Positive electrode material for lithium ion battery and preparation method therefor, positive electrode piece, and secondary battery

Abstract

A positive electrode material for a lithium ion battery, a preparation method therefor, a positive electrode piece, and a secondary battery. The positive electrode material comprises an inner core, a first shell layer, and a second shell layer. The first shell layer covers the surface of the inner core, and the second shell layer covers the surface of the first shell layer that is away from the inner core. The inner core comprises a first transition metal oxide having a (003) crystal plane, and the first shell layer comprises a second transition metal oxide. For the first transition metal oxide and the second transition metal oxide at least one of the following are different: the space groups and the materials. The included angle between a first interface and plane occupied by the at least part of the (003) crystal plane in the inner core ranges from 80 degrees to 100 degrees, where the first interface is the surface of the second shell layer away from the first shell layer. The material of the second shell layer comprises an amorphous conductive material.

Description

Positive electrode material for lithium-ion battery, preparation method thereof, positive electrode sheet, and secondary battery

[0001] This disclosure claims priority to a Chinese patent application filed with the Patent Office of China on September 20, 2023, with application number 202311223067.7 and application name “Positive Electrode Materials for Lithium-ion Batteries, Preparation Methods, and Applications,” the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0002] The present disclosure relates to the field of battery technology, and in particular to a positive electrode material for a lithium-ion battery and a preparation method thereof, a positive electrode sheet, and a secondary battery. Background Art

[0003] Currently, layered transition metal oxide materials are popular in the market due to their simple structure, easy processing, and high capacity. However, during the charge-discharge cycle, mechanical stress caused by anisotropic volume changes in layered materials can lead to internal cracks. This in turn increases the contact area between the electrode active material and the electrolyte, causing side reactions, resulting in a shortened cycle life and reduced rate performance.

[0004] Changing the material and / or space group structure of the layered material can alleviate the above-mentioned problems. Therefore, the industry generally coats the surface of the layered transition metal oxide material with an isomeric and / or different material inert layer to reduce side reactions at the interface of the core positive electrode material, thereby alleviating cracking of the core positive electrode layered material and improving the cycle life of the positive electrode material. However, the difference in space group and / or material between the coating layer and the core material can lead to increased steric hindrance for the deintercalation / embedding of active ions, hindering the deintercalation / embedding of active ions, reducing the migration rate of active ions in the positive electrode material, causing polarization of the electrode sheet, and also detrimental to the battery's rate performance.

[0005] Summary of the Invention

[0006] In view of this, the present disclosure provides a positive electrode material for a lithium-ion battery, in which at least part of the (003) crystal plane in the core of the positive electrode material is located at a specific angle to the first interface, which can reduce the steric hindrance caused by the difference in space group and / or material between the core material and the first shell material, thereby facilitating the deintercalation / embedding of active ions and improving the rate performance of the battery; at the same time, it can reduce polarization and extend the cycle life of the battery.

[0007] In a first aspect, the present disclosure provides a positive electrode material for a lithium-ion battery. The positive electrode material comprises a core, a first shell, and a second shell, wherein the first shell is coated on a surface of the core, and the second shell is coated on a surface of the first shell facing away from the core; the core comprises a first transition metal oxide having a (003) crystal face, and the first shell comprises a second transition metal oxide;

[0008] The first transition metal oxide and the second transition metal oxide are different in at least one of the following: space group and material;

[0009] The angle between the plane where at least part of the (003) crystal plane in the core is located and the first interface is 80° to 100°, wherein the first interface is defined as the surface of the second shell layer facing away from the first shell layer;

[0010] The material of the second shell layer includes an amorphous conductive material.

[0011] The presence of the first shell prevents direct contact between the core and the electrolyte or electrolyte solution, thereby suppressing the cracking of the layered active material exacerbated by side reactions, thereby improving the structural stability of the core and extending the cycle life of the material. At the same time, the angle between the plane where at least some (003) crystal planes exist in the core and the first interface is within the range of 80°-100°, which can reduce the steric hindrance caused by the space group and / or material changes between the core and the first shell, increase the solid-phase diffusion rate of active ions, and thus improve the rate performance of the material. At the same time, it can also reduce polarization, improve the safety performance of the battery, and extend the cycle life of the battery. The second shell not only provides more channels for the migration of electrons and ions, but also increases the infiltration of the electrolyte, reduces the contact impedance of the positive electrode material, and improves the power performance of the material. Therefore, the above-mentioned positive electrode material can have good rate and power performance and a long cycle life.

[0012] In some embodiments, in the core, at least 50% of the (003) crystal planes are located at an angle of 80° to 100° with the first interface.

[0013] In some embodiments, in the core, the angle between the plane where at least part of the (003) crystal plane is located and the first interface is 89° to 91°.

[0014] In some embodiments, the first transition metal oxide comprises Li 1-a A a (Ni x Co y Mn z )M 1-x-y-z O 2-v X w; Wherein, the A element includes at least one of Na, K, Be, Mg, Ca, and B, 0≤a≤0.1; 0≤1-xyz≤0.1, x≥0, y≥0, z≥0, 0≤v≤0.05, 0≤w≤0.1; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; the X element includes one or more of F, S, and Cl.

[0015] In some embodiments, the second transition metal oxide comprises Li 1-a1 A a1 (Ni x1 Co y1 Mn z1 )M 1-x1-y1-z1 O 2-v1 X w1 ; Wherein, the A element includes at least one of Na, K, Be, Mg, Ca, and B, 0≤a1≤0.1; 0≤1-x1-y1-z1≤0.1, x1≥0, y1≥0, z1≥0, 0≤v1≤0.05, 0≤w1≤0.1; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; the X element includes one or more of F, S, and Cl.

[0016] In some embodiments, the space group of the second transition metal oxide is different from the space group of the first transition metal oxide.

[0017] In some embodiments, the space group of the second transition metal oxide is at least one of Fd3m and Fm3m.

[0018] In some embodiments, the thickness of the first shell layer is in the range of 1 nm to 10 nm.

[0019] In some embodiments, the amorphous conductive material includes at least one of a non-metallic conductive material, a lithium-containing compound, and a metal oxide; wherein the non-metallic conductive material includes at least one of graphite, carbon nanotubes, carbon black, graphene, silicon, silicon oxide, and germanium oxide; the lithium-containing compound includes at least one of lithium aluminate, lithium borate, lithium tungstate, lithium lanthanate, lithium titanate, lithium phosphate, lithium titanate, lithium aluminum titanium phosphate, and lithium fluoride; the metal oxide includes at least one of aluminum oxide, titanium oxide, tungsten oxide, yttrium oxide, and strontium oxide.

[0020] In some embodiments, the thickness of the second shell layer is in the range of 5 nm to 40 nm.

[0021] In some embodiments, the ratio of the thickness of the first shell layer to the thickness of the second shell layer is 1:(1-40).

[0022] In some embodiments, the D50 particle size of the positive electrode material is in the range of 3 μm-15 μm.

[0023] In some embodiments, the second shell layer coating the surface of the first shell layer facing away from the core includes: the second shell layer coating an aggregate formed by a plurality of cores coated with the first shell layer.

[0024] A second aspect of the present disclosure provides a method for preparing a positive electrode material for a lithium-ion battery. The method comprises: mixing a lithium source and a transition metal element source to obtain a first raw material; sintering the first raw material in an oxygen-containing atmosphere to obtain a precursor material; and dispersing the precursor material in an amorphous conductive material, mixing the precursor material and the amorphous conductive material, and then sintering the mixture a second time to obtain the positive electrode material.

[0025] In some embodiments, the first sintering is performed at 700° C. to 1000° C. for 16 h to 32 h.

[0026] In some embodiments, the temperature of the second sintering is 100°C-600°C.

[0027] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium nitrate, lithium oxalate, lithium hydroxide, and an organic lithium source.

[0028] In some embodiments, the transition metal element source includes a nickel source, a manganese source, and a cobalt source; the nickel source includes one or more of nickel nitrate, nickel sulfate, and nickel chloride; the cobalt source includes one or more of cobalt nitrate, cobalt sulfate, and cobalt chloride; the manganese source includes one or more of manganese nitrate, manganese sulfate, and manganese chloride.

[0029] In some embodiments, during the first sintering process, the mass percentage of oxygen in the oxygen-containing atmosphere is in the range of 18% to 100%.

[0030] In some embodiments, the preparation method further comprises: adding a doping element source to the first raw material, the doping element source comprising at least one of an A element source, an M element source, and an X element source; the A element comprises at least one of Na, K, Be, Mg, Ca, and B; the M element comprises one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; and the X element is selected from strongly electronegative elements, comprising at least one of F, S, and Cl.

[0031] A third aspect of the present disclosure provides a positive electrode plate. The positive electrode plate comprises the positive electrode material for the lithium-ion battery provided in the first aspect of the present disclosure, or the positive electrode material prepared by the preparation method provided in the second aspect of the present disclosure. The positive electrode plate can be used to provide a secondary battery having both good rate and power performance and a long cycle life.

[0032] A fourth aspect of the present disclosure provides a secondary battery. The secondary battery includes the positive electrode sheet provided in the third aspect of the present disclosure. Due to the use of the positive electrode sheet provided in the present disclosure, the secondary battery can achieve good rate and power performance and a long cycle life.

[0033] A fifth aspect of the present disclosure provides an electrical device. The electrical device includes the secondary battery provided in the fourth aspect of the present disclosure. Because the secondary battery provided in the present disclosure is used for power supply, the electrical device has good market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1A is a schematic diagram of the cross-sectional structure of a positive electrode material provided in one embodiment of the present disclosure.

[0035] FIG1B is a partial enlarged view of the area marked by the black circle in FIG1A .

[0036] FIG2 is a transmission electron microscope (TEM) photograph of a cross section of the positive electrode material of Example 1. FIG.

[0037] FIG3 is a schematic structural diagram of a positive electrode plate provided in one embodiment of the present disclosure.

[0038] FIG4 is a schematic structural diagram of a secondary battery provided in one embodiment of the present disclosure.

[0039] FIG5 is a schematic structural diagram of an electrical device provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0040] During the charge and discharge cycle, the mechanical stress caused by the anisotropic volume change of the layered transition metal oxide material will cause cracks to form inside it, which will increase the contact area between the electrode active material and the electrolyte, causing side reactions, thereby shortening the cycle life of the material and reducing the rate performance. In addition, the above side reactions will aggravate the electrochemical polarization of the battery, increase the battery operating voltage, prolong the charging time, and severe polarization will also affect the safety performance of the battery. The industry has attempted to reduce the side reactions at the interface of the core positive electrode material by coating an isomeric and / or material-different inert layer on the surface of the high-capacity layered transition metal oxide, thereby alleviating the cracking of the core positive electrode layered material and extending the cycle life of the material. However, the structural and / or elemental differences between the core and the inert layer materials often lead to greater steric hindrance to the diffusion of active ions at the core-shell interface (the migration path of the active ions becomes tortuous), resulting in a decrease in the migration rate of the active ions, impairing the rate performance of the material, and aggravating the electrochemical polarization. Furthermore, the active ion transmission channel is blocked, and lithium accumulation will form in the inert layer. The accumulation of lithium atoms may also cause the high-valent nickel ions that may exist in the material to continue to react with the electrolyte, thereby causing the above-mentioned accumulated lithium to gradually become "dead lithium", resulting in serious attenuation of the cycle performance.

[0041] To solve the above problems, please refer to Figures 1A and 1B. An embodiment of the present disclosure provides a positive electrode material 100 for a lithium-ion battery. The positive electrode material 100 for a lithium-ion battery includes a core 10, a first shell 20, and a second shell 30. The first shell 20 is coated on the surface of the core 10. The second shell 30 is coated on the surface of the first shell 20 facing away from the core 10. The core 10 includes a first transition metal oxide having a (003) crystal plane. The first shell 20 includes a second transition metal oxide. The (003) crystal plane of the transition metal oxide is a characteristic crystal plane of the R3m space group.

[0042] The angle θ between the plane where at least part of the (003) crystal plane in the core 10 is located and the first interface 301 is 80° to 100°, wherein the first interface 301 is defined as the surface of the second shell 30 facing away from the first shell 20;

[0043] The material of the second shell layer 30 includes an amorphous conductive material.

[0044] In the disclosed embodiments, the first transition metal oxide (i.e., the core material) and the second transition metal oxide (i.e., the first shell material) have different space groups and / or materials. Optionally, the space group of the first transition metal oxide is different from the space group of the second transition metal oxide. Optionally, the material of the first transition metal oxide is different from the material of the second transition metal oxide. Optionally, the space group of the first transition metal oxide is different from the space group of the second transition metal oxide, and the material of the first transition metal oxide is different from the material of the second transition metal oxide.

[0045] Specifically, the space group of the first transition metal oxide (i.e., the core material) is different from the space group of the second transition metal oxide (i.e., the first shell material), and / or the material (i.e., molecular formula) of the first transition metal oxide is different from the material (i.e., molecular formula) of the second transition metal oxide. For example, the first transition metal oxide is in the R3m space group, and the second transition metal oxide is in the Fd3m and / or Fm3m space group. In this case, the material (i.e., molecular formula) of the first transition metal oxide and the material (i.e., molecular formula) of the second transition metal oxide may be the same or different.

[0046] Specifically, in the embodiment of the present disclosure, the material of the first transition metal oxide is different from the material of the second transition metal oxide, including but not limited to the following two situations: (a) the elemental composition of the first transition metal oxide is different from that of the second transition metal oxide; for example, the first transition metal oxide is LiNi 0.8 Co 0.1 Mn 0.1 O2, the second transition metal oxide is Li 1.01 Na 0.01 Ni 0.8 Co 0.1 Mn 0.1 (b) The first transition metal oxide and the second transition metal oxide have the same elemental composition, but the molar amounts of the elements in one molecule are different; for example, the first transition metal oxide is LiNi 0.8 Co 0.1 Mn 0.1 O2, the second transition metal oxide is LiNi 0.5 Co 0.2 Mn 0.3 Regardless of the above case (a) or (b), in this case, the space group of the first transition metal oxide and the space group of the second transition metal oxide may be the same or different.

[0047] The positive electrode material 100 includes a core 10, a first shell 20, and a second shell 30. The presence of the first shell 20 can prevent the core 10 from direct contact with the electrolyte or electrolyte solution, thereby alleviating the cracking of the layered active material that is exacerbated by the side reaction between the core 10 and the electrolyte (e.g., electrolyte solution), thereby improving the structural stability of the core 10 and extending the cycle life of the material. More importantly, the angle between the plane where at least a portion of the (003) crystal planes in the core 10 are located and the first interface 301 is within the range of 80°-100°. This can reduce the steric hindrance caused by the difference in space group and / or material between the core material and the first shell material, increase the solid-phase diffusion rate of active ions (lithium ions), and thus improve the rate performance of the material. At the same time, it can reduce polarization, improve the safety performance of the battery, and extend the cycle life of the battery.

[0048] Furthermore, the surface of the first shell 20 is coated with a second shell 30 made of an amorphous (i.e., non-crystalline) conductive material. The relatively loose structure of the amorphous material not only provides more channels for the migration of electrons and ions, but also increases the electrolyte's wetting of the positive electrode material 100, reducing the contact impedance of the positive electrode material 100 and improving the material's power performance. Furthermore, based on the inherent high capacity of the layered transition metal oxide with a (003) crystal plane in the core 10, the positive electrode material 100 can achieve high energy density, good rate and power performance, a long cycle life, and high safety performance.

[0049] In the present disclosure, a transmission electron microscope (TEM) can be used to characterize the angle between the (003) crystal plane in the core 10 and the first interface 301. Specifically, a particle of positive electrode material 100 is sliced ​​to expose its cross-section. The slice of positive electrode material 100 is placed in a TEM. The alternating light and dark stripes at the boundary of the material cross-section are observed to represent the (003) crystal plane of the core material. The angle θ between a single stripe or the extension of a single stripe (i.e., the plane in which the (003) crystal plane lies) and the first interface 301 is measured. Referring to FIG. 1B , at the intersection of the single stripe or its extension with the first interface 301, the angle θ between the tangent line of the second shell 30 and the extension of the (003) crystal plane at that intersection is within a range of 80° to 100°.

[0050] In the present disclosure, the angle between the plane where the (003) crystal plane is located and the first interface 301 can be 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, 95°, 96°, 97°, 98°, 99°, etc. In some embodiments of the present disclosure, in the core 10, the angle between the plane where at least part of the (003) crystal plane is located and the first interface 301 is 89° to 91°. This is more conducive to the extraction / intercalation of active ions, thereby further improving the rate performance of the positive electrode material 100.

[0051] In the present disclosure, the positive electrode material 100 may be spherical, quasi-spherical, or irregularly shaped. For a single particle of the positive electrode material 100, a single core 10 may be sequentially coated with a first shell 20 and a second shell 30. Alternatively, a single core 10 may be coated with the first shell 20, and multiple cores 10 with the first shell 20 may form an agglomerate, with the second shell 30 then coating the agglomerate.

[0052] In some embodiments of the present disclosure, the first transition metal oxide (ie, core material) includes but is not limited to Li 1-a A a (Ni x Co y Mn z )M 1-x-y-z O2; wherein the A element includes at least one of Na, K, Be, Mg, Ca and B, 0≤a≤0.1; 0≤1-xyz≤0.1, x≥0, y≥0, z≥0; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os and W. Exemplarily, the first transition metal oxide may be, but is not limited to, LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811); LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523); Li(Ni 0.6 Co 0.2 Mn 0.2 ) 1.15 O2 (abbreviated as NCM622); LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM111); LiNi 0.4 Co 0.3 Mn 0.3 O2 (abbreviated as NCM433).

[0053] In some embodiments of the present disclosure, the second transition metal oxide (ie, the first shell material) includes but is not limited to Li 1-a1 A a1 (Ni x1 Co y1 Mn z1 )M 1-x1-y1-z1 O 2-v1 X w1 ; Wherein, the A element includes at least one of Na, K, Be, Mg, Ca and B, 0≤a1≤0.1; 0≤1-x1-y1-z1≤0.1, x1≥0, y1≥0, z1≥0, 0≤v1≤0.05, 0≤w1≤0.1; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os and W; the X element includes one or more of F, S and Cl.

[0054] In some specific embodiments of the present disclosure, the space group of the first transition metal oxide is different from the space group of the second transition metal oxide, that is, the space group of the core material is different from the space group of the first shell material. In some specific embodiments of the present disclosure, the space group of the second transition metal oxide may include, but is not limited to, Fd3m and / or Fm3m. In this way, the first shell 20 has a higher density and better structural stability, which is more conducive to suppressing side reactions between the core 10 and the electrolyte, thereby improving the structural stability of the positive electrode material 100 and further extending the cycle life of the positive electrode material 100.

[0055] In some embodiments of the present disclosure, in the core 10, at least 50% of the (003) crystal planes are located at an angle of 80° to 100° with the first interface 301. For example, in the core 10, the proportion of (003) crystal planes with an angle of 80° to 100° with the first interface 301 can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc. In this way, the positive electrode material 100 has more fast ion channels, which is more conducive to increasing the average rate of solid-phase diffusion of active ions in the positive electrode material 100, thereby further facilitating the battery's rate performance and reducing battery polarization. In some specific embodiments, at least 50% of the (003) planes are located at an angle of 89° to 91° with the first interface 301. For example, in the core 10, the proportion of the (003) crystal plane with an angle of 89° to 91° with the first interface 301 can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, etc.

[0056] In some embodiments of the present disclosure, the thickness of the first shell layer 20 is in the range of 1 nm to 10 nm. For example, the thickness of the first shell layer 20 can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, etc. In some specific embodiments, the thickness of the first shell layer 20 is in the range of 2 nm to 5 nm. Controlling the thickness of the first shell layer 20 within the above range is beneficial for controlling the extraction / embedding path of the active ions to control the diffusion rate of the active ions in the positive electrode material 100 within a suitable range, and can also provide a protective layer with a suitable thickness for the core material, thereby effectively suppressing the side reactions of the core material and the electrolyte.

[0057] In some embodiments of the present disclosure, the thickness of the second shell 30 is in the range of 5nm to 40nm. In some specific embodiments, the thickness of the second shell 30 is in the range of 10nm to 15nm. For example, the thickness of the second shell 30 can be, but is not limited to, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nmn, 22nm, 25m, 28nmn, 30nm, 32m, 35nmn, 38nm, etc. By controlling the thickness of the second shell 30 within the above range, it is possible to effectively improve the electronic conductivity of the material, control the length of the migration path of the active ions in the second shell 30 to be more appropriate, and have sufficient pores or channels to adsorb the electrolyte, so that the positive electrode material 100 has both good power performance and high rate performance.

[0058] In some embodiments of the present disclosure, the thickness ratio of the first shell layer 20 to the second shell layer 30 is in the range of 1: (1 to 40). For example, the thickness ratio of the first shell layer 20 to the second shell layer 30 can be 1: 1, 1: 2, 1: 5, 1: 8, 1: 10, 1: 12, 1: 15, 1: 18, 1: 20, 1: 22, 1: 25, 1: 28, 1: 30, 1: 32, 1: 35, 1: 38, etc. In some specific embodiments of the present disclosure, the thickness ratio of the first shell layer 20 to the second shell layer 30 is in the range of 1: (3 to 8). In this way, the rate performance and power performance of the entire positive electrode material 100 are more balanced, which is more conducive to the application prospects of the positive electrode material 100.

[0059] In some embodiments of the present disclosure, the amorphous conductive material (i.e., the material of the second shell 30) includes, but is not limited to, at least one of a non-metallic conductive material, a lithium-containing compound, and a metal oxide. The non-metallic conductive material includes, but is not limited to, at least one of graphite, carbon tubes, carbon black, graphene, silicon, silicon oxide, and germanium oxide. The lithium-containing compound includes, but is not limited to, at least one of lithium aluminate, lithium borate, lithium tungstate, lithium lanthanate, lithium titanate, lithium phosphate, lithium titanate, lithium aluminum titanium phosphate, and lithium fluoride. The metal oxide includes, but is not limited to, at least one of aluminum oxide, titanium oxide, tungsten oxide, yttrium oxide, and strontium oxide.

[0060] In some embodiments of the present disclosure, the D50 particle size of the positive electrode material 100 is in the range of 3μm-15μm. By controlling the D50 of the positive electrode material 100 within the above range, the transmission path of lithium ions in the positive electrode material 100 can be controlled to be shorter, thereby ensuring better rate performance of the battery; at the same time, it is also conducive to achieving a higher compaction density. For example, the D50 particle size of the positive electrode material 100 can be, but is not limited to, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, etc. In the embodiments of the present disclosure, the D50 of the positive electrode material 100 is tested using a laser particle size analyzer.

[0061] The present disclosure also provides a method for preparing a positive electrode material 100. The method for preparing the positive electrode material 100 includes:

[0062] S01, mixing a lithium source and a transition metal element source to obtain a first raw material; sintering the first raw material for the first time in an oxygen-containing atmosphere to obtain a precursor material; and

[0063] S02. Dispersing the precursor material in the amorphous conductive material, mixing, and performing a second sintering process to obtain the positive electrode material 100.

[0064] The preparation method is simple to operate and has strong process reliability, and is suitable for large-scale industrial production.

[0065] In some embodiments of the present disclosure, the first sintering condition is: sintering at 700°C to 1000°C for 16 hours to 32 hours. This is more conducive to the transformation of the surface layer of the core precursor material into a transition metal oxide with a space group of Fm3m (i.e., the second shell layer 30 with a space group of Fm3m) to obtain the precursor material, and is more conducive to improving the structural stability of the density of the material with a space group of Fm3m. At the same time, it is also conducive to improving the interfacial bonding strength between the core 10 and the second shell layer 30, thereby further improving the cycle life of the positive electrode material 100.

[0066] In some embodiments of the present disclosure, the equipment used in the first sintering includes but is not limited to a rotary kiln, a rotary kiln, a box furnace, a tube furnace, a roller kiln, a pusher kiln or a fluidized bed.

[0067] In some embodiments of the present disclosure, the lithium source includes but is not limited to at least one of lithium carbonate, lithium nitrate, lithium oxalate, lithium hydroxide, and an organic lithium source.

[0068] In some embodiments of the present disclosure, the above-mentioned transition metal element source includes but is not limited to a nickel source, a manganese source, and a cobalt source. The nickel source includes but is not limited to one or more of nickel nitrate, nickel sulfate, and nickel chloride. The cobalt source includes but is not limited to one or more of cobalt nitrate, cobalt sulfate, and cobalt chloride, and the manganese source includes one or more of manganese nitrate, manganese sulfate, and manganese chloride. In some specific embodiments of the present disclosure, the above-mentioned gradient temperature increase includes: heating to less than or equal to 500°C at a heating rate of not more than 10°C / min, holding for 2h to 9h, then heating to less than or equal to 850°C at a heating rate of not more than 13.3°C / min, and holding for 8h to 25h. In this way, the lithium source can be fully melted, the contact between the lithium source and the transition metal source can be enhanced, the occurrence of solid-phase reaction can be promoted, and the lithium ions can be embedded in the crystal lattice to form the core material. At the same time, the density of the core material is improved, thereby facilitating the migration of lithium ions between the core 10 and the core 10 and the first shell 20 during the charge and discharge cycle; at the same time, it will not affect the migration rate of lithium ions during the reaction, and fully reduce the risk of forming a superlattice at the crystal plane in the core material, affecting the crystal plane orientation in the core 10.

[0069] In some embodiments of the present disclosure, during the first sintering process, the mass percentage of oxygen in the oxygen-containing atmosphere varies within the range of 18% to 100%. For example, the mass percentage of oxygen in the oxygen-containing atmosphere in each time period can be independently selected from 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, etc. In some specific embodiments, the mass percentage of oxygen in the oxygen-containing atmosphere varies within the range of 19% to 95%. This facilitates the transformation of the surface layer of the core precursor material into a space group structure different from that of the core material, thereby forming the first shell 20. Controlling the oxygen mass percentage within the aforementioned range further enhances the density of the first shell 20 material and the interfacial bonding strength between the first shell 20 and the core 10. In some specific embodiments, the oxygen mass percentage in the oxygen-containing atmosphere is first gradually increased and then maintained constant. Thus, at high temperatures, other components (e.g., a transition metal source) can co-melt with the lithium source, lowering the melting point of the lithium source and the formation energy of the solid-phase reaction, thereby inducing the core 10 material to grow along the (003) crystal plane.

[0070] Some embodiments of the present disclosure further include adding a doping element source to the first raw material. The doping element source includes at least one of an A element source, an M element source, and an X element source. The A element includes at least one of Na, K, Be, Mg, Ca, and B; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; and the X element is selected from strongly electronegative elements, including but not limited to at least one of F, S, and Cl. These doping elements are incorporated into the core material to optimize its electrochemical performance or structural stability. For example, Ti can improve the material's cycling and rate performance without reducing the core material's theoretical capacity; Mg can expand the atomic layer spacing to stabilize the material's post-lithiation configuration or enhance the initial discharge capacity of the core 10. More importantly, these doping elements can, after forming the core precursor during the first sintering process, continue to infiltrate the surface layer of the core precursor and dope it, thereby forming a material different from the core 10, thereby transforming the core precursor into the first shell 20. It is understandable that, in the above process, continued doping of elements may change the space group of the material in the first shell layer 20 , or may simply change the elemental composition.

[0071] In the embodiments of the present disclosure, in S02, a precursor material is first dispersed in an amorphous conductive material, and after mixing, a second raw material is obtained, which is then subjected to a second sintering process. In some embodiments of the present disclosure, in S02, the mixing includes but is not limited to solid-phase dispersion or liquid-phase dispersion. Solid-phase dispersion can be performed in a solid-phase mixing device, such as a planetary ball mill.

[0072] In some embodiments of the present disclosure, in S02, the temperature of the second sintering may be 100°C-600°C. In some specific embodiments, the second sintering is also performed using a gradient heating method, wherein the gradient heating method includes heating at a third heating rate of less than or equal to 10°C / min and holding the temperature for 1 to 5 hours. In some specific embodiments, during the cooling process after the second sintering, the cooling rate is greater than or equal to 50°C / min.

[0073] The present disclosure also provides a positive electrode plate. As shown in FIG3 , the positive electrode plate 1 comprises the aforementioned positive electrode material 100. The positive electrode plate 1 can be used to realize a secondary battery having high energy density, good rate and power performance, long cycle life, and high safety performance.

[0074] In some embodiments of the present disclosure, the positive electrode sheet 1 includes a (positive electrode) current collector and a positive electrode active material layer disposed on at least one side of the current collector. The positive electrode active material layer includes the aforementioned positive electrode material, a binder, and a conductive agent.

[0075] In the disclosed embodiment, the positive electrode current collector is selected from any known positive electrode current collector in the art, such as aluminum foil, etc. The binder and the conductive agent can also be selected from any known materials in the art.

[0076] The present disclosure also provides a secondary battery. As shown in FIG4 , the secondary battery 3 includes a positive electrode plate 1 provided in an embodiment of the present disclosure. Due to the use of the positive electrode plate 1 provided in the present disclosure, the secondary battery 3 has a high energy density, and can achieve good rate and power performance, a long cycle life, and high safety performance.

[0077] In the embodiment of the present disclosure, the secondary battery 3 may be a liquid battery using an electrolyte, or a solid-state battery or a semi-solid-state battery.

[0078] In some embodiments of the present disclosure, the secondary battery 3 includes a positive electrode sheet 1, a separator (not shown), a negative electrode sheet 2, and an electrolyte (not shown). The negative electrode sheet can be any negative electrode sheet known in the art. The separator can be any separator known in the art. The electrolyte can be selected from electrolyte formulas well known to those skilled in the art.

[0079] The present disclosure also provides an electrical device. As shown in FIG5 , the electrical device 4 includes a secondary battery 3 provided in an embodiment of the present disclosure. In some embodiments of the present disclosure, the electrical device 4 also includes a load (such as a motor) connected to the secondary battery 3. The secondary battery 3 is used to power the load. Due to the use of the secondary battery 3 provided in the present disclosure for power supply, the electrical device 4 has a good market prospect.

[0080] In some embodiments of the present disclosure, the electrical equipment 4 includes but is not limited to 3C electronic products, power vehicles, etc.

[0081] The technical solution of the present disclosure is further illustrated below with multiple embodiments.

[0082] Examples 1-11

[0083] For ease of comparison and reading, various parameters of the positive electrode materials 100 provided in Examples 1-11 are summarized in Table 1.

[0084] In order to highlight the beneficial effects of the embodiments of the present disclosure, the following comparative examples are provided.

[0085] Comparative Examples 1-9

[0086] For the convenience of comparison and reading, the various parameters of the positive electrode materials 100 of Comparative Examples 1-9 are also summarized in Table 1.

[0087] TEM characterization test

[0088] TEM was used to select the boundary of the positive electrode material slice for observation, and the angle between the core (003) crystal plane and the first interface 301 was measured. For the same positive electrode material, 5-10 slices were tested, and 2-3 20nm×20nm fields of view were observed in each slice. The obtained data were fitted with a normal distribution, and the median of the distribution was taken as the angle θ. The distribution probability that θ fell in the range of 80° to 100° was taken as the proportion of angles satisfying the (003) crystal plane, and recorded in Table 1. At the same time, the thickness of the first shell 20 and the second shell 30 were measured, and the average value was calculated. The results are recorded in Table 1. Figure 2 is a typical TEM image of a cross-section of the positive electrode material of Example 1.

[0089] Table 1

[0090] Electrochemical performance test

[0091] (1) Test battery assembly

[0092] Preparation of positive electrode sheets: The positive electrode materials of each embodiment and comparative example in Table 2 were mixed with a binder (e.g., styrene-butadiene rubber) and a conductive agent (e.g., super P) in a mass ratio of 98:1:1, and then added with an appropriate amount of solvent (e.g., N-methylpyrrolidone, NMP) and stirred for 2 h to obtain a positive electrode slurry; the above-mentioned positive electrode slurry was coated on the surface of the positive electrode current collector (e.g., aluminum foil), dried, rolled, and cut to obtain each positive electrode sheet.

[0093] Preparation of negative electrode sheets: Mix the negative electrode material (e.g., graphite), thickener (specifically sodium carboxymethyl cellulose, CMC), binder (e.g., styrene-butadiene rubber, SBR), and conductive agent (e.g., acetylene black) in a mass ratio of 97:1:1:1, add an appropriate amount of deionized water, stir and disperse completely to obtain a negative electrode slurry, and evenly apply the obtained negative electrode slurry on the surface of the negative electrode collector (e.g., copper foil), dry, roll-press, and cut to obtain each negative electrode sheet.

[0094] Battery assembly: The prepared positive electrode and negative electrode sheets are stacked in the order of positive electrode / diaphragm / negative electrode, where a polypropylene diaphragm is used as the separator. The stacked battery cells are placed in a vacuum oven at 100°C and baked for 12 hours. The electrolyte is injected, where the electrolyte is 1 mol LiPF6 dissolved in an organic solvent with a mass ratio of ethylene carbonate: ethyl methyl carbonate of 7:3. After sealing, the lithium-ion battery is obtained after aging, formation, aging, capacity separation and other processes.

[0095] (2) Cycle life test: At 25°C, the lithium-ion battery was charged and discharged at a rate of 1C and a depth of 100% (DOD) for cycle testing until the battery capacity retention rate was less than 70%. The number of cycles at this time was recorded, which was the cycle life of the battery. The results are summarized in Table 2.

[0096] (3) Rate performance test: At 25°C, the lithium-ion battery was charged to 100% SOC at a rate of 0.2C and discharged to the lower limit voltage at a rate of 5C. The ratio of the discharge capacity at 5C to the discharge capacity at 0.33C was recorded. The results are summarized in Table 2.

[0097] Table 2

[0098] Combining the data in Table 1 and Table 2, it can be seen that the positive electrode material 100 provided in the embodiment of the present disclosure has both a long cycle life and good rate performance. Comparing the data of Examples 1-4, it can be seen that when other parameters are similar, when the angle θ between the (003) crystal plane in the core 10 of the positive electrode material 100 and the first interface 301 is in the range of 80°-100°, the proportion of the (003) crystal plane is within the range further suggested by the present disclosure, which is more conducive to the cycle performance and rate performance of the positive electrode material 100. Furthermore, when the above proportions are greater than or equal to 50%, the greater the proportion of the (003) crystal plane defined in the present disclosure, the more conducive to the electrochemical performance of the positive electrode material 100.

[0099] Comparing the data of Examples 7-9, it is not difficult to find that when the thicknesses of the first shell layer 20 and the second shell layer 30 are both within the range further suggested by the embodiments of the present disclosure (Example 7), the cycle performance and rate performance of the positive electrode material 100 are also better.

[0100] The above is an exemplary embodiment of the present disclosure. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present disclosure. These improvements and modifications are also considered to be within the scope of protection of the present disclosure.

Claims

1. A positive electrode material (100) for a lithium ion battery, characterized in that: The positive electrode material (100) comprises a core (10), a first shell layer (20), and a second shell layer (30), wherein the first shell layer (20) is coated on a surface of the core (10), and the second shell layer (30) is coated on a surface of the first shell layer (20) that is away from the core (10); The core (10) comprises a first transition metal oxide having a (003) crystal plane, and the first shell (20) comprises a second transition metal oxide; The first transition metal oxide and the second transition metal oxide are different in at least one of the following: space group and material; The angle between the plane where at least part of the (003) crystal plane in the core (10) is located and the first interface (301) is 80° to 100°, wherein the first interface (301) is defined as the surface of the second shell layer (30) facing away from the first shell layer (20); and The material of the second shell layer (30) includes an amorphous conductive material.

2. The positive electrode material (100) according to claim 1, characterized in that: In the core (10), at least 50% of the (003) crystal planes are located at an angle of 80° to 100° with the first interface (301).

3. The positive electrode material (100) according to claim 1, characterized in that: In the core (10), the angle between the plane where at least part of the (003) crystal plane is located and the first interface (301) is 89° to 91°.

4. The positive electrode material (100) according to any one of claims 1 to 3, characterized in that: The first transition metal oxide includes Li 1-a A a (Ni x Co y Mn z )M 1-x-y-z O 2-v X w ; wherein the A element includes at least one of Na, K, Be, Mg, Ca, and B, 0≤a≤0.1; 0≤1-xyz≤0.1, x≥0, y≥0, z≥0, 0≤v≤0.05, 0≤w≤0.1; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; the X element includes one or more of F, S, and Cl.

5. The positive electrode material (100) according to any one of claims 1 to 4, characterized in that: The second transition metal oxide includes Li 1-a1 A a1 (Ni x1 Co y1 Mn z1 )M 1-x1-y1-z1 O 2-v1 X w1 ; Wherein, the A element includes at least one of Na, K, Be, Mg, Ca, and B, 0≤a1≤0.1; 0≤1-x1-y1-z1≤0.1, x1≥0, y1≥0, z1≥0, 0≤v1≤0.05, 0≤w1≤0.1; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; the X element includes one or more of F, S, and Cl.

6. The positive electrode material (100) according to any one of claims 1 to 5, characterized in that: The space group of the second transition metal oxide is different from the space group of the first transition metal oxide.

7. The positive electrode material (100) according to any one of claims 1 to 6, characterized in that: The space group of the second transition metal oxide is at least one of Fd3m and Fm3m.

8. The positive electrode material (100) according to any one of claims 1 to 7, characterized in that: The thickness of the first shell layer (20) is in the range of 1 nm to 10 nm.

9. The positive electrode material (100) according to any one of claims 1 to 8, characterized in that: The amorphous conductive material includes at least one of a non-metallic conductive material, a lithium-containing compound, and a metal oxide; wherein the non-metallic conductive material includes at least one of graphite, carbon nanotubes, carbon black, graphene, silicon, silicon oxide, and germanium oxide; the lithium-containing compound includes at least one of lithium aluminate, lithium borate, lithium tungstate, lithium lanthanate, lithium titanate, lithium phosphate, lithium titanate, lithium aluminum titanium phosphate, and lithium fluoride; the metal oxide includes at least one of aluminum oxide, titanium oxide, tungsten oxide, yttrium oxide, and strontium oxide.

10. The positive electrode material (100) according to any one of claims 1 to 9, characterized in that: The thickness of the second shell layer (30) is in the range of 5 nm to 40 nm.

11. The positive electrode material (100) according to any one of claims 1 to 10, characterized in that: The thickness ratio of the first shell layer (20) to the second shell layer (30) is 1:(1-40).

12. The positive electrode material (100) according to any one of claims 1 to 11, characterized in that: The D50 particle size of the positive electrode material (100) is in the range of 3 μm-15 μm.

13. The positive electrode material (100) according to any one of claims 1 to 12, characterized in that: The second shell layer (30) is coated on the surface of the first shell layer (20) facing away from the core (10) and comprises: the second shell layer (30) is coated on an agglomerate formed by a plurality of cores (10) coated with the first shell layer (20).

14. A method for preparing a positive electrode material for a lithium ion battery, characterized in that: include: Mixing a lithium source and a transition metal element source to obtain a first raw material; Sintering the first raw material for the first time in an oxygen-containing atmosphere to obtain a precursor material; as well as The precursor material is dispersed in an amorphous conductive material, and the precursor material and the amorphous conductive material are mixed and then sintered for a second time to obtain the positive electrode material.

15. The preparation method according to claim 14, characterized in that: The conditions of the first sintering are: sintering at 700° C. to 1000° C. for 16 h to 32 h.

16. The preparation method according to claim 14 or 15, characterized in that: The temperature of the second sintering is 100°C-600°C.

17. The preparation method according to any one of claims 14 to 16, characterized in that: During the first sintering process, the mass percentage of oxygen in the oxygen-containing atmosphere is in the range of 18% to 100%.

18. The preparation method according to any one of claims 14 to 17, characterized in that: Also includes: A doping element source is added to the first raw material, wherein the doping element source includes at least one of an A element source, an M element source, and an X element source; the A element includes at least one of Na, K, Be, Mg, Ca, and B; the M element includes one or more of V, Ti, Cr, Fe, Co, Ni, Zn, Nb, Mo, Os, and W; and the X element is selected from strongly electronegative elements, including at least one of F, S, and Cl.

19. A positive electrode sheet (1), characterized in that: The positive electrode sheet (1) comprises the positive electrode material (100) for a lithium ion battery according to any one of claims 1 to 13 or the positive electrode material prepared by the preparation method according to any one of claims 14 to 18.

20. A secondary battery (3), characterized in that: The secondary battery (3) comprises the positive electrode material (100) of the lithium ion battery according to any one of claims 1 to 13 or the positive electrode material prepared by the preparation method according to any one of claims 14 to 18.

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