O2-phase lithium cobalt oxide positive electrode material and preparation method and application thereof

Abstract

The invention provides an O2-phase lithium cobalt oxide positive electrode material and a preparation method and application thereof, and the preparation method of the O2-phase lithium cobalt oxide positive electrode material comprises the following steps: mixing P2-phase sodium cobalt oxide, a first lithium source and a solvent to obtain a mixed solution, and carrying out liquid-phase ion exchange to obtain an O2-phase lithium cobalt oxide precursor; and mixing the O2-phase lithium cobalt oxide precursor with a second lithium source, and carrying out solid-phase ion exchange to obtain the O2-phase lithium cobalt oxide positive electrode material. According to the invention, P2-phase sodium cobaltate is taken as a raw material, and a preparation process of firstly carrying out liquid-phase ion exchange and then carrying out solid-phase ion exchange is adopted, so that the lithium-cobalt ratio of the obtained O2-phase lithium cobaltate positive electrode material is increased, the crystal structure stability of the O2-phase lithium cobaltate positive electrode material is improved, the first charge capacity is further improved, meanwhile, the first effect can be controlled within 100%, and the cycle stability is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to cathode materials, and more particularly to an O2 phase lithium cobalt oxide cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of the electronic equipment and electric vehicle industries, increasingly higher demands are being placed on the energy density, cycle life, and safety of lithium-ion batteries. Lithium cobalt oxide, as one of the important cathode materials for lithium-ion batteries, has always been a research hotspot due to its structural and performance optimization. O2-phase lithium cobalt oxide, due to its unique structural advantages, possesses high theoretical specific capacity, rate performance, and good cycle stability. However, current methods for preparing O2-type lithium cobalt oxide have some problems. Commonly used methods include first preparing P2-type sodium cobalt oxide, followed by solid-phase ion exchange, liquid-phase ion exchange, or a combination of both. However, these methods result in O2-type lithium cobalt oxide with low crystallinity and poor coating effect, especially with a low initial lithium-cobalt ratio and a large amount of Li in the crystals. + The empty space resulted in the initial charge capacity being lower than the initial discharge capacity during the coin cell test, manifesting as an initial efficiency greater than 100%. This was due to excessive Li. + The presence of vacancies limits its further performance improvement and application in full cells. Furthermore, due to the poor thermal stability of O2 phase lithium cobalt oxide, it will gradually transform into the O3 phase structure at high temperatures, thereby losing the unique advantages of O2 phase lithium cobalt oxide. Therefore, the modification scheme of O2 phase lithium cobalt oxide is also limited by the process temperature.

[0003] CN119480994A discloses a lithium cobalt oxide cathode material, which has a boron-containing compound coating layer on an O2 phase lithium cobalt oxide host material. The process of forming the boron-containing compound coating layer includes: mixing the O2 phase lithium cobalt oxide with the boron-containing coating material, and performing low-temperature solid-state sintering at 150℃-230℃ for 1h-12h. The surface-optimized O2 phase lithium cobalt oxide cathode material provided has higher initial efficiency, capacity and cycle stability than conventional O3 phase lithium cobalt oxide.

[0004] CN119108551A discloses an O2 phase lithium-rich cathode material for lithium-ion batteries and its preparation method. The method uses aluminum isopropoxide as the aluminum source and adopts liquid phase coating technology combined with low temperature heat treatment process to generate a stable Al2O3 coating layer without changing the O2 phase crystal structure. This reduces the contact between particles and electrolyte, reduces the side reactions between particles and electrolyte, and improves the material interface stability and electrochemical performance through Co doping and Al coating synergistic modification.

[0005] CN118712376A discloses a lithium cobalt oxide material, which is mainly composed of O2 phase lithium cobalt oxide and supplemented by T2 phase lithium cobalt oxide. Under the synergistic effect of O2 phase lithium cobalt oxide and T2 phase lithium cobalt oxide, it has good structural stability under high voltage and has high capacity and excellent cycle stability.

[0006] In summary, current technologies can only modify O2-phase lithium cobalt oxide or change the crystal structure of lithium cobalt oxide materials through low-temperature processes to improve its performance. Therefore, the improvement of O2-phase lithium cobalt oxide performance remains limited. Thus, developing an O2-phase lithium cobalt oxide cathode material with high specific capacity and excellent cycle stability, along with its preparation method, is of great significance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an O2-phase lithium cobalt oxide cathode material, its preparation method, and its applications. This invention utilizes a preparation process involving first liquid-phase ion exchange followed by solid-phase ion exchange to prepare an O2-phase lithium cobalt oxide cathode material with a high initial lithium-to-cobalt ratio, thereby reducing Li... + The absence of vacancies increases the initial charging capacity of the O2 phase lithium cobalt oxide cathode material, while the initial efficiency can be controlled within 100%, and the cycle stability is improved.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing an O2-phase lithium cobalt oxide cathode material, the method comprising:

[0010] A mixed solution is obtained by mixing P2 phase sodium cobalt oxide, a first lithium source, and a solvent. Liquid-phase ion exchange is then performed to obtain an O2 phase lithium cobalt oxide precursor. The O2 phase lithium cobalt oxide precursor is then mixed with a second lithium source and solid-phase ion exchange is performed to obtain the O2 phase lithium cobalt oxide cathode material.

[0011] This invention uses P2-phase sodium cobaltate as raw material and employs a preparation process involving first liquid-phase ion exchange followed by solid-phase ion exchange. The first liquid-phase ion exchange converts most of the P2-phase sodium cobaltate into O2-phase lithium cobaltate, leaving a small portion of P2-phase sodium cobaltate. Simultaneously, the phase transition accumulates lattice stress in the crystal structure. The subsequent solid-phase ion exchange further consumes the remaining small amount of P2-phase sodium cobaltate, yielding pure O2-phase lithium cobaltate. Furthermore, the solid-phase exchange releases the lattice stress accumulated during the liquid-phase ion exchange, which improves the robustness and stability of the crystal structure, enhancing cycle stability. Simultaneously, the Li in the lattice... + The significant reduction in vacancies can improve the lithium-cobalt ratio of the resulting O2 phase lithium cobalt oxide cathode material, thereby increasing the initial charge capacity and enabling the initial efficiency to be controlled within 100%, effectively promoting its application prospects in the field of full batteries.

[0012] Preferably, the molar ratio of Li in the first lithium source to Na in the P2 phase sodium cobaltate is (2-10):1.

[0013] Preferably, the concentration of the first lithium source in the mixed solution is 1 mol / L to 10 mol / L.

[0014] Preferably, the liquid-phase ion exchange is carried out under stirring, the stirring temperature is 80℃-100℃, and the stirring time is 12h-36h.

[0015] Preferably, the mass ratio of the second lithium source to the O2 phase lithium cobalt oxide precursor is (0.5-3):1.

[0016] Preferably, the solid-phase ion exchange is performed at a temperature of 150℃-200℃ for a time of 0.5h-3h.

[0017] Preferably, the method for preparing the P2 phase sodium cobaltate includes:

[0018] A cobalt source, a sodium source, and a first metal compound are mixed and subjected to a first sintering process to prepare a P2 phase sodium cobaltate precursor; the P2 phase sodium cobaltate precursor and a second metal compound are mixed and subjected to a second sintering process to prepare the P2 phase sodium cobaltate.

[0019] Preferably, the first metal compound includes oxides and / or halides of metal element M1.

[0020] Preferably, in the P2 phase sodium cobaltate precursor, the mass ratio of metal element M1 is 0-1%.

[0021] Preferably, the metallic element M1 includes any one or a combination of at least two of Al, Mg, Ti, La, Ce, Y, Zr, Sc, Ca, Ni, or Mn.

[0022] Preferably, in the P2 phase sodium cobaltate, the mass ratio of the second metal compound is 0-1%.

[0023] Preferably, the second metal compound includes any one or a combination of at least two of Al2O3, MgO, TiO2, Y2O3, Nb2O5, WO3, La2O3, ZrO2, Ce2O3, MgF2, MgHPO4, MoO2, or B2O3.

[0024] In a second aspect, the present invention provides an O2-phase lithium cobalt oxide cathode material, which is prepared by the preparation method described in the first aspect; the lithium-cobalt ratio of the O2-phase lithium cobalt oxide cathode material is greater than 1.

[0025] Thirdly, the present invention provides a positive electrode sheet, wherein the positive active material of the positive electrode sheet comprises the O2 phase lithium cobalt oxide positive electrode material as described in the second aspect.

[0026] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode as described in the third aspect.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a method for preparing O2-phase lithium cobalt oxide cathode material, using P2-phase sodium cobalt oxide as raw material, employing a process of first performing liquid-phase ion exchange and then solid-phase ion exchange. The first liquid-phase ion exchange converts most of the P2-phase sodium cobalt oxide into O2-phase lithium cobalt oxide, leaving a small portion of P2-phase sodium cobalt oxide. Simultaneously, the phase transition accumulates lattice stress in the crystal structure. The subsequent solid-phase ion exchange further consumes the remaining small amount of P2-phase sodium cobalt oxide, yielding pure O2-phase lithium cobalt oxide. Furthermore, the solid-phase exchange releases the lattice stress accumulated during the phase transition in the liquid-phase ion exchange, which is beneficial for improving the robustness and stability of the crystal structure, thus enhancing cycle stability. Simultaneously, the Li in the crystal lattice... + The significant reduction in vacancies can improve the lithium-cobalt ratio of the resulting O2 phase lithium cobalt oxide cathode material, thereby increasing the initial charge capacity and enabling the initial efficiency to be controlled within 100%, effectively promoting its application prospects in the field of full batteries. Attached Figure Description

[0029] Figure 1 These are the XRD patterns of the O2 phase lithium cobalt oxide cathode materials prepared in Examples 1, 1, and 2 of this invention. Detailed Implementation

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0031] It should be noted that in the description of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.

[0032] In one specific embodiment, the present invention provides a method for preparing an O2-phase lithium cobalt oxide cathode material, the method comprising:

[0033] A mixed solution is obtained by mixing P2 phase sodium cobalt oxide, a first lithium source, and a solvent. Liquid-phase ion exchange is then performed to obtain an O2 phase lithium cobalt oxide precursor. The O2 phase lithium cobalt oxide precursor is then mixed with a second lithium source and solid-phase ion exchange is performed to obtain the O2 phase lithium cobalt oxide cathode material.

[0034] This invention uses P2-phase sodium cobaltate as raw material and employs a preparation process involving first liquid-phase ion exchange followed by solid-phase ion exchange. The first liquid-phase ion exchange converts most of the P2-phase sodium cobaltate into O2-phase lithium cobaltate, leaving a small portion of P2-phase sodium cobaltate. Simultaneously, the phase transition accumulates lattice stress in the crystal structure. The subsequent solid-phase ion exchange further consumes the remaining small amount of P2-phase sodium cobaltate, yielding pure O2-phase lithium cobaltate. Furthermore, the solid-phase exchange releases the lattice stress accumulated during the liquid-phase ion exchange, which improves the robustness and stability of the crystal structure, enhancing cycle stability. Simultaneously, the Li in the lattice... + The significant reduction in vacancies can improve the lithium-cobalt ratio of the resulting O2 phase lithium cobalt oxide cathode material, thereby increasing the initial charge capacity and enabling the initial efficiency to be controlled within 100%, effectively promoting its application prospects in the field of full batteries.

[0035] In the preparation method provided by this invention, if the molar ratio of Li in the first lithium source to Na in the P2 phase sodium cobaltate is too small during the liquid-phase ion exchange process, i.e., if Li is too little, the reaction will be insufficient.

[0036] In some embodiments, the molar ratio of Li in the first lithium source to Na in the P2 phase sodium cobaltate is (2-10):1, for example, it can be 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] In some embodiments, the concentration of the first lithium source in the mixed solution is 1 mol / L to 10 mol / L, for example, it can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0038] In some embodiments, the liquid-phase ion exchange is carried out under stirring, and the stirring temperature is 80℃-100℃, for example, it can be 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 93℃, 95℃, 97℃ or 100℃, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the stirring time is 12h-36h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h or 36h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0039] In the solid-phase ion exchange process, if the mass ratio of the second lithium source to the O2 phase lithium cobalt oxide precursor is too small, that is, if the second lithium source is too small, the reaction will be insufficient.

[0040] In some embodiments, the mass ratio of the second lithium source to the O2 phase lithium cobalt oxide precursor is (0.5-3):1, for example, it can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0041] In this invention, both the first lithium source and the second lithium source are commonly used lithium sources in the art, and the solvent is a commonly used solvent in the art, without any particular limitation. Exemplarily, the first lithium source and the second lithium source each independently include any one or at least two combinations of lithium nitrate, lithium hydroxide, lithium chloride, lithium bromide, or lithium oxalate. Typical but non-limiting combinations include combinations of lithium nitrate and lithium hydroxide, combinations of lithium chloride and lithium bromide, or combinations of lithium oxalate and lithium hydroxide; the solvent includes water.

[0042] In some embodiments, the solid-phase ion exchange is carried out in an air atmosphere.

[0043] In this invention, the temperature and time of solid-phase ion exchange affect the crystal structure and electrochemical performance of the final O2 phase lithium cobalt oxide.

[0044] If the temperature of solid-phase ion exchange is too high, the final product may transform into the O3 phase lithium cobalt oxide, which has poor electrochemical performance. If the temperature is too low, the effect of molten salt cannot be achieved, leaving the P2 phase still residual, which is not conducive to the performance of electrochemical properties.

[0045] If the solid-phase ion exchange time is too long, there is a tendency for it to transition to the O3 phase, which wastes synthesis time and affects the increase in production capacity.

[0046] In some embodiments, the temperature of the solid-phase ion exchange is 150℃-200℃, for example, it can be 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃ or 200℃, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable; the time of the solid-phase ion exchange is 0.5h-3h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h or 3h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] In some embodiments, the method for preparing the P2 phase sodium cobaltate includes:

[0048] A cobalt source, a sodium source, and a first metal compound are mixed and subjected to a first sintering process to prepare a P2 phase sodium cobaltate precursor; the P2 phase sodium cobaltate precursor and a second metal compound are mixed and subjected to a second sintering process to prepare the P2 phase sodium cobaltate.

[0049] In this invention, the process of preparing the P2 phase sodium cobalt oxide matrix by first sintering using cobalt source and sodium source as raw materials is existing technology, and there are no special restrictions on the type of cobalt source, the type of sodium source, or the ratio of cobalt source and sodium source.

[0050] Exemplarily, the cobalt source includes any one or a combination of at least two of cobalt tetroxide, cobalt carbonate, cobalt oxalate, cobalt trioxide, cobalt hydroxide, or cobalt chloride. Typical but non-limiting combinations include a combination of cobalt tetroxide and cobalt carbonate, a combination of cobalt oxalate and cobalt trioxide, or a combination of cobalt hydroxide and cobalt chloride. The sodium source includes any one or a combination of at least two of sodium carbonate, sodium chloride, sodium hydroxide, sodium acetate, or sodium nitrate. Typical but non-limiting combinations include a combination of sodium carbonate and sodium chloride, a combination of sodium hydroxide and sodium acetate, or a combination of sodium nitrate and sodium hydroxide. The molar ratio of Na in the sodium source to Co in the cobalt source is (0.65-0.72):1, for example, it can be 0.65:1, 0.67:1, 0.69:1, 0.70:1, 0.71:1, or 0.72:1, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] In some embodiments, the first metal compound comprises an oxide and / or a halide of a metal element M1, wherein the halide comprises any one or a combination of at least two of a fluoride, chloride, bromide or iodide of the metal element M1, and typical but non-limiting combinations include a combination of a fluoride and a chloride, a combination of a bromide and an iodide, a combination of a fluoride and an iodide, or a combination of a bromide and a chloride.

[0052] In some embodiments, the mass ratio of metal element M1 in the P2 phase sodium cobaltate precursor is 0-1%, for example, it can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0053] In some embodiments, the metal element M1 includes any one or a combination of at least two of Al, Mg, Ti, La, Ce, Y, Zr, Sc, Ca, Ni or Mn. Typical but non-limiting combinations include combinations of Al and Mg, Ti and La, Ce and Y, Zr and Sc, Ca and Ni, or Mn and Al.

[0054] In some embodiments, the mass ratio of the second metal compound in the P2 phase sodium cobaltate is 0-1%, for example, it can be 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0055] In some embodiments, the second metal compound includes any one or a combination of at least two of Al2O3, MgO, TiO2, Y2O3, Nb2O5, WO3, La2O3, ZrO2, Ce2O3, MgF2, MgHPO4, MoO2, or B2O3. Typical but non-limiting combinations include combinations of Al2O3 and MgO, combinations of TiO2 and Y2O3, combinations of Nb2O5 and WO3, combinations of La2O3 and ZrO2, combinations of Ce2O3 and MgF2, combinations of MgHPO4 and MoO2, or combinations of B2O3 and Al2O3.

[0056] In some embodiments, the first sintering temperature is 780℃-850℃, for example, it can be 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable. The first sintering time is 10h-24h, for example, it can be 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] In some embodiments, the second sintering temperature is 700℃-780℃, for example, it can be 700℃, 720℃, 740℃, 760℃ or 780℃, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable. The second sintering time is 3h-10h, for example, it can be 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0058] In some embodiments, the P2 phase sodium cobalt oxide matrix is ​​further subjected to a pulverization process before being mixed with the metal oxide.

[0059] In some embodiments, the pulverizing process includes air jet pulverization.

[0060] In some embodiments, the method for preparing the P2 phase sodium cobaltate further includes sieving the prepared P2 phase sodium cobaltate, the purpose of which is to remove impurities generated during the preparation process.

[0061] In some embodiments, after the liquid-phase ion exchange is completed and before the solid-phase ion exchange is performed, the O2 phase lithium cobalt oxide precursor is further washed and vacuum dried.

[0062] In some embodiments, the preparation method further includes washing and vacuum drying the prepared O2 phase lithium cobalt oxide cathode material.

[0063] In this invention, the purpose of washing the O2 phase lithium cobalt oxide precursor or O2 phase lithium cobalt oxide cathode material is to remove unreacted lithium source or other impurities remaining on the material surface. The specific washing method, number of times, and solvent used are all existing technologies and are not specifically limited in this invention. For example, the washing method can be filtration, centrifugation, or ultrasonic cleaning, the number of times of washing can be 1, 2, 3, 4, or 5 times, and the solvent used for washing can be water or ethanol.

[0064] The purpose of vacuum drying the washed O2 phase lithium cobalt oxide precursor is to fully evaporate the solvent used in the washing process. The temperature and time of vacuum drying are existing technologies and are not specifically limited in this invention. For example, the vacuum drying temperature can be 100℃-150℃, such as 100℃, 110℃, 120℃, 130℃, 140℃, 145℃ or 150℃, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable. The time can be 10h-30h, such as 10h, 15h, 20h, 25h or 30h, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] In another specific embodiment, the present invention provides an O2 phase lithium cobalt oxide cathode material, which is prepared by the preparation method provided by the present invention; the lithium-cobalt ratio of the O2 phase lithium cobalt oxide cathode material is greater than 1.

[0066] In this invention, the lithium-cobalt ratio of the O2 phase lithium cobalt oxide cathode material refers to the molar ratio of Li to Co. The lithium-cobalt ratio affects the lattice stability of the O2 phase lithium cobalt oxide cathode material, and thus affects the initial charge capacity and cycle stability.

[0067] In another specific embodiment, the present invention provides a positive electrode sheet, wherein the positive active material of the positive electrode sheet includes the O2 phase lithium cobalt oxide positive electrode material provided by the present invention.

[0068] In another specific embodiment, the present invention provides a lithium-ion battery, the lithium-ion battery including the positive electrode sheet provided by the present invention.

[0069] Example 1

[0070] This embodiment provides a method for preparing an O2-phase lithium cobalt oxide cathode material, the method comprising the following steps:

[0071] (1) Preparation of P2 phase sodium cobaltate: Cobalt tetroxide, sodium carbonate and Y2O3 are mixed, wherein the molar ratio of Na in sodium carbonate to Co in cobalt tetroxide is 0.7:1. The mixture is subjected to a first sintering at 800℃ for 12h to prepare a 0.25% Y-doped P2 phase sodium cobaltate precursor. The Y2O3-doped P2 phase sodium cobaltate precursor is subjected to air jet pulverization. The P2 phase sodium cobaltate precursor and TiO2 are mixed at a mass ratio of 100:0.3 and subjected to a second sintering at 750℃ for 6h. After sieving, Y-doped and TiO2-coated P2 phase sodium cobaltate is obtained.

[0072] (2) Liquid phase ion exchange: Lithium hydroxide and lithium chloride with a molar ratio of 1:1 are used as the second lithium source. The molar ratio of Li in the second lithium source to Na in the Y-doped, TiO2-coated modified P2 phase sodium cobalt oxide prepared in step (1) is 5:1. They are mixed in water to obtain a mixed solution. The total concentration of lithium hydroxide and lithium chloride in the mixed solution is 5 mol / L, and the molar ratio of lithium hydroxide to lithium chloride is 1:1. The mixture is stirred at 97.5℃ for 15 h. The solid material is collected, washed with deionized water, and vacuum dried at 120℃ for 12 h to obtain the O2 phase lithium cobalt oxide precursor.

[0073] (3) Solid-phase ion exchange: Lithium nitrate and the O2 phase lithium cobalt oxide precursor obtained in step (2) are mixed at a mass ratio of 1.5:1, kept at 170℃ for 2h, cooled, washed with deionized water, and vacuum dried at 130℃ for 12h to prepare the O2 phase lithium cobalt oxide cathode material.

[0074] like Figure 1 As shown, the XRD diffraction peaks of the O2 phase lithium cobalt oxide cathode material prepared in this embodiment correspond to those in PDF#36-1004, proving that a pure phase O2 phase lithium cobalt oxide cathode material was prepared in this embodiment.

[0075] Example 2

[0076] This embodiment provides a method for preparing an O2-phase lithium cobalt oxide cathode material, the method comprising the following steps:

[0077] (1) Preparation of P2 phase sodium cobaltate: Cobalt tetroxide, sodium carbonate and MgF2 are mixed, wherein the molar ratio of Na in sodium carbonate to Co in cobalt tetroxide is 0.65:1. The mixture is subjected to a first sintering at 780℃ for 10h to prepare a 0.1% Mg-doped P2 phase sodium cobaltate precursor. The prepared P2 phase sodium cobaltate precursor is subjected to air jet milling. The P2 phase sodium cobaltate precursor and Al2O3 are mixed at a mass ratio of 100:0.5 and subjected to a second sintering at 780℃ for 10h. After sieving, Mg-doped and Al2O3-coated P2 phase sodium cobaltate is obtained.

[0078] (2) Liquid phase ion exchange: Lithium hydroxide and lithium chloride with a molar ratio of 0.8:1 are used as the second lithium source. The molar ratio of Li in the second lithium source to Na in the Mg-doped and Al2O3-coated sodium cobalt oxide prepared in step (1) is 10:1. They are mixed in water to obtain a mixed solution. The total concentration of lithium hydroxide and lithium chloride in the mixed solution is 1 mol / L, and the molar ratio of lithium hydroxide to lithium chloride is 1:1. The mixture is stirred at 100°C for 12 h, and the solid material is collected. The collected solid material is washed with deionized water and dried under vacuum at 120°C for 12 h to obtain the O2 phase lithium cobalt oxide precursor.

[0079] (3) Solid-phase ion exchange: Lithium nitrate and the O2 phase lithium cobalt oxide precursor obtained in step (2) are mixed at a mass ratio of 0.5:1, kept at 200℃ for 3h, cooled, washed with deionized water, and vacuum dried at 100℃ for 20h to prepare the O2 phase lithium cobalt oxide cathode material.

[0080] Example 3

[0081] This embodiment provides a method for preparing an O2-phase lithium cobalt oxide cathode material, the method comprising the following steps:

[0082] (1) Preparation of P2 phase sodium cobaltate: Cobalt tetroxide, sodium carbonate and ZrO2 are mixed, wherein the molar ratio of Na in sodium carbonate to Co in cobalt tetroxide is 0.72:1. The mixture is subjected to a first sintering at 850℃ for 20h to prepare a 0.5% Zr-doped P2 phase sodium cobaltate precursor. The prepared Zr-doped P2 phase sodium cobaltate precursor is subjected to air jet milling. The P2 phase sodium cobaltate precursor and Y2O3 are mixed at a mass ratio of 100:0.1 and subjected to a second sintering at 700℃ for 3h. After sieving, Zr-doped and Y2O3-coated P2 phase sodium cobaltate is obtained.

[0083] (2) Liquid phase ion exchange: Lithium hydroxide and lithium chloride with a molar ratio of 1:0.9 are used as the second lithium source. The molar ratio of Li in the second lithium source to Na in the Zr-doped and Y2O3-coated modified P2 phase sodium cobalt oxide prepared in step (1) is 2:1. They are mixed in water to obtain a mixed solution. The total concentration of lithium hydroxide and lithium chloride in the mixed solution is 10 mol / L, and the molar ratio of lithium hydroxide to lithium chloride is 1:1. The mixture is stirred at 80°C for 36 h. The solid material is collected, washed with deionized water, and vacuum dried at 120°C for 12 h to obtain the O2 phase lithium cobalt oxide precursor.

[0084] (3) Solid-phase ion exchange: Lithium hydroxide and the O2 phase lithium cobalt oxide precursor obtained in step (2) are mixed in a mass ratio of 3:1, kept at 150°C for 0.5 h, cooled, washed with deionized water, and vacuum dried at 150°C for 15 h to prepare the O2 phase lithium cobalt oxide cathode material.

[0085] Example 4

[0086] This embodiment provides a method for preparing an O2 phase lithium cobalt oxide cathode material. Except for step (1) where Y2O3 and TiO2 are not added, the preparation method is the same as in Example 1.

[0087] Example 5

[0088] This embodiment provides a method for preparing O2 phase lithium cobalt oxide cathode material. Except for step (2), in which the molar ratio of Li in the second lithium source to Na in the Y-doped, TiO2-coated sodium cobalt oxide prepared in step (1) is 1.5:1, and the mixture is mixed in water to obtain a mixed solution, the rest of the method is the same as in Example 1.

[0089] Example 6

[0090] This embodiment provides a method for preparing O2 phase lithium cobalt oxide cathode material. Except for step (2), in which the molar ratio of Li in the second lithium source to Na in the Y-doped, TiO2-coated sodium cobalt oxide prepared in step (1) is 20:1, and the mixture is mixed in water to obtain a mixed solution, the rest of the method is the same as in Example 1.

[0091] Example 7

[0092] This embodiment provides a method for preparing an O2 phase lithium cobalt oxide cathode material. Except for step (3), which involves mixing lithium nitrate and the O2 phase lithium cobalt oxide precursor obtained in step (2) at a mass ratio of 0.2:1, the preparation method is the same as in Example 1.

[0093] Example 8

[0094] This embodiment provides a method for preparing an O2 phase lithium cobalt oxide cathode material. Except for step (3), which involves mixing lithium nitrate and the O2 phase lithium cobalt oxide precursor obtained in step (2) at a mass ratio of 4.5:1, the preparation method is the same as in Example 1.

[0095] Example 9

[0096] This embodiment provides a method for preparing O2 phase lithium cobalt oxide cathode material. Except for the heat preservation time of 0.5h during solid phase ion exchange in step (3), the preparation method is the same as in embodiment 1.

[0097] Example 10

[0098] This embodiment provides a method for preparing O2 phase lithium cobalt oxide cathode material. Except for the heat preservation time of 5h during solid phase ion exchange in step (3), the preparation method is the same as that in Example 1.

[0099] Example 11

[0100] This embodiment provides a method for preparing an O2 phase lithium cobalt oxide cathode material. Except for the temperature of 130°C during the solid-phase ion exchange process in step (3), the preparation method is the same as that in Example 1.

[0101] Example 12

[0102] This embodiment provides a method for preparing O2 phase lithium cobalt oxide cathode material. Except for the temperature of 250°C during the solid-phase ion exchange process in step (3), the preparation method is the same as that in Example 1.

[0103] Comparative Example 1

[0104] This comparative example provides a method for preparing an O2 phase lithium cobalt oxide cathode material. The preparation method is the same as in Example 1 except that step (3) is omitted, i.e., solid-phase ion exchange is not performed.

[0105] like Figure 1 As shown, the XRD diffraction peaks of the O2 phase lithium cobalt oxide cathode material prepared in this comparative example contain a small amount of diffraction peaks corresponding to the P2 phase sodium cobalt oxide in PDF#30-1182, in addition to the O2 phase lithium cobalt oxide. That is, a pure phase O2 phase lithium cobalt oxide cathode material was not obtained.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing an O2 phase lithium cobalt oxide cathode material. The preparation method is the same as that in Example 1 except that step (2) is omitted, i.e., liquid phase ion exchange is not performed.

[0108] like Figure 1As shown, the XRD diffraction peaks of the O2 phase lithium cobalt oxide cathode material prepared in this comparative example contain a small number of diffraction peaks corresponding to the T2 phase lithium cobalt oxide in PDF#37-1162, in addition to the O2 phase lithium cobalt oxide. This indicates that the O2 phase lithium cobalt oxide prepared by this method is not a single component.

[0109] Performance testing:

[0110] The electrochemical performance of the O2-phase lithium cobalt oxide cathode materials prepared by the preparation methods provided in all the above embodiments and comparative examples was tested, and the test methods are as follows:

[0111] First, coin cells were prepared using the O2-phase lithium cobalt oxide cathode materials provided in Examples 1 to 12 and Comparative Examples 1 to 2 as cathode active materials. Specifically, the process included: mixing O2-phase lithium cobalt oxide cathode materials, carbon black, and polyvinylidene fluoride in an appropriate amount of NMP at a mass ratio of 9:0.5:0.5; coating the obtained cathode active material slurry onto the surface of aluminum foil; and drying to obtain the O2-phase lithium cobalt oxide cathode.

[0112] Then, using lithium metal sheets as the negative electrode, polypropylene microporous membranes as the separator, and 1 mol / L LiPF6+EC / DMC / EMC as the electrolyte, an O2 phase lithium cobalt oxide coin cell was assembled in an environment filled with argon gas and with a moisture content of less than 0.1 ppm.

[0113] At 25℃, the prepared O2 phase lithium cobalt oxide coin cells were charged and discharged at a rate of 0.1C within a voltage range of 2.5V-4.65V. The specific capacity of the first charge, the first efficiency, and the specific capacity of the first discharge were tested. The first efficiency = the specific capacity of the first discharge / the specific capacity of the first charge.

[0114] At 45℃, within a voltage range of 2.5V-4.65V, the prepared O2 phase lithium cobalt oxide coin cell was subjected to 50 charge-discharge cycles at a 1C rate to test the cycle capacity retention rate, where the cycle capacity retention rate = specific capacity of the 50th discharge / specific capacity of the first discharge.

[0115] The test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] This invention uses metal oxides to modify P2 phase sodium cobalt oxide, and then uses the metal oxide-modified P2 phase sodium cobalt oxide as raw material to prepare O2 phase lithium cobalt oxide cathode material with high initial lithium-cobalt ratio through a preparation process of liquid phase ion exchange followed by solid phase ion exchange, thereby improving the initial charging capacity and cycle stability of O2 phase lithium cobalt oxide cathode material.

[0119] Based on the test results of Example 1 and Comparative Examples 1-2, it can be determined that, compared with preparation processes that only perform liquid-phase ion exchange or only perform solid-phase ion exchange, the preparation process provided by the present invention, which first performs liquid-phase ion exchange and then solid-phase ion exchange, is more conducive to obtaining pure-phase sodium cobalt oxide, increasing the lithium-cobalt ratio of the obtained O2-phase lithium cobalt oxide cathode material, improving its crystal structure stability, thereby increasing the initial charge capacity, while the initial efficiency can be controlled within 100%, and the cycle stability is improved.

[0120] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an O2-phase lithium cobalt oxide cathode material, characterized in that, The preparation method includes: A mixed solution is obtained by mixing P2 phase sodium cobalt oxide, a first lithium source, and a solvent. Liquid-phase ion exchange is then performed to obtain an O2 phase lithium cobalt oxide precursor. The O2 phase lithium cobalt oxide precursor is then mixed with a second lithium source and solid-phase ion exchange is performed to obtain the O2 phase lithium cobalt oxide cathode material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of Li in the first lithium source to Na in the P2 phase sodium cobaltate is (2-10):1; Preferably, in the mixed solution, the concentration of the first lithium source is 1 mol / L to 10 mol / L; Preferably, the liquid-phase ion exchange is carried out under stirring, the stirring temperature is 80℃-100℃, and the stirring time is 12h-36h.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the second lithium source to the O2 phase lithium cobalt oxide precursor is (0.5-3):1; Preferably, the solid-phase ion exchange is performed at a temperature of 150℃-200℃ for a time of 0.5h-3h.

4. The preparation method according to claim 1, characterized in that, The preparation method of the P2 phase sodium cobaltate includes: A cobalt source, a sodium source, and a first metal compound are mixed and subjected to a first sintering process to prepare a P2 phase sodium cobaltate precursor; the P2 phase sodium cobaltate precursor and a second metal compound are mixed and subjected to a second sintering process to prepare the P2 phase sodium cobaltate.

5. The preparation method according to claim 4, characterized in that, The first metal compound includes oxides and / or halides of the metal element M1.

6. The preparation method according to claim 5, characterized in that, In the P2 phase sodium cobalt oxide precursor, the mass ratio of metal element M1 is 0-1%; Preferably, the metallic element M1 includes any one or a combination of at least two of Al, Mg, Ti, La, Ce, Y, Zr, Sc, Ca, Ni, or Mn.

7. The preparation method according to claim 4, characterized in that, In the P2 phase sodium cobaltate, the mass ratio of the second metal compound is 0-1%; Preferably, the second metal compound includes any one or a combination of at least two of Al2O3, MgO, TiO2, Y2O3, Nb2O5, WO3, La2O3, ZrO2, Ce2O3, MgF2, MgHPO4, MoO2, or B2O3.

8. An O2-phase lithium cobalt oxide cathode material, characterized in that, The O2 phase lithium cobalt oxide cathode material is prepared by the preparation method according to any one of claims 1-7; The lithium-cobalt ratio of the O2 phase lithium cobalt oxide cathode material is greater than 1.

9. A positive electrode plate, characterized in that, The positive electrode active material of the positive electrode sheet includes the O2 phase lithium cobalt oxide positive electrode material as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode as described in claim 9.

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