A mixed-phase lithium battery cathode material, its preparation method and application

Abstract

This application discloses a mixed-phase lithium-ion battery cathode material, its preparation method, and its applications. The lithium-ion battery cathode material of this application has a mixed-phase structure of layered and non-layered phases in its crystal structure, with the layered and non-layered phases arranged alternately. During high-voltage charging, the lattice oxygen migration and oxygen evolution processes in the layered phase of this lithium-ion battery cathode material are suppressed by the adjacent non-layered phase, alleviating irreversible oxygen loss and structural disorder in the layered phase during cycling, improving the structural stability of the layered phase, and suppressing voltage decay. Simultaneously, the synergistic effect of the layered and non-layered phases also reduces the changes in the lattice parameters of the cathode material during charging and discharging, reducing the generation of microcracks within the particles. Therefore, the lithium-ion battery cathode material of this application exhibits a capacity exceeding 440 mAh g at high voltages greater than 4.5V. ‑1 Its reversible capacity, excellent rate capability, and cycling stability demonstrate superior electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery cathode materials, in particular to a lithium battery cathode material with a mixed phase structure and a preparation method and application thereof. BACKGROUND

[0002] The global new energy vehicle market penetration rate is rapidly increasing, and the demand for power batteries is booming, which has greatly promoted the research and development and industrialization progress of lithium battery cathode materials. Layered cathode materials are currently the mainstream cathode materials for lithium batteries, including lithium cobaltate, nickel cobalt manganese ternary materials, and lithium-rich manganese cathode materials, etc. However, these layered materials will undergo a redox process of lattice oxygen under high-voltage service conditions (voltage greater than 4.5V), which leads to a dramatic phase structure evolution, resulting in a decrease in cycle capacity and voltage decay. Taking lithium-rich manganese-based cathode materials as an example, this cathode material is a typical lithium-ion battery cathode material that can undergo reversible oxidation and reduction reactions of anions and cations, and has a discharge specific capacity much higher than that of high-voltage lithium cobaltate and high-nickel ternary cathode materials. This makes lithium-rich manganese-based cathode materials exhibit high specific capacity and strong endurance advantages, and is a next-generation new energy vehicle lithium-ion battery cathode material with great development potential. Lithium-rich manganese-based cathode materials have great application potential in developing high-energy-density lithium batteries, especially in developing all-solid-state lithium metal batteries. In the near future, with the reduction of lithium salt prices, lithium-rich manganese-based cathode materials are expected to be applied in the market. Research shows that lithium-rich manganese-based cathode materials have shown a potential market space of more than 100 billion.

[0003] In 1997, Numata et al. first reported a layered Li2MnO3·LiCoO2 solid solution material, which obtained an initial discharge capacity of nearly 280mAh g -1 , opening up the research and development of lithium-rich manganese materials. Lithium-rich manganese-based cathode material xLiMO2·(1-x)Li2MnO3, where M is a doping element, is a material that has attracted much attention from academia and industry in recent years, with a theoretical capacity of more than 300mAh g -1 , an actual capacity of more than 200mAh g -1 , and a working voltage of about 4.5V, which has high energy density; therefore, it has the potential to develop into a power battery cathode material. Currently, academia and industry are focusing on the research and development and application of pure Mn-based or small amount of doped lithium-rich manganese cathodes.

[0004] Generally, lithium-rich manganese cathode materials are solid solution structures of lithium-rich lithium manganate and classic layered lithium transition metal oxides, which are two-phase compounds uniformly mixed on a nanoscale. It is generally believed that the two phase structures in pure manganese-based lithium-rich manganese cathode materials are a layered Li2MnO3 belonging to the c2 / m space group, a monoclinic system, in which the 3a site is occupied by Li + , and the 3b site is occupied by 1 / 3 of Li+ and 2 / 3 of Mn 4+ Occupied, 6c site is O 2- Occupied by Li ions; the other is LiMnO2layer structure belongs to R-3m space group, hexagonal system, wherein 3a site is occupied by Li + Occupied, 3b site is occupied by Mn 3+ Occupied, 6c site is O 2- Occupied by Li ions. Thus, the molecular formula of pure manganese-based lithium-rich manganese material can be written as xLiMnO2·(1-x)Li2MnO3, wherein 0≤x≤1.

[0005] The high capacity and high voltage characteristics of lithium-rich manganese cathode materials are related to their composition, structure, size and morphology to varying degrees. Previous studies believe that the capacity and voltage change mechanism of lithium-rich manganese is a "complex process with multiple atoms participating and a sequential tendency", which is the reason for its ultra-high capacity and voltage that cannot be stably maintained for multiple times. Among them, the oxygen valence change, oxygen migration and even oxygen precipitation in the lattice framework at high voltage are one of the fundamental reasons for capacity and voltage attenuation.

[0006] Although lithium-rich manganese cathode materials exhibit great advantages of high capacity, high voltage and low cost; however, their poor conductivity, low capacity utilization and poor cycle stability also restrict the industrial application of this type of material. Therefore, how to inhibit the oxygen valence change and oxygen migration process from the perspective of crystal structure design, and enhance the reversible capacity, rate capability and cycle stability of lithium-rich manganese cathode materials, is the research focus and difficulty of all layered structure materials including lithium-rich manganese cathode materials. SUMMARY

[0007] The purpose of the present application is to provide a new lithium battery cathode material with a mixed phase structure and a preparation method and application thereof.

[0008] The technical scheme adopted by the present application is as follows:

[0009] One aspect of the present application discloses a lithium battery cathode material with a mixed phase structure, which has a mixed phase structure of layered phase and non-layered phase in the crystal structure of the lithium battery cathode material, and the layered phase and the non-layered phase are arranged alternately.

[0010] It should be noted that the lithium battery cathode material of the present application has a crystal with a mixed phase structure in which the layered phase and the non-layered phase are arranged alternately, the migration of lattice oxygen and the oxygen precipitation process in the layered phase structure are inhibited by the adjacent non-layered phase during high-voltage charging, the irreversible oxygen loss and structural disorder of the layered phase during the cycle process are greatly relieved, thereby improving the stability of the layered phase structure and inhibiting the voltage attenuation; at the same time, the synergistic effect of the layered phase and the non-layered phase also reduces the change of the lattice parameters of the lithium battery cathode material during the charging and discharging process, and reduces the generation of micro-cracks in the particles. Therefore, the lithium battery cathode material of the present application exhibits a reversible capacity of more than 440 mAh g -1 at a high voltage of greater than 4.5 V, excellent rate and cycle stability, and excellent electrochemical performance under high-voltage charging and discharging conditions.

[0011] It should also be noted that in the crystal structure of the lithium battery cathode material of the present application, the layered phase and the non-layered phase are arranged alternately, forming a microstructure similar to a "mosaic" distribution. For example, the arrangement of the layered phase and the non-layered phase is layered phase-non-layered phase-layered phase-non-layered phase-layered phase-non-layered phase-layered phase-non-layered phase, regardless of the direction from which it is viewed.

[0012] In an implementation manner of the present application, the non-layered phase is nanoscale. Preferably, the nanoscale is 0.5-10 nm, that is, the non-layered phase is 0.5-10 nm.

[0013] It should be noted that the main role of the non-layered phase in the present application is to improve the structural stability by inhibiting the migration of lattice oxygen and the oxygen precipitation process in the adjacent layered phase structure, and to improve the rate performance as a high-speed ion and / or electron transmission channel. The size of the non-layered phase of the present application is preferably 0.5-10 nm. If the size is less than 0.5 nm, the phase is usually regarded as a crystal defect rather than a separate non-layered phase structure; if the size of the non-layered phase is greater than 10 nm, the proportion of the non-layered phase in the entire cathode material will increase. Since the non-layered phase is not the main capacity contribution phase, the increase of the proportion of the phase is not conducive to the capacity of the cathode material. Therefore, in order to ensure the comprehensive performance of the cathode material, the size of the non-layered phase is preferably controlled to be between 0.5-10 nm during the synthesis process.

[0014] In an implementation manner of the present application, the mixed phase structure of the layered phase and the non-layered phase is uniformly distributed in the particles of the lithium battery cathode material.

[0015] It should be noted that one of the effects of the non-layered phase of the lithium battery positive electrode material of the present application is to reduce the overall crystal structure parameter change of the positive electrode material and reduce the generation of internal micro-cracks through the synergistic effect between the layered phase. In the mixed phase positive electrode material of the present application, the TM-O layer slip (TM includes Ni, Co, Mn, etc.) of the layered phase structure during the charging and discharging process is the main reason for the change of the lattice parameters of the positive electrode material. The uniform distribution of the non-layered nanophase with a size of 0.5-10 nm in the crystal structure of the material can effectively inhibit the slip of the TM-O layer in the layered phase structure. In the traditional positive electrode material protection strategy, the non-layered phase is only enriched on the surface of the positive electrode material. Although the interface side reaction of the material under high voltage service conditions can be inhibited, the problem of micro-crack generation caused by the change of the lattice parameters during the charging and discharging process has not been improved. Therefore, in the present application, the mixed phase structure of the layered phase and the non-layered phase is uniformly distributed in the positive electrode material particles, which can effectively alleviate the problem of internal micro-crack generation caused by the change of the lattice parameters.

[0016] In an implementation manner of the present application, the interfacial crystal domain lattice of the layered phase and the non-layered phase is adapted.

[0017] It should be noted that the interfacial crystal domain lattice of the mixed phase structure of the positive electrode material of the present application can effectively alleviate the lattice disorder and the lattice stress caused by the difference in the phase structure of the two-phase interface structure. At the same time, the interfacial crystal domain lattice adaptation of the two-phase interface is also conducive to the efficient transmission of lithium ions in the framework of the crystal structure of the positive electrode material, and increases the rate performance of the material.

[0018] In an implementation manner of the present application, the non-layered phase includes at least one of a spinel phase, a perovskite phase and a rock salt phase.

[0019] It should be noted that the non-layered phase in the positive electrode material of the present application, whether it is a spinel phase, a perovskite phase or a rock salt phase structure, can realize the lattice adaptation of the two phases between the layered phase, which ensures the low lattice disorder and internal stress in the crystal structure of the material; at the same time, the three kinds of phase structures all contain a three-dimensional lithium ion transport network, which can realize the efficient transmission of lithium ions; and the three kinds of phase structures all show higher structural stability than the layered phase, and this higher structural stability is the structural origin of effectively inhibiting oxygen migration and oxygen precipitation.

[0020] In an implementation manner of the present application, the non-layered phase has high ion and / or electronic conductivity to ensure efficient lithium ion and electron transmission. Generally, the lithium ion conductivity and the electronic conductivity of the non-layered phase structure are both greater than 10 -5 Scm -1 .

[0021] In one implementation of this application, the non-layered phase improves the structural stability of the layered phase by suppressing lattice oxygen migration and / or oxygen evolution processes, thereby enhancing the cycle stability of the lithium-ion battery cathode material under high voltage. In this application, high voltage refers to a voltage greater than 4.4V or greater than 4.5V.

[0022] In one implementation of this application, the molecular formula of the battery positive electrode active material is Li. x TM y O2A z Where 1≤x≤2, 0.5≤y≤1.5, 0≤z≤0.2, TM is at least one of Mn, Co, Ni, Al, Ti, Zr and Nb; A is at least one of F, BO3, SiO4, PO4 and SO4.

[0023] In one implementation of this application, the molecular formula of the layered phase is Li2TMO3 or LiTMO2, wherein TM is at least one of Mn, Co and Ni.

[0024] In one implementation of this application, lithium and TM antisites are present in the layered phase.

[0025] In one implementation of this application, the content of lithium and TM antisite is 1-40%.

[0026] It should be noted that, in this application, the presence of lithium and TM antisites in the layered phase refers to the phenomenon of TM ions in some transition metal layers exchanging positions with lithium ions in the lithium layer. Through lithium and TM antisites, the crystal structure parameters of the mixed-phase structure are regulated and optimized to better achieve lattice matching between the layered and non-layered phases, reducing lattice stress at the two-phase interface. This plays a crucial role in the high cycle stability and capacity of the mixed-phase cathode material. The ease of matching between the two phases varies depending on the combination of layered and non-layered phases, resulting in different lithium and TM antisite contents in the layered phase. In this application, due to the differences in the two-phase structures, at least 1% lithium and TM antisites exist in the layered phase; simultaneously, to ensure the basic structural framework of the layered phase, up to 40% of the TM in the transition metal layer enters the lithium layer.

[0027] In one implementation of this application, the molecular formula of the non-layered phase is spinel phase Li. x TM2O4, perovskite phase LiTMO3, or rock salt phase Li x TM 1-x O, where 0≤x≤1, and TM is at least one of Mn, Co, Ni, Al, Ti, Zr and Nb.

[0028] In one implementation of this application, lithium and TM are mixed in the non-layered phase.

[0029] In one implementation of this application, the content of lithium and TM mixed arrangement is 1%-10%.

[0030] It should be noted that in this application, the presence of lithium and TM mixing in the non-layered phase refers to the phenomenon where Li and TM co-occupy cation sites in the crystal structure in a certain proportion. Through lithium and TM mixing, the crystal structure parameters of the non-layered phase are optimized to better match the crystal structure of the layered phase, reducing lattice stress and lattice disorder at the two-phase interface. This plays a crucial role in the high cycle stability and capacity of the mixed-phase cathode material. In this application, the mixed-phase structure of the cathode material inevitably leads to more than 1% lithium and TM mixing in the non-layered phase. However, because the non-layered phase has higher crystal structure stability compared to the layered phase, the proportion of lithium and TM mixing in the crystal structure is relatively small, generally not exceeding 10%.

[0031] In one implementation of this application, the lithium battery cathode material is a large primary particle or a secondary particle formed by stacking small primary particles; wherein the size of the large primary particle is 1-20μm; the size of the secondary particle is 1-20μm; and the size of the small primary particle is 50nm-2μm.

[0032] It should be noted that the lithium battery cathode material in this application can be primary particles or secondary particles formed by the stacking of primary particles, depending on the specific requirements.

[0033] In one implementation of this application, the size of the interphase domains between the layered and non-layered phases is 0.5-10 nm.

[0034] Another aspect of this application discloses a method for preparing the lithium battery cathode material, including using at least one of high-temperature sintering, chemical method and electrochemical method to obtain a lithium battery cathode material with a mixed phase structure in which the layered phase and the non-layered phase are arranged in an alternating manner in the crystal structure.

[0035] In one implementation of this application, the chemical method includes placing the sintered lithium-rich manganese-based cathode material in a molten salt containing at least one of lithium nitrate, lithium chloride, and lithium oxide, and treating it at a temperature of 250-350°C for 1-24 hours to obtain a lithium battery cathode material with a mixed phase structure of layered and non-layered phases.

[0036] In one implementation of this application, the electrochemical method includes mixing a sintered lithium-rich manganese-based cathode material, conductive carbon, and polyvinylidene fluoride binder in a 90:5:5 ratio to form an electrode sheet, and then placing the electrode sheet in a lithium salt electrolyte for charging and discharging for no more than 3 cycles to obtain a lithium battery cathode material with a mixed phase structure of layered and non-layered phases.

[0037] In one implementation of this application, a high-temperature sintering method is preferred, which includes mixing and sintering a multiphase mixed precursor for preparing lithium battery cathode material with lithium carbonate in a certain proportion, with a sintering temperature of 800-1000℃ and a sintering time of 1-24h, to obtain a lithium battery cathode material with a mixed phase structure of layered and non-layered phases; the multiphase mixed precursor is an oxide of each metal element in the lithium battery cathode material.

[0038] Another aspect of this application discloses the application of the lithium battery cathode material in the preparation of power batteries, energy storage batteries, or lithium-ion batteries for 3C consumer electronics products, drones, or e-cigarettes.

[0039] Another aspect of this application discloses a lithium-ion battery using the lithium battery cathode material of this application.

[0040] The beneficial effects of this application are as follows:

[0041] The lithium-ion battery cathode material of this application exhibits improved stability and reduced voltage decay during high-voltage charging. In the layered phase structure, lattice oxygen migration and precipitation are suppressed by adjacent non-layered phases, mitigating irreversible oxygen loss and structural disorder during cycling. Simultaneously, the synergistic effect of the mixed layered and non-layered phases reduces changes in the lattice parameters of the cathode material during charging and discharging, minimizing the formation of microcracks within the particles. Therefore, the lithium-ion battery cathode material of this application demonstrates a capacity exceeding 440 mAh g at high voltages greater than 4.5V. -1 Its reversible capacity, excellent rate capability, and cycling stability demonstrate superior electrochemical performance. Attached Figure Description

[0042] Figure 1 These are schematic diagrams (a) of the mosaic mixed distribution of the mixed phase structure of the cathode material in the embodiments of this application, and (b, c) of the crystal structure of the layered phase and the non-layered spinel phase.

[0043] Figure 2 Li is an example of this application. 1.13 Mn 0.75 The surface morphology (a), TEM and electron diffraction (b) characteristics of O2 are analyzed, with scale bars of 200 nm and 10 nm, respectively.

[0044] Figure 3 Li is an example of this application. 1.13 Mn 0.75 Crystal structure analysis of O2 (a), high-resolution TEM crystal structure characterization (b), and schematic diagram of lattice adaptation between layered phase and spinel phase (c);

[0045] Figure 4 Li is an example of this application. 1.13 Mn0.75 Comparison of the electrochemical curves of three materials with pure layered, pure spinel phase, and layered / spinel mixed phase structures of O2 (a), comparison of the cycle stability and median voltage changes of the layered phase and mixed phase structure materials (b, c); Li 1.13 Mn 0.75 In-situ XRD results of the mixed phase structure of O2 (d). Detailed implementation manners

[0046] In recent years, lithium-rich manganese materials have received extensive attention from the academic and industrial circles due to their high voltage, high capacity, and low cost. Traditional layered cathode materials, including lithium cobalt oxide LiCoO2 and ternary cathode materials Li[Ni x Co y Mn 1-x-y O2 (0 < x < 1, 0 < y < 1) as representative layered cathode active materials achieve capacity by cation valence change and a small amount of anion valence change. Their reversible capacity is generally < 200 mAh g -1 , and the energy density is generally < 800 Wh kg -1 . However, through the effective utilization of the anion valence change reaction, the reversible capacity of lithium-rich manganese cathode materials is ≥ 250 mAh g -1 , and the energy density ≥ 1000 Wh kg -1 becomes possible.

[0047] When there are doping elements, the molecular formula of lithium-rich manganese materials can be written as xLiMn y M 1-y O2·(1 - x)Li2MnO3, where M is the doping element, 0 < x < 1, 0 < y < 1. From a structural perspective, lithium-rich manganese cathode materials can be regarded as a solid solution structure of classical layered lithium transition metal oxides and lithium-rich manganese lithium oxides, which is a two-phase compound uniformly mixed at the nanoscale. That is to say, there are two phase structures at the nanoscale in lithium-rich manganese cathode materials: one is the LiMnO2 layered structure belonging to the R-3m space group, hexagonal crystal system, where the 3a site is occupied by Li + , the 3b site is occupied by Mn 3+ , the 6c site is occupied by O 2- ions, and the reversible discharge capacity is < 200 mAh g -1 ; the other structure is the layered Li2MnO3, belonging to the c2 / m space group, monoclinic crystal system, where the 3a site is occupied by Li + , the 3b site is occupied by 1 / 3 of Li + and 2 / 3 of Mn 4+ , the 6c site is occupied by O 2- ions, and the reversible capacity is ≥ 459 mAh g -1In summary, attributed to its unique structure and the electrochemical reaction process involving changing valences of cations and anions, lithium-rich manganese cathode materials exhibit superior performance at 2.0-4.8 V compared to Li / Li. + Within the specified range, it can deliver more than 300mAh g. -1 The capacity.

[0048] Despite the significant advantages of high capacity, high voltage, and low cost exhibited by lithium-rich manganese cathode materials, their poor conductivity, low capacity utilization, and poor cycle stability also hinder their industrial application. Research indicates that the capacity / voltage change mechanism of lithium-rich manganese cathode materials is a complex process involving atoms and exhibiting a sequential tendency. During the first charging cycle, Li... + From LiMn y M 1-y O2 is extracted from the Li layer, Li + The process of extracting Li and Mn layers from Li2MnO3 to generate Li2O; simultaneously, accompanied by Li + The extraction of oxygen ions into the Li₂MnO₃ lattice leads to the formation of oxygen vacancies, indicating that some metal ions also migrate inward, resulting in an irreversible phase transition of the lattice framework. During subsequent discharge, due to the reduction of oxygen vacancies, some Li₂MnO₃... + The inability to reintegrate into the bulk phase leads to significant capacity loss during the initial charge-discharge cycle. In subsequent charge-discharge cycles, the lithium-rich manganese cathode material exhibits drastic capacity and voltage decay due to the gradual increase in oxygen vacancy generation / disappearance and crystal structure phase transitions.

[0049] In summary, the capacity and voltage decay of lithium-rich manganese cathode materials originate from the processes of oxygen valence change and oxygen migration to form oxygen vacancies. Therefore, if oxygen migration can be suppressed from a structural design perspective, the structural stability of lithium-rich manganese materials can be significantly improved, thereby enhancing cycle stability and suppressing voltage decay. LiMn₂O₄ materials, with their spinel structure characteristics, have high oxygen valence change and oxygen migration barriers. Introducing Mn-O structural units of LiMn₂O₄ with spinel structure characteristics into the lattice of lithium-rich manganese cathode materials is expected to achieve oxygen migration suppression.

[0050] Based on the aforementioned research and development challenges and inventive concepts, this application innovatively introduces a non-layered phase into lithium-rich manganese materials, resulting in a mixed phase structure of layered and non-layered phases in the crystal structure of the lithium battery cathode material, with the layered and non-layered phases arranged alternately. Furthermore, in a further improved embodiment, the mixed phase structure of the layered and non-layered phases is nanoscale, uniformly distributed within the particles of the lithium battery cathode material, and the nanoscale domains of the layered and non-layered phases are lattice-matched.

[0051] Taking the spinel nanophase structure of LiMn2O4 as an example, the novel lithium-ion battery cathode material of this application is expressed by the molecular formula xLiM2O4·(1-x)Li2MnO3. In this structure, the LiMn2O4 spinel phase structure does not produce oxygen valence change even at voltages above 4.8V; at the same time, the existence of the LiMn2O4 spinel phase structure also solves the structural instability problem caused by oxygen valence change / oxygen migration in the Li2MnO3 layered phase. Specifically, for the Li2MnO3 layered phase, after partial delithiation, spontaneous oxygen migration caused by oxygen valence change in the lattice framework is due to the extremely low oxygen vacancy formation energy. However, in the LiMn2O4 spinel phase, the oxygen vacancy formation energy is as high as 2.9 eV, and the migration energy is as high as 2.07 eV, so oxygen vacancy formation and oxygen migration are difficult to occur. Therefore, in the mixed-phase structure composed of LiMn2O4 spinel nanophase and Li2MnO3 layered nanophase, the formation of oxygen vacancies and oxygen migration are significantly suppressed, thus greatly improving the structural stability of the Li2MnO3 layered nanophase structure. Furthermore, during charging, the lattice volume of the Li2MnO3 layered phase expands while the lattice volume of the LiMn2O4 spinel phase contracts. This results in the lattice volume contraction and expansion of the mixed-phase structure canceling each other out during charging, greatly reducing volumetric deformation stress. This is another reason for suppressing structural degradation and the formation of internal microcracks. The novel cathode material developed in this application, with a mixed-phase structure of layered and non-layered phases distributed in a "mosaic" pattern, can solve the fundamental scientific problem of capacity and voltage degradation in lithium-rich manganese-based cathode materials due to irreversible oxygen valence changes and oxygen migration from a crystal structure design perspective. It also greatly improves rate capability and cycle stability, opening up a new paradigm for the research of lithium-rich manganese cathode materials. The novel xLiMn2O4·(1-x)Li2MnO3 lithium-rich manganese cathode material of this application exhibits not only a lattice structure matching feature between the LiMn2O4 spinel nanophase and the Li2MnO3 layered nanophase, but also allows the small amount of Mn in the structure to be replaced by other elements, including Co, Ni, Al, Ti, Zr, Nb, etc. Therefore, the mixed-phase lithium battery cathode material of this application possesses diverse structural / elemental control capabilities. Based on the unique mixed-phase structure of layered and non-layered phases in this application, the mixed-phase lithium battery cathode material of this application achieves a capacity exceeding 440 mAh g⁻¹. -1 It exhibits reversible capacity and high rate capability and cycle stability.

[0052] It should be noted that, besides the LiMn2O4 spinel nanophase, other non-layered phases with high ionic and / or electronic conductivity can also improve the structural stability of layered phases by increasing the activation of lattice oxygen migration and / or oxygen evolution, thereby improving the cycle stability of lithium battery cathode materials at high voltages >4.5V. For example, the spinel phase Li... xTM2O4, and for example, perovskite phase LiTMO3, rock salt phase Li x TM 1-x O, etc., where 0≤x≤1, and TM is at least one of Mn, Co, Ni, Al, Ti, Zr and Nb.

[0053] The present application will be further described in detail below with reference to specific embodiments and accompanying drawings. The following embodiments are only for further illustration of the present application and should not be construed as limiting the present application.

[0054] Example 1

[0055] This example combines solid-state sintering and molten salt ion exchange methods to obtain a lithium-ion battery cathode material with a "mosaic" pattern of layered and non-layered phases arranged in a mixed phase structure, where the layered and non-layered phases are alternately arranged. Specifically, the non-layered phase in this example is a spinel phase, i.e., spinel nanocrystals. The specific preparation method of this lithium-ion battery cathode material is as follows:

[0056] Step 1: Preparation of manganese carbonate. Manganese nitrate and sodium carbonate were weighed according to stoichiometry and mixed. The mixture was stirred in a solution at 90℃ for 3 hours to obtain the MnCO3 precursor. Solid-state sintering. The prepared manganese carbonate, sodium carbonate and lithium carbonate were mixed and ground in a ratio of Na:Li:Mn of 0.7:0.3:0.7. The mixture was sintered in a muffle furnace at 550℃ for 24 hours under air atmosphere to obtain a brown powder.

[0057] Step 2: Molten salt ion exchange. The resulting brownish-red powder is mixed and ground with a LiNO3 / LiCl (88 / 12) mixture at a 1:2 ratio, and then treated at 280℃ for 12 hours to achieve Li / Na exchange in the powder's crystal structure. After cooling, the mixture is washed in deionized water and dried in a vacuum oven at 80℃ to obtain a powder with a mixed-phase structure of layered nanophases and spinel nanophases and the chemical formula Li. 1.13 Mn 0.75 The lithium-rich manganese cathode material with O2 is labeled LS-LMO.

[0058] Electrochemical testing: Using NMP as solvent, LiCoO2@LCAF-Spinel, carbon black, and PVDF were uniformly mixed in a mass ratio of 8:1:1 to prepare a positive electrode sheet with an active material loading of approximately 5 mg / cm³. -2 A half-cell with a lithium-ion electrode was fabricated using 2032 coin cells and a Celgard 2035 separator and a high-voltage electrolyte. This half-cell was tested at 2.0–4.9 V (vs. Li / Li). +The electrolyte is cyclic between LiPF6, EMC, and FEC. The mass ratio of the high-voltage electrolyte is LiPF6:EMC:FEC = 15:55:30. Simultaneously, this example also compares and tests the electrochemical performance of pure layered phase cathode material Li2MnO3 and pure spinel phase cathode material LiMn2O4.

[0059] Figure 1 A schematic diagram of the mosaic-like mixed distribution of the mixed-phase structure of the cathode material is shown (a), and crystal structures of the layered and non-layered spinel phases are shown (b, c). The lithium-rich manganese mixed-phase structure cathode material of LS-LMO in this application contains a spinel phase structure arranged in a "mosaic" pattern in its crystal structure.

[0060] The LS-LMO prepared in this example was observed using a scanning electron microscope (SEM), and the results are as follows: Figure 2 As shown. Figure 2 The results show that the lithium-rich manganese cathode material of LS-LMO synthesized in this example is characterized by spherical secondary particles with a size of about 2 μm, primary particles with a size of about 200 nm, and nanocrystal domains of layered nanophase and spinel nanophase with a size of about 10 nm.

[0061] XRD and neutron diffraction analyses were performed on the phase structure of the LS-LMO material prepared in this example. The results showed that the phase structure of the lithium-rich manganese material prepared in this example is a mixed-phase structure of layered nanophases and spinel nanophases. High-resolution TEM results showed that the layered nanophases and spinel nanophases exhibit lattice-matched characteristics, such as... Figure 3 As shown.

[0062] Electrochemical results show that the electrochemical charge-discharge curves of LS-LMO exhibit characteristics of both layered Li₂MnO₃ and spinel-phase LiMn₂O₄. Furthermore, the reversible discharge capacity of LS-LMO exceeds 440 mAh / g, significantly higher than that of pure layered Li₂MnO₃ and spinel LiMn₂O₄. Figure 4 As shown, compared to Li2MnO3, it exhibits higher capacity, rate capability, and cycle stability, while the voltage decay problem is greatly improved.

[0063] In-situ XRD results show that the overall unit cell parameters of LS-LMO remain basically unchanged during the charge and discharge process. This is due to the opposite trend of the unit cell parameters of the layered Li2MnO3 phase and the spinel LiMn2O4 phase during the charge and discharge process, which greatly improves the structural stability of the material.

[0064] Example 2

[0065] This example, based on Example 1, replaces the spinel phase with a perovskite phase; specifically, it uses the perovskite phase LiTi. 0.5 Mn 0.5O3. In this embodiment, the layered phase is Li2Mn. 0.95 Ti 0.05 O3, the non-layered phase is LiTi 0.5 Mn 0.5 The perovskite phase structure of O3. The synthesis method of the lithium-ion battery cathode material with a mixed layered and non-layered phase structure in this example is as follows:

[0066] Step 1: Synthesis of a multi-component mixed precursor. Dissolve 0.01 mol of tetraethyl titanate in 50 mL of ethanol to form solution A; dissolve 0.03 mol of manganese sulfate and 0.01 mol of ammonium sulfate in 200 mL of deionized water to form solution B; dissolve 0.03 mol of NaOH in 50 mL of deionized water to form solution C. Heat solution B to 60°C in a water bath. While stirring, add solutions A and C dropwise to solution B over 3 hours using a peristaltic pump. After the reaction is complete, continue heating the mixed solution in a 60°C water bath for another 3 hours. The total liquid-phase reaction time is 6 hours. After the reaction is complete, filter and wash with deionized water and ethanol. Heat the obtained precursor in a muffle furnace (at air atmosphere) at 500°C for 6 hours to obtain the multi-component mixed precursor.

[0067] Step 2: High-temperature sintering. The precursor obtained in Step 1 is mixed with Li / (Mn+Ti) = 1.15, and LiOH is used as the lithium source. After uniform mixing, the sintering conditions are 800-12h, thus obtaining a lithium battery cathode material with a layered and non-layered mixed phase structure, designated LPO-LMO.

[0068] TEM and XRD refinement were used to determine that the crystal structure of LPO-LMO is a layered phase Li2Mn. 0.95 Ti 0.05 O3 and non-layered perovskite phase LiTi 0.5 Mn 0.5 The O3 exhibits a miscible structure. Electrochemical results show that the electrochemical charge-discharge curves of LPO-LMO also exhibit characteristics of the layered phase Li2Mn. 0.95 Ti 0.05 O3 and non-layered perovskite phase LiTi 0.5 Mn 0.5 The charge-discharge curve characteristics of O3 were observed, and LPO-LMO exhibited a reversible discharge capacity exceeding 400 mAh / g and high cycle stability.

[0069] Example 3

[0070] This example, based on Example 1, replaces the spinel phase with a rock salt phase; specifically, it uses the rock salt phase Li. 0.1 Mn 0.5 Ni 0.4O is a non-layered phase structure. In this embodiment, the layered phase is Li₂Mn. 0.9 Ni 0.1 O3, the non-layered phase is Li 0.1 Mn 0.5 Ni 0.4 The rock salt phase structure of O. The synthesis method of the lithium-ion battery cathode material with a layered and non-layered mixed-phase structure in this example is as follows:

[0071] Step 1: Synthesis of the multi-component mixed precursor. Dissolve 0.005 mol of nickel acetate in 50 mL of aqueous solution to form solution A; dissolve 0.03 mol of manganese sulfate and 0.01 mol of ammonium sulfate in 200 mL of deionized water to form solution B; dissolve 0.035 mol of NaOH in 50 mL of deionized water to form solution C. Heat solution B to 60°C in a water bath. While stirring, add solutions A and C dropwise to solution B over 3 hours using a peristaltic pump. After the reaction is complete, continue heating the mixed solution in a 60°C water bath for another 3 hours. The total liquid-phase reaction time is 6 hours. After the reaction is complete, filter and wash with deionized water and ethanol. Heat the obtained precursor in a muffle furnace (at air atmosphere) at 500°C for 6 hours to obtain the multi-component mixed precursor.

[0072] Step 2: High-temperature sintering. The precursor obtained in Step 1 is mixed in a ratio of Li / (Mn+Ni) = 1.25, with Li2CO3 as the lithium source. After homogenization, the mixture is sintered at 800°C for 24 hours to obtain a lithium battery cathode material with a mixed layered and non-layered phase structure, designated LRO-LMO.

[0073] TEM and XRD refinement were used to determine that the crystal structure of LRO-LMO is a layered phase Li₂Mn. 0.9 Ni 0.1 O3 and non-layered rock salt phase Li 0.1 Mn 0.5 Ni 0.4 The LRO-LMO exhibits a miscible structure. Electrochemical results show that the electrochemical charge-discharge curves of LRO-LMO also exhibit characteristics of the layered phase Li₂Mn. 0.9 Ni 0.1 O3 and non-layered rock salt phase Li 0.1 Mn 0.5 Ni 0.4 The LRO-LMO exhibits the characteristic charge-discharge curve of O, and its reversible discharge capacity exceeds 380 mAh / g, while also demonstrating high cycle stability.

[0074] The above description, in conjunction with specific embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of this application, and all such modifications or substitutions should be considered within the scope of protection of this application.

Claims

1. A lithium battery cathode material of a misfit structure, characterized by: The lithium battery cathode material has a mixed phase structure of a layered phase and a non-layered phase in the crystal structure, and the layered phase and the non-layered phase are arranged alternately; The non-layered phase includes at least one of a spinel phase, a perovskite phase and a rock salt phase; The molecular formula of the battery positive electrode active material is Li x TM y O2A z , wherein, 1≤x≤2, 0.5≤y≤1.5, 0≤z≤0.2, TM is at least one of Mn, Co, Ni, Al, Ti, Zr and Nb; A is at least one of F, BO3, SiO4, PO4 and SO4.

2. The lithium battery cathode material of claim 1, wherein: The non-layered phase is in nanoscale.

3. The lithium battery cathode material of claim 2, wherein: The nanoscale is 0.5-10 nm.

4. The lithium battery cathode material of claim 1, wherein: The mixed phase structure of the layered phase and the non-layered phase is uniformly distributed in the particles of the lithium battery cathode material.

5. The lithium battery cathode material of claim 1, wherein: The molecular formula of the layered phase is Li2TMO3 or LiTMO2, wherein TM is at least one of Mn, Co and Ni.

6. The lithium battery cathode material of claim 5, wherein: The lithium and TM anti-site exist in the layered phase.

7. The lithium battery cathode material of claim 6, wherein: The ion content of the lithium and TM anti-site is 1-40%.

8. The lithium battery cathode material of claim 1, wherein: The non-layered phase has a formula of spinel phase Li x TM2O4, perovskite phase LiTMO3, or rock salt phase Li x TM 1-x O, where 0≤x≤1, and TM is at least one of Mn, Co, Ni, Al, Ti, Zr, and Nb.

9. The lithium battery cathode material of claim 8, wherein: The lithium and TM mixed arrangement exist in the non-layered phase.

10. The lithium battery cathode material of claim 9, wherein: The ion content of the lithium and TM mixed arrangement is 1%-10%.

11. The lithium battery cathode material of any one of claims 1-10, wherein: The lithium battery cathode material is a large primary particle, or a secondary particle formed by accumulation of small primary particles; The size of the large primary particle is 1-20 μm; The size of the secondary particle is 1-20 μm; The size of the small primary particle is 50 nm-2 μm.

12. The lithium battery cathode material of claim 11, wherein: The interface domain size between the layered phase and the non-layered phase is 0.5-10 nm.

13. Use of the lithium battery cathode material in any one of claims 1-12 in preparation of a lithium ion battery for a power battery, an energy storage battery, or a 3C consumer electronic product, a drone or an electronic cigarette.

14. A lithium ion battery using the lithium battery cathode material in any one of claims 1-12.

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