wt% of aqueous polyurethane and 20 wt% of lithium hexafluorophosphate, and the aqueous polyurethane solid electrolyte layer accounts for 10% of the total thickness of the positive electrode excluding the aluminum foil.

[0096] Comparative Example 1

[0097] This comparative example provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, wherein the positive electrode active material layer consists of 96 wt % NCM622, 2 wt % super-P and 2 wt % PVDF.

[0098] Comparative Example 2

[0099] This comparative example provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, wherein the positive electrode active material layer is composed of 96wt% LiMn 0.5 Fe 10.5 PO4, 2wt% super-P and 2wt% PVDF.

[0100] Comparative Example 3

[0101] This comparative example provides a positive electrode, which includes an aluminum foil and a positive electrode active material layer arranged on the surface of the aluminum foil, an oily polymer solid electrolyte layer is arranged on the surface of the positive electrode active material layer, and the positive electrode active material layer is composed of 96wt% NCM622, 2wt% super-P and 2wt% PVDF, and the aqueous polyurethane solid electrolyte layer is composed of 80wt% aqueous polyurethane and 20wt% lithium hexafluorophosphate.

[0102] Preparation of the battery:

[0103] The positive electrode sheets prepared in each embodiment and comparative example were compounded with the negative electrode and the electrolyte to obtain a lithium ion battery, wherein the negative electrode active material layer of the negative electrode was composed of 95 wt% graphite, 2 wt% conductive carbon black and 3 wt%.

[0104] test:

[0105] 1. Capacity retention rate after 500 cycles at room temperature

[0106] (1) Charge at 1C to the final voltage, with a cutoff current of 0.05C, and let stand for 30 minutes;

[0107] (2) Discharge at 1C to the final discharge voltage, record the discharge capacity, and let it stand for 30 minutes;

[0108] Cycle (1)-(2) to test the capacity retention rate after 500 cycles at room temperature. The test results are shown in Table 1.

[0109] 2. Acupuncture test

[0110] (1) Fully charge the battery;

[0111] (2) Use a φ8mm high-temperature resistant steel needle (the cone angle of the needle tip is 45° to 60°, the surface of the needle is smooth, free of rust, oxide layer and oil), and penetrate the battery cell plate at a speed of (25±5)mm / s from a direction perpendicular to the battery cell plate. The penetration position should be close to the geometric center of the punctured surface, and the steel needle should stay in the battery cell;

[0112] (3) Observe for 1 hour.

[0113] Record the battery cell safety level. See Table 1 for test results.

[0114] Table 1

[0115] 500-cycle capacity retention rate (%) 8mm needle penetration rate (%) Example 1 94.2 100 Example 2 94.1 100 Example 3 94.5 100 Example 4 95.6 100 Comparative Example 1 91.5 0 Comparative Example 2 93.8 10 Comparative Example 3 94.4 30

[0116] Comparing Examples 1-4 with the comparative examples, it can be seen that by using the method of the present application, a lithium manganese iron phosphate layer with high safety performance is provided as a protective layer on the surface of the ternary positive electrode active material, thereby improving the safety performance of the battery while maintaining a high energy density. At the same time, the aqueous polyurethane is used as the polymer matrix of the solid electrolyte. The polyurethane soft segment can dissolve a large amount of lithium salt and has good flexibility, which can provide excellent ion conductivity. At the same time, there are a large number of hydrogen bonding groups in the aqueous polyurethane, and the strong hydrogen bonding effect provides good mechanical properties for the polymer electrolyte. The aqueous polyurethane-based solid polymer electrolyte layer exhibits good mechanical strength and thermal stability, further improving the safety performance of the battery cell. The above multiple factors work together to effectively improve the safety and cycle performance of the battery, solving the problem of insufficient safety of current ternary materials.

[0117] At the same time, setting an oily polymer solid electrolyte layer on the surface of the ternary positive electrode material and lithium manganese iron phosphate can further improve the battery's cycle performance.

[0118] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A positive electrode material layer, characterized in that: The positive electrode material layer includes an active material layer, and a lithium manganese iron phosphate layer and an aqueous polyurethane-based solid electrolyte layer are sequentially arranged in a direction away from the active material layer; The active material layer includes a positive electrode active material, and the positive electrode active material is Li 1-z Na z Ni x Co y Mn 1-x-y O2 (0<x<1, 0<y<1, 0≤z<1); The active material layer accounts for 60-80% of the total thickness of the positive electrode material layer; The aqueous polyurethane-based solid electrolyte layer includes non-ionic aqueous polyurethane and lithium salt; The aqueous polyurethane-based solid electrolyte layer accounts for 5-15% of the total thickness of the positive electrode material layer; The ionic conductivity of the aqueous polyurethane-based solid electrolyte layer is (6.0-7.0)×10 -5 S cm -1 .

2. The positive electrode material layer according to claim 1, characterized in that The aqueous polyurethane-based solid electrolyte layer accounts for 7-12% of the total thickness of the positive electrode material layer.

3. The positive electrode material layer according to claim 1, characterized in that The ionic conductivity of the aqueous polyurethane-based solid electrolyte layer is 6.6×10 -5 S cm -1 .

4. The positive electrode material layer according to claim 1, characterized in that The lithium salt content in the aqueous polyurethane-based solid electrolyte layer is 10-60 wt.%.

5. The positive electrode material layer according to claim 1, characterized in that The active material layer includes a first binder and a first conductive material.

6. The positive electrode material layer according to claim 1, characterized in that The lithium iron manganese phosphate layer accounts for 10-30% of the total thickness of the positive electrode material layer.

7. The positive electrode material layer according to claim 1, characterized in that The lithium manganese iron phosphate layer includes lithium manganese iron phosphate.

8. The positive electrode material layer according to claim 7, characterized in that The chemical formula of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, where x is 0.4-0.

6.

9. The positive electrode material layer according to claim 1, characterized in that The lithium manganese iron phosphate layer further includes a second binder and a second conductive material, and the second conductive material includes at least one of single-walled carbon nanotubes and VGCF.

10. The positive electrode material layer according to claim 1, characterized in that An oily polymer solid electrolyte layer is further provided between the active material layer and the lithium manganese iron phosphate layer.

11. The positive electrode material layer according to claim 10, characterized in that The oily polymer solid electrolyte layer accounts for 5-15% of the total thickness of the positive electrode material layer.

12. The positive electrode material layer according to claim 10, characterized in that The ionic conductivity of the oily polymer-based solid electrolyte layer is lower than the ionic conductivity of the aqueous polyurethane-based solid electrolyte layer.

13. The positive electrode material layer according to claim 10, characterized in that The ionic conductivity of the oily polymer solid electrolyte layer is (5.0-6.0)×10 -5 S cm -1 .

14. The positive electrode material layer according to claim 13, characterized in that The ionic conductivity of the oily polymer solid electrolyte layer is 5.6×10 -5 S cm -1 .

15. The positive electrode material layer according to claim 10, characterized in that The oily polymer solid electrolyte layer includes a polymer and a lithium salt.

16. The positive electrode material layer according to claim 15, characterized in that The polymer in the oily polymer-type solid electrolyte includes at least one of PEO and PEG.

17. A positive electrode, characterized in that The positive electrode includes a current collector and a positive electrode material layer according to any one of claims 1 to 16 disposed on a surface of the current collector, and the active material layer is close to a side of the current collector.

18. A lithium ion battery, characterized in that: The positive electrode of the lithium ion battery comprises the positive electrode material layer according to any one of claims 1 to 16, or the positive electrode in the lithium ion battery adopts the positive electrode according to claim 17.