High-performance lithium manganate battery positive plate, preparation method thereof and application of high-performance lithium manganate battery positive plate in high-performance lithium manganate battery

Abstract

The invention provides a high-performance lithium manganate battery positive plate, a preparation method thereof and application of the high-performance lithium manganate battery positive plate to a high-performance lithium manganate battery. The positive plate is sequentially coated with LFMP and LMO and then dried to obtain a double-layer functional coating. Compared with the prior art, a novel double-layer electrode structure is adopted, so that the internal resistance is greatly reduced, and the power performance of the battery is effectively improved; compared with a traditional lithium manganate battery, the safety is greatly improved, and the needling passing rate is 100%; the use of the lithium manganate material can be reduced, and the cost is saved. The paint is non-toxic and environment-friendly; the operation is simple, the effect is obvious, and mass production can be realized; the mass energy density and the safety performance of the product are greatly improved, maximum benefits are brought to enterprises and customers, and the method has wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of new energy batteries, and specifically relates to the preparation of a high-performance lithium manganese oxide battery positive electrode sheet and a preparation method thereof, and application in a high-performance lithium manganese oxide battery. Background Art

[0002] Improving safety and reducing costs are the core trends of technological development. After the vigorous development of my country's new energy industry in recent years, by the end of 2023, the number of new energy vehicles in the country will reach 20.41 million, accounting for 6.1% of the total number of vehicles. Among them, the number of pure electric vehicles is 15.52 million, accounting for 76.04% of the total number of new energy vehicles; with the increase in sales and ownership of new energy vehicles, more and more quality and safety problems have emerged. In addition, with the intensification of market competition, in order to increase user appeal, various car companies have started the "price for volume" model, and the price reduction boom has continued. Therefore, improving battery safety and reducing costs have become the focus of industrial development.

[0003] Lithium manganese oxide, with the chemical formula LiMn2O4, presents a cubic spinel crystal structure and has three lithium ion space transmission channels. Because of this, it has a higher ion diffusion rate than other positive electrode materials, and is particularly suitable for lithium-ion batteries that require high-rate charging. Lithium manganese oxide is regarded as one of the most promising lithium-ion positive electrode materials, with a theoretical specific capacity of up to 148mAh / g. Thanks to its three-dimensional tunnel structure, lithium ions can be reversibly deintercalated in the spinel lattice without causing structural collapse, giving it excellent rate performance and stability. In addition, lithium manganese oxide adopts a spinel structure, which is more stable than a layered structure, so it is more widely used in the actual application of lithium batteries. In addition, lithium manganese oxide has many other advantages, such as abundant manganese resources, which can reduce battery costs and facilitate large-scale industrial production; its battery is safe, resistant to overcharge and discharge, has excellent rate performance, and is resistant to low temperatures; at the same time, manganese is non-toxic and pollution-free, and its recycling problem has rich experience in the field of primary batteries, which is beneficial to environmental protection. However, lithium manganese oxide has low energy density and instability, which limits its use.

[0004] The patent with publication number CN 113346203 A, published on September 3, 2021, discloses a high-performance lithium manganese oxide battery and its preparation method, and discloses a soft-pack lithium manganese oxide battery with anti-overcharge function including a protective shell, but it is impossible to improve the performance from the monomer end. Summary of the invention

[0005] The purpose of the present invention is to provide a high-performance lithium manganese oxide battery positive electrode sheet and a preparation method thereof, wherein the positive electrode sheet coating is a double-layer coating structure of first preparing a lithium iron manganese phosphate coating and then coating a lithium manganese oxide coating on the coating. The battery of this method has the advantages of high energy density, high safety, environmental protection and low cost.

[0006] Another object of the present invention is to provide an application of a high-performance cathode plate of a lithium manganese oxide battery in a high-performance lithium manganese oxide battery, which is used for a high-performance lithium manganese oxide battery to improve the safety and energy density of the battery.

[0007] The specific technical solution of the present invention is as follows:

[0008] A high-performance cathode plate of a lithium manganese oxide battery, the high-performance cathode plate of the lithium manganese oxide battery includes a lithium iron manganese phosphate coating, and a lithium manganese oxide coating provided on the lithium iron manganese phosphate coating.

[0009] The thickness of the lithium iron manganese phosphate coating is 30-50 μm, and the thickness of the lithium manganese oxide coating is 20-150 μm.

[0010] The mass ratio of the solid content in the lithium iron manganese phosphate coating to the solid content in the lithium manganese oxide coating is X:10-X, where 0 < X < 10.

[0011] A preparation method of a high-performance cathode plate of a lithium manganese oxide battery provided by the present invention is specifically as follows: First, coat a lithium iron manganese phosphate slurry on a current collector to obtain an LMFP cathode plate; then coat a lithium manganese oxide slurry on the LMFP cathode plate to obtain a high-performance cathode plate of a lithium manganese oxide battery.

[0012] The preparation method of the lithium iron manganese phosphate slurry is as follows:

[0013] S1. Weigh 90-99% of the cathode active material LMFP, 1-5% of binder A, 1-5% of binder B, and 1-5% of conductive agent based on the total weight of the powder, stir and mix for 0.5-1 h, the rotation speed is 500-1000 r / min, and the stirring temperature is 10-60 °C to mix evenly;

[0014] S2. Add a cathode solvent to the material obtained in step S1 to make the overall solid content 75%, 0.1-1% of dispersant, and 0.5-2% of conductive agent, stir and mix for 0.5-2 h, the rotation speed is 500-2000 r / min, and the stirring temperature is 10-60 °C;

[0015] S3. Add a cathode solvent to the material obtained in S2 to make the overall solid content 64%, stir and mix for 0.5-5 h, the rotation speed is 1000-3000 r / min, and the stirring temperature is 10-60 °C to obtain the LMFP cathode electrode slurry;

[0016] In the preparation method of the lithium iron manganese phosphate slurry, the powder refers to 90-99% of the cathode active material LMFP, 1-5% of binder A, 1-5% of binder B, 1-5% of conductive agent in step S1 and 0.1-1% of dispersant, 0.5-2% of conductive agent in step S2, and the total amount used is 100%.

[0017] In the preparation of the LMFP positive electrode slurry, it is necessary to add the solvent step by step. By adding the solvent step by step, the binder can be first fully kneaded with the dry powder to form a better dispersion.

[0018] In this application, the steps of S1, S2, and S3 cannot be arbitrarily replaced. The reason for adding lithium iron manganese phosphate first is that adding the powder for dry mixing first enables the lithium iron manganese phosphate material to come into full contact with the binder and the conductive agent. The solvent added later mainly plays a role in lubrication and dispersion.

[0019] In step S1, the positive electrode active material LMFP is one or more of those with a molar ratio of manganese to iron of 6:4 or 5:5 or 7:3.

[0020] In steps S1 and S2, the conductive agent is one or more of carbon nanotubes, graphene, carbon black, and acetylene black.

[0021] In step S1, the binder A and the binder B are respectively selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), acrylic resin (PAA), and styrene-butadiene rubber (SBR). The binder A and the binder B can be the same or different.

[0022] In steps S2 and S3, the positive electrode solvent is N-methylpyrrolidone (NMP);

[0023] In step S2, the dispersant includes one or both of polyvinylpyrrolidone PVP and cetyltrimethylammonium bromide CTAB.

[0024] The method of coating the lithium iron manganese phosphate slurry on the current collector is as follows: The obtained LMFP positive electrode slurry is uniformly coated on the current collector by a coater at 10 - 120 °C to obtain an LFMP active material thin sheet with a thickness of 30 - 200 μm, and then roll-pressed to obtain an LMFP positive electrode sheet with a thickness of 30 - 50 μm;

[0025] The preparation method of the lithium manganate slurry is as follows:

[0026] 1) Weigh 90 - 98% of the lithium manganate material, 1 - 5% of the binder A, and 1 - 5% of the conductive agent based on the total weight of the powder, stir and mix for 0.5 - 1 h at a rotation speed of 500 - 1000 r / min and a stirring temperature of 10 - 60 °C until evenly mixed;

[0027] 2) Add the positive electrode solvent to the material obtained in step 1) to make the overall solid content 60%, stir and mix for 0.5 - 5 h at a rotation speed of 1000 - 3000 r / min and a stirring temperature of 10 - 60 °C to obtain the lithium manganate slurry;

[0028] In the method for preparing the lithium manganate slurry, the powder is composed of 90-98% lithium manganate material, 1-5% binder A, and 1-5% conductive agent, and the total amount of these three raw materials is 100%.

[0029] The binder A in step 1) is the same as the binder A in the above step S1.

[0030] The conductive agent in step 1) is one or more of carbon nanotubes, graphene, carbon black, and acetylene black.

[0031] The positive electrode solvent in step 2) is the same as the positive electrode solvent selected in the preparation of the lithium iron manganese phosphate slurry.

[0032] The method of coating the lithium manganate slurry on the LMFP positive electrode sheet is as follows: The lithium manganate slurry is evenly coated on the LMFP positive electrode sheet by a coater at 10-120 °C, the thickness of a single-layer coating is 20-150 μm, and then roller-pressed to obtain a double-layer functional coating positive electrode sheet with a thickness of 50-200 μm, that is, the positive electrode sheet of a high-performance lithium manganate battery.

[0033] A high-performance lithium manganate battery provided by the present invention includes the above-mentioned high-performance lithium manganate battery positive electrode sheet and also includes a negative electrode sheet.

[0034] The method for preparing the negative electrode sheet is as follows: The negative electrode slurry is evenly coated on the current collector by a coater at 10-110 °C to obtain an active material thin sheet with a thickness of 100-200 μm, and then roller-pressed to obtain a negative electrode sheet with a thickness of 50-150 μm.

[0035] The method for preparing the negative electrode slurry is as follows:

[0036] Step 1: Weigh 90-99% of the negative electrode active material, 0-2% of the thickener A, and 1-5% of the conductive agent based on the total weight of the powder, stir and mix for 0.5-1 h at a rotation speed of 500-1000 r / min and a stirring temperature of 10-60 °C until evenly mixed.

[0037] Step 2: Add the negative electrode solvent to the material obtained in step 1 to make the overall solid content 68%, stir and mix for 0.5-2 h at a rotation speed of 500-1000 r / min and a stirring temperature of 10-60 °C.

[0038] Step 3: Add the negative electrode solvent to the material obtained in step 2 to make the overall solid content 68% and 1-5% of the binder A, stir and mix for 0.5-5 h at a rotation speed of 500-2000 r / min and a stirring temperature of 10-60 °C; thus, the negative electrode slurry is obtained.

[0039] In the method for preparing the negative electrode slurry, the powder refers to 90-99% of the negative electrode active material, 0-2% of thickener A, 1-5% of conductive agent in step 1, and 1-5% of binder A in step 3, and the total dosage is 100%.

[0040] The negative electrode active material described in step 1 is one or more of graphite, silicon oxide, and silicon carbon.

[0041] The thickener A described in step 1 is one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0042] The conductive agent described in step 1 is one or more of carbon nanotubes, graphene, carbon black, acetylene black, and conductive graphite.

[0043] In steps 2 and 3, the negative electrode solvent is water or NMP, and the solvents selected in steps 2 and 3 are the same.

[0044] The binder A described in step 3 is one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), acrylic resin (PAA), and styrene-butadiene rubber (SBR).

[0045] Preferably, the battery includes any one of a liquid lithium-ion battery, a lithium-sulfur battery, a lithium-air battery, a solid-liquid hybrid lithium battery, or an all-solid-state lithium battery.

[0046] The design concept of the present invention is as follows:

[0047] Similar to the structure of lithium iron phosphate, manganese and iron are combined to make up for each other's strengths and weaknesses. The lithium iron phosphate crystal is in the olivine type, and the basic structural unit is composed of LiO6 octahedrons, FeO6 octahedrons, and PO4 tetrahedrons. Among them, the FeO6 octahedrons and PO6 tetrahedrons are cross-linked to form a polyanion framework structure, and Li + transmits along a single b-axis. Adding'manganese' helps to iterate and upgrade the cathode material. By introducing the Mn element on the basis of lithium iron phosphate, the voltage platform is increased to 3.7V, which can further improve the energy density of the battery cell. Therefore, lithium manganese iron phosphate has become an important direction for the development of cathode material technology.

[0048] Lithium manganese iron phosphate adds the Mn element on the basis of the structure of lithium iron phosphate, but it is not a simple physical mixture of LiFePO4 and LiMnPO4. Fe 2+ and Mn 2+ have very similar ionic radii. Relying on the synergistic effect between LiFePO4 and LiMnPO4, a stable and uniform solid solution is formed, thus combining the stable electrochemical performance of LiFePO4 and the high potential of LiMnPO4. The Mn element can increase the discharge voltage to 4.1V, greatly improving the energy density of the cathode material.

[0049] Compared with lithium iron phosphate, lithium manganese iron phosphate (LMFP) has better energy density and low-temperature performance. Lithium manganese iron phosphate has two major advantages compared with lithium iron phosphate - increased energy density and excellent low-temperature performance. First, the theoretical voltage plateau of lithium iron phosphate is about 3.4 - 3.5V. The introduction of manganese element enables the voltage plateau of lithium manganese iron phosphate to reach 4.1V, and the theoretical energy density is increased by 10 - 20% compared with lithium iron phosphate, which helps to increase the driving range of new energy vehicles. Second, under the condition of -20°C, the capacity of the Mn platform of lithium manganese iron phosphate accounts for 95% of that at room temperature, while the capacity of the Fe platform is only about 50%, showing better low-temperature performance.

[0050] Compared with ternary materials, LMFP has higher stability and prominent cost advantages. Ternary materials belong to the layered structure, while lithium manganese iron phosphate is of the olivine structure, with better stability during charge and discharge. When Li + is removed, there will be no problem of structural collapse; moreover, in lithium manganese iron phosphate, P atoms form PO4 tetrahedrons through strong P-O covalent bonds, and O atoms are difficult to be removed from the structure, making lithium manganese iron phosphate have higher stability and safety. At the same time, the main elements of lithium manganese iron phosphate are manganese and iron, avoiding the use of precious metals nickel and cobalt in ternary materials and significantly reducing costs.

[0051] The lithium manganate material belongs to a single-phase reaction, and its voltage curve shows a slope of 2.8 - 4.35V. Lithium iron phosphate is a two-phase reaction during charge and discharge, so its voltage shows a single plateau of 3.5V. The incorporation of manganese element makes lithium manganese iron phosphate have two voltage plateaus, namely 4.1V of manganese and 3.5V of iron; it can be seen that the voltage plateau ranges of lithium manganese iron phosphate and lithium manganate materials highly overlap. Therefore, using them together can be one of the application solutions for lithium manganese iron phosphate. This solution can not only take into account the safety problem of lithium manganate and the double voltage plateau problem of lithium manganese iron phosphate, but also improve other electrochemical properties such as the capacity retention rate and safety of the composite material. Mixing lithium manganate with lithium manganese iron phosphate can increase the energy density of the battery, improve the safety of the battery, and the cost is relatively low.

[0052] In the present invention, the olivine structure of LMFP has a higher theoretical capacity and voltage platform. Direct contact with the current collector can maximize its capacity advantage and provide an energy density basis as the main active layer. Moreover, it has a low volume expansion rate and a strong covalent bond structure that can withstand charge and discharge stress. As a bottom layer, it can avoid the peeling of the coating and the current collector due to expansion. The spinel structure (Mn3O4 framework) of LMO is more stable in the electrolyte, and preferentially reacts with the electrolyte to form a dense SEI film, reducing corrosion to LMFP; and it has a three-dimensional lithium ion diffusion channel, which can accelerate the transmission of lithium ions at the electrode-electrolyte interface as a surface layer and reduce polarization. The electrons of LMFP directly contact the current collector (such as aluminum foil) to shorten the electron transmission path and reduce the interface resistance; and the LMO surface layer has high ionic conductivity and low dependence on electron transmission, so it is used as a surface layer; and the LMO three-dimensional ion channel can provide a path for lithium ions to quickly enter the electrolyte, avoiding the capacity decay of the LMFP layer due to slow ion diffusion. Mn in LMFP is prone to disproportionation reaction under high pressure, resulting in Mn 2+ dissolution; the LMO surface acts as a physical barrier to block the dissolution of Mn 2+ Entering the electrolyte, the Mn in its spinel structure 3+ More stable (stronger oxygen coordination environment), further reducing dissolution. In addition, the thermal expansion coefficient of the LMFP bottom layer is more matched with that of the current collector, while the flexibility of the LMO surface layer is higher. The double-layer structure of the present invention can disperse the mechanical stress during the charge and discharge process and prevent crack propagation. The decomposition temperature of LMO is higher than that of LMFP. As a surface layer, it can delay the transfer of heat to the inside during thermal runaway and protect LMFP and the current collector. The LMFP material has a lower electrical conductivity, which inhibits the occurrence of the Al-Anode short-circuit mode during the needle puncture process. See the schematic diagram of the mechanism for achieving high safety of needle puncture. Figure 1 .

[0053] If the order of LMFP and LMO is changed, the adhesion between LMO and the current collector is likely to be poor (due to a higher volume expansion rate), which may easily lead to powder removal; LMFP as the surface layer will directly contact the electrolyte, aggravating manganese dissolution and interfacial side reactions; the ion diffusion of the LMO bottom layer is slow, which limits the high-rate performance and cannot achieve the effect of the present invention.

[0054] Compared with the prior art, the energy density of the present invention is increased by about 8-16% compared with the traditional lithium manganese oxide battery; the new double-layer electrode structure is adopted, which greatly reduces the internal resistance and effectively improves the battery power performance; compared with the traditional lithium manganese oxide battery, the safety is greatly improved, and the needle puncture pass rate is 100%;

[0055] The use of lithium manganate materials is reduced, and costs are saved. Moreover, the present invention is non-toxic and environmentally friendly; it is simple to operate, has obvious effects, and can be mass-produced; it greatly improves the quality energy density and safety performance of the product, brings the greatest benefits to enterprises and customers, and has broad application prospects. Brief Description of the Drawings

[0056] Figure 1 This is a schematic diagram of the battery of the present invention. Detailed Description of the Invention

[0057] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0058] The test materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions.

[0059] For those not specifying specific techniques or conditions in the embodiments, they can all be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications.

[0060] To ensure the consistency of the experiment, raw materials produced in the same batch are used. The production process includes a series of standard production line processes such as stirring, coating, rolling, pre-cutting, die-cutting, slitting, winding, hot pressing, casing, drying, infiltration, formation, aging, capacity, OCV, etc., to obtain lithium iron manganese phosphate batteries; the differences between different examples mainly lie in the different coating weight distributions of the positive electrode. The present invention will be described in detail below in conjunction with the embodiments.

[0061] A high-performance lithium manganese oxide battery provided by the present invention includes a positive electrode and a negative electrode by weight percentage of the coating weight of the positive electrode. Among them:

[0062] I. Preparation of the positive electrode sheet:

[0063] S1. Weigh 90-99% of the positive electrode active material LMFP, 1-5% of binder A, 1-5% of binder B, and 1-5% of conductive agent based on the total weight of the powder, stir and mix for 0.5-1 h at a rotation speed of 500-1000 r / min and a stirring temperature of 10-60 °C until evenly mixed;

[0064] S2. Add 44% of the positive electrode solvent (total solid content is about 75%), 0.1-1% of dispersant, and 0.5-2% of conductive agent based on the total weight of the powder to the material obtained in step S1, stir and mix for 0.5-2 h at a rotation speed of 500-2000 r / min and a stirring temperature of 10-60 °C;

[0065] S3. Add a cathode solvent accounting for 6% of the total weight of the powder (the overall solid content is about 64%) to the material obtained in step S2, stir and mix for 0.5 - 5 h at a rotation speed of 1000 - 3000 r / min and a stirring temperature of 10 - 60 °C to obtain the LMFP cathode electrode paste.

[0066] S4. Coating the paste obtained in step S3 evenly on the current collector at 10 - 120 °C through a coater to obtain a LFMP active material thin sheet with a thickness of 30 - 200 μm, and then roll pressing to obtain a LMFP positive electrode sheet with a thickness of 30 - 50 μm.

[0067] S5. Weigh lithium manganate material accounting for 90 - 98% of the total weight of the powder, 1 - 5% binder A, 1 - 5% conductive agent, stir and mix for 0.5 - 1 h at a rotation speed of 500 - 1000 r / min and a stirring temperature of 10 - 60 °C, and mix evenly.

[0068] S6. Add a cathode solvent accounting for 70% of the total weight of the powder (the overall solid content is about 60%) to the material obtained in S5, stir and mix for 0.5 - 5 h at a rotation speed of 1000 - 3000 r / min and a stirring temperature of 10 - 60 °C to obtain the lithium manganate paste.

[0069] S7. Coating the paste obtained in step S6 evenly on the positive electrode sheet obtained in step S4 at 10 - 120 °C through a coater, with a single-layer coating thickness of 20 - 150 μm, and then roll pressing to obtain a double-layer functional coating positive electrode sheet with a thickness of 50 - 200 μm.

[0070] II. Preparation of negative electrode sheet:

[0071] S8. Weigh negative active material accounting for 90 - 99% of the total weight of the powder, 0 - 2% thickener A, 1 - 5% conductive agent, stir and mix for 0.5 - 1 h at a rotation speed of 500 - 1000 r / min and a stirring temperature of 10 - 60 °C, and mix evenly.

[0072] S9. Add a negative electrode solvent accounting for 40% of the total weight of the powder (the overall solid content is about 68%) to the material obtained in step S8, stir and mix for 0.5 - 2 h at a rotation speed of 500 - 1000 r / min and a stirring temperature of 10 - 60 °C.

[0073] S10. Add a negative electrode solvent accounting for 40% of the total weight of the powder (the overall solid content is about 68%) and 1 - 5% binder A to the material obtained in S9, stir and mix for 0.5 - 5 h at a rotation speed of 500 - 2000 r / min and a stirring temperature of 10 - 60 °C; thus obtaining the negative electrode electrode paste.

[0074] S11. Coating the slurry obtained in step S6 evenly on the current collector at 10 - 110 °C using a coater to obtain an active material thin sheet with a thickness of 100 - 200 μm, and then roll-pressing to obtain a negative electrode sheet with a thickness of 50 - 150 μm;

[0075] III. Battery Preparation:

[0076] S12. Assemble the above positive electrode sheet, negative electrode sheet, and separator by stacking or winding, and inject an appropriate amount of electrolyte to obtain a lithium manganate lithium battery.

[0077] The following are specific technical embodiments of the present invention:

[0078] The specific preparation methods of the following embodiments are as follows:

[0079] A high-performance lithium manganate battery, calculated by weight percentage of the positive electrode coating, the high-performance lithium manganate battery includes a positive electrode and a negative electrode. Among them:

[0080] I. Positive Electrode Sheet Preparation:

[0081] S1. Weigh 93% of the positive electrode active material LMFP (manganese-iron molar ratio is 6:4), 2% of PVDF, and 2% of carbon black SP based on the total weight of the powder, stir and mix for 1 h at a rotation speed of 1000 r / min and a stirring temperature of 25 °C until evenly mixed;

[0082] S2. Add 44% of NMP (total solid content is about 75%), 1% of PVP, and 2% of carbon nanotubes based on the total weight of the powder to the material obtained in step S1, stir and mix for 1.5 h at a rotation speed of 1500 r / min and a stirring temperature of 25 °C;

[0083] S3. Add 6% of NMP (total solid content is about 64%) based on the total weight of the powder to the material obtained in step S2, stir and mix for 2 h at a rotation speed of 2500 r / min and a stirring temperature of 25 °C to obtain the LMFP positive electrode slurry;

[0084] S4. Coating the slurry obtained in step S3 evenly on the current collector at 100 °C using a coater to obtain an LFMP active material thin sheet with a thickness of 200 μm, and then roll-pressing to obtain a LMFP positive electrode sheet with a thickness of 50 μm;

[0085] S5. Weigh 95% of the lithium manganate material LMO, 2% of PVDF, and 3% of SP based on the total weight of the powder, stir and mix for 1 h at a rotation speed of 1000 r / min and a stirring temperature of 25 °C until evenly mixed;

[0086] S6. Add NMP accounting for 70% of the total weight of the powder (overall solid content is about 60%) to the material obtained in S5, stir and mix for 2 h at a rotation speed of 2500 r / min and a stirring temperature of 25 °C to obtain the lithium manganate slurry.

[0087] S7. Coating the slurry obtained in step S6 evenly on the positive electrode sheet obtained in step S4 at 110 °C through a coater, with a single-layer coating thickness of 150 μm, and then roll-pressing to obtain a double-layer functional coating positive electrode sheet with a thickness of 200 μm.

[0088] II. Preparation of the negative electrode sheet:

[0089] S8. Weigh 95% graphite, 1% CMC, and 2% SP accounting for the total weight of the powder, stir and mix for 1 h at a rotation speed of 1000 r / min and a stirring temperature of 25 °C until evenly mixed.

[0090] S9. Add deionized water accounting for 40% of the total weight of the powder (overall solid content is about 68%) to the material obtained in step S8, stir and mix for 1 h at a rotation speed of 1000 r / min and a stirring temperature of 25 °C.

[0091] S10. Add deionized water accounting for 40% of the total weight of the powder (overall solid content is about 68%) and 2% SBR to the material obtained in S9, stir and mix for 2 h at a rotation speed of 2000 r / min and a stirring temperature of 25 °C to obtain the negative electrode slurry.

[0092] S11. Coating the slurry obtained in step S6 evenly on the current collector at 100 °C through a coater to obtain an active material thin sheet with a thickness of 200 μm, and then roll-pressing to obtain a negative electrode sheet with a thickness of 150 μm.

[0093] III. Battery preparation:

[0094] S12. Assemble the above positive electrode sheet, negative electrode sheet, and separator by stacking or winding, and inject an appropriate amount of lithium hexafluorophosphate electrolyte to prepare the lithium manganate lithium battery.

[0095] Example 1 (for comparison)

[0096] According to the above preparation method, a 0 wt% LMFP coating and a 100 wt% LMO coating are prepared. That is, without using the LMFP coating, only the LMO coating is used.

[0097] Example 2

[0098] According to the above preparation method, only a 30 wt% LMFP coating and a 70 wt% LMO coating are prepared.

[0099] Among them, the 30 wt% LMFP coating means that the solid content in the LMFP coating slurry accounts for 30 wt% of the total mass of the solid content in the LMFP coating slurry + the solid content in the LMO coating. The 70 wt% LMO coating means that the solid content in the LMO coating accounts for 70 wt% of the total mass of the solid content in the LMFP coating slurry + the solid content in the LMO coating. The same applies hereinafter.

[0100] Example 3

[0101] According to the above preparation method, only a 50 wt% LMFP coating and a 50 wt% LMO coating are prepared.

[0102] Example 4

[0103] According to the above preparation method, only a 70 wt% LMFP coating and a 30 wt% LMO coating are prepared.

[0104] Example 5 (for comparison)

[0105] According to the above preparation method, only a 100 wt% LMFP coating and a 0 wt% LMO coating are prepared.

[0106] Example 6 (for comparison)

[0107] According to the above preparation method, only a 50 wt% LMFP coating and a 50 wt% LMO coating are prepared, but the LMO coating is on the inner layer and the LMFP coating is on the outer layer (that is, the LMO coating is on the current collector and the LMFP coating is on the LMO coating).

[0108] Lithium battery preparation: The positive electrode sheets of each example are respectively assembled into batteries together with the same negative electrode sheet, separator, and electrolyte.

[0109] Table 1 Data such as the energy density, DC internal resistance (DCR) of the battery, number of 1C-80% SOH cycles, and nail penetration test of the lithium manganate battery after being made.

[0110] Table 1 Test performance of each example

[0111]

[0112] As can be seen from Table 1, Examples 2 and 3 in the preparation of Example 1-5 of the present invention show relatively excellent energy density and safety. Since LMFP has a relatively high platform voltage of 3.6V (although the energy density of Examples 4 and 5 is increased, the internal resistance is increased and thus the cycle performance is reduced. In summary, Example 3 is the best), the energy density of the LMFP battery is increased by 15% compared with the LMO (Example 1) battery. The LMFP material has a low conductivity, which inhibits the occurrence of the Al-Anode short-circuit mode during the pinprick process. It can also be found from Example 6 that changing the positions of the LMO coating and the LMFP coating will result in a performance decline and a decrease in the pinprick passing rate.

[0113] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A high-performance lithium manganese oxide battery positive electrode plate, characterized in that: The high-performance lithium manganese oxide battery positive electrode sheet comprises a lithium iron manganese phosphate coating and a lithium manganese oxide coating arranged on the lithium iron manganese phosphate coating.

2. The high-performance lithium manganese oxide battery positive electrode according to claim 1, characterized in that: The thickness of the lithium iron manganese phosphate coating is 30-50 μm, and the thickness of the lithium manganate coating is 20-150 μm.

3. The high-performance lithium manganese oxide battery positive electrode according to claim 1 or 2, characterized in that: The mass ratio of the solid content in the lithium manganese iron phosphate coating to the solid content in the lithium manganate coating is X:10-X, 0<X<10.

4. A method for preparing a high-performance lithium manganese oxide battery positive electrode sheet according to any one of claims 1 to 3, characterized in that: The preparation method is specifically as follows: firstly, coating lithium iron manganese phosphate slurry on a current collector to obtain a LMFP positive electrode sheet; and then coating lithium manganate slurry on the LMFP positive electrode sheet to obtain a high-performance lithium manganate battery positive electrode sheet.

5. The preparation method according to claim 4, characterized in that: The preparation method of the lithium manganese iron phosphate slurry is: S1. Weigh 90-99% of the total weight of the powder, the positive electrode active material LMFP, 1-5% of the binder A, 1-5% of the binder B, and 1-5% of the conductive agent, stir and mix for 0.5-1h, at a speed of 500-1000r / min and a stirring temperature of 10-60°C, and mix evenly; S2. Add cathode solvent to the material obtained in step S1 to make the overall solid content 75%, 0.1-1% dispersant, and 0.5-2% conductive agent, and stir and mix for 0.5-2h at a speed of 500-2000r / min and a stirring temperature of 10-60°C; S3. Add cathode solvent to the material obtained in S2 to make the overall solid content 64%, stir and mix for 0.5-5h, with a rotation speed of 1000-3000r / min and a stirring temperature of 10-60°C to obtain LMFP cathode electrode slurry.

6. The preparation method according to claim 4 or 5, characterized in that: The method for coating the lithium manganese iron phosphate slurry on the current collector is: uniformly coating the obtained LMFP positive electrode slurry on the current collector at 10-120° C. by a coating machine to obtain a LFMP active material sheet with a thickness of 30-200 μm, and then rolling to obtain a LMFP positive electrode sheet with a thickness of 30-50 μm.

7. The preparation method according to claim 4, characterized in that: The preparation method of the lithium manganate slurry is: 1) Weigh 90-98% of lithium manganate material, 1-5% of binder A, and 1-5% of conductive agent, and stir for 0.5-1h at a speed of 500-1000r / min and a stirring temperature of 10-60°C until the mixture is evenly mixed; 2) Adding a cathode solvent to the material obtained in step 1) to make the overall solid content 60%, stirring and mixing for 0.5-5h, the rotation speed is 1000-3000r / min, and the stirring temperature is 10-60°C to obtain lithium manganate slurry.

8. The preparation method according to claim 4 or 7, characterized in that: The lithium manganate slurry is coated on the LMFP positive electrode sheet. The specific method is: the lithium manganate slurry is evenly coated on the LMFP positive electrode sheet at 10-120° C. by a coating machine, and the thickness of the single-layer coating is 20-150 μm. After rolling, a double-layer functional coating positive electrode sheet with a thickness of 50-200 μm is obtained, that is, a high-performance lithium manganate battery positive electrode sheet.

9. A high-performance lithium manganese oxide battery, characterized in that: The invention comprises the high-performance lithium manganate battery positive electrode sheet as described in any one of claims 1 to 3, and also comprises a negative electrode sheet.

10. The high performance lithium manganate battery according to claim 9, characterized in that: The preparation method of the negative electrode sheet is as follows: the negative electrode slurry is evenly coated on the current collector at 10-110° C. by a coating machine to obtain an active material sheet with a thickness of 100-200 μm, and then rolled to obtain a negative electrode sheet with a thickness of 50-150 μm.

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