Positive electrode material containing O2-phase single crystal lithium-rich material, pole piece, preparation method and application

Abstract

The invention relates to a positive electrode material containing an O2-phase single crystal lithium-rich material, a pole piece, a preparation method and application. The positive electrode material containing the O2-phase single crystal lithium-rich material is a mixed composite material of an O2-phase single crystal lithium-rich positive electrode material and an O3-phase polycrystal lithium-rich positive electrode material, and in the positive electrode material containing the O2-phase single crystal lithium-rich material, the O2-phase single crystal lithium-rich positive electrode material and the O3-phase polycrystal lithium-rich positive electrode material keep respective crystal structure independence; the mass ratio of the O2-phase single crystal lithium-rich positive electrode material to the O3-phase polycrystal lithium-rich positive electrode material is (1: 1)-(1: 10); the O2-phase single-crystal lithium-rich positive electrode material is of a micron-grade pure-phase structure, the particle size is 1-5 microns, the chemical structural formula is LimLi < x > < 1 > Ni < y > < 1 > Co < z > < 1 > Mn < 1-x-y-z > < 1 > O2, m ranges from 0.72 to 0.75, x1 ranges from 0.17 to 0.22, y1 ranges from 0.04 to 0.08, and z1 ranges from 0 to 0.05; the particle size of the O3-phase polycrystalline lithium-rich positive electrode material is 8-10 [mu] m, the chemical structural formula of the O3-phase polycrystalline lithium-rich positive electrode material is Li < x > < 2 > Ni < y > < 2 > Co < z > < 2 > Mn < 1-x-y-z > < 2 > O < 2 >, the range of x < 2 > is 1-1.2, the range of y < 2 > is 0.13-0.4, and the range of z < 2 > is 0-0.13.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and particularly to a cathode material, a pole piece, a preparation method and an application thereof, which are single crystal lithium-rich materials containing an O2 phase. Background Art

[0002] Due to its unique oxygen redox mechanism, lithium-rich manganese-based layered oxides (LRMs) can achieve a high discharge specific capacity of over 300 mAh / g and are regarded as important candidates for the cathode materials of the new generation of high-energy-density lithium-ion batteries. However, in practical applications, it still faces many challenges, including low initial Coulomb efficiency, voltage hysteresis, significant voltage decay, and poor safety, which seriously restrict its commercialization process.

[0003] The high capacity in LRMs mainly comes from the reversible redox behavior of lattice oxygen. However, this mechanism has high activity and instability, and is prone to induce a series of structural and interfacial problems. For example, irreversible oxygen redox reactions will cause the migration and valence change of transition metal ions, leading to a decrease in the voltage plateau and severe voltage decay. In addition, the release of oxygen will induce surface side reactions, exacerbate electrolyte decomposition and interfacial instability, and affect the cycle life and safety. At the same time, the structural reorganization caused by oxygen redox during cycling will also form cracks and voids inside the material bulk, further weakening the integrity of the electrode structure.

[0004] In addition, the lithium-ion diffusion kinetics of the lithium-rich manganese-based material itself is slow, which is not conducive to the improvement of rate performance. Currently, in order to improve its tap density, some studies adopt a single-crystallization strategy. However, due to the poor structural stability and slow kinetics of the lithium-rich material, the prepared single-crystalline particles are still concentrated in the sub-micron or nano scale, and it is difficult to achieve both high gravimetric capacity and high volumetric energy density.

[0005] Although there have been various technical paths to attempt to optimize the performance of lithium-rich materials, such as element doping, surface coating, electrolyte additives, etc., the problems of structural evolution and performance decline caused by oxygen redox cannot be fundamentally solved.

[0006] Compared with traditional O3-phase lithium-rich materials, O2-phase lithium-rich layered oxides have a higher energy barrier for the migration of transition metals in the crystal structure due to their different oxygen ion stacking methods, which can effectively inhibit structural transformation and oxygen release, and fundamentally improve the stability and reversibility of the materials. At the same time, the O2-phase material has a larger interlayer spacing in the structure, a smoother lithium-ion diffusion path, and better rate performance, and is suitable for preparing single-crystalline lithium-rich cathode materials with larger particle sizes. However, the existing O2-phase lithium-rich materials still have problems such as low specific capacity, difficult control of structural phase purity, and low tap density, which limit their further application.

[0007] However, currently, lithium-rich materials with an O2 structure still have defects such as low specific capacity. For example, Chinese Patent Application CN117996067A provides a lithium-rich manganese-based cathode material with an O2 phase, its preparation, and application, including the preparation of a P2 sodium-ion cathode precursor and the preparation of a lithium-rich manganese-based cathode material with an O2 phase by an ion exchange method. The raw materials used in the preparation process of the P2 sodium-ion cathode precursor are a sodium source, a lithium source, an aluminum oxide, and a nickel-manganese co-precipitated precursor. The obtained lithium-rich manganese-based cathode material with an O2 phase is cycled 200 times at a current density of a normal rate of 1C (200 mA·g-1) and a low rate of 0.3C (60 mA·g-1) at a high cut-off voltage of 2 to 4.8V, and the capacity retention rate can only reach 87.5% at most. In this solution, the introduction of transition metal elements uses a co-precipitated precursor, such as Ni 0.16 Co 0.16 Mn 0.68 CO3 and Ni 0.2 Mn 0.6 CO3 and other precursors have a fixed ratio of nickel, cobalt, and manganese. If the sodium dosage / lithium dosage increases, using a co-precipitated precursor will cause impurities in the P2-phase sodium-containing layered oxide cathode material, while a low sodium / lithium dosage will lead to a decrease in the specific capacity of the lithium-rich material, making it difficult to exert the high specific capacity of the lithium-rich cathode material. The ratio of transition metal elements such as nickel and manganese or the ratio of nickel, cobalt, and manganese in this existing co-precipitated precursor is fixed, which is determined by the co-precipitation process. Therefore, when using a co-precipitated precursor as a raw material, the problem is that it must match the sodium dosage and / or lithium dosage within a fixed range. When the sodium dosage / lithium dosage increases, co-precipitation cannot adapt to the changes in sodium and lithium contents through element ratio adjustment, which will lead to more impurity phases in the P2-phase sodium-containing layered oxide cathode material. Therefore, a pure-phase P2 sodium-ion cathode precursor cannot be obtained by this technical solution. According to the description in its specification, the presence of a small protrusion peak at about 21° in the diffraction peak of the P2 sodium-ion cathode precursor represents the Li-Mn-O ordered honeycomb superlattice structure, which is actually the impurity peak of Li2MnO3. Therefore, it is difficult to exert the advantage of its high discharge specific capacity; in addition, this solution can only obtain a polycrystalline lithium-rich manganese-based cathode material with an O2 phase, and its tap density is low, resulting in difficulty in further improving the volume energy density.

[0008] In addition, some literatures have proposed using cathode materials with an O2-O3 composite structure. For example, Chinese Patent Application CN117577794A discloses a cathode material for lithium-ion batteries with an O2-O3 composite structure and its preparation method. By mixing metal oxides, lithium sources, and sodium sources in a specific molar ratio, and through two-step calcination treatment and ion exchange treatment, the target O2-O3 composite structure material is obtained. However, this composite structure is essentially a heterophase composite at the crystal scale. The obtained material does not contain pure-phase O2-phase material, and its composite structure is limited to the nano-scale O2 and O3 heterophase structure, and cannot fully exert the advantages of O2-phase single-crystal materials in rate performance and structural stability. In addition, the specific capacity of this material is still low, and the tap density is also insufficient, making it difficult to meet the development requirements of high-volume energy density lithium batteries. Summary of the Invention

[0009] The object of the present invention is to provide a cathode material, a cathode sheet, a preparation method and an application thereof containing an O2-phase single-crystal rich-lithium material, aiming at the defects existing in the prior art. The O2-phase single-crystal rich-lithium material proposed by the present invention can effectively solve problems such as serious irreversible oxygen release on the surface of the cathode material, voltage decay and structural rearrangement caused by the migration of transition metals. And this single-crystal material can take into account a relatively high discharge specific capacity and has a relatively large particle size, showing good rate performance and high tap density, and can be applied to battery systems with high mass energy density and high volume energy density; by compounding the O2-phase single-crystal rich-lithium material with the O3-phase polycrystalline rich-lithium material, it can have both high specific capacity, high rate performance and structural stability, and further improve the tap density through the particle size grading of the two, thereby significantly improving the cycle performance and energy density of the cathode material.

[0010] To achieve the above object, in the first aspect, the present invention provides a cathode material containing an O2-phase single-crystal rich-lithium material. The cathode material containing the O2-phase single-crystal rich-lithium material is a blended composite material of an O2-phase single-crystal rich-lithium cathode material and an O3-phase polycrystalline rich-lithium cathode material. And, in the cathode material containing the O2-phase single-crystal rich-lithium material, the O2-phase single-crystal rich-lithium cathode material and the O3-phase polycrystalline rich-lithium cathode material maintain the independence of their respective crystal structures;

[0011] The mass ratio of the O2-phase single-crystal rich-lithium cathode material to the O3-phase polycrystalline rich-lithium cathode material is 1:1 - 1:10;

[0012] The O2-phase single-crystal rich-lithium cathode material is a micron-scale pure-phase structure, with a particle size of 1 - 5 μm, and its chemical formula is Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1O2, where the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.05;

[0013] The particle size of the O3 - phase polycrystalline lithium - rich cathode material is 8 - 10 μm, and its chemical structural formula is: Li x2 Ni y2 Co z2 Mn 1-x2-y2-z2 O2, where the range of x2 is 1 - 1.2, the range of y2 is 0.13 - 0.4, and the range of z2 is 0 - 0.13.

[0014] In a second aspect, an embodiment of the present invention provides a preparation method of the cathode material described in the first aspect above, including:

[0015] Mixing the O2 - phase single - crystal lithium - rich cathode material and the O3 - phase polycrystalline lithium - rich cathode material according to a mass ratio of 1:1 - 1:10 to obtain the cathode material containing the O2 - phase single - crystal lithium - rich material;

[0016] Among them, the O2 - phase single - crystal lithium - rich cathode material is obtained by ion - exchange after uniformly mixing the P2 - pure - phase sodium - containing layered oxide cathode material and a second lithium source; the P2 - pure - phase sodium - containing layered oxide cathode material is obtained by ball - milling and mixing a sodium source, a first lithium source, and a transition metal oxide and then calcining;

[0017] The O3 - phase polycrystalline lithium - rich cathode material is obtained by ball - milling and mixing a transition metal compound precursor and a lithium source and then calcining.

[0018] In a third aspect, an embodiment of the present invention provides an O2 - phase single - crystal lithium - rich cathode material. The O2 - phase single - crystal lithium - rich cathode material has a micron - level pure - phase structure, the particle size is 1 - 5 μm, and its chemical structural formula is Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O2;

[0019] Among them, the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.05.

[0020] In a fourth aspect, an embodiment of the present invention provides a preparation method of the O2 - phase single - crystal lithium - rich cathode material described in the third aspect above, including:

[0021] Mix a sodium source, a first lithium source, and oxides containing transition metals Ni, Co, and Mn respectively in a molar ratio of Na:Li:Ni:Co:Mn = m':x3:y3:z3:1 - x3 - y3 - z3 by ball milling. After mixing evenly, calcine to obtain a P2 pure phase sodium-containing layered oxide cathode material Na m’

[0022] Li x3 Ni y3 Co z3 Mn 1-x3-y3-z3 O2; wherein, the range of m' is 0.72 - 0.75, the range of x3 is 0.17 - 0.22, the range of y3 is 0.04 - 0.08, and the range of z3 is 0 - 0.05;

[0023] Mix the P2 pure phase sodium-containing layered oxide cathode material Na m’ Li x3 Ni y3 Co z3 Mn 1-x3-y3-z3 O2 with a second lithium source in a mass ratio of 1:2 - 10, mix evenly, then perform ion exchange, and then obtain an O2 phase single crystal lithium-rich cathode material Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O2; wherein, the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.05.

[0024] Preferably, the sodium source includes at least one of sodium nitrate, sodium carbonate, sodium acetate, and sodium oxide; preferably sodium carbonate;

[0025] The first lithium source includes one or more of lithium nitrate, lithium carbonate, lithium acetate, lithium oxide, or lithium hydroxide; preferably lithium carbonate;

[0026] The oxides containing transition metals Ni, Co, and Mn respectively include nickel-containing oxide, manganese-containing oxide, and cobalt-containing oxide; the nickel-containing oxide includes NiO; the manganese-containing oxide includes one or more of MnO2, Mn3O4, or Mn2O3; the cobalt-containing oxide includes one or more of CoO, Co2O3, or Co3O4;

[0027] The second lithium source includes one or more of lithium nitrate, lithium chloride, lithium hydroxide, lithium acetate, or lithium bromide; preferably a mixture of lithium nitrate and lithium chloride.

[0028] Preferably, the ball milling speed for the ball milling mixture is 400 - 500 rpm, and the ball milling time is 5 - 10 h;

[0029] The atmosphere for the calcination includes one or more of air, argon, and synthetic air. The specific process of the calcination includes: heating up to 450°C - 700°C at a heating rate of 2 - 10°C / min, pre-calcining for 4 - 5 h, then heating up to 800 - 900°C, and calcining for 8 - 15 h; then cooling to room temperature at a cooling rate of 2 - 5°C / min.

[0030] Preferably, the temperature for the ion exchange is 280 - 300°C, and the ion exchange time is 1 - 10 h.

[0031] In a fifth aspect, an embodiment of the present invention provides a positive electrode plate, including: the positive electrode material containing the O2-phase single crystal lithium-rich material described in the first aspect above, or the O2-phase single crystal lithium-rich positive electrode material described in the third aspect above.

[0032] In a sixth aspect, an embodiment of the present invention provides a lithium battery, including: the positive electrode material containing the O2-phase single crystal lithium-rich material described in the first aspect above, or the O2-phase single crystal lithium-rich positive electrode material described in the third aspect above, or the positive electrode plate described in the fifth aspect above.

[0033] Preferably, the lithium battery includes one or more of a liquid lithium-ion battery, a liquid metal lithium battery, a hybrid solid-liquid lithium-ion battery, a hybrid solid-liquid metal lithium battery, an in-situ solidified lithium battery, a solid-state lithium-ion battery, or a solid-state metal lithium battery.

[0034] The positive electrode material of the O2-phase single-crystal lithium-rich material provided by the embodiments of the present invention is a blended composite material of an O2-phase single-crystal lithium-rich positive electrode material and an O3-phase polycrystalline lithium-rich positive electrode material. The two materials each maintain an independent crystal structure, ensuring that the rate advantage and structural stability of the O2 phase and the high-capacity characteristics of the O3 phase can be fully exerted. Among them, the pure-phase O2-phase single-crystal lithium-rich material of the present invention is obtained by ion exchange based on the P2 pure-phase sodium-containing layered oxide positive electrode material, which can inhibit the migration of transition metals and structural transformation, effectively reduce the uncontrolled lattice oxygen release phenomenon that part of the lattice oxygen of the lithium-rich material is oxidized and released as oxygen during charging (especially high-voltage charging), and then improve the specific capacity and cycle stability of the material, etc., and has good rate performance. The present invention can also obtain an O2-phase single-crystal lithium-rich positive electrode material with controllable composition. The proportion of each transition metal element in the single-crystal material is optimized to the maximum. The molar ratio of nickel element is controlled at 0.04-0.08, which is beneficial to giving full play to the high specific capacity of the lithium-rich positive electrode material. Moreover, the O2 single-crystal material of the present invention has good structural stability, can inhibit the migration of transition metals and maintain good structural stability. At the same time, the single-crystal material has good mechanical strength and can avoid the generation of intergranular cracks caused by long-term cycling of polycrystalline materials. Combining the O2-phase single-crystal lithium-rich positive electrode material with stable structure, high mechanical strength and excellent rate performance with the O3-phase polycrystalline lithium-rich positive electrode material with high discharge specific capacity and lithium-rich characteristics can use the O3 lithium-rich phase as a "lithium supplement agent" to continuously transfer lithium ions to the O2 phase during the cycling process, thereby significantly improving the cycle stability and capacity retention rate of the composite material. Therefore, the obtained positive electrode material has both high specific capacity, high structural stability and high rate performance.

[0035] The O2-phase single-crystal lithium-rich material proposed by the present invention can not only effectively solve the problems such as severe irreversible oxygen release on the surface of the positive electrode material, voltage attenuation and structural rearrangement caused by the migration of transition metals, but also the single-crystal material can take into account a relatively high discharge specific capacity and has a relatively large particle size, showing good rate performance and high tap density. On this basis, the O2-phase single-crystal lithium-rich material is combined with the O3-phase polycrystalline lithium-rich material, and the particle size of the O2-phase single-crystal material is limited to 1-5 μm, and the particle size of the O3-phase polycrystalline material is limited to 8-10 μm. The difference in size between the two forms a reasonable particle size grading, which is beneficial to the close packing between particles, thereby improving the tap density of the positive electrode material and further enhancing the volume energy density of the battery cell system. Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the structural change from the P2-phase precursor structure to the O2-phase single-crystal lithium-rich material structure in the preparation process of the present invention;

[0037] Figure 2 is an X-ray diffraction (XRD) pattern of the positive electrode materials of Example 1 and Comparative Example 1 of the present invention;

[0038] Figure 3 It is the scanning electron microscope (SEM) image of the cathode materials of Embodiments 1-3 of the present invention;

[0039] Figure 4 It is the charge-discharge curves of the O2-phase single-crystal lithium-rich cathode material of Embodiments 1-3 of the present invention in the first two weeks;

[0040] Figure 5 It is the electrochemical cycling curve of the O2-phase single-crystal lithium-rich cathode material of Embodiment 1 of the present invention;

[0041] Figure 6 It is the electrochemical cycling curve of the O3-phase single-crystal lithium-rich cathode material of Comparative Example 1 of the present invention. Detailed implementation manners

[0042] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments.

[0043] The embodiment of the present invention provides a cathode material containing an O2-phase single-crystal lithium-rich material, which is a blended composite material of an O2-phase single-crystal lithium-rich cathode material and an O3-phase polycrystalline lithium-rich cathode material. Moreover, in the cathode material containing the O2-phase single-crystal lithium-rich material, the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material maintain the independence of their respective crystal structures.

[0044] The mass ratio of the O2-phase single-crystal lithium-rich cathode material to the O3-phase polycrystalline lithium-rich cathode material is 1:1 - 1:10;

[0045] The O2-phase single-crystal lithium-rich cathode material is a micron-scale pure-phase structure with a particle size of 1 - 5 μm, and its chemical structural formula is Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O2, where the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.05.

[0046] The particle size of the O3-phase polycrystalline lithium-rich cathode material is 8 - 10 μm, and its chemical structural formula is: Li x2 Ni y2 Co z2 Mn 1-x2-y2-z2 O2, where the range of x2 is 1 - 1.2, the range of y2 is 0.13 - 0.4, and the range of z2 is 0 - 0.13.

[0047] Among them, due to the O2-phase single-crystal rich-lithium cathode material in the cathode material containing the O2-phase single-crystal rich-lithium material of the present invention, the O2-phase single-crystal rich-lithium cathode material itself has a micron-scale pure-phase structure, and the particle size is 1-5 μm, which can be any value within the above range, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm. Therefore, it has a higher tap density. In addition to being used in combination with the O3-phase polycrystalline rich-lithium cathode material, it can also be used alone as the cathode material.

[0048] Traditional polycrystalline rich-lithium cathode materials such as Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 is a secondary polycrystalline structure with primary particle agglomeration and is a porous structure. Therefore, after the material is made into a cathode electrode sheet, it only has a low tap density, usually only 2.5 g / cm 3 , and this low tap density seriously affects the volumetric energy density of the battery cell. In the present invention, the O2-phase single-crystal rich-lithium material can effectively improve the influence of the tap density by forming a single-crystal structure of primary particles. After the electrode sheet is made, its tap density can reach 2.9 g / cm 3 or more, higher than the existing polycrystalline structure system, thereby effectively improving the energy density of the battery cell.

[0049] The cathode material containing the O2-phase single-crystal rich-lithium material of the present invention can be prepared by the following method:

[0050] Mix the O2-phase single-crystal rich-lithium cathode material and the O3-phase polycrystalline rich-lithium cathode material according to a mass ratio of 1:1 - 1:10 to obtain the cathode material containing the O2-phase single-crystal rich-lithium material.

[0051] Among them, the O2-phase single-crystal rich-lithium cathode material is obtained by ion exchange after the P2 pure-phase sodium-containing layered oxide cathode material and the second lithium source are mixed evenly; the P2 pure-phase sodium-containing layered oxide cathode material is obtained by ball-milling and mixing a sodium source, a first lithium source, and a transition metal oxide and then calcining;

[0052] The O3-phase polycrystalline rich-lithium cathode material is obtained by ball-milling and mixing a transition metal compound precursor and a lithium source and then calcining.

[0053] Among them, the O2-phase single-crystal rich-lithium cathode material can be obtained by the following method:

[0054] Step 11: Ball-mill and mix a sodium source, a first lithium source, and oxides containing transition metals Ni, Co, and Mn respectively according to a molar ratio of Na:Li:Ni:Co:Mn = m':x3:y3:z3:1 - x3 - y3 - z3, and after mixing evenly, calcine to obtain the P2 pure-phase sodium-containing layered oxide cathode material Na m’ Li x3 Niy3 Co z3 Mn 1-x3-y3-z3 O₂; wherein, the range of m' is 0.72 - 0.75, the range of x3 is 0.17 - 0.22, the range of y3 is 0.04 - 0.08, and the range of z3 is 0 - 0.05.

[0055] Among them, the ball - milling rotation speed for ball - milling and mixing is 400 - 500 rpm, and the ball - milling time is 5 - 10 h; the calcination atmosphere includes one or more of air, argon, and synthetic air; the specific process of calcination includes: heating to 450°C - 700°C at a heating rate of 2 - 10°C / min, pre - calcining for 4 - 5 h, then heating to 800 - 900°C, and calcining for 8 - 15 h; then cooling to room temperature at a cooling rate of 2 - 5°C / min.

[0056] The sodium source includes at least one of sodium nitrate, sodium carbonate, sodium acetate, and sodium oxide; preferably sodium carbonate.

[0057] The first lithium source includes one or more of lithium nitrate, lithium carbonate, lithium acetate, lithium oxide, or lithium hydroxide; preferably lithium carbonate.

[0058] The oxides containing transition metals Ni, Co, and Mn respectively include nickel - containing oxide, manganese - containing oxide, and cobalt - containing oxide; the nickel - containing oxide includes NiO; the manganese - containing oxide includes one or more of MnO₂, Mn₃O₄, or Mn₂O₃; the cobalt - containing oxide includes one or more of CoO, Co₂O₃, or Co₃O₄.

[0059] Step 12, uniformly mix the P2 - phase sodium - containing layered oxide cathode material Na m’ Li x3 Ni y3 Co z3 Mn 1-x3-y3-z3 O₂ and the second lithium source in a mass ratio of 1:2 - 10, conduct ion exchange, and then obtain the O₂ - phase single - crystal lithium - rich cathode material Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O₂ after washing and drying; wherein, the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.05.

[0060] Among them, the second lithium source includes one or more of lithium nitrate, lithium chloride, lithium hydroxide, lithium acetate, or lithium bromide; preferably a mixture of lithium nitrate and lithium chloride.

[0061] The temperature of ion exchange is 280 - 300 °C, and the time of ion exchange is 1 - 10 h. The ion exchange process is as Figure 1 shown. By mixing the P2 pure-phase sodium-containing layered oxide cathode material Na m’ Li x3 Ni y3 Co z3 Mn 1-x3-y3-z3 O2 after high-temperature sintering with a certain amount of mixed second lithium salt and sintering at a low temperature. During the sintering process, lithium in the second lithium salt can exchange sodium in the P2 pure-phase sodium-containing layered oxide cathode material, and lithium enters the interlayer of transition metals to form octahedral occupancy, and the structure of the material changes from the original P2 phase to the O2 phase.

[0062] Specifically, in the preparation of the O2-phase single-crystal lithium-rich cathode material of the present invention, the co-precipitation method is not used, nor is the co-precipitation precursor (transition metal carbonate) disclosed in the prior art used as a raw material. Instead, transition metal oxides are used as raw materials. By optimizing the ratio of nickel, cobalt, and manganese, it is possible to ensure that a pure P2-phase structure can still be obtained under the conditions of high sodium content and lithium content. That is, the O2-phase lithium-rich cathode material Li m Li x Ni y Co z Mn 1-x-y-z O2 prepared by the present invention does not have any O3 or Li2MnO3 heterophase. Therefore, the structural advantages of O2 can be fully utilized, and it has a strong ability to inhibit the migration of transition metals, thereby reducing the structural transformation of the material, alleviating the voltage decay of the material, improving the capacity retention rate, and obtaining a high discharge specific capacity. The O2-phase single-crystal lithium-rich cathode material prepared by the present invention has better rate performance than the conventional O3 lithium-rich single-crystal material.

[0063] The calcination of the present invention includes two stages: pre-calcination and high-temperature sintering.

[0064] The pre-calcination platform of the present invention is 450 °C - 700 °C, and it can be any value within the above range, such as 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C. By adding a pre-calcination platform, the particle size of the O2-phase single-crystal lithium-rich cathode material can be effectively controlled, so that the lithium-rich cathode material prepared by this method is composed of micron-sized single-crystal particles, the particle size is controllable (1 - 5 μm), micron-sized single-crystal particles can be obtained with good consistency, and the compaction density of the electrode sheet can be greatly improved. At the same time, better cycle stability can be obtained.

[0065] The high-temperature sintering temperature range of the present invention is 800 - 900 °C, and it can be any value within the above range, such as 800 °C, 820 °C, 850 °C, 880 °C, 900 °C. A decrease in temperature will result in poor crystallinity of the material, affecting the rate performance of the material, while a higher temperature will lead to the formation of Li2MnO3 impurity phases.

[0066] In the ion exchange step of the present invention, the mass ratio of the second lithium source to the P2 pure-phase sodium-containing layered oxide cathode material is 2 - 10, and it can be any value within the above range, such as 2, 3, 4, 5, 6, 7, 8, 9, 10. This range is the preferred range. If the mass ratio of the second lithium source to the P2 pure-phase sodium-containing layered oxide cathode material is too low, sodium in the sodium-containing layered oxide cathode cannot be completely replaced by lithium, thereby affecting the transport of lithium ions and thus the electrochemical performance of the material; while too high a mass ratio will lead to a reduction in lithium in the transition metal layer, thereby affecting the capacity of the material.

[0067] In the present invention, the ion exchange temperature range is 280 - 300 °C, and it can be any value within the above range, such as 280 °C, 290 °C, 300 °C. The ion exchange time is 1 - 10 h, and the exchange time is preferably within this range. Too short an exchange time will result in incomplete replacement of sodium in the sodium-containing layered oxide cathode, and too long an exchange time will lead to a decrease in the lithium content in the O2 phase, thereby reducing the capacity of the material.

[0068] The O2-phase single-crystal lithium-rich cathode material prepared by the above method has unique structural characteristics, high discharge specific capacity and capacity retention rate, and is all composed of micron-sized single-crystal particles. The grain size is distributed between 1 and 5 microns, the particle size is controllable, the batch consistency is good, it has excellent thermal stability, and has a higher tap density compared to polycrystalline lithium-rich materials.

[0069] The structure of the O2 single-crystal material obtained by the preparation method of the present invention is stable. It can inhibit the migration of transition metals and maintain good structural stability. At the same time, the single-crystal material has good mechanical strength, thus avoiding the generation of intergranular cracks caused by long-term cycling of polycrystalline materials, and it has excellent rate performance. Therefore, the O2-phase single-crystal lithium-rich cathode material of the present invention can be used alone as a cathode material in energy storage devices such as ultra-high specific energy lithium-ion battery cells. It can also be further compounded with the O3-phase polycrystalline lithium-rich cathode material to obtain a cathode material with better performance.

[0070] The O3-phase polycrystalline lithium-rich cathode material compounded with the O2-phase single-crystal lithium-rich cathode material in the present invention can be prepared by the following method.

[0071] Step 21, ball-mill and mix the transition metal compound precursor and the lithium source according to the molar ratio of Li:Ni:Co:Mn = x2:y2:z2:1 - x2 - y2 - z2, and then screen to obtain a mixed material;

[0072] Among them, the range of x2 is 1 - 1.2, the range of y2 is 0.13 - 0.4, and the range of z2 is 0 - 0.13.

[0073] The ball - milling speed for ball - milling mixing is 200 - 300 rpm, and the ball - milling time is 1 - 5 h.

[0074] Step 22: Calcinate the mixed material to obtain an O3 - phase polycrystalline lithium - rich cathode material, which is spherical polycrystalline particles.

[0075] Among them, the calcination atmosphere includes one or more of air, argon, and synthetic air; the specific process of calcination includes: heating at a heating rate of 2 - 10 °C / min to 300 °C - 500 °C, pre - calcining for 4 - 5 h; then heating at a heating rate of 2 - 10 °C / min to 600 °C - 750 °C, holding for 8 - 20 h; finally heating at a heating rate of 2 - 10 °C / min to 800 - 900 °C, calcining for 3 - 10 h; and then cooling to room temperature at a cooling rate of 2 - 5 °C / min.

[0076] The particle size of the O3 - phase polycrystalline lithium - rich cathode material prepared by the above method of the present invention is 8 - 10 μm, and it can be any value within the above range, such as 8 μm, 9 μm, 10 μm. The chemical structural formula is: Li x2 Ni y2 Co z2 Mn 1-x2-y2-z2 O2, where the range of x2 is 1 - 1.2, the range of y2 is 0.13 - 0.4, and the range of z2 is 0 - 0.13.

[0077] The cathode material containing O2-phase single-crystalline rich-lithium material is prepared by mixing the O2-phase single-crystalline rich-lithium cathode material and the O3-phase polycrystalline rich-lithium cathode material according to a mass ratio of 1:1 to 1:10. The specific mixing mass ratio can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, etc. The particle size of the O2-phase single-crystalline material is 1-5 μm, and the particle size of the O3-phase polycrystalline material is 8-10 μm. Mixing the above two materials according to the above mass ratio can form a reasonable particle size grading due to the difference in their sizes, which can further improve the tap density of the composite material and can take into account better stability and better thermal stability. The present invention macroscopically physically mixes the O2 single-crystalline rich-lithium cathode material and the O3 polycrystalline rich-lithium cathode material, which has obvious advantages compared with the existing cathode material with the coexistence of O2 / O3 microscopic crystal structures prepared by synthesis. The form of the O2 / O3 microscopic crystal structure composite cannot effectively solve the disadvantage of low tap density, and the discharge specific capacity of the existing rich-lithium cathode material with the coexistence of O2 / O3 microscopic crystal structures obtained by the sintering process combined with ion exchange is relatively low. The composite of the present invention does not damage the crystal structures of the O2 single-crystalline rich-lithium cathode material and the O3 polycrystalline rich-lithium cathode material. By combining the pure-phase O2 single-crystalline rich-lithium cathode material with stable structure, good mechanical strength and high rate performance with the O3 polycrystalline rich-lithium material with high discharge specific capacity, it can not only take into account high specific capacity but also greatly improve the tap density of the electrode sheet and further improve the volume energy density of the battery cell system through particle size grading, and at the same time has very good thermal stability.

[0078] That is to say, the present invention can make full use of the advantages of the two materials. Although the existing O3 polycrystalline rich-lithium cathode material can give play to the advantage of a relatively high discharge specific capacity, its structural stability is poor, and serious migration of transition metals and oxygen evolution problems will occur during charge and discharge cycling, resulting in capacity attenuation and voltage decline. The pure-phase O2 single-crystalline material of the present invention has better structural stability, can inhibit the migration of transition metals and thus maintain good structural stability. At the same time, the single-crystalline material has good mechanical strength, which can avoid the generation of intergranular cracks caused by the long cycle of polycrystalline materials. Moreover, the rate performance of the pure-phase O2-structured rich-lithium cathode material is also more excellent than that of the O3-structured rich-lithium cathode material. The present invention combines the synthesized micron-scale pure-phase structured O2-phase single-crystalline rich-lithium cathode material with the O3-structured rich-lithium cathode material, which can form the complementary advantages of the two materials. Among them, the O3-structured rich-lithium cathode material serves as a lithium supplement agent for the micron-scale pure-phase O2-structured single-crystalline rich-lithium cathode material, and together they can have the advantages of high specific capacity, high stability and high rate. At the same time, for solid-state batteries, the composite cathode includes the single-crystalline rich-lithium material with O2 structure, which can alleviate the problem of internal particle lithium ion transport in polycrystalline materials in the solid-state composite cathode, so it has broad application prospects.

[0079] In addition, one of the factors currently limiting the commercialization process of existing lithium-rich cathode materials includes low volumetric energy density caused by low tap density. Since the single-crystal material with an O2-phase structure in the present invention has a micron-sized particle size of 1-5 μm, and the polycrystalline lithium-rich cathode material with an O3-phase structure has a particle size of 8-10 μm, the mixing of such sized particles can further improve the tap density of the material, and can take into account good stability and high discharge specific capacity, thereby improving the energy density and cycle performance of the cell system, etc.

[0080] In addition, the single-crystal material with an O2-phase structure in the present invention is a lithium-poor phase, while the polycrystalline material with an O3-phase structure is a lithium-rich phase. After the two are combined, the O3 lithium-rich phase can continuously transfer lithium ions to the O2 phase as a "lithium supplement agent". Therefore, it can make up for the poor cycle result caused by the fact that the single O2 phase has a poor lithium source mainly from the negative electrode side due to lithium poverty.

[0081] In summary, the present invention can give full play to the respective performance advantages of the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material. Although the existing O3-phase polycrystalline lithium-rich cathode material has a high discharge specific capacity, its structural stability is poor, and transition metal migration and oxygen evolution are likely to occur during charge and discharge, resulting in capacity attenuation and voltage decline. The O2-phase single-crystal lithium-rich cathode material in the present invention has excellent structural stability, can effectively inhibit transition metal migration, and maintain the integrity of the crystal structure; in addition, this material has high mechanical strength, which helps to avoid intergranular cracks in polycrystalline materials during long cycles, and also has better rate performance than the O3-phase polycrystalline lithium-rich cathode material.

[0082] By combining the O2-phase single-crystal lithium-rich cathode material with a micron-sized pure-phase structure and the O3-phase polycrystalline lithium-rich cathode material, not only the complementary of material properties is achieved, but also the O3-phase polycrystalline lithium-rich cathode material can be used as a "lithium supplement agent" for the O2-phase single-crystal lithium-rich cathode material to continuously provide lithium ions to it during the cycle, thereby realizing the synergistic improvement of high specific capacity, high structural stability and high rate performance.

[0083] Furthermore, for solid-state batteries, introducing the O2-phase single-crystal lithium-rich cathode material into the composite cathode helps to alleviate the problem of limited lithium-ion transport between particles inside polycrystalline materials. Therefore, it also has broad application prospects in the field of solid-state batteries.

[0084] In addition, an important bottleneck faced by existing lithium-rich cathode materials in the commercialization process is the insufficient volumetric energy density caused by low tap density. In the present invention, the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material are used in combination to form a particle size gradation, which can significantly improve the tap density of the cathode material, while taking into account good structural stability and high discharge specific capacity, thereby improving the energy density and cycle performance of the entire cell system.

[0085] The positive electrode material proposed by the present invention can be applied to the active material of the positive electrode sheet. For example, the O2-phase single-crystal lithium-rich positive electrode material can be used alone as the active material of the positive electrode sheet, or a composite material of the O2-phase single-crystal lithium-rich positive electrode material and the O3-phase polycrystalline lithium-rich positive electrode material can be used as the active material of the positive electrode sheet. When the O2-phase single-crystal lithium-rich positive electrode material is used alone, the single-crystal particle structure can effectively improve the tap density due to its larger particle size, and the tap density can reach 2.9 g / cm 3 or more. When using a composite material of O2 single crystal and O3 polycrystal, since the tap density can be further improved, the tap density can reach 3.1 g / cm 3 or more after the electrode sheet is made, thus effectively improving the energy density of the battery cell

[0086] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0087] In the following examples and comparative examples, the reagents and materials used, including electrolytes, electrolyte additives, negative electrode metallic lithium, etc., are all conventional reagent products obtained through commercial purchases, and can also be prepared by conventional methods. For those where specific experimental steps or conditions are not indicated in the examples, the operations or conditions of the conventional experimental steps in the art are followed.

[0088] For example, the particle size of the materials in the present invention refers to the particle size D50, that is, the median particle size of the materials, which can be the median sorted by volume, mass or quantity. In the embodiments of the present invention, it is the median particle size sorted by quantity, indicating the particle size at the 50% position in the quantity distribution. The particle size D50 has a well-known meaning in the art. The particle size of the materials provided in the embodiments of the present invention can be measured by well-known instruments and conventional methods in the art. Specifically, in this embodiment, the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Limited, UK, is used to measure the particle size.

[0089] Example 1

[0090] In this example, an O2-phase single-crystal lithium-rich positive electrode material was prepared, and the sample number was O2-phase single-crystal lithium-rich positive electrode material-1.

[0091] Step 1: Weigh the corresponding raw materials of sodium carbonate, lithium carbonate, nickel oxide, cobalt tetroxide, and manganese oxide according to the molar ratio of Na, Li, Ni, Co, and Mn being 0.75:0.22:0.04:0.01:0.73. Add them to the ball milling tank, add zirconia milling beads and ethanol, and ball mill at a speed of 500 rpm for 5 h. Then, dry, sieve, and grind in a forced-air oven at 120 °C.

[0092] Step 2: Perform high-temperature calcination on the powder obtained in Step 1: Heat the powder in an air atmosphere at a heating rate of 5 °C / min to 450 °C and hold for 4 h, then heat to 800 °C and hold for 10 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2 sodium-containing layered oxide cathode material.

[0093] Step 3: Mix the P2-phase sodium-containing layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. In this step, the total mass ratio of the lithium source to the P2-phase sodium-containing layered oxide cathode material is 10:1. Heat the uniformly mixed material in an air atmosphere at a heating rate of 5 °C / min to 280 °C and hold for 4 h, then naturally cool to room temperature. After washing with water and filtering, place it in a vacuum oven and dry at 120 °C for 12 h to obtain the O2-phase single-crystal lithium-rich material. The single-crystal particle size is about 1 μm, and the chemical formula is Li 0.97 Ni 0.04 Co 0.01 Mn 0.73 O2 (corresponding to Li 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2, Li 0.75 used to represent the lithium content in the lithium layer, Li 0.22 used to represent the lithium content in the transition metal layer).

[0094] Mix the O2-phase single-crystal lithium-rich cathode material-1, conductive carbon black, and polyvinylidene fluoride (PVDF) binder according to a mass ratio of 95:3:2 to make a slurry, coat it on an Al foil current collector, dry it, and cut it to obtain a positive electrode plate. After rolling, measure the tap density of the electrode plate, and the tap density is 2.91 g / cm 3 .

[0095] Example 2

[0096] In this example, a single-crystalline O2-phase lithium-rich cathode material was prepared, and the sample number was O2-phase single-crystalline lithium-rich cathode material - 2.

[0097] Step 1: Weigh the corresponding raw materials of sodium carbonate, lithium carbonate, nickel oxide, cobalt tetroxide, and manganese oxide according to the molar ratio of Na:Li:Ni:Co:Mn of 0.75:0.22:0.04:0.01:0.73, add them to a ball-milling jar, add zirconia ball-milling beads and ethanol, ball-mill at a speed of 500 rpm for 5 h, then dry, sieve, and grind in a forced-air oven at 120 °C.

[0098] Step 2: Perform high-temperature calcination on the powder obtained in Step 1: Heat the powder in an air atmosphere at a heating rate of 5 °C / min to 450 °C and hold for 4 h, then heat to 900 °C and hold for 10 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2-containing sodium layered oxide cathode material.

[0099] Step 3: Mix the P2-phase sodium layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. In this step, the total mass ratio of the lithium source to the P2-phase sodium layered oxide cathode material is 10:1. Heat the uniformly mixed material in an air atmosphere at a heating rate of 5 °C / min to 280 °C, hold for 4 h, then naturally cool to room temperature, wash with water, filter, and then dry in a vacuum oven at 120 °C for 12 h to obtain the O2-phase single-crystalline lithium-rich material. The single-crystalline particle size is about 2 μm, and the chemical formula is Li 0.97 Ni 0.04 Co 0.01 Mn 0.73 O2 (corresponding to Li 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2, Li 0.75 used to represent the lithium content in the lithium layer, Li 0.22 used to represent the lithium content in the transition metal layer).

[0100] Mix the O2-phase single-crystalline lithium-rich cathode material - 2, conductive carbon black, and PVDF binder in a mass ratio of 95:3:2 to make a slurry, coat it on an Al foil current collector, dry, and cut to obtain a positive electrode plate. After rolling, measure the tap density of the electrode plate, and the tap density is 2.93 g / cm 3 .

[0101] Example 3

[0102] In this example, a single-crystalline O2-phase lithium-rich cathode material was prepared, and the sample number was O2-phase single-crystalline lithium-rich cathode material - 3.

[0103] Step 1: Weigh the corresponding raw materials of sodium carbonate, lithium carbonate, nickel oxide, cobalt tetroxide, and manganese oxide according to the molar ratio of Na, Li, Ni, Co, and Mn being 0.75:0.22:0.04:0.01:0.73. Add them to a ball-milling jar, add zirconia ball-milling beads and ethanol, and ball-mill at a speed of 500 rpm for 5 h. Then, dry, sieve, and grind in a forced-air oven at 120 °C.

[0104] Step 2: Subject the powder obtained in Step 1 to high-temperature calcination: Heat the powder in an air atmosphere at a heating rate of 2 °C / min to 700 °C and hold for 4 h, then heat to 900 °C and hold for 15 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2-containing sodium layered oxide cathode material.

[0105] Step 3: Mix the P2-phase sodium layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. In this step, the total mass of the lithium source and the mass of the P2-phase sodium layered oxide cathode material are in a ratio of 10:1. Heat the uniformly mixed material in an air atmosphere at a heating rate of 5 °C / min to 280 °C, hold for 4 h, then cool naturally to room temperature. After washing with water and filtering, dry in a vacuum oven at 120 °C for 12 h to obtain the O2-phase single-crystalline lithium-rich material. The single-crystalline particle size is about 4 μm, and the chemical formula is Li 0.97 Ni 0.04 Co 0.01 Mn 0.73 O2 (corresponding to Li 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2, Li 0.75 used to represent the lithium content in the lithium layer, Li 0.22 used to represent the lithium content in the transition metal layer).

[0106] Mix the O2-phase single-crystalline lithium-rich cathode material - 3, conductive carbon black, and PVDF binder according to a mass ratio of 95:3:2 to make a slurry, then coat it on an Al foil current collector, dry, and cut to obtain a positive electrode sheet. Measure the compaction density of the sheet after pressing, and the compaction density is 3.05 g / cm 3 .

[0107] Example 4

[0108] In this example, a single-crystalline O2-phase lithium-rich cathode material was prepared, and the sample was numbered as single-crystalline O2-phase lithium-rich cathode material - 4.

[0109] Step 1: Weigh the corresponding sodium carbonate, lithium carbonate, nickel oxide, and manganese oxide according to the molar ratio of Na:Li:Ni:Mn = 0.74:0.22:0.04:0.74, add them to a ball-milling jar, add zirconia ball-milling beads and ethanol, ball-mill at a speed of 500 rpm for 5 h, then dry, sieve, and grind in a forced-air oven at 120 °C.

[0110] Step 2: High-temperature calcination of the powder obtained in Step 1: Heat the powder in an air atmosphere at a heating rate of 5 °C / min to 450 °C, hold for 4 h, then heat to 800 °C and hold for 10 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.74 Li 0.22 Ni 0.04 Mn 0.74 O2-containing sodium-layered oxide cathode material.

[0111] Step 3: Mix the P2-phase sodium-layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. In this step, the total mass ratio of the lithium source to the P2-phase is 10:1. Heat the uniformly mixed material in an air atmosphere at a heating rate of 5 °C / min to 280 °C, hold for 4 h, then cool naturally to room temperature. After washing with water and filtering, dry in a vacuum oven at 120 °C for 12 h to obtain the O2-phase single-crystalline lithium-rich material, with a single-crystalline particle size of about 1 μm, and the chemical formula is Li 0.96 Ni 0.04 Mn 0.74 O2 (corresponding to Li 0.74 Li 0.22 Ni 0.04 Mn 0.74 O2, where Li 0.74 represents the lithium content in the lithium layer, and Li 0.22 represents the lithium content in the transition metal layer).

[0112] Mix the single-crystalline O2-phase lithium-rich cathode material - 4, conductive carbon black, and PVDF binder according to a mass ratio of 95:3:2 to make a slurry, coat it on an Al foil current collector, dry, and cut to obtain a positive electrode sheet. After rolling, measure the tap density of the electrode sheet, and the tap density is 2.92 g / cm 3 .

[0113] Example 5

[0114] In this example, a single-crystalline O2-phase lithium-rich cathode material was prepared, and the sample number was O2-phase single-crystalline lithium-rich cathode material - 5.

[0115] Step 1: Weigh the corresponding sodium carbonate, lithium carbonate, nickel oxide, cobalt tetroxide, and manganese oxide according to the molar ratio of Na, Li, Ni, Co, and Mn being 0.72:0.19:0.06:0.03:0.72. Add them to a ball-milling jar, add zirconia ball-milling beads and ethanol, and ball-mill at a speed of 500 rpm for 5 h. Then dry, sieve, and grind in a forced-air oven at 120 °C.

[0116] Step 2: Perform high-temperature calcination on the powder obtained in Step 1: Heat the powder in an air atmosphere at a heating rate of 5 °C / min to 450 °C, hold for 4 h, then heat to 800 °C and hold for 10 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.72 Li 0.19 Ni 0.06 Co 0.03 Mn 0.72 O2-containing sodium layered oxide cathode material.

[0117] Step 3: Mix the P2-phase sodium layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. The total mass of the lithium source and the mass of the P2-phase are in a ratio of 10:1. After mixing the materials evenly, heat them in an air atmosphere at a heating rate of 5 °C / min to 280 °C, hold for 4 h, then cool naturally to room temperature. After washing with water and filtering, dry in a vacuum oven at 120 °C for 12 h to obtain the O2-phase single-crystalline lithium-rich material. The single-crystalline particle size is about 1 μm, Li 0.91 Ni 0.06 Co 0.03 Mn 0.72 O2 (corresponding to Li 0.72 Li 0.19 Ni 0.06 Co 0.03 Mn 0.72 O2, Li 0.72 represents the lithium content in the lithium layer, and Li 0.19 represents the lithium content in the transition metal layer).

[0118] Mix the O2-phase single-crystalline lithium-rich cathode material - 5, conductive carbon black, and PVDF binder in a mass ratio of 95:3:2 to make a slurry, then coat it on an Al foil current collector, dry, and cut to obtain a positive electrode sheet. After rolling, measure the tap density of the electrode sheet, and the tap density is 2.92 g / cm 3 .

[0119] Example 6

[0120] In this example, a single-crystalline O2-phase lithium-rich cathode material was prepared, and the sample number was O2-phase single-crystalline lithium-rich cathode material - 6.

[0121] Step 1: Weigh the corresponding sodium carbonate, lithium carbonate, nickel oxide, and manganese oxide according to the molar ratio of Na, Li, Ni, and Mn being 0.73:0.19:0.08:0.73. Add them to a ball-milling jar, add zirconia ball-milling beads and ethanol, and ball-mill at a speed of 500 rpm for 5 h. Then, dry in a forced-air oven at 120 °C, sieve, and grind.

[0122] Step 2: Perform high-temperature calcination on the powder obtained in Step 1: Heat the powder in an air atmosphere at a heating rate of 5 °C / min to 450 °C and hold for 4 h, then heat to 800 °C and hold for 10 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.73 Li 0.19 Ni 0.08 Mn 0.73 O2-containing sodium layered oxide cathode material.

[0123] Step 3: Mix the P2-phase sodium layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. In this step, the total mass ratio of the lithium source to the P2-phase sodium layered oxide cathode material is 10:1. After mixing the materials evenly, heat them in an air atmosphere at a heating rate of 5 °C / min to 280 °C, hold for 4 h, and then cool naturally to room temperature. After washing with water and filtering, dry in a vacuum oven at 120 °C for 12 h to obtain the O2-phase single-crystalline lithium-rich material, which is a single crystal with a particle size of about 1 μm, and the chemical formula is Li 0.92 Ni 0.08 Mn 0.73 O2 (corresponding to Li 0.73 Li 0.19 Ni 0.08 Mn 0.73 O2, Li 0.73 represents the lithium content in the lithium layer, and Li 0.19 represents the lithium content in the transition metal layer).

[0124] Mix the O2-phase single-crystalline lithium-rich cathode material - 6, conductive carbon black, and PVDF binder according to a mass ratio of 95:3:2 to make a slurry, then coat it on an Al foil current collector, dry, and cut to obtain a positive electrode plate. After rolling, measure the tap density of the electrode plate, and the tap density is 2.91 g / cm 3 .

[0125] Example 7

[0126] In this example, a single-crystalline O2-phase lithium-rich cathode material was prepared, and the sample number was O2-phase single-crystalline lithium-rich cathode material - 7.

[0127] Step 1: Weigh the corresponding sodium carbonate, lithium carbonate, nickel oxide, cobalt tetroxide, and manganese oxide according to the molar ratio of Na, Li, Ni, Co, and Mn being 0.72:0.17:0.08:0.05:0.7, add them to a ball milling jar, add zirconia milling beads and ethanol, ball mill at a speed of 500 rpm for 5 h, then dry, sieve, and grind in a forced air oven at 120 °C.

[0128] Step 2: Perform high-temperature calcination on the powder obtained in Step 1: Heat the powder in an air atmosphere at a heating rate of 5 °C / min to 450 °C, hold for 4 h, then heat to 800 °C and hold for 10 h, and then cool to room temperature at a cooling rate of 2 °C / min to obtain the P2-phase Na 0.72 Li 0.17 Ni 0.08 Co 0.05 Mn 0.7 O2 sodium-containing layered oxide cathode material.

[0129] Step 3: Mix the P2-phase sodium-containing layered oxide cathode material obtained in Step 2 with a lithium source. The lithium source is a mixture of lithium nitrate and lithium chloride, and the mass ratio of the two is 88:12. In this example, the mass ratio of the total mass of the lithium source to the mass of the P2-phase sodium-containing layered oxide cathode material is 10:1. Heat the uniformly mixed material in an air atmosphere at a heating rate of 5 °C / min to 280 °C, hold for 4 h, then cool naturally to room temperature, wash with water, filter, and dry in a vacuum oven at 120 °C for 12 h to obtain the O2-phase single crystal lithium-rich material, with a single crystal particle size of about 1 μm, and the chemical formula is Li 0.89 Ni 0.08 Co 0.05 Mn 0.7 O2 (corresponding to Li 0.72 Li 0.17 Ni 0.08 Co 0.05 Mn 0.7 O2, Li 0.72 represents the lithium content in the lithium layer, and Li 0.17 represents the lithium content in the transition metal layer.

[0130] After mixing the O2-phase single crystal lithium-rich cathode material -7, conductive carbon, and PVDF binder in a mass ratio of 95:3:2 to form a slurry, coat it on an Al foil current collector, dry, and cut to obtain a positive electrode plate. After rolling, measure the tap density of the electrode plate, and the tap density is 2.90 g / cm 3 .

[0131] Example 8

[0132] In this example, a single-crystalline O2-phase - polycrystalline O3-phase lithium-rich composite cathode material was prepared, and the sample number was O2-O3 composite cathode material - 1.

[0133] O3 polycrystalline Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 Preparation of O2:

[0134] Step 1: Add 10 grams of Ni 0.16 Co 0.16 Mn 0.68 CO3 precursor and 4.125 grams of lithium carbonate into a ball milling jar, add polyurethane balls as ball milling beads according to a volume ratio of 1:1, and then ball mill at a speed of 200 rpm on a planetary ball mill for 3 hours and then screen.

[0135] Step 2: Take the powder obtained in Step 1 and put it into a crucible and then place it in a muffle furnace. First, heat it to 350 °C at a heating rate of 5 °C / min and hold for 5 hours, then heat it to 700 °C at a heating rate of 5 °C / min and hold for 15 hours, and finally heat it to 860 °C at a heating rate of 5 °C / min and hold for 5 hours to obtain the lithium-rich manganese-based cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, which is spherical polycrystalline particles with a particle size of 10 μm.

[0136] Mix the O2 single-crystalline lithium-rich cathode material in Example 1 with O3 polycrystalline Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 in a mass ratio of 3:7 and mix evenly to obtain a manganese-based lithium-rich composite cathode material.

[0137] Mix the manganese-based lithium-rich composite cathode material, conductive carbon black, and PVDF binder evenly into a slurry according to a mass ratio of 95:3:2, coat the slurry on an Al foil current collector, dry it, and cut it to obtain a composite cathode electrode sheet. After rolling, measure the compaction density of the electrode sheet, and the compaction density is 3.1 g / cm 3 .

[0138] Example 9

[0139] In this example, a single-crystalline O2-phase - polycrystalline O3-phase lithium-rich composite cathode material was prepared, and the sample number was O2-O3 composite cathode material - 2.

[0140] O3 polycrystalline Li 1.2 Ni 0.2 Mn 0.6 Preparation of O2:

[0141] Step 1: Add 10 g of Ni 0.25 Mn 0.75 CO3 precursor and 4.21 g of lithium carbonate into a ball milling jar, add polyurethane balls as ball milling beads according to a volume ratio of 1:1, and then ball mill at 200 rpm on a planetary ball mill for 3 h and then screen.

[0142] Step 2: Take the powder obtained in Step 1 and put it into a crucible, then place it in a muffle furnace. Heat it at a heating rate of 5 °C / min to 350 °C and hold for 5 h, then heat it at a heating rate of 5 °C / min to 700 °C and hold for 15 h, and finally heat it at a heating rate of 5 °C / min to 860 °C and hold for 5 h to obtain the lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O2. It is spherical polycrystalline particles with a particle size of 10 μm.

[0143] Mix the O2 single-crystal lithium-rich cathode material in Example 1 with O3 polycrystalline Li 1.2 Ni 0.2 Mn 0.6 O2 in a mass ratio of 3:7 to obtain a manganese-based lithium-rich composite cathode material.

[0144] Mix the manganese-based lithium-rich composite cathode material, conductive carbon black, and PVDF binder in a mass ratio of 95:3:2 to make a slurry, then coat it on an Al foil current collector, dry it, and cut it to obtain a composite cathode sheet. Measure the tap density of the sheet after rolling, and the tap density is 3.13 g / cm 3 .

[0145] Example 10

[0146] In this example, an O2-phase single crystal - O3-phase polycrystalline lithium-rich composite cathode material was prepared, and the sample number was O2 - O3 composite cathode material - 3.

[0147] Preparation of O3 polycrystalline Li 1.13 Ni 0.30 Mn 0.56 O2:

[0148] Step 1: Add 10 g of Ni 0.35 Mn 0.65 CO3 precursor and 4.15 g of lithium carbonate into a ball milling jar, add polyurethane balls as ball milling beads according to a volume ratio of 1:1, and then ball mill at a speed of 200 rpm on a planetary ball mill for 3 h and then screen.

[0149] Step 2: Put the powder obtained in Step 1 into a crucible and place it in a muffle furnace. First, heat it at a heating rate of 5 °C / min to 350 °C and hold for 5 h. Then, heat it at a heating rate of 5 °C / min to 700 °C and hold for 15 h. Finally, heat it at a heating rate of 5 °C / min to 860 °C and hold for 5 h to obtain the lithium-rich manganese-based cathode material Li 1.15 Ni 0.30 Mn 0.55 O2, which is spherical polycrystalline particles with a particle size of 8 μm.

[0150] Mix the O2 single-crystal lithium-rich cathode material in Example 1 with O3 polycrystalline Li 1.13 Ni 0.30 Mn 0.56 O2 in a mass ratio of 3:7 and mix them evenly to obtain a manganese-based lithium-rich composite cathode material.

[0151] Mix the manganese-based lithium-rich composite cathode material, conductive carbon black, and PVDF binder in a mass ratio of 95:3:2 to make a slurry, then coat it on an Al foil current collector, dry it, and cut it to obtain a composite cathode plate. After rolling, measure the tap density of the plate, and the tap density is 3.15 g / cm 3 .

[0152] Comparative Example 1

[0153] This comparative example prepared an O3-structured Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 single-crystal material.

[0154] Step 1: Add the Ni 0.16 Co 0.16 Mn 0.68 CO3 precursor and lithium carbonate into a ball-milling jar. The Li:TM molar ratio is 1.44:0.8, where TM is the total molar number of transition metals Ni, Mn, and Co, and the mass ratio of lithium carbonate is 20% in excess. Add zirconia balls as ball-milling beads in a volume ratio of 1:1, then ball-mill at a speed of 300 rpm on a planetary ball mill for 3 h and then screen.

[0155] Step 2: Put the powder obtained in Step 1 into a crucible and place it in a muffle furnace. First, heat it at a heating rate of 5 °C / min to 700 °C and hold for 5 h. Finally, heat it at a heating rate of 5 °C / min to 900 °C and hold for 15 h, then cool it to room temperature, wash it with water, and dry it to obtain an O3-phase single-crystal lithium-rich manganese-based cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, with a particle size of 3 μm.

[0156] The Li of the O3 structure 1.2 Ni 0.13 Co 0.13 Mn 0.54 The O2 single crystal material, conductive carbon black, and PVDF binder are made into a slurry according to a mass ratio of 95:3:2, then coated on an Al foil current collector, dried, and cut to obtain a composite positive electrode sheet. After rolling, the tap density of the electrode sheet is measured, and the tap density is 3.01 g / cm 3 .

[0157] Comparative Example 2

[0158] This comparative example prepared an O3 structure Li 1.2 Ni 0.2 Mn 0.6 O2 single crystal material.

[0159] Step 1: Put the Ni 0.25 Mn 0.75 CO3 precursor and lithium carbonate into a ball milling jar. The ratio of Li:TM is 1.44:0.8, where TM is the total molar amount of transition metals Ni and Mn, and the mass ratio of lithium carbonate is 20% in excess. Zirconia balls are added as ball milling beads according to a volume ratio of 1:1, and then ball milled at a speed of 300 rpm on a planetary ball mill for 3 h and then sieved.

[0160] Step 2: Put the powder obtained in Step 1 into a crucible and place it in a muffle furnace. First, heat it to 700 °C at a heating rate of 5 °C / min and hold for 5 h. Finally, heat it to 900 °C at a heating rate of 5 °C / min and hold for 15 h, then cool to room temperature, wash with water, and dry to obtain the O3-phase single crystal lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O2, with a particle size of 3 μm.

[0161] The O3 structure Li 1.2 Ni 0.2 Mn 0.6 O2 single crystal material, conductive black, and PVDF binder are made into a slurry according to a mass ratio of 95:3:2, then coated on an Al foil current collector, dried, and cut to obtain a composite positive electrode sheet. After rolling, the tap density of the electrode sheet is measured, and the tap density is 3.02 g / cm 3 .

[0162] Comparative Example 3

[0163] This comparative example prepared an O3 structure Li 1.15 Ni 0.30 Mn 0.55 O2 single crystal material.

[0164] Step 1: Put the Ni 0.35 Mn0.65 The CO3 precursor and lithium carbonate were added to a ball milling jar. The ratio of Li:TM was 1.34:0.8, where TM is the total molar amount of transition metals Ni and Mn, and the mass ratio of lithium carbonate was in excess by 20%. Zirconia balls were added as ball milling beads according to a volume ratio of 1:1, and then ball milled at a speed of 300 rpm for 3 h on a planetary ball mill and then sieved.

[0165] Step 2: The powder obtained in Step 1 was placed in a crucible and then placed in a muffle furnace. First, it was heated to 700 °C at a heating rate of 5 °C / min and held for 5 h. Finally, it was heated to 900 °C at a heating rate of 5 °C / min and held for 15 h, and then cooled to room temperature, washed with water, and dried to obtain the O3-phase single-crystal lithium-rich manganese-based cathode material Li 1.15 Ni 0.30 Mn 0.55 O2 with a particle size of 3 μm.

[0166] The Li 1.15 Ni 0.30 Mn 0.55 O2 single-crystal material, conductive carbon black, and PVDF binder were made into a homogeneous slurry according to a mass ratio of 95:3:2, coated on an Al foil current collector, dried, and cut to obtain a composite positive electrode sheet. At the same time, the compaction density of the electrode sheet was measured after rolling, and its compaction density was 3.04 g / cm 3 .

[0167] Comparative Example 4

[0168] The O3-phase polycrystalline Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 powder prepared in Example 8 was measured for its compaction density, and the compaction density was 2.5 g / cm 3 .

[0169] Comparative Example 5

[0170] The O3-phase polycrystalline Li 1.2 Ni 0.2 Mn 0.60 O2 powder prepared in Example 9 was measured for its compaction density, and the compaction density was 2.65 g / cm 3 .

[0171] Comparative Example 6

[0172] The O3-phase polycrystalline Li 1.13 Ni 0.30 Mn 0.56 O2 powder prepared in Example 10 was measured for its compaction density, and the compaction density was 2.78 g / cm 3 .

[0173] Performance parameter characterization:

[0174] (1) Structure characterization:

[0175] The crystal structures of the cathode materials prepared in Example 1 and Comparative Example 1 were characterized by X-ray diffraction (XRD), as shown in Figure 2. The lower graph shown in Figure 2(a) is the XRD pattern of the P2-phase Na 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.7 3O2 sodium-containing layered oxide cathode material obtained in Step 2 of Example 1. It can be seen from the test results that the diffraction peaks (002), (100), (102), etc. are consistent with the P2-phase PDF card, indicating that it is a pure P2-phase material. The upper graph in Figure 2(a) is the XRD of the O2-phase single-crystal lithium-rich material after ion exchange in Example 1. It can also be seen that its diffraction peak (002), etc. is completely consistent with the O2-phase standard PDF card, proving that the P2-phase Na 0.75 Li 0.22 Ni 0.04 Co 0.01 Mn 0.73 O2 can obtain a pure O2-phase structured lithium-rich material after ion exchange. Therefore, the O2-phase single-crystal lithium-rich material prepared by the present invention is a pure phase without impurity phases, ensuring that the material has good discharge specific capacity and cycle stability.

[0176] As shown in Figure 2(b), for the O3-phase structured Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 single-crystal cathode material, it can be seen that its main (003), (104) peaks are all consistent with the standard layered structure peaks. The peaks between 20-25 degrees are the superlattice peaks of Li2MnO3, proving that it is a pure lithium-rich cathode material.

[0177] (2) Particle morphology characterization:

[0178] To confirm the morphology of the prepared O2-phase single-crystal lithium-rich material, the morphology of the materials prepared in Examples 1-3 was tested by scanning electron microscopy (SEM), as shown respectively in Figure 3as shown in a, b, and c. In Example 1, the particle size is about 1 μm. In Example 2, the particle size is about 2 μm and the size is uniform. In Example 3, the particle size is about 4 μm and the size is uniform, indicating that the preparation method of the present invention has good consistency and can obtain a material with a uniform particle size distribution. In addition, through observation, it can be seen that the primary particles are single crystals, the morphology of the single crystals is an irregular spherical shape, the particle size distribution is between 1-5 μm, and the morphology of the single crystal particles is beneficial to improving the compaction density of the lithium-rich cathode. Therefore, the O2 single crystal lithium-rich material prepared by the present invention has good application prospects.

[0179] (III) Electrochemical performance test:

[0180] Perform electrochemical tests on each example and comparative example:

[0181] 1) Prepare a lithium-ion coin half-cell.

[0182] Use the cathode materials of each example and comparative example to prepare a lithium-ion coin half-cell. The specific steps for making the coin half-cell are as follows:

[0183] Preparation of the positive electrode sheet: Homogenize according to the mass ratio of cathode material: Super P: PVDF = 95:2.5:2.5, coat it on a 20-μm-thick aluminum foil, and make the areal density of the positive electrode sheet 4-5 mg / cm 2 .

[0184] Battery assembly: Use an R2032 button battery case for button cell assembly. The lithium-rich cathode materials of Examples 1-10 and the cathode materials of Comparative Examples 1-3 are used to obtain the positive electrode sheets. Metallic lithium is used as the negative electrode. A separator made of alumina-coated PE material is used, and 80 μL of electrolyte is added dropwise. The electrolyte composition is a solution of 1 M LiPF6, where the solvent is a mixture of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) with a volume ratio of 3:7 to obtain a button battery.

[0185] Perform electrochemical charge and discharge tests on each battery:

[0186] 1C cycle performance test at 30°C: Use a BlueTester to test the coin cells assembled with the cathode materials in Examples 1-10 and Comparative Examples 1-3. Place the prepared button batteries in a high-temperature oven at 30°C for charge and discharge tests. The voltage range is 2.0V-4.8V. Activate for two cycles at 0.1C charge and discharge, and then perform constant current charge and discharge at 1C current for 100 cycles to obtain relevant data such as the first discharge capacity, first Coulombic efficiency, 100th cycle discharge capacity, 100th cycle capacity retention rate, and voltage retention rate. Table 1 shows the electrochemical performance of the lithium-ion liquid coin half-cells assembled with the cathode materials of each example and comparative example at a current density of 1C at 30°C.

[0187] Table 1 shows the electrochemical performance at a current density of 1C at 30°C.

[0188]

[0189]

[0190] Figure 4 a, b, and c are the charge-discharge curves of the O2-phase single-crystal lithium-rich cathode materials of Examples 1-3 of the present invention in the first two weeks; Figure 5 is the electrochemical cycling curve of the O2-phase single-crystal lithium-rich cathode material of Example 1 of the present invention; Figure 6 is the electrochemical cycling curve of the O3-phase single-crystal lithium-rich cathode material of Comparative Example 1 of the present invention.

[0191] Combined with Table 1 and Figures 4 - 6 As shown. The initial discharge specific capacities of the O2-phase single-crystal lithium-rich cathode materials of Examples 1-3 at 0.1C are 301 mAh / g, 280 mAh / g, and 270 mAh / g respectively, while the initial discharge capacity of the O3-phase single-crystal lithium-rich cathode material of Comparative Example 1 at 0.1C is 180 mAh / g. It can be seen that the initial discharge specific capacity of the O2-phase single-crystal lithium-rich cathode material is significantly higher than that of the O3-phase single-crystal lithium-rich material. Among them, the O2-phase single-crystal lithium-rich cathode materials of Examples 1-3 are 121 mAh / g, 100 mAh / g, and 90 mAh / g higher than the O3-phase lithium-rich cathode material of Comparative Example 1 respectively. The initial discharge capacities of the O2-phase single-crystal lithium-rich cathode materials of Examples 1-3 at 1C are 260 mAh / g, 240 mAh / g, and 223 mAh / g respectively, while the discharge specific capacity of the O3-phase single-crystal lithium-rich cathode material of Comparative Example 1 at 1C is 132 mAh / g. The 1C discharge specific capacities of the O2-phase single-crystal lithium-rich cathode materials of Examples 1-3 are increased by 128 mAh / g, 108 mAh / g, and 91 mAh / g respectively compared with Comparative Example 1. From the perspective of the initial Coulombic efficiency, Examples 1-3 are 130%, 128%, and 130% respectively, while Comparative Example 1 is only 73%. Therefore, from the perspective of the first-week electrochemical performance, the O2-phase single-crystal lithium-rich cathode material of the present invention is significantly superior to the O3-phase single-crystal lithium-rich cathode material of the comparative example.

[0192] The battery was cycled 100 times between 2.0 V and 4.8 V at a current density of 1C at 30 °C. The capacity retention rates of the cathode materials of Examples 1-3 were 86.1%, 85.1% and 85.9% respectively, while that of Comparative Example 1 was only 72.3%. Examples 1-3 were respectively 13.8%, 12.8% and 13.6% higher than Comparative Example 1. Thus, it can be seen that the O2-phase single-crystal lithium-rich manganese-based cathode material has an excellent capacity retention rate at a high voltage of 4.8 V compared with the O3-phase single-crystal lithium-rich material. The 1C rate performance of the O2-phase single-crystal lithium-rich materials of Examples 1-3 was significantly better than that of the O3-phase single-crystal lithium-rich cathode material of Comparative Example 1.

[0193] In addition, the voltage decay of the materials of Examples 1-3 after 100 cycles was 1.17 mV / week, 1.04 mV / week and 1.12 mV / week respectively, while that of Comparative Example 1 was 2.53 mV / week. It can be seen that the voltage decay of the O3-phase single-crystal lithium-rich material of Comparative Example 1 was 1.36 mV / week, 1.49 mV / week and 1.41 mV / week higher than that of Examples 1-3 respectively, that is, about 116%, 143% and 126% higher. Therefore, the O2 single-crystal lithium-rich manganese-based cathode material has a very low voltage decay. The cathode materials of Examples 1-3 of the present invention had a smaller voltage decay and a higher discharge specific capacity after 100 cycles. Therefore, it can be seen that the O2-phase single-crystal lithium-rich cathode material has a higher energy density.

[0194] Through the comparison between Examples 1-3 and Comparative Example 1, it can be seen that the O2-phase single-crystal lithium-rich cathode material of the present invention has very excellent high-voltage cycle stability and a small voltage decay. This is because the O2-phase structure material prepared by the present invention has a strong ability to inhibit the migration of transition metals, reduces irreversible oxygen release and has a better structural transformation. Therefore, the lithium-rich manganese-based material prepared by this method has excellent high-voltage cycle stability, high specific capacity and high energy density, which will greatly enhance the competitive advantage of the lithium-rich manganese-based cathode material in the market.

[0195] By comparing Examples 1-3, it can be known that the chemical structural formulas of the O2-phase single-crystal lithium-rich materials in Examples 1-3 are the same, but there are differences in the preparation processes. Compared with Example 1, the high-temperature calcination temperature of the P2-phase precursor in Example 2 was higher and the calcination time was longer. Compared with Example 2, the pre-calcination platform calcination temperature of the P2-phase precursor in Example 3 was higher and the high-temperature calcination time was longer. From the size of the obtained single-crystal particles, the particle size in Example 1 was about 1 μm, the particle size in Example 2 was about 2 μm and the size was uniform, and the particle size in Example 3 was about 4 μm and the size was uniform. It can be seen that the pre-calcination temperature, high-temperature calcination temperature and time of the P2-phase precursor will directly affect the size of the single-crystal particles. The tap densities of the electrode sheets prepared from the cathode materials of Examples 1-3 were 2.91 g / cm 3, 2.93 g / cm 3 and 3.05 g / cm 3 . From the perspective of the discharge specific capacity and capacity retention rate at 0.1C and 1C, all three have a high initial discharge specific capacity and excellent cycling performance, and the voltage decay after 100 cycles is relatively low, indicating that the single crystal material prepared by the preparation process of the present invention has better cycling stability and higher energy density.

[0196] Compared with Example 1, in the single crystal lithium-rich cathode material with an O2 phase structure in Example 4, the molar ratios of the transition metal elements Ni and Mn are increased, and Co is not contained. Other preparation process conditions are the same as those in Example 1. The initial discharge capacity of the cathode material in Example 4 is 278 mAh / g at 0.1C and 238 mAh / g at 1C, slightly lower than that in Example 1, but 98 mAh / g and about 106 mAh / g higher than those in Comparative Example 1 respectively. The initial Coulombic efficiency of the cathode material in Example 4 is about 141%, higher than that in Example 1. The voltage decay rate of the cathode material in Example 4 after 100 cycles is 0.84 mV / week, 0.33 mV / week lower than that in Example 1, and 1.69 mV / week lower than that in Comparative Example 1. The capacity retention rate of the cathode material in Example 4 after 100 cycles at a current density of 1C between 2.0V and 4.8V at 30°C is 89.4%, 3.3% higher than that in Example 1 and 17.1% higher than that in Comparative Example 1. It can be seen that although the initial discharge specific capacity of the single crystal lithium-rich cathode material with an O2 phase structure without Co in Example 4 is lower than that in Example 1, its initial Coulombic efficiency, long-term cycling stability, etc. have more excellent performance. And compared with the single crystal lithium-rich cathode material with an O3 structure containing Co in Comparative Example 1, it has significant advantages in both the initial electrochemical performance and long-term cycling stability.

[0197] Comparative Examples 2-3 are single-crystalline Li-rich cathode materials with an O3-phase structure without Co, and their initial discharge capacities at 0.1C are 122 mAh / g and 141 mAh / g, and their initial discharge capacities at 1C are 113 mAh / g and 119 mAh / g. It can be seen that the initial discharge capacity of Example 4 at 0.1C is 156 mAh / g and 137 mAh / g higher than that of Comparative Example 2 and Comparative Example 3 respectively, and the initial discharge capacity at 1C is 125 mAh / g and 119 mAh / g higher than that of Comparative Example 2 and Comparative Example 3 respectively. The initial Coulombic efficiency of the cathode material of Example 4 is 73% and 66% higher than that of Comparative Examples 2-3 respectively. The voltage decay rate of the cathode material of Example 4 after 100 cycles is 1.02 mV / week and 0.58 mV / week lower than that of Comparative Examples 2-3 respectively. The capacity retention rate of the cathode material of Example 4 after 100 cycles at a current density of 1C between 2.0V and 4.8V at 30℃ is 16% and 13.8% higher than that of Examples 2-3 respectively. It can be seen that the single-crystalline Li-rich cathode material with an O2-phase structure without Co in Example 4 has significant advantages in terms of the first-week electrochemical performance, long-cycle stability, and energy density compared with the single-crystalline Li-rich cathode material with an O3-phase structure without Co.

[0198] Compared with Example 1, in the single-crystalline Li-rich cathode material with an O2 structure in Example 5, the molar ratios of the transition metal elements Ni and Co are increased, and the molar ratio of Mn is slightly decreased. The initial discharge capacity of the cathode material of Example 5 at 0.1C is 279 mAh / g, and the initial discharge capacity at 1C is 240 mAh / g, which is slightly lower than that of Example 1, but still 99 mAh / g and about 108 mAh / g higher than that of Comparative Example 1 respectively. The initial Coulombic efficiency of the cathode material of Example 5 is about 139%, which is 9% higher than that of Example 1 and 66% higher than that of Comparative Example 1. The voltage decay rate of the cathode material of Example 5 after 100 cycles is 0.93 mV / week, which is 0.24 mV / week lower than that of Example 1 and 1.6 mV / week lower than that of Comparative Example 1. The capacity retention rate of the cathode material of Example 5 after 100 cycles at a current density of 1C between 2.0V and 4.8V at 30℃ is 88.0%, which is 15.7% higher than that of Comparative Example 1. It can be seen that the single-crystalline Li-rich cathode material with an O2-phase structure in Example 5 has obvious advantages in terms of both the first-week electrochemical performance and long-cycle stability compared with the single-crystalline Li-rich cathode material with an O3-phase structure in Comparative Example 1.

[0199] Compared with Example 4, in the single-crystal lithium-rich cathode material with an O2-phase structure in Example 6, the molar ratio of the transition metal element Ni is further increased. The initial discharge capacity of the cathode material in Example 6 is 267 mAh / g at 0.1C and 234 mAh / g at 1C, slightly lower than that in Example 4, but still significantly higher than those in Comparative Examples 1-3. The initial Coulombic efficiency of the cathode material in Example 6 is about 141%, and the voltage decay rate after 100 cycles is 1.06 mV / week. The capacity retention rate of the cathode material in Example 6 after 100 cycles at a current density of 1C between 2.0V and 4.8V at 30°C is 90.5%. It can be seen that the single-crystal lithium-rich cathode material with an O2-phase structure in Example 6 has obvious advantages in terms of the first-week electrochemical performance, long-cycle stability, and energy density compared with the single-crystal lithium-rich cathode material with an O3-phase structure.

[0200] Compared with Example 5, in the single-crystal lithium-rich cathode material with an O2-phase structure in Example 7, the molar ratios of the transition metal elements Ni and Co are increased, and the molar ratio of Mn is slightly decreased. The initial discharge capacity of the cathode material in Example 7 is 265 mAh / g at 0.1C and 221 mAh / g at 1C, lower than those in Example 1 and Example 5, but still about 85 mAh / g and about 89 mAh / g higher than those in Comparative Example 1 respectively. The initial Coulombic efficiency of the cathode material in Example 7 is about 137%, about 64% higher than that in Comparative Example 1. The voltage decay rate of the cathode material in Example 7 after 100 cycles is 1.14 mV / week, 1.39 mV / week lower than that in Comparative Example 1. The capacity retention rate of the cathode material in Example 7 after 100 cycles at a current density of 1C between 2.0V and 4.8V at 30°C is 91.9%, 5.8% and 6.8% higher than those in Example 1 and Example 5 respectively, and 19.6% higher than that in Comparative Example 1.

[0201] The O2-phase single-crystal lithium-rich materials prepared in Examples 1-7 all have better improvements in the first-week discharge specific capacity, first-week Coulombic efficiency, cycle stability, and voltage decay compared with the O3-phase single-crystal lithium-rich materials in Comparative Examples 1-3, indicating the superiority of the O2-phase structure compared with the O3-phase single-crystal lithium-rich cathode material, and at the same time indicating that the preparation method in the present invention has good consistency.

[0202] In addition, after mixing and compounding the O2-phase single-crystal lithium-rich cathode material prepared in the present invention with the O3-phase polycrystalline lithium-rich cathode material, it can be seen that the tap densities of the composite electrode sheets in Examples 8-10 are all greater than 3 g / cm 3, whether it is relative to the single-crystal lithium-rich cathode material with an O2-phase structure or the single-crystal lithium-rich cathode material with an O3-phase structure in Comparative Examples 1-3, its tap density is greatly improved, and it can reach a 26% increase in this embodiment, proving that this composite electrode has the advantage of better improving the volume energy density. At the same time, the composite cathode material has relatively high improvements in discharge specific capacity, 1C rate, and cycle stability. It can be seen that the first discharge capacities of Examples 8-10 at 0.1C are 297 mAh / g, 273 mAh / g, and 281 mAh / g, and the first discharge capacities at 1C are 248 mAh / g, 212 mAh / g, and 221 mAh / g, which are 117 mAh / g, 93 mAh / g, and 101 mAh / g higher than that of Comparative Example 1. The first Coulombic efficiencies of the composite cathode materials in Examples 8-10 are approximately 92%, 85%, and 88%, respectively, all higher than that of Comparative Example 1. The voltage decay rates of the composite cathode materials in Examples 8-10 after 100 cycles are 1.75 mV / week, 1.56 mV / week, and 0.86 mV / week, which are 0.78 mV / week, 0.97 mV / week, and 1.67 mV / week lower than that of Comparative Example 1. The capacity retention rates of the cathode materials in Examples 8-10 after cycling 100 times at a current density of 1C between 2.0V and 4.8V at 30°C are 92.5%, 93.3%, and 96.5%. It can be seen that from the perspective of the 100-week capacity retention rate, Examples 8-10 are 6.4%, 7.2%, and 10.4% higher than Example 1 respectively, indicating that the composite of the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material prepared by the present invention can effectively improve the cycle performance of the cathode material. The O3-phase polycrystalline lithium-rich cathode material forms a lithium supplementation effect on the O2-phase single-crystal lithium-rich cathode material.

[0203] In addition, it can be seen that the tap densities of the electrodes obtained from the composite cathode materials in Examples 8-10 are 3.10 g / cm 3 , 3.13 g / cm 3 , and 3.15 g / cm 3 respectively. For Comparative Examples 4-6, the electrodes are made of the O3-phase polycrystalline lithium-rich materials prepared in Examples 8-10, and the tap densities are 2.52 g / cm 3 , 2.61 g / cm 3 , and 2.71 g / cm 3, therefore, the composite cathode materials of Examples 8-10 have a higher tap density of the electrode sheet than that of the O2-phase single-crystal lithium-rich cathode material, and also higher than that of the O3-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material. In addition, this indicates that after forming a particle size grading of large and small particles by compounding the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material, the tap density of the electrode sheet can be significantly improved. It can also be seen from Table 1 that the cycling performance of the composite of the O2-phase single crystal and the O3-phase polycrystalline lithium-rich cathode materials in Examples 8-10 is also better than that of the O3-phase polycrystalline lithium-rich cathode materials in Comparative Examples 4-6. Compared with Comparative Examples 1-3, Examples 8-10 have a significant improvement in the first-week discharge specific capacity, capacity at 1C rate, first-week Coulombic efficiency, cycle retention rate, and voltage decay. It can be seen from Table 1 that the cycling performance of the composite of the O2-phase single crystal and the O3-phase polycrystalline lithium-rich cathode materials in Examples 8-10 is significantly better than that of the O3-phase single-crystal lithium-rich cathode material. In addition, from the comparison with Example 1, it can be seen that the cycling performance of the composite of the O2-phase single crystal and the O3-phase polycrystalline lithium-rich cathode material is significantly better than that of the O2-phase single-crystal lithium-rich cathode material, proving that the composite cathode material has good discharge specific energy and energy retention rate. A synergistic complementary advantage is formed between the O2-phase single crystal and the O3-phase polycrystalline lithium-rich cathode material, and it has good application prospects, especially in improving the disadvantages of low tap density and poor rate performance of lithium-rich cathode materials.

[0204] 2) Prepare an in-situ solidified lithium-ion battery.

[0205] According to the preparation process of the positive electrode sheet in the preparation of the lithium-ion button half-cell in 1) above, the positive electrode materials of Example 1 and Comparative Example 1 are respectively prepared into positive electrode sheets as the positive electrode of the lithium battery. Metallic lithium is used as the negative electrode, a separator made of polyethylene (PE) coated with alumina is used, and a button battery case of R2032 is used for button cell assembly of the solid-state battery, and a polymerization precursor solution is injected into the battery case. The polymerization precursor solution includes: butyl acrylate monomer, lithium salt LiTFSi, additive lithium difluorooxalate borate (LiDFOB), solvent succinonitrile, and initiator azobisisobutyronitrile (AIBN). Among them, the butyl acrylate monomer is 80 μl, the lithium salt LiTFSi is 0.8 mol / L, the additive is 0.2 mol / L, the solvent succinonitrile accounts for 40 wt% of the total mass of the entire precursor solution, and the initiator azobisisobutyronitrile accounts for 0.5 wt% of the total mass of the entire precursor solution. The assembled button cell is heated in an oven at 60 °C for 24 h for polymerization to obtain an in-situ solidified battery.

[0206] The in-situ solidified button cells assembled with the cathode materials in Example 1 and Comparative Example 1 were tested using a Blue Electric Tester. The prepared button cells were placed in a high-temperature oven at 30 °C for charge-discharge testing. The voltage range was 2.0 V - 4.8 V. The cells were activated by charge-discharge at 0.1 C for two cycles, and then constant current charge-discharge was carried out at a current of 1 C for 100 cycles. The cells in Example 1 could stably cycle 100 times, and the capacity retention rate reached over 80%. However, the cells in Comparative Example 1 failed after less than 100 cycles.

[0207] In Comparative Example 1, the O3-type single-crystal lithium-rich cathode material used is prone to irreversible oxygen release during high-voltage cycling, resulting in unstable crystal structure and capacity decay. While the O2-type single-crystal lithium-rich cathode material in Example 1 has a more stable layered structure, which can effectively inhibit oxygen release and reduce the risk of structural collapse. At the same time, the O2-type single-crystal material can better maintain crystal integrity during the structural evolution process, reduce stress concentration, thereby endowing the battery with more excellent cycle stability and high-voltage working performance.

[0208] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cathode material containing a single-crystalline O2-phase rich lithium material, characterized in that, The cathode material of the O2-phase single-crystal lithium-rich material is a blended composite material of an O2-phase single-crystal lithium-rich cathode material and an O3-phase polycrystalline lithium-rich cathode material. Moreover, in the cathode material of the O2-phase single-crystal lithium-rich material, the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material maintain the independence of their respective crystal structures; The mass ratio of the O2-phase single-crystal lithium-rich cathode material to the O3-phase polycrystalline lithium-rich cathode material is 1:1 - 1:10; The O2-phase single-crystal lithium-rich cathode material is a micron-scale pure-phase structure with a particle size of 1-5 μm, and its chemical structural formula is Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O2, where the range of m is 0.72-0.75, the range of x1 is 0.17-0.22, the range of y1 is 0.04-0.08, and the range of z1 is 0-0.05; The particle size of the O3-phase polycrystalline lithium-rich cathode material is 8 - 10 μm, and its chemical structural formula is: Li x2 Ni y2 Co z2 Mn 1-x2-y2-z2 O2, where the range of x2 is 1 - 1.2, the range of y2 is 0.13 - 0.4, and the range of z2 is 0 - 0.

13.

2. A method for preparing the cathode material according to claim 1 above, characterized in that, The preparation method includes: Mixing the O2-phase single-crystal lithium-rich cathode material and the O3-phase polycrystalline lithium-rich cathode material according to a mass ratio of 1:1 - 1:10 to obtain the cathode material of the O2-phase single-crystal lithium-rich material; Among them, the O2-phase single-crystal lithium-rich cathode material is obtained by ion exchange after uniformly mixing a P2 pure-phase sodium-containing layered oxide cathode material and a second lithium source; the P2 pure-phase sodium-containing layered oxide cathode material is obtained by ball-milling and mixing a sodium source, a first lithium source, and a transition metal oxide and then calcining; The O3-phase polycrystalline lithium-rich cathode material is obtained by ball-milling and mixing a transition metal compound precursor and a lithium source and then calcining.

3. A single-crystalline O2-phase lithium-rich cathode material, characterized in that, The O2-phase single-crystalline lithium-rich cathode material has a micron-sized pure-phase structure with a particle size of 1-5 μm, and its chemical structural formula is Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O2; Among them, the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.

05.

4. A method for preparing the O2-phase single-crystal lithium-rich cathode material according to claim 3 above, characterized in that, The preparation method includes: Mix a sodium source, a first lithium source, and oxides containing transition metals Ni, Co, and Mn respectively in a molar ratio of Na:Li:Ni:Co:Mn = m':x3:y3:z3:1 - x3 - y3 - z3 by ball milling. After uniform mixing, perform calcination to obtain a P2 pure-phase sodium-containing layered oxide cathode material Na m’ Li x3 Ni y3 Co z3 Mn 1-x3-y3-z3 O₂; wherein, the range of m' is 0.72 - 0.75, the range of x3 is 0.17 - 0.22, the range of y3 is 0.04 - 0.08, and the range of z3 is 0 - 0.05; The P2 pure-phase sodium-containing layered oxide cathode material Na m’ Li x3 Ni y3 Co z3 Mn 1-x3-y3-z3 O2 is mixed evenly with a second lithium source in a mass ratio of 1:2 - 10, followed by ion exchange, and then obtained as the O2-phase single-crystal lithium-rich cathode material Li m Li x1 Ni y1 Co z1 Mn 1-x1-y1-z1 O2; where the range of m is 0.72 - 0.75, the range of x1 is 0.17 - 0.22, the range of y1 is 0.04 - 0.08, and the range of z1 is 0 - 0.

05.

5. According to the preparation method described in claim 4, wherein, The sodium source includes at least one of sodium nitrate, sodium carbonate, sodium acetate, and sodium oxide; preferably sodium carbonate; The first lithium source includes one or more of lithium nitrate, lithium carbonate, lithium acetate, lithium oxide, or lithium hydroxide; preferably lithium carbonate; The oxides containing transition metals Ni, Co, and Mn respectively include nickel-containing oxide, manganese-containing oxide, and cobalt-containing oxide; the nickel-containing oxide includes NiO; the manganese-containing oxide includes one or more of MnO2, Mn3O4, or Mn2O3; the cobalt-containing oxide includes one or more of CoO, Co2O3, or Co3O4; The second lithium source includes one or more of lithium nitrate, lithium chloride, lithium hydroxide, lithium acetate, or lithium bromide; preferably a mixture of lithium nitrate and lithium chloride.

6. The preparation method according to claim 4, wherein, The ball-milling speed for the ball-milling and mixing is 400 - 500 rpm, and the ball-milling time is 5 - 10 h; The atmosphere for the calcining includes one or more of air, argon, and synthetic air. The specific process of the calcining includes: heating at a heating rate of 2 - 10 °C / min to 450 °C - 700 °C, pre-calcining for 4 - 5 h, then heating to 800 - 900 °C, and calcining for 8 - 15 h; then cooling to room temperature at a cooling rate of 2 - 5 °C / min.

7. The preparation method according to claim 4, characterized in that, The temperature for the ion exchange is 280 - 300 °C, and the time for the ion exchange is 1 - 10 h.

8. A positive electrode sheet, characterized in that, The positive electrode sheet includes: the cathode material of the O2-phase single-crystal lithium-rich material described in claim 1 above or the O2-phase single-crystal lithium-rich cathode material described in claim 3 above.

9. A lithium battery, characterized in that, The lithium battery includes: the positive electrode material containing the O2-phase single-crystal lithium-rich material described in claim 1 above, or, the O2-phase single-crystal lithium-rich positive electrode material described in claim 3 above, or, the positive electrode sheet described in claim 8 above.

10. The lithium battery according to claim 9, characterized in that, The lithium battery includes: one or more of a liquid lithium-ion battery, a liquid metal lithium battery, a hybrid solid-liquid lithium-ion battery, a hybrid solid-liquid metal lithium battery, an in-situ solidified lithium battery, a solid-state lithium-ion battery, or a solid-state metal lithium battery.

Images