Positive electrode material and preparation method thereof, pole piece and battery

Abstract

The invention relates to the technical field of batteries, and particularly discloses a positive electrode material, a preparation method thereof, a pole piece and a battery. The disclosed positive electrode material comprises an inner core and a coating layer arranged on at least part of the surface of the inner core, the inner core comprises lithium manganese iron phosphate and a ternary material; a coating agent for forming the coating layer includes a silane compound. The positive electrode material has high energy density, excellent cycling stability and safety performance, the problem of dissolution of manganese in lithium manganese iron phosphate is effectively solved, and the structural stability of the positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a positive electrode material and a preparation method thereof, a pole piece and a battery. Background Art

[0002] The rapid development of electric vehicles has led to higher demands on the comprehensive performance of lithium-ion batteries, including energy density and cycle performance. Commonly used batteries on the market include ternary lithium batteries and lithium iron phosphate batteries. Lithium iron phosphate batteries offer significant advantages in safety and stability, but their energy density is slightly lower than that of ternary materials. By adding manganese, lithium iron phosphate (LiMnFePO4) increases its voltage platform from 3.4V to 4.1V. Its energy density is approximately 15% to 20% higher than that of LiFePO4, and it also offers higher voltage and superior low-temperature performance.

[0003] Lithium manganese iron phosphate also has some inherent performance flaws, such as low first-cycle efficiency, low compaction, and poor processing performance, which to some extent limit its large-scale industrial application. To address these shortcomings, the industry generally uses coating, doping, nano-scaling, and ternary material composites to improve performance. For example, some literature addresses the poor conductivity of lithium manganese iron phosphate by compounding it with highly conductive carbon materials such as carbon nanotubes and graphene to improve conductivity and achieve optimization of energy density, cycle life, and rate performance.

[0004] However, although the capacity of lithium manganese iron phosphate coating has been improved, the tortuosity has been increased. There is also the problem of manganese dissolution during the cycle, which affects the cycle performance and stability of the battery. Summary of the Invention

[0005] In view of this, the present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention provides a cathode material and a preparation method thereof, a cathode plate, and a battery, which have high energy density, excellent cycle stability, and safety performance, can effectively solve the problem of manganese dissolution in lithium manganese iron phosphate, and can improve the structural stability of the cathode material.

[0006] According to a first aspect of the present invention, the present invention provides a positive electrode material comprising: a core, and a coating layer disposed on at least a portion of the surface of the core;

[0007] The core includes lithium manganese iron phosphate and a ternary material; and the coating agent used to form the coating layer includes a silane compound.

[0008] In an optional embodiment, the silane compound includes at least one of alkylsilane, olefinsilane or nitrogen-containing functional group silane.

[0009] In an optional embodiment, the alkylsilane includes at least one of methylsilane, trisilane, butasilane or polysilane.

[0010] In an alternative embodiment, the olefinic silane comprises vinyl silane.

[0011] In an optional embodiment, the nitrogen-functional silane includes cyanosilane.

[0012] In an optional embodiment, the coating layer has a thickness of 1 nm to 10 nm.

[0013] In an optional embodiment, the molar ratio of carbon element to silicon element in the coating layer is (2-3):1.

[0014] In an optional embodiment, the molar ratio of carbon element to silicon element in the coating layer is 2.4:1.

[0015] In an optional embodiment, in the core, the mass ratio of the ternary material to the lithium manganese iron phosphate is (0-1):1, and the mass of the ternary material is not 0.

[0016] In an optional embodiment, the median particle size D of the core v50 2μm~15μm.

[0017] In an optional embodiment, the ternary material includes lithium nickel cobalt manganese oxide, and the molar ratio of the elements Ni:Co:Mn in the lithium nickel cobalt manganese oxide is (6-9):(0.5-2):(0.5-2), preferably 6:2:2.

[0018] In an optional embodiment, the ternary material includes lithium nickel cobalt aluminum oxide, and the molar ratio of the elements Ni:Co:Al in the lithium nickel cobalt aluminum oxide is (6-9):(0.5-2):(0.5-2), preferably 6:2:2.

[0019] In an optional embodiment, the molar ratio of the elements Mn:Fe in the lithium manganese iron phosphate is (5-9):(1-5), preferably 6:4.

[0020] According to a second aspect of the present invention, the present invention provides a method for preparing a positive electrode material, comprising the following steps:

[0021] The iron source, phosphorus source, manganese source, lithium source and the ternary material are uniformly mixed and ball-milled to obtain a slurry;

[0022] drying and sintering the slurry to obtain a core;

[0023] The core and the coating solution are mixed and stirred to obtain a suspension, and the suspension is dried to obtain the positive electrode material; wherein the coating solution is obtained by dissolving a silane compound in a solvent.

[0024] In an optional embodiment, the iron source is selected from one or more of ferrous phosphate, ferrous oxalate, ferrous chloride, ferrous nitrate, ferrous oxide, ferrous sulfate, ferric chloride, ferric nitrate, ferric sulfate, ferric oxide, ferric oxide or ferric phosphate.

[0025] In an optional embodiment, the phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid or phosphorous acid.

[0026] In an optional embodiment, the manganese source is selected from one or more of manganese carbonate, manganese phosphate, manganous phosphate, manganese sulfate, manganese oxalate, manganese acetate, manganese chloride, manganese trioxide or manganese tetraoxide.

[0027] In an optional embodiment, the lithium source is selected from one or more of lithium carbonate, lithium bicarbonate, lithium acetate, lithium chloride, lithium bromide, lithium hydroxide, lithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate or lithium sulfate.

[0028] In an optional embodiment, the solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide or acetone.

[0029] In an optional embodiment, the concentration of the coating solution is 9-14 g / L.

[0030] In an optional embodiment, the suspension is dried by spray drying, the spray drying temperature is 200° C. to 300° C., and the spray drying time is 20 min to 40 min.

[0031] In an optional embodiment, the sintering temperature is 650° C. to 850° C., and the sintering time is 6 h to 12 h.

[0032] In an optional embodiment, the sintering further includes rolling, jaw crushing, pulverizing and demagnetizing.

[0033] According to the third aspect of the present invention, the present invention provides a pole piece, comprising: a current collector, and the positive electrode material described in any embodiment of the first aspect of the present invention, and / or the positive electrode material obtained by the preparation method described in any embodiment of the second aspect of the present invention, arranged on at least one side of the current collector.

[0034] According to the fourth aspect of the present invention, the present invention provides a battery comprising: a negative electrode sheet, a separator, and the positive electrode material described in any embodiment of the first aspect of the present invention, and / or the positive electrode material obtained by the preparation method described in any embodiment of the second aspect of the present invention, and / or the electrode sheet described in any embodiment of the third aspect of the present invention.

[0035] The positive electrode material and preparation method thereof, the electrode sheet and the battery provided by the present invention have at least the following beneficial effects:

[0036] 1. In a preferred embodiment of the present invention, the provided positive electrode material is modified by mutual doping of lithium manganese iron phosphate and a ternary material to obtain a positive electrode material that can take into account both energy density and safety. At the same time, the manganese dissolution of the positive electrode material during the charge and discharge process is suppressed, and the electrochemical performance is optimized by synergistic effect. The obtained positive electrode material has excellent energy density and long cycle performance.

[0037] 2. In a preferred embodiment of the present invention, the performance of the positive electrode material is controlled by selecting the blending ratio of the ternary material and lithium manganese iron phosphate, which effectively compensates for the low volume density, high cost and safety problems of the ternary material, improves the volume density and safety of the positive electrode active material, and reduces the cost.

[0038] 3. In a preferred embodiment of the present invention, a silane compound coating solution is used to coat and modify the positive electrode material. By precisely controlling the concentration of the silane compound in the coating solution, a more complete coating layer is formed to coat the core. The silane compound is selected as the raw material for forming the coating layer because the silane compound contains amino, imino, carboxyl, hydroxyl, thiol and other functional groups. 2+ During the dissolution process, these functional groups can complex the dissolved Mn 2+ , thereby reducing manganese dissolution and improving the structural stability of lithium manganese iron phosphate and the stability of the positive and negative electrode interfaces.

[0039] 4. During the charge and discharge process of the battery, the decomposition of the lithium salt in the electrolyte will produce a small amount of HF, and the presence of HF will corrode the lithium iron manganese phosphate and reduce the interfacial stability of the lithium iron manganese phosphate; in a preferred embodiment of the present invention, the coating layer contains Si, which can absorb the HF generated in the electrolyte and form SiF4, thereby alleviating the corrosion effect of HF on the surface of the lithium iron manganese phosphate. The coating layer is coated on the surface of the core, which not only solves the manganese dissolution problem of the lithium iron manganese phosphate, but also can alleviate the corrosion effect of HF on the lithium iron manganese phosphate, which is beneficial to improving the stability and cycle performance of the battery.

[0040] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0042] Figure 1 Shown is the SEM image of the positive electrode material in Comparative Example 1 of the present invention.

[0043] The above drawings illustrate specific embodiments of the present invention, which will be described in more detail below. These drawings and the accompanying description are not intended to limit the scope of the present invention in any way, but rather to illustrate the concept of the present invention to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0045] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0048] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0049] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0050] Lithium iron manganese phosphate (LMP) is manufactured by adding manganese to LMP, increasing its voltage platform from 3.4V to 4.1V. Its energy density is approximately 15% to 20% higher than LMP, resulting in a higher energy density. Therefore, LMP offers advantages over LMP, including higher voltage, higher energy density, and superior low-temperature performance. Compared to ternary materials, it also boasts lower cost, higher safety, and longer cycle life.

[0051] However, lithium manganese iron phosphate also has the following shortcomings: First, lithium manganese iron phosphate has a one-dimensional structure. Its crystal structure is relatively stable, but it also limits the transport of lithium ions in the one-dimensional channel, resulting in low ionic conductivity and electronic conductivity. The diffusion rate of lithium ions is much lower than that of lithium iron phosphate and ternary materials (two orders of magnitude lower). Second, when lithium manganese iron phosphate (LMFP) is used in lithium-ion batteries, manganese dissolution occurs due to the Jan-Teller effect of manganese ions, causing manganese to precipitate and enter the electrolyte. The precipitated manganese ions will deposit on the surface of the negative electrode, destroying the solid electrolyte interface film (SEI film), and will also increase the internal resistance of the lithium-ion battery and reduce the lithium ion deintercalation ability, thereby reducing the electrochemical performance of the lithium-ion battery. Third, due to the presence of manganese and iron in LMFP, two voltage platforms exist at 4.1V and 3.5V respectively, causing platform instability. Fourth, lithium manganese iron phosphate also has problems such as low first-cycle efficiency, low compaction density, and poor processing performance, which to a certain extent limit large-scale industrial applications.

[0052] In view of this, the present invention provides a positive electrode material, a preparation method thereof, a pole piece, and a battery. The present invention effectively addresses the aforementioned issues of LMFP by coating a core containing two active materials, lithium manganese iron phosphate and a ternary material, with a silane compound to form a coating layer. The specific technical solutions of the present invention are as follows:

[0053] [Cathode material]

[0054] In some embodiments of the present invention, a positive electrode material is provided, comprising: a core, and a coating layer arranged on at least a portion of the surface of the core; the core comprises lithium manganese iron phosphate and a ternary material; and the coating agent used to form the coating layer comprises a silane compound.

[0055] Optionally, ternary materials include but are not limited to NCM (LiNi x Co y Mn x O2) or NCA(LiNi x Co y Al zO2) one or more, specifically, it can be one or more of NCM811 or NCM532.

[0056] The core includes lithium manganese iron phosphate and ternary material, and the content of lithium manganese iron phosphate and ternary material in the core is not zero; that is, the core contains two active substances, lithium manganese iron phosphate and ternary material; of course, those skilled in the art can understand that the mass proportion of lithium manganese iron phosphate and ternary material in the core is not specifically limited in this embodiment, and is within the scope of protection of the present invention.

[0057] It should also be noted that the positive electrode material in this embodiment does not include a core containing only lithium manganese iron phosphate, with a coating layer coated on the surface of the lithium manganese iron phosphate; and a core containing only ternary material, with a coating layer coated on the surface of the ternary material.

[0058] The core contains two active substances, lithium manganese iron phosphate and ternary material. Lithium manganese iron phosphate and ternary material can work synergistically. For example, ternary material has high energy density, but it has low volume density, easy to release excessive heat, and the risk of thermal runaway. Lithium manganese iron phosphate has excellent thermal stability and can effectively suppress the internal side reactions and thermal runaway risks of the battery during the charging and discharging process. The positive electrode material doped with the two active substances has excellent energy density and long cycle performance.

[0059] Silane compounds include but are not limited to one or more of methylsilane, trisilane, butane, diethylethylchlorosilane, polysilane, methyltris(2,3-dichloropropoxy)silane, vinylsilane or cyanosilane. By coating the two active substances, lithium manganese iron phosphate and ternary material, in the coating layer, the two can be better distributed more evenly, avoiding the large differences in the coating layer thickness, the particle size of the positive electrode material, etc. on different active materials caused by coating a single active material (lithium manganese iron phosphate or ternary material) separately, thereby affecting the overall performance of the battery. Moreover, the overall coating of the two active materials can also better protect the contact interface between lithium manganese iron phosphate and the ternary material in the coating layer, avoiding the active material from directly contacting the substance in the coating layer, inducing chemical reactions or physical changes at the interface of the active material, thereby improving the battery cycle stability and safety.

[0060] By limiting the inclusion of silane compounds in the coating agent for forming the coating layer, the problem of manganese ion dissolution in lithium manganese iron phosphate can be effectively solved. Since silane compounds contain abundant functional groups such as amino, imino, carboxyl, hydroxyl or thiol, the lone pair electrons on the nitrogen atom in the amino (-NH2) and imino (-NH) groups interact with Mn 2+ Easy to form coordination bonds; the oxygen atom in the carboxyl group (-COOH) has a lone pair of electrons that can be donated to Mn 2+, forming a coordination bond, or in some cases, the carboxyl group can also form a bidentate ligand with Mn 2+ Combination, that is, coordination with metal ions through hydroxyl oxygen and carbonyl oxygen at the same time; similarly, hydroxyl (-OH) or thiol (-SH) can also easily form Mn 2+ Coordination bond. Therefore, in Mn 2+ During the dissolution process, the rich functional groups in the silane compound can complex the dissolved Mn 2+ , thereby reducing the dissolution of manganese and improving the structural stability of lithium manganese iron phosphate and the stability of the positive and negative electrode interfaces. When the coating agent is coated on the surface of the core, Mn 2+ It can form coordination bonds with the functional groups in the coating agent, and after the subsequent coating agent forms a coating layer, Mn 2+ Encapsulated in this coating layer, reducing Mn 2+ The dissolution of ions improves the stability of the cathode material.

[0061] In this embodiment, by coating the surface of the core containing lithium manganese iron phosphate and the ternary material with a coating layer of silicon groups, the obtained positive electrode material has high energy density, excellent cycle stability and safety performance, effectively solves the problem of manganese dissolution in lithium manganese iron phosphate, and improves the structural stability of the positive electrode material.

[0062] In some embodiments, the silane compound includes at least one of an alkyl silane, an alkyl silane, or a nitrogen-functional silane.

[0063] The silane compound can be selected from one or more of alkylsilanes, olefinsilanes or nitrogen-containing functional group silanes; preferably, the alkylsilane can be selected from at least one or more of methylsilane, trisilane, butasilane or polysilane; preferably, the olefinsilane can be vinylsilane; preferably, the nitrogen-containing functional group silane can be selected from cyanosilane. By limiting the silane compound, the interfacial stability of the lithium iron manganese phosphate in the positive electrode material can be effectively improved, and the decomposition of lithium salts in the electrolyte to produce HF (hydrofluoric acid) to corrode the lithium iron manganese phosphate during charging and discharging can be avoided. The above-mentioned silane compound contains Si groups, which can absorb the HF generated in the electrolyte and react to form SiF4, effectively alleviating the corrosive effect of HF on the surface of the lithium iron manganese phosphate. Therefore, the coating agent forming the coating layer in the positive electrode material contains the above-mentioned silane compound, which can not only solve the problem of manganese dissolution in the lithium iron manganese phosphate, but also alleviate the corrosive effect of HF in the electrolyte on the surface of the lithium iron manganese phosphate, which is beneficial to improving the stability and cycle performance of the battery.

[0064] In some embodiments, the coating layer has a thickness of 1 nm to 10 nm.

[0065] Specifically, the thickness of the coating layer can be any one of 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm or 10nm, or any point value in any two of them. By limiting the thickness of the coating layer to this range, it can effectively ensure that the positive electrode material has good interface stability and reduce the dissolution of manganese; at the same time, the coating layer contains carbon and silicon elements. The silicon element can reduce the corrosion of the electrolyte on the surface of the lithium manganese iron phosphate, and the carbon element can improve the ionic conductivity of the positive electrode material. If the thickness of the coating layer is less than this range, it cannot effectively and long-term protect the lithium manganese iron phosphate in the core from being corroded by HF; and because the thickness of the coating layer is too thin, the positive electrode material is in the electrolyte for a long time, and the coating layer is corroded by HF for a long time, making it difficult to ensure that Mn 2+ If the coating layer is too thick, it will waste raw materials and increase costs. On the other hand, it will affect the ionic conductivity of the positive electrode material and thus affect the cycle performance of the battery.

[0066] In some embodiments, the molar ratio of carbon element to silicon element in the coating layer is (2-3):1.

[0067] Specifically, the molar ratio of carbon to silicon in the coating layer can be any one of 2:1, 2.05:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 2.95:1 or 3:1, or any ratio of any two. By limiting the ratio of carbon to silicon in the coating layer to within this range, the problem of manganese dissolution in the core of the positive electrode material can be effectively solved, while also ensuring that the coating layer has excellent ionic conductivity and anti-electrolyte corrosion performance of the lithium manganese iron phosphate in the core. If the ratio of carbon to silicon exceeds this range, either the ionic conductivity of the positive electrode material is affected, thereby affecting the cycle rate performance of the battery; or if there is too little silicon, the coating layer cannot effectively absorb the HF generated in the electrolyte, thereby causing the surface of the lithium manganese iron phosphate in the core to be corroded, affecting the energy density of the positive electrode material.

[0068] In a preferred embodiment, the molar ratio of carbon to silicon in the coating layer is 2.4: 1. This optimizes the overall performance of the positive electrode material, ensuring not only excellent energy density but also cycle rate performance and safety of the battery.

[0069] In some embodiments, the mass ratio of the ternary material to the lithium manganese iron phosphate in the core is (0-1):1, and the mass of the ternary material is not zero.

[0070] Specifically, the mass ratio of the ternary material and lithium iron manganese phosphate in the core is 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 0.95:1 or 1:1, or any ratio of any two. By limiting the mass ratio of the ternary material and lithium iron manganese phosphate in the core, it can be ensured that the ternary material and lithium iron manganese phosphate in the core work together, so that the positive electrode material has good comprehensive performance. If it only contains ternary materials, although the ternary materials have high energy density, their safety performance is poor, and the battery is prone to risks such as thermal runaway. If it only contains lithium iron manganese phosphate, it has low ionic conductivity and electronic conductivity, as well as poor stability, which affects the cycle rate performance of the battery.

[0071] In some embodiments, the median particle size D of the core v50 2μm~15μm.

[0072] Specifically, the median particle size D of the core v50 The median particle size D of the core can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, or any two of them. v50 Within this range, lithium ion insertion and extraction can be guaranteed, giving the battery good rate performance; at the same time, the positive electrode material can have a high initial capacity. If it exceeds this range, the larger core particle size will easily cause particle cracking, and the lithium manganese iron phosphate in the core will be easily corroded by HF in the electrolyte, which will have a negative impact on the battery life and reduce the compaction density of the positive electrode material, thereby affecting the battery's capacity density. If it is less than this range, the dispersion performance of the positive electrode material will deteriorate, affecting the battery's cycle rate performance.

[0073] In some embodiments, the ternary material includes lithium nickel cobalt manganese oxide, and the molar ratio of the elements Ni:Co:Mn in the lithium nickel cobalt manganese oxide is (6-9):(0.5-2):(0.5-2), preferably 6:2:2.

[0074] Specifically, the molar ratio of Ni:Co:Mn in the ternary material lithium nickel cobalt manganese oxide can be any one of 6:0.5:0.5, 6.5:0.7:0.8, 7:1:1, 7.5:1.2:1.5, 8:1.5:1.2, or 9:2:2, or any two of them. By limiting the molar ratio of Ni:Co:Mn in the ternary material, the battery can have a higher energy density and the positive electrode material can have a higher and more stable operating voltage, thereby improving the stability of the battery.

[0075] In some embodiments, the ternary material includes lithium nickel cobalt aluminum oxide, and the molar ratio of the elements Ni:Co:Al in the lithium nickel cobalt aluminum oxide is (6-9):(0.5-2):(0.5-2), preferably 6:2:2.

[0076] Specifically, the molar ratio of Ni:Co:Mn in the ternary material lithium nickel cobalt aluminum oxide can be any one of 6:0.5:0.5, 6.5:0.7:0.8, 7:1:1, 7.5:1.2:1.5, 8:1.5:1.2, or 9:2:2, or any two of them. Similarly, the molar ratio of Ni:Co:Al in lithium nickel cobalt aluminum oxide is limited to ensure that the positive electrode material has high energy density and good stability. If it is outside this range, the energy density, cycle performance, and thermal stability of the battery are easily adversely affected.

[0077] In some embodiments, the molar ratio of Mn:Fe in the lithium manganese iron phosphate is (5-9):(1-5), preferably 6:4.

[0078] Specifically, the molar ratio of Mn:Fe in the lithium manganese iron phosphate can be any one of 5:1, 5.5:1.2, 6:2, 6.5:2.2, 7:3, 8:4, or 9:5, or any two of these. By limiting the molar ratio of Mn:Fe in the lithium manganese iron phosphate, the positive electrode material can maintain a stable voltage platform, improving the stability of the positive electrode material and the overall energy output of the battery. Exceeding this range can easily lead to an unstable voltage platform, affecting the battery's cycling performance.

[0079] [Method for preparing positive electrode material]

[0080] In some embodiments of the present invention, a method for preparing a positive electrode material is further provided, comprising the following steps:

[0081] S101. Evenly mix the iron source, phosphorus source, manganese source, lithium source and ternary material, and ball-mill to obtain a slurry.

[0082] The iron source includes but is not limited to one or more of ferrous phosphate, ferrous oxalate, ferrous chloride, ferrous nitrate, ferrous oxide, ferrous sulfate, ferric chloride, ferric oxide or ferric phosphate; the phosphorus source includes but is not limited to one or more of diammonium hydrogen phosphate, phosphorus pentoxide, phosphoric acid or phosphorous acid; the manganese source includes but is not limited to one or more of manganese carbonate, manganese phosphate, manganous phosphate, manganese sulfate, manganese trioxide or manganese tetraoxide; the lithium source includes but is not limited to one or more of lithium carbonate, lithium dihydrogen phosphate, lithium oxalate or lithium sulfate; ball milling by a ball mill can well control the particle size of the slurry particles, and thus better control the particle size of the core particles, thereby ensuring the overall performance of the battery.

[0083] S102, drying and sintering the slurry to obtain a core.

[0084] The slurry can be dried by freeze drying, heat drying or spray drying; sintering can be carried out in an inert gas atmosphere such as nitrogen, helium or argon. The dried slurry particles may undergo side reactions, affecting the performance of the subsequent positive electrode material.

[0085] S103, mixing and stirring the core and the coating solution to obtain a suspension, and drying the suspension to obtain a positive electrode material; wherein the coating solution is obtained by dissolving a silane compound in a solvent.

[0086] The coating solution is obtained by dissolving the silane compound in a solvent, which can be one or more of N-methylpyrrolidone, N,N-dimethylformamide or acetone; the suspension is preferably dried by spray drying, which can evenly coat the coating solution on the core surface.

[0087] In this embodiment, the raw materials (iron source, phosphorus source, manganese source, lithium source and ternary material) of lithium iron manganese phosphate and ternary material are directly mixed to form a slurry, so that they can better penetrate and combine with each other during the reaction process to form a more uniform composite structure. Secondly, compared with the direct mixing of lithium iron manganese phosphate and ternary material, the interface bonding between the two active materials is weak, which easily leads to a decrease in electrochemical performance; and the raw materials will form a stronger chemical bond during the reaction, thereby enhancing the interface bonding between lithium iron manganese phosphate and ternary material. Thirdly, the above method is used to prepare, which can make the crystal structure of lithium iron manganese phosphate better match the crystal structure of the ternary material to form a more stable positive electrode material; compared with the direct mixing of lithium iron manganese phosphate and ternary material, the crystal structures of the two active materials may not be fully compatible, affecting the overall performance of the positive electrode material. In addition, the use of raw material mixing synthesis can more flexibly adjust the composition and proportion of various raw materials and optimize the performance of the positive electrode material, while the direct mixing of finished product lithium iron manganese phosphate and ternary material, the composition and proportion of the two active materials are fixed, and it is difficult to further optimize the performance of the positive electrode material.

[0088] In some embodiments, the iron source is selected from one or more of ferrous phosphate, ferrous oxalate, ferrous chloride, ferrous nitrate, ferrous oxide, ferrous sulfate, ferric chloride, ferric nitrate, ferric sulfate, ferric oxide, ferric oxide, or ferric phosphate.

[0089] In some embodiments, the phosphorus source is selected from one or more of diammonium phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid, or phosphorous acid.

[0090] In some embodiments, the manganese source is selected from one or more of manganese carbonate, manganese phosphate, manganous phosphate, manganese sulfate, manganese oxalate, manganese acetate, manganese chloride, dimanganese trioxide, or trimanganese tetraoxide.

[0091] In some embodiments, the lithium source is selected from one or more of lithium carbonate, lithium bicarbonate, lithium acetate, lithium chloride, lithium bromide, lithium hydroxide, lithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate, or lithium sulfate.

[0092] In some embodiments, the solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, or acetone.

[0093] In some embodiments, the concentration of the coating solution is 9-14 g / L.

[0094] Specifically, the concentration of coating solution can be any one of 9g / L, 9.5g / L, 10g / L, 10.5g / L, 11g / L, 11.5g / L, 12g / L, 13g / L or 14g / L or any point value in any two. By the concentration of coating solution, it is possible to ensure that kernel can be uniformly dispersed in coating solution, and coating solution can be coated on kernel surface simultaneously. If the concentration of coating solution is less than this scope, coating solution is too diluted, can not effectively be coated on kernel surface, is difficult to form a coating layer of certain thickness; If greater than this scope, coating solution is too viscous, and kernel can not be uniformly dispersed in this coating solution, is difficult to form uniform positive electrode material particles, and then affects the overall performance of battery.

[0095] In some embodiments, the suspension is dried by spray drying, the spray drying temperature is 200° C. to 300° C., and the spray drying time is 20 min to 40 min.

[0096] In this embodiment, the suspension can be dried by freeze drying or heat drying, preferably spray drying. The spray drying temperature can be any one of 200°C, 220°C, 230°C, 250°C, 280°C, or 300°C, or any two of them. By limiting the spray drying temperature, uniform and dispersed particles can be formed, making the coating layer covering the core less susceptible to cracking, thereby ensuring that manganese dissolution of the positive electrode material is reduced and that the positive electrode material has a high energy density.

[0097] In some embodiments, the sintering temperature is 650° C. to 850° C., and the sintering time is 6 h to 12 h.

[0098] Specifically, the sintering temperature can be any one of 650°C, 700°C, 750°C, 800°C, or 850°C, or any two thereof; and the sintering time can be any one of 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours, or any two thereof. Controlling the sintering temperature within this temperature range can effectively improve the structural integrity of the positive electrode material, while also controlling the particle size of the positive electrode material and achieving a good particle morphology.

[0099] In some embodiments, the sintering process further includes rolling, jaw crushing, pulverizing and demagnetizing.

[0100] After sintering, further steps such as rolling, jaw crushing, pulverizing and demagnetization are used to further accurately control the particle size of the positive electrode material, make the particle size of the positive electrode material uniform, and at the same time improve the purity of the positive electrode material, thereby ensuring the comprehensive performance of subsequent batteries.

[0101] [Pole piece]

[0102] In some embodiments of the present invention, a pole piece is further provided, comprising: a current collector, and the positive electrode material according to any one of the above embodiments disposed on at least one side of the current collector.

[0103] The current collector includes but is not limited to copper foil, aluminum foil or aluminum alloy foil. The positive electrode material in any of the above embodiments or the positive electrode material prepared by the preparation method of the positive electrode material in any of the embodiments is arranged on one side or both sides of the current collector; the electrode sheet may also include a binder and a conductive agent.

[0104] [Battery]

[0105] In some embodiments of the present invention, a battery is further provided, comprising: a negative electrode sheet, a separator, and the positive electrode material in any of the above embodiments.

[0106] In some embodiments, the battery further comprises a positive electrode material prepared by the method of any of the above embodiments.

[0107] In some embodiments, the battery further comprises a pole piece according to any of the above embodiments.

[0108] The battery in the embodiment of the present invention further includes a negative electrode sheet, a separator, and an electrolyte. While the specific type of battery is not limited, by way of example, the battery can be any of a cylindrical lithium battery, a soft-pack lithium battery, or an aluminum-cased lithium battery. The battery, including the aforementioned positive electrode material provided by the present invention, thus exhibits high energy density, excellent cycling stability, and safety performance, such as a lithium-ion secondary battery. It effectively addresses the issue of manganese dissolution in lithium manganese iron phosphate and enhances the structural stability of the positive electrode material.

[0109] Since the battery provided by the embodiment of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0110] The present application is described in detail below with reference to the following examples and comparative examples, but the implementation and protection of the present invention are not limited thereto. The following examples are only some examples of the present application and are not limitations of the present application.

[0111] Example 1

[0112] Example 1 provides a positive electrode material, the core of which includes LiMn 0.6 Fe 0.4 PO4 and ternary material LiNi 0.6 Mn 0.2 Co 0.2 O2; wherein the mass ratio of the ternary material to lithium manganese iron phosphate is 0.2:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0113] S11. Weigh the corresponding lithium source, iron source, manganese source, phosphorus source and ternary material according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0114] S12. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of the lithium manganese iron phosphate composite ternary material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and sinter for 8 hours; finally grind and sieve to obtain the core.

[0115] S13. The core is dispersed in a coating solution containing methylsilane by magnetic stirring. The coating solution is obtained by dissolving a silane compound in an organic solvent; wherein the solvent is N-methylpyrrolidone (NMP), the concentration of the silane compound in the coating solution is 10g / L, the speed of mechanical stirring can be 600rpm, and the stirring time is 6h. Spray drying is then performed to evaporate the solvent. The temperature of the spray dryer inlet and outlet can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5MPa to obtain a positive electrode material with a coating layer.

[0116] Example 2

[0117] Example 2 provides a positive electrode material, the core of which includes LiMn 0.6 Fe 0.4 PO4 and ternary material LiNi 0.6 Mn 0.2 Co 0.2 O2; wherein the mass ratio of the ternary material to the lithium manganese iron phosphate material is 0.6:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0118] S21. Weigh the corresponding lithium source, iron source, manganese source, phosphorus source and ternary material according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0119] S22. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate composite ternary material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the core.

[0120] S23. The core is dispersed in a coating solution containing methylsilane by magnetic stirring. The coating solution is obtained by dissolving a silane compound in an organic solvent; wherein the solvent is N-methylpyrrolidone (NMP), the concentration of the silane compound in the coating solution is 12g / L, the speed of mechanical stirring can be 600rpm, and the stirring time is 6h. Spray drying is then performed to volatilize the solvent. The temperature of the spray dryer inlet and outlet can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5MPa to obtain a positive electrode material with a coating layer.

[0121] Example 3

[0122] Example 3 provides a positive electrode material, the core of which includes LiMn 0.6 Fe 0.4 PO4 and ternary material LiNi 0.6 Mn 0.2 Co 0.2 O2, wherein the mass ratio of the ternary material and the lithium manganese iron phosphate material is 0.8:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0123] S31. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source and ternary material according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0124] S32. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate composite ternary material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the core.

[0125] S33, the core is dispersed in a coating solution containing methylsilane by magnetic stirring, the coating solution being obtained by dissolving a silane compound in an organic solvent; wherein the solvent is N-methylpyrrolidone (NMP), the concentration of the silane compound in the coating solution is 14g / L, the speed of mechanical stirring can be 600rpm, and the stirring time is 6h. The material is then spray-dried to evaporate the solvent on the surface. The temperature at the inlet and outlet of the spray dryer can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5MPa, to obtain a positive electrode material with a coating layer.

[0126] Example 4

[0127] Example 4 provides a positive electrode material, the core of which includes LiMn 0.6 Fe 0.4 PO4 and ternary material LiNi 0.6 Mn 0.2 Co 0.2 O2; wherein the mass ratio of the ternary material and the lithium manganese iron phosphate material is 1:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0128] S41. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source and ternary material according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0129] S42. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate composite ternary material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the core.

[0130] S43. The core is dispersed in a coating solution containing methylsilane by magnetic stirring. The coating solution is obtained by dissolving a silane compound in an organic solvent. The solvent is N-methylpyrrolidone (NMP). The concentration of the silane compound in the coating solution is 12 g / L. The mechanical stirring speed can be 600 rpm and the stirring time is 6 hours. Spray drying is then performed to evaporate the solvent. The temperature at the inlet and outlet of the spray dryer can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5 MPa to obtain a positive electrode material with a coating layer.

[0131] Example 5

[0132] Example 5 provides a positive electrode material, the core of which includes LiMn 0.7 Fe 0.3 PO4 and ternary material LiNi 0.6 Mn 0.2 Co 0.2 O2; wherein the mass ratio of the ternary material to the lithium manganese iron phosphate material is 0.6:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0133] S51. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source and ternary material according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball milling beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0134] S52. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate composite ternary material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the core.

[0135] S53. The core is dispersed in a coating solution containing methylsilane by magnetic stirring. The coating solution is obtained by dissolving a silane compound in an organic solvent. The solvent is N-methylpyrrolidone (NMP). The concentration of the silane compound in the coating solution is 12 g / L. The mechanical stirring speed can be 600 rpm and the stirring time is 6 hours. Spray drying is then performed to evaporate the solvent. The temperature at the inlet and outlet of the spray dryer can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5 MPa to obtain a positive electrode material with a coating layer.

[0136] Example 6

[0137] Example 6 provides a positive electrode material, the core of which includes LiMn 0.6 Fe 0.4 PO4 and ternary material LiNi 0.8 Mn 0.1 Co 0.1 O2; wherein the mass ratio of the ternary material to the lithium manganese iron phosphate material is 0.6:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0138] S61. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source and ternary material according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0139] S62. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate composite ternary material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the core.

[0140] S63. Disperse the core in a coating solution containing methylsilane by magnetic stirring. The coating solution is obtained by dissolving a silane compound in an organic solvent. The solvent is N-methylpyrrolidone (NMP). The concentration of the silane compound in the coating solution is 12 g / L. The mechanical stirring speed can be 600 rpm and the stirring time is 6 hours. Spray drying is then performed to evaporate the solvent. The temperature at the inlet and outlet of the spray dryer can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5 MPa to obtain a positive electrode material with a coating layer.

[0141] Comparative Example 1

[0142] Comparative Example 1 provides a positive electrode material that does not use ternary materials to dope lithium manganese iron phosphate (LiMn 0.6 Fe 0.4 PO4) without a coating layer; the specific preparation steps are as follows:

[0143] S71. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0144] S72. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the positive electrode material.

[0145] Comparative Example 2

[0146] Comparative Example 2 provides a positive electrode material that does not use ternary materials to dope lithium manganese iron phosphate (LiMn 0.6 Fe 0.4 PO4); the specific preparation steps are as follows:

[0147] S81. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source according to a certain stoichiometric ratio, add them to a ball mill, then add an appropriate amount of ethanol and ball mill beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0148] S82. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain a core.

[0149] S83. Disperse the core in a coating solution containing methylsilane by magnetic stirring. The coating solution is obtained by dissolving a silane compound in an organic solvent. The solvent is N-methylpyrrolidone (NMP). The concentration of the silane compound in the coating solution is 12 g / L. The mechanical stirring speed can be 600 rpm, and the stirring time is 6 hours. The material is then spray-dried to evaporate the solvent on the surface. The temperature at the inlet and outlet of the spray dryer can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5 MPa. This yields a positive electrode material with a coating layer.

[0150] Comparative Example 3

[0151] Comparative Example 3 provides a positive electrode material including a ternary material (LiNi 0.6 Mn 0.2 Co0.2 O2) and lithium manganese iron phosphate (LiMn 0.6 Fe 0.4 PO4); the specific preparation steps are as follows:

[0152] S91. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source as well as the ternary material according to a certain stoichiometric ratio, wherein the mass ratio of the ternary material to the lithium iron manganese phosphate material is 0.6:1, add them into a ball mill, and then add an appropriate amount of ethanol and ball milling beads, and mix them by ball milling at a speed of 500 r / min for 4 hours to obtain a slurry.

[0153] S92. Spray-dry the slurry at 80°C for 6 hours to obtain a precursor of lithium manganese iron phosphate material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat to 650°C and calcine for 8 hours; finally grind and sieve to obtain the positive electrode material.

[0154] Comparative Example 4

[0155] Comparative Example 4 provides a positive electrode material, the core of which includes lithium manganese iron phosphate (LiMn 0.6 Fe 0.4 PO4) and ternary materials (LiNi 0.6 Mn 0.2 Co 0.2 O2), wherein the mass ratio of the ternary material to the lithium manganese iron phosphate material is 1.2:1, and the surface of the core is coated with a coating layer; the specific preparation steps are as follows:

[0156] S101. Weigh the corresponding lithium source, iron source, manganese source and phosphorus source and ternary material according to a certain stoichiometric ratio, wherein the mass ratio of the ternary material to the lithium manganese iron phosphate material is 1.2:1, add them into a ball mill, and then add an appropriate amount of ethanol and ball milling beads, and ball mill at a speed of 500 r / min for 4 hours to obtain a slurry.

[0157] S102. Spray-dry the slurry at 80° C. for 6 hours to obtain a precursor of lithium manganese iron phosphate material; grind the precursor into powder and pour it into a quartz porcelain boat, place it in a tube furnace, pass inert gas, heat it to 650° C. and calcine it for 8 hours; finally, grind and sieve it to obtain a core.

[0158] S103, the core is dispersed in a coating solution containing methylsilane by magnetic stirring, the coating solution being obtained by dissolving a silane compound in a solvent; wherein the solvent is N-methylpyrrolidone (NMP), the concentration of the silane compound in the coating solution is 16g / L, the speed of mechanical stirring can be 600rpm, and the stirring time is 6h. The material is then spray-dried to evaporate the solvent. The temperature at the inlet and outlet of the spray dryer can be set to 300°C, and the pressure of the compressed air introduced into the spray dryer can be 0.5MPa, thereby obtaining a positive electrode material.

[0159] Performance testing:

[0160] 1. Electrochemical performance test:

[0161] The positive electrode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were used to prepare positive electrode sheets, and button cells were assembled to perform electrochemical performance tests and analyses, as follows:

[0162] (1) Preparation of positive electrode sheet

[0163] The positive electrode materials obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were dissolved in N-methylpyrrolidone (NMP) with conductive carbon (super-p) and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1 and stirred to form a uniform and stable slurry. The slurry was then coated on the surface of the carbon-coated aluminum foil by a doctor blade method with a coating thickness of about 100 μm. The slurry was dried and punched into discs with a diameter of 14 mm using a slicer to obtain the positive electrode sheets. The sheets were weighed, sealed, and placed in a drying dish for later use.

[0164] (2) Assembling batteries

[0165] A metallic lithium sheet was used as the negative electrode sheet and the above-prepared positive electrode sheet was assembled with a CR2032 button cell in a glove box filled with a high-purity argon atmosphere. The electrolyte was 1M LiPF6, and the solvent was a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. A PP separator was used as the separator. The assembled CR2032 button cell was subjected to constant current charge / discharge tests using a LAND CT2001A battery testing system, and the charge / discharge voltage window was 2.0 to 4.3 V.

[0166] (3) Electrochemical performance test

[0167] First, ensure that the battery has been assembled and left to stand for 6 hours. Then, use the CT2001A battery test system to perform a constant current charge and discharge test on the battery. Set the voltage range to 2.0-4.3V, and set the charge and discharge current and other parameters according to the experimental requirements. Start the test and record the relevant data. Specifically:

[0168] Specific capacity test: At 25°C, first discharge the battery to 2V at a constant current of 0.1C. After standing for 10 minutes, charge the battery to 4.3V at a constant current of 0.1C. The charge specific capacity at this time is recorded as the first charge specific capacity. After standing for 10 minutes, discharge the battery to 2.0V at a constant current of 0.1C. The discharge specific capacity at this time is recorded as the first discharge specific capacity.

[0169] The first coulombic efficiency at 0.1C = first discharge specific capacity / first charge specific capacity*100%.

[0170] Capacity retention test: At 25°C, discharge at a constant current of 1C to 2V. After standing for 10 minutes, charge at a constant current of 1C to 4.3V. The resulting charge value is the first cycle charge capacity. After standing for 10 minutes, discharge at a constant current of 1C to 2.0V. The resulting discharge value is the first cycle discharge capacity. This is one cycle. Repeat this process until the number of cycles reaches 200. End the test and record the discharge capacity at the 200th cycle. Therefore, the capacity retention rate at the 200th cycle = the discharge capacity at the 200th cycle / the initial discharge capacity * 100%.

[0171] The test results are shown in Table 1.

[0172] Table 1. Electrochemical performance test results:

[0173]

[0174] Results Analysis Table 1: From the results of Examples 1 to 6 and Comparative Examples 1 to 2, it can be seen that the core includes a ternary material and lithium manganese iron phosphate, which can obtain a positive electrode material that takes into account both energy density and long cycle performance. The ternary material and lithium manganese iron phosphate are both modified by doping and coating, and the synergistic effect of doping and coating can be used to optimize the long cycle performance of the positive electrode material. Examples 1 to 6 use ternary materials and lithium manganese iron phosphate to blend, which improves the specific capacity of the composite positive electrode material. From the comparison of Comparative Example 4, it can be seen that when the composite mass ratio of the ternary material and lithium manganese iron phosphate is not within the preferred range provided by the present invention, the resulting positive electrode material is difficult to take into account both energy density and long cycle performance. From the results of Comparative Example 3, it can be seen that Examples 1 to 6 use a coating layer containing amino, imino, carboxyl, hydroxyl, thiol and other functional groups that can adsorb manganese ions, which can effectively alleviate the impact of manganese ion dissolution on battery performance, improve the structural stability of the positive electrode material and the stability of the positive and negative electrode interfaces, and thus can improve the battery's first efficiency and capacity retention to a certain extent. The capacity retention rate of 200 cycles at 1C exceeds 98%.

[0175] 2. ICP test:

[0176] After cycling 200 cycles at 1C, the negative electrode of a CR2032 button cell was removed and subjected to ICP testing using an iCAP 7200 ICP-OES spectrometer. The results are shown in Table 2.

[0177] Table 2. ICP test results:

[0178] Test items Mn (μg / g) Fe (μg / g) Example 1 13 50 Example 2 11 40 Example 3 15 55 Example 4 20 58 Example 5 25 61 Example 6 23 65 Comparative Example 1 120 180 Comparative Example 2 18 57 Comparative Example 3 130 200 Comparative Example 4 30 60

[0179] Result Analysis Table 2: From the results of Examples 1 to 3 and Comparative Example 3, it can be seen that the embodiment uses a silane compound to coat the inner core, and the manganese ion and iron ion contents detected in the negative electrode sheet are significantly reduced, which shows that the coating layer containing amino, imino, hydroxyl, thiol, and carboxyl functional groups plays a major role in alleviating the dissolution of manganese ions and iron ions in the positive electrode material. The reason is that such functional groups can adsorb manganese ions and iron ions, thereby alleviating the dissolution of manganese ions and iron ions, and thus greatly reducing the content of manganese ions and iron ions in the negative electrode sheet; the content of manganese ions and iron ions detected in Example 2 is the lowest, that is, when the coating solution concentration is 12 g / L, the effect is best, the manganese ion content is only 11 μg / g, and the iron ion content is only 40 μg / g. It can be seen from the results of Example 2 and Comparative Examples 3 and 4 that when the concentration of the coating solution is not within the preferred range provided by the present invention, it is not conducive to suppressing the dissolution of manganese ions and iron ions in the positive electrode material. This is mainly because if the concentration is too low, it is difficult to form a complete coating layer, or the thickness of the formed coating layer is too thin; if the concentration is too high, the thickness of the formed coating layer is too thick, and too thin or too thick organic layer will adversely affect the performance of the positive electrode material.

[0180] Depend on Figure 1 It can be seen that the particle size of the positive electrode material in Comparative Example 1 is in the range of 200 nm to 400 nm. The particle size of the positive electrode material is relatively small overall, the particle distribution is relatively uniform, the surface is rounded, and there is no coating layer on the particle surface.

[0181] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0182] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0183] It should be noted that the terms "and / or" or " / " used herein are merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The singular forms "a," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0184] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0185] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that include: a core, and a coating layer disposed on at least a portion of a surface of the core; The core includes lithium manganese iron phosphate and ternary materials; The coating agent used to form the coating layer includes a silane compound.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies at least one of the following characteristics (1) to (3): (1) The silane compound includes at least one of an alkylsilane, an olefinsilane or a nitrogen-containing functional group silane; Preferably, the alkylsilane includes at least one of methylsilane, trisilane, butasilane or polysilane; Preferably, the olefinic silane comprises vinyl silane; Preferably, the nitrogen-functional silane includes cyanosilane; (2) The thickness of the coating layer is 1 nm to 10 nm; (3) The molar ratio of carbon element to silicon element in the coating layer is (2-3):1; Preferably, the molar ratio of carbon element to silicon element in the coating layer is 2.4:

1.

3. The positive electrode material according to claim 1, characterized in that In the core, the mass ratio of the ternary material to the lithium manganese iron phosphate is (0-1):1, and the mass of the ternary material is not 0; and / or, the median particle size D of the core v50 2μm~15μm.

4. The positive electrode material according to any one of claims 1 to 3, characterized in that The ternary material includes lithium nickel cobalt manganese oxide, wherein the molar ratio of the elements Ni:Co:Mn in the lithium nickel cobalt manganese oxide is (6-9):(0.5-2):(0.5-2), preferably 6:2:2; And / or, the ternary material comprises lithium nickel cobalt aluminate, wherein the molar ratio of the elements Ni:Co:Al in the lithium nickel cobalt aluminate is (6-9):(0.5-2):(0.5-2), preferably 6:2:2; And / or, the molar ratio of Mn:Fe in the lithium manganese iron phosphate is (5-9):(1-5), preferably 6:

4.

5. A method for preparing a positive electrode material, characterized in that: The following steps are involved: The iron source, phosphorus source, manganese source, lithium source and ternary material are mixed uniformly, and ball milled to obtain a slurry; drying and sintering the slurry to obtain a core; Mixing and stirring the core and the coating solution to obtain a suspension, and drying the suspension to obtain the positive electrode material; The coating solution is obtained by dissolving a silane compound in a solvent.

6. The method for preparing the positive electrode material according to claim 5, wherein: The preparation method satisfies at least one of the characteristics (1) to (4): (1) The iron source is selected from one or more of ferrous phosphate, ferrous oxalate, ferrous chloride, ferrous nitrate, ferrous oxide, ferrous sulfate, ferric chloride, ferric nitrate, ferric sulfate, ferric oxide, ferric oxide or ferric phosphate; (2) The phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium phosphate, phosphorus pentoxide, phosphoric acid or phosphorous acid; (3) The manganese source is selected from one or more of manganese carbonate, manganese phosphate, manganous phosphate, manganese sulfate, manganese oxalate, manganese acetate, manganese chloride, manganese trioxide, or manganese tetraoxide; (4) The lithium source is selected from one or more of lithium carbonate, lithium bicarbonate, lithium acetate, lithium chloride, lithium bromide, lithium hydroxide, lithium phosphate, dilithium hydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate or lithium sulfate.

7. The method for preparing the positive electrode material according to claim 5, wherein: The solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide or acetone; And / or, the concentration of the coating solution is 9-14 g / L.

8. The method for preparing a positive electrode material according to any one of claims 5 to 7, characterized in that: The suspension is dried by spray drying, the spray drying temperature is 200° C. to 300° C., and the spray drying time is 20 min to 40 min. And / or, the sintering temperature is 650° C. to 850° C., and the sintering time is 6 h to 12 h; And / or, after sintering, the steps of rolling, jaw crushing, pulverizing and demagnetizing are also included.

9. A pole piece, characterized in that: include: A current collector, and the positive electrode material according to any one of claims 1 to 4, and / or the positive electrode material obtained by the preparation method according to any one of claims 5 to 8, arranged on at least one side of the current collector.

10. A battery, characterized in that: include: A negative electrode sheet, a separator, and the positive electrode material according to any one of claims 1 to 4, and / or the positive electrode material obtained by the preparation method according to any one of claims 5 to 8, and / or the electrode sheet according to claim 9.

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