Boron gradient doped single crystal lithium-rich manganese-based material@li3bo3 composite material, preparation and application thereof

Abstract

The application belongs to the field of lithium ion battery materials, and particularly relates to a boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material, which comprises a core and a shell in-situ compounded on the surface of the core, the core is a boron doped single crystal lithium-rich manganese-based material with oxygen vacancies, and the amount of boron is gradiently reduced from the outer surface of the core to the inner core. The application also provides preparation of the material and application of the material in lithium batteries. The material has excellent wide temperature range stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to the field of lithium-ion battery cathode materials. Background Technology

[0002] The cathode material is a key factor limiting the energy density of lithium-ion batteries and accounts for 40-50% of the overall cost. Currently, the actual capacity of commercially available cathode materials is generally below 200 mAh / g, which is insufficient to meet the current demand for high energy density in lithium-ion batteries. The lithium-rich manganese-based cathode material xLi₂MnO₃·(1-x)LiTMO₂ (TM being Mn, Ni, or Co) has a capacity of 250 mAh / g. -1 With its ultra-high specific capacity and high voltage (~3.6V), lithium-rich manganese-based cathode materials are considered an ideal choice for next-generation high-energy-density lithium-ion battery cathode materials. The high capacity of lithium-rich manganese-based cathode materials comes from their unique anion redox reaction. Anion redox reactions are divided into reversible and irreversible processes. Irreversible oxygen release can exacerbate interfacial side reactions and trigger irreversible structural transformations, inducing the generation of micro-defects and cracks. Ultimately, this leads to the deterioration of the crystal structure and the degradation of electrochemical performance, such as low first-cycle coulombic efficiency, continuous capacity and voltage decay, poor rate performance, and voltage hysteresis. These problems limit the commercial application of lithium-rich manganese-based cathode materials.

[0003] Research reports on single-crystal lithium-rich manganese-based cathode materials have been published. Compared to polycrystalline lithium-rich manganese-based cathode materials formed by primary particle agglomeration, single-crystal materials lack grain boundaries, possess better mechanical strength, are considered to resist lattice stress, and can suppress oxygen release. Their smaller specific surface area alleviates side reactions under high voltage. Therefore, single-crystal lithium-rich manganese-based cathode materials are currently under research. However, single-crystal materials also have significant problems. Due to the significantly larger particle size compared to primary particles, lithium-ion transport paths are long, making lithium-ion diffusion difficult. In addition, the Li2MnO3 phase itself has low electrochemical activity, resulting in significantly worse kinetic performance and rate performance of single-crystal materials. Severe side reactions also exist at the contact point between the surface of single-crystal materials and the electrolyte, triggering electrolyte decomposition under high voltage, causing loss of active lithium and surface structural instability, thus leading to continuous capacity decay.

[0004] In view of the problems faced by the lithium-rich manganese-based material, the prior art also provides some improvement ideas such as changing the morphology of single crystals or doping. For example, the Chinese patent document with the publication number CN109537054A discloses a high-rate lithium-rich manganese-based positive electrode material single crystal, which is composed of one or several polyhedral single crystals such as a cube, a cuboid, a hexahedron, a tetrahedron and an octahedron with a side length of 0.1-10 microns. For another example, the Chinese patent document with the publication number CN115395007A discloses a layered-spinel composite phase single crystal lithium-rich manganese-based positive electrode material, which has a chemical formula of LixMnaNibCocBdMeO2-δ, wherein M is at least one element selected from Al, Ti, W, Mo, La, V and Y, 1

[0005] In summary, the prior art can improve the rate of the lithium-rich manganese-based material to a certain extent, but it is still difficult to effectively control the lattice oxygen activity of the lithium-rich manganese-based material, it is difficult to fully activate the reversible anion redox, the lattice oxygen reaction kinetics is slow, and the bulk and surface structure stability is not ideal, which is difficult to adapt to high and low temperature application scenarios. SUMMARY

[0006] In view of the existing problems, the first object of the present application is to provide a boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material, which aims to improve the lattice oxygen activity and structure stability, and further improve the high and low temperature cycle stability and other electrochemical properties.

[0007] The second object of the present application is to provide a preparation method and application of the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0008] The third object of the present application is to provide a lithium ion battery, a positive electrode and a positive electrode material comprising the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0009] The current research on single crystal lithium-rich manganese-based positive electrode materials in the industry is still in the initial stage. There are only a few reports on single crystal lithium-rich manganese-based positive electrode materials, and the lattice oxygen activity and structure stability are still not ideal, which leads to a low capacity of the material, and the stable performance of high capacity cannot be achieved, the rate performance is not ideal, and the voltage decay is still serious. In addition, it is difficult to adapt to high and low temperature application scenarios. In view of the problems faced by the lithium-rich manganese-based material, the present application provides the following improvement scheme after in-depth research:

[0010] The boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material comprises a core and a shell in-situ compounded on the surface of the core, the core is a single crystal lithium-rich manganese-based material doped with boron and having oxygen vacancies, and the amount of boron decreases gradually from the outer surface of the core to the core.

[0011] The shell comprises lithium borate.

[0012] The material of the application has a core of a single crystal lithium-rich manganese-based material doped with boron and having oxygen vacancies, and a shell of Li3BO3 in-situ coated on the surface of the core. Research shows that the composite material can unexpectedly improve the lattice oxygen activity and structural stability of the single crystal lithium-rich manganese-based material, and can enhance the Li insertion and de-insertion rate and continuously activate the anion redox reaction during the cycle process. Research shows that the new composite material can unexpectedly improve the capacity, high and low temperature cycle stability and other electrochemical properties.

[0013] In the application, the combined coating of the decreasing boron doping, oxygen vacancies and lithium borate of the lithium-rich manganese-based material is the key to cooperatively improve the problems of the lithium-rich manganese-based material, such as the unsatisfactory lattice oxygen activity and the low structural stability, and to improve the capacity, high and low temperature cycle stability.

[0014] In the application, the thickness of the shell is 3-5 nm.

[0015] In the application, the content of boron in the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material is 2-4 wt%.

[0016] The application also provides a preparation method of the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material. The single crystal lithium-rich manganese-based material and boric acid are solid-phase compounded and then calcined in an oxygen-containing atmosphere to prepare the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0017] Research shows that for the modification of the single crystal lithium-rich manganese-based material, the single crystal lithium-rich manganese-based material is prone to problems such as single crystal agglomeration, lithium loss, surface structure damage and difficulty in uniform coating modification. In view of the problem, the single crystal lithium-rich manganese-based material and boric acid are solid-phase compounded and then calcined in an oxygen-containing atmosphere, so that the surface of the material can be modified based on the special liquid-solid-gas solid reaction process during the reaction, and the problems such as single crystal agglomeration, lithium loss, surface structure damage and difficulty in uniform coating modification of the single crystal lithium-rich manganese-based material during the coating process can be solved, the surface in-situ coating and gradient doping of lithium borate can be successfully achieved, and the single crystal lithium-rich manganese-based material with good lattice oxygen activity and high and low temperature cycle stability can be prepared.

[0018] In the present application, the single-crystal lithium-rich manganese-based material has an expression of xLi2MnO3·(1-x)LiMO2, wherein M is one or more of transition metals Ni, Mn and Co, and 0.3≤x≤0.6;

[0019] Preferably, the single-crystal lithium-rich manganese-based material has a particle size of 0.5-2 μm.

[0020] In the present application, the single-crystal lithium-rich manganese-based material can be a conventional commercial product or can be prepared based on conventional means.

[0021] In a preferred method for preparing the single-crystal lithium-rich manganese-based material, a molten salt method is used, and the steps are as follows: a nickel-cobalt-manganese hydroxide precursor, a lithium source and a molten salt are mixed uniformly and then subjected to multi-stage calcination to obtain the single-crystal lithium-rich manganese-based material.

[0022] The lithium salt is at least one of lithium hydroxide, lithium carbonate and lithium oxide.

[0023] The molar ratio of the lithium source to the nickel-cobalt-manganese hydroxide precursor is 1.65-2.2:1, preferably 1.7-1.9:1. The present application surprisingly shows that the content of lithium can unexpectedly further facilitate the preparation of the single-crystal lithium-rich manganese-based material suitable for subsequent boron roasting, which is helpful for the combination with the subsequent process and further improves the wide-temperature-range stability of the prepared material.

[0024] In the present application, the molten salt is at least one of potassium chloride, lithium chloride, lithium nitrate and sodium chloride.

[0025] Preferably, the molten salt is more than 1 times, preferably 4-6 times, the weight of the nickel-cobalt-manganese hydroxide precursor.

[0026] Preferably, the calcination process includes a three-stage gradient holding process, wherein the temperature of the first-stage holding process is 300-700℃ (further can be 500-600℃), the temperature of the second-stage holding process is 800-900℃, and the temperature of the third-stage holding process is 1000-1300℃.

[0027] Preferably, the first-stage holding time is 3-8 h, preferably 4-6 h.

[0028] Preferably, the second-stage holding time is 5-15 h, preferably 10-12 h.

[0029] Preferably, the third-stage holding time is 0.5-6 h, preferably 1-2 h.

[0030] Preferably, the calcination process is carried out in an oxygen-containing atmosphere, and the oxygen-containing atmosphere can further be air in consideration of the process simplicity.

[0031] In the present application, the first-stage calcination to the third-stage calcination process is preferably carried out in a flowing oxygen-containing atmosphere. The present application shows that, under the calcination mechanism, further combined with the control of the atmosphere flow, it is helpful to further facilitate the preparation of the single-crystal lithium-rich manganese-based material suitable for subsequent boric acid calcination, which can unexpectedly further and synergistically combine with the subsequent process to improve the wide-temperature-range stability of the prepared material.

[0032] In the present application, after the calcination is completed, water washing and fourth-stage heat preservation treatment can be carried out, and the single-crystal lithium-rich manganese-based material is obtained.

[0033] Preferably, the temperature of the fourth-stage heat preservation treatment is 400-600℃.

[0034] Preferably, the time of the fourth-stage heat preservation treatment is 1-6h, and further can be 2-4h.

[0035] In the present application, the weight ratio of the boric acid to the single-crystal lithium-rich manganese-based material is 1:0.005-0.1, preferably 1:0.01-0.05, and further 1:0.03-0.05.

[0036] Preferably, the oxygen-containing atmosphere in the calcination stage is, for example, oxygen or air.

[0037] In the present application, the temperature in the calcination stage is 300-600℃.

[0038] In the present application, the heat preservation treatment time in the calcination stage is 4-10h.

[0039] Preferably, the calcination process includes a first-stage heat preservation calcination process and a second-stage heat preservation calcination process carried out in sequence, wherein the temperature of the first-stage heat preservation calcination process is 300-400℃; and the temperature of the second-stage heat preservation calcination process is 450-600℃.

[0040] In the present application, the time of the first-stage heat preservation calcination process is 1-4h; and the time of the second-stage heat preservation process is 3-6h.

[0041] The present application also provides an application of the boron-gradient-doped single-crystal lithium-rich manganese-based material@Li3BO3 composite material as an active material for a positive electrode, for preparing a lithium ion battery.

[0042] The present application also provides a positive electrode material of a lithium ion battery, which comprises the boron-gradient-doped single-crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0043] In the present application, the positive electrode material further comprises a conductive agent and a binder.

[0044] In the present application, the content of the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material is 60-90 wt.%, the content of the binder is less than or equal to 15 wt.% (for example, it can be 5-15 wt.%); and the content of the conductive agent is less than or equal to 15 wt.% (for example, it can be 5-15 wt.%).

[0045] The present application also provides a positive electrode of a lithium ion battery, which comprises a current collector and a positive electrode material compounded on the surface of the current collector, wherein the positive electrode material is the positive electrode material comprising the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0046] The present application also provides a lithium ion battery, wherein the positive electrode is the positive electrode comprising the positive electrode material comprising the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0047] The lithium ion battery provided by the present application can be conventional in other components, parts and structures except for the boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material.

[0048] For example, the lithium ion battery comprises a positive electrode and a negative electrode compounded in sequence, wherein a separator and / or a solid-state electrolyte are arranged between the positive electrode and the negative electrode. The battery can also contain an electrolyte.

[0049] Advantages

[0050] The present application provides a brand-new boron gradient doped single crystal lithium-rich manganese-based material@Li3BO3 composite material, which can unexpectedly improve the high-capacity performance, high-low temperature cycle stability and other electrochemical properties based on the joint synergy of composition and structure.

[0051] In the present application, the single crystal lithium-rich manganese-based material and boric acid are compounded and then calcined in an oxygen-containing atmosphere, which can solve the problems of single crystal agglomeration, lithium loss, surface structure damage and difficulty in modification during the coating process of the single crystal lithium-rich manganese-based material, and can successfully realize the in-situ coating and gradient doping of lithium borate on the surface, and can significantly improve the capacity and high-low temperature cycle stability of the prepared lithium-rich manganese-based material.

[0052] In the present application, the preparation process of the single crystal lithium-rich manganese-based material is further optimized, and a two-stage calcination process is further used, which can unexpectedly further improve the process synergy and help to further improve the capacity and high-low temperature performance of the prepared material.

[0053] Content of the drawings

[0054] Figure 1X-ray diffraction patterns of the blank sample (the single-crystal lithium-rich manganese-based material prepared in step A of Example 1, labeled LLO) and the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material finally prepared in step B of Example 1 (labeled LLO-3B).

[0055] Figure 2 The image shown is a scanning electron microscope (SEM) image of the boron gradient doped single-crystal lithium-rich manganese-based composite material @Li3BO3, which was finally prepared in step B of Example 1.

[0056] Figure 3 The image shows an HRTEM image of the boron gradient-doped single-crystal lithium-rich manganese-based composite material @Li3BO3 that was finally prepared in step B of Example 1.

[0057] Figure 4 The image shows the XPS etching results of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material finally prepared in step B of Example 1.

[0058] Figure 5 The image shows the elemental B distribution of the boron gradient-doped single-crystal lithium-rich manganese-based composite material @Li3BO3 prepared in step B of Example 1 under HADDF-EDS mode. Detailed Implementation

[0059] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention. Unless otherwise specified, the methods used in the embodiments of the present invention are conventional methods in the art, and the reagents used are all obtainable through conventional commercial channels.

[0060] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. In the following examples:

[0061] (1) Battery assembly: The materials prepared in the examples or comparative examples are used as active materials. The active materials are mixed with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) is added and ground into a slurry. The slurry is coated on aluminum foil with a scraper, dried, and cut into positive electrode sheets. Then, CR2025 coin cell half-cells are assembled in an argon glove box (water < 0.01 ppm, oxygen < 0.01 ppm). The positive electrode is the above-mentioned positive electrode sheet, the counter electrode is a lithium sheet, the separator is Celgard 2500, and the electrolyte is a solution prepared with dimethyl carbonate, diethyl carbonate, and ethyl carbonate in a volume ratio of 1:1:1 as solvents and 1 mol / L LiPF6 as solute.

[0062] (2) Battery performance test: LAND CT 2001A tester was used, which was purchased from Wuhan Land Electronics Co., Ltd.; at 25℃, 0.1C (1C=250mA / g) was used to charge and discharge in 2.0V-4.8V voltage range for 3 weeks, then 1C was used to continue to charge and discharge in 2.0V-4.8V voltage range for 200 weeks (200 cycles). The test voltage range and rate were kept unchanged, and the test temperature was changed to high temperature 60℃ and low temperature 0℃.

[0063] In the present application, the single-crystal lithium-rich manganese-based positive electrode material is prepared based on the existing molten salt method, for example, a hydroxide or carbonate precursor of the positive electrode element is prepared in advance, then mixed with a lithium source and a molten salt, and sintered, then washed with deionized water to remove excess lithium salt and molten salt, and sintered and dried again to obtain the single-crystal lithium-rich manganese-based positive electrode material.

[0064] Example 1

[0065] In the present application, a preparation and modification method of a single-crystal lithium-rich manganese-based positive electrode material is provided.

[0066] Step (A): Preparation of single-crystal lithium-rich manganese-based material

[0067] (A-1) Manganese sulfate, nickel sulfate and cobalt sulfate were used as raw materials, and the reaction raw materials were weighed according to the molar ratio of Mn:Ni:Co elements 4:1:1, and deionized water was added to prepare a 2mol / L metal salt solution.

[0068] (A-2) The above solution was mixed with a 2mol / L sodium hydroxide solution in a continuous stirred tank reactor under N2 atmosphere. The temperature was 65℃ and the pH was 10 throughout the process. The precursor suspension was filtered, washed with deionized water, and then dried at 80℃ for 24h to obtain the hydroxide precursor.

[0069] (A-3) The hydroxide precursor was mixed with lithium salt (lithium hydroxide) and molten salt (potassium chloride) according to the molar ratio of hydroxide precursor: lithium salt: molten salt 1:2:4 (the excess coefficient of lithium salt is 2 / 1.5), and the materials were placed in a defoaming machine and mixed uniformly at a speed of 2000rpm, then placed in a muffle furnace, heated from room temperature to 500℃ (marked as T1) at a rate of 2℃ / min in air atmosphere (without forming directional airflow), and sintered for 5h (marked as t1), then heated to 900℃ (marked as T2) at the same rate, and sintered for 10h (marked as t2), then heated to 1000℃ (marked as T3), and sintered for 1h (marked as t3), naturally cooled to room temperature, washed with deionized water to remove excess lithium salt and molten salt, then sintered at 500℃ (marked as T4) in the muffle furnace for 3h (marked as t4), and dried to obtain the single-crystal lithium-rich manganese-based positive electrode material.

[0070] Step (B): modification of single-crystal lithium-rich manganese-based material

[0071] According to a mass ratio of 100:1, 1 g of the single-crystal lithium-rich manganese-based positive electrode material synthesized above and 0.01 g of boric acid were weighed, dry-mixed by high-speed rotation of a defoaming machine, uniformly mixed at a high speed of 2000 rpm, taken out and placed in a corundum square boat, and then placed in a sealed muffle furnace through which oxygen could be introduced. Sintering was performed at a controlled oxygen flow rate (50-500 seem), the temperature was increased to 300°C (marked as T5) from room temperature at a temperature increase rate of 3°C / min, and then held for 3 h (marked as t5). Then, the temperature was increased to 450°C (marked as T6) and held for 4 h (marked as t6). Finally, the temperature was cooled to room temperature, and the boron gradient-doped single-crystal lithium-rich manganese-based material @ Li3BO3 composite material was obtained after grinding.

[0072] As shown in the XRD spectrum of FIG. 1, the single-crystal lithium-rich manganese-based positive electrode material synthesized in Example 1 has sharp characteristic diffraction peaks, all of which belong to the α-NaFeO2layered structure of the R-3m space group, indicating that a single-crystal lithium-rich manganese-based positive electrode material with good crystallinity is prepared. Figure 1 As shown in the SEM image of FIG. 2, the single-crystal lithium-rich manganese-based positive electrode material synthesized in Example 1 has a regular and smooth single-crystal morphology, indicating the successful preparation of the single-crystal lithium-rich manganese-based positive electrode material.

[0073] Figure 2 As shown in the HRTEM image of FIG. 3, the boric acid gradient-doped single-crystal lithium-rich manganese material @ Li3BO3 synthesized in Example 1 has a typical layered structure in the bulk phase, and a lithium borate coating layer appears on the surface.

[0074] As shown in the etching result of B1s XPS of FIG. 4, the boric acid gradient-doped single-crystal lithium-rich manganese material @ Li3BO3 synthesized in Example 1 still has a boron signal at a certain etching depth, indicating that the bulk phase gradient doping of boron elements is achieved. Figure 3 As shown in the HADDF-EDS result of FIG. 5, the surface B element is uniformly distributed, indicating that the Li3BO3 is uniformly coated on the surface of the single-crystal material.

[0075] Figure 4 Example 2 - change of single-crystal preparation process

[0076] Compared with Example 1, the only difference is that the single-crystal preparation process of step (A) is changed, and the experimental groups are as follows: Figure 5

[0077] Example 2 - change of single-crystal preparation process

[0078] Compared with Example 1, the only difference is that the single-crystal preparation process of step (A) is changed, and the experimental groups are as follows:

[0079] ​​​Group A: In step (A-1), cobalt sulfate is absent, and the molar ratio of the remaining manganese sulfate and nickel sulfate is 2:1, and the other operations and parameters are the same as in Example 1.

[0080] Group B: In step (A-3), the molar ratio of the hydroxide precursor, lithium salt lithium hydroxide, and molten salt potassium chloride is 1:1.8:4, and the other operations and parameters are the same as in Example 1.

[0081] Group C: In step (A-3), T1 is 600, t1 is 4h, T2 is 800℃, t2 is 12h, T3 is 1200℃, t3 is 1h, T4 is 400℃, and t4 is 4h; the other operations and parameters are the same as in Example 1.

[0082] Group D: In step (A-3), the T1 holding period is absent.

[0083] Group E: In step (A-3), the T3 holding period is absent.

[0084] Group F: In step (A-3), the T1-T3 holding processes are carried out in a flowing air atmosphere (flow rate of 100-200sccm).

[0085] The other operations and parameters are the same as in Example 1.

[0086] Example 3 - Change of Step (B) Preparation Process

[0087] Compared with Example 1, the only difference is that the process of step B is changed, and the experimental groups are as follows:

[0088] Group A: The holding time at T5 temperature is omitted, and the original t5 time is combined into t6 (i.e., t6 is extended to 7h), and the other operations and parameters are the same as in Example 1.

[0089] Group B: T5 is controlled at 400℃, t5 is 2h, T6 is controlled at 550℃, t6 is 3h, and the other operations and parameters are the same as in Example 1.

[0090] Example 4 - Change of Step (B) Preparation Process

[0091] Compared with Example 1, the only difference is that the amount of single-crystal lithium-rich manganese-based positive electrode material remains unchanged, and the amount of boric acid is changed, and the experimental groups are as follows:

[0092] Group A: The weight ratio of single-crystal lithium-rich manganese-based positive electrode material to boric acid is 100:3.

[0093] Group B: The weight ratio of single-crystal lithium-rich manganese-based positive electrode material to boric acid is 100:5.

[0094] The other operations and parameters are the same as in Example 1.

[0095] Example 5

[0096] Compared with Example 1, the difference is that in step A-3, the molten salt potassium chloride is replaced by sodium chloride, which is 5 times the molar amount of the precursor, and other operations and parameters are the same as Example 1.

[0097] Comparative Example 1

[0098] Compared with Example 1, the only difference is that step B is missing, and the single-crystal lithium-rich manganese-based positive electrode material prepared in step A-3 is directly subjected to electrochemical assembly measurement according to the method of the example.

[0099] Comparative Example 2

[0100] Compared with Example 1, the only difference is that in step B, boric acid is not added, and other operations and parameters are the same as Example 1.

[0101] Comparative Example 3

[0102] Compared with Example 1, the only difference is that in step B, after dissolving boric acid in deionized water, the single-crystal lithium-rich manganese-based positive electrode material prepared in step 1 is added and stirred uniformly mixed, and then the material is evaporated to obtain a mixed material, and other operations and parameters are the same as Example 1.

[0103] Comparative Example 4

[0104] Compared with Example 1, the only difference is that in step B, an equal weight of nano-tungsten oxide is used to replace boric acid, and other operations and parameters are the same as Example 1.

[0105] Each case is subjected to high-temperature and low-temperature cycle tests, and the results are shown in Table 1

[0106] Table 1

[0107]

[0108] As can be seen from Table 1, by Example 1 and Example 2 (2B and 2F), it can be seen that the content of lithium in the single-crystal preparation process is optimized and controlled, and the three-stage calcination process and the airflow calcination process are used to further unexpectedly improve the adaptation and synergistic effect of the single-crystal and the subsequent boron calcination process, which helps to unexpectedly improve the wide-temperature-range stability of the prepared material. Furthermore, further combined with the two-stage treatment in the post-boron calcination stage, based on the solid-liquid-gas reaction transformation idea, the wide-temperature-range stability of the prepared material can be improved.

[0109] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A boron gradient-doped single-crystal lithium-rich manganese-based composite material @Li3BO3, characterized in that, It includes a core and a shell in situ composite on the surface of the core, wherein the core is a boron-doped single-crystal lithium-rich manganese-based material with oxygen vacancies, and the amount of boron decreases from the outer surface of the core to the inner core. The shell comprises lithium borate; The thickness of the shell is 3~5 nm; In the boron gradient-doped single-crystal lithium-rich manganese-based composite material @Li3BO3, the boron content is 2~4wt%; The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material is as follows: the single-crystal lithium-rich manganese-based material and boric acid solid phase composite are combined and then calcined in an oxygen-containing atmosphere to obtain the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material.

2. A method for preparing the boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material according to claim 1, characterized in that, The boron gradient doped single-crystal lithium-rich manganese-based material was prepared by calcining it in an oxygen-containing atmosphere after combining it with a solid phase of boric acid.

3. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 2, characterized in that, The expression for the single-crystal lithium-rich manganese-based material is: xLi2MnO3·(1-x)LiMO2, where M is one or more of the transition metals Ni, Mn, and Co, and 0.3≤x≤0.

6.

4. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 3, characterized in that, The particle size of the single-crystal lithium-rich manganese-based material is 0.5~2μm.

5. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 3, characterized in that, The single-crystal lithium-rich manganese-based material is prepared by the molten salt method, which involves mixing a nickel-cobalt-manganese hydroxide precursor, a lithium source, and molten salt evenly, followed by multi-stage calcination.

6. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 5, characterized in that, The lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium oxide.

7. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 6, characterized in that, The molar ratio of the lithium source to the nickel-cobalt-manganese hydroxide precursor is 1.65~2.2:

1.

8. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 7, characterized in that, The molar ratio of the lithium source to the nickel cobalt manganese hydroxide precursor is 1.7~1.9:

1.

9. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 5, characterized in that, The molten salt is at least one of potassium chloride, lithium chloride, sodium chloride, and lithium nitrate.

10. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 5, characterized in that, The molten salt is more than 1 times the weight of the nickel-cobalt-manganese hydroxide precursor.

11. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 10, characterized in that, The molten salt is 4 to 6 times the weight of the nickel-cobalt-manganese hydroxide precursor.

12. The preparation method of the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 5, characterized in that, The calcination process includes three stages of gradient heat preservation: the first stage heat preservation process is at a temperature of 300~700℃, the second stage heat preservation process is at a temperature of 800~900℃, and the third stage heat preservation process is at a temperature of 1000~1300℃.

13. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 12, characterized in that, The first stage of heat preservation time is 3-8 hours; The second insulation period is 5-15 hours; The third insulation period is 0.5 to 6 hours.

14. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 13, characterized in that, The first stage of heat preservation time is 4-6 hours; The second insulation period is 10-12 hours; The third insulation period is 1-2 hours.

15. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 12, characterized in that, The calcination process is carried out in a circulating oxygen-containing atmosphere.

16. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 12, characterized in that, After calcination, the material is washed with water and then subjected to a fourth stage of heat preservation to obtain the single-crystal lithium-rich manganese-based material.

17. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 12, characterized in that, The temperature for the fourth stage of insulation is 300~600℃.

18. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 17, characterized in that, The fourth stage of heat preservation treatment takes 1 to 6 hours.

19. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 2, characterized in that, The weight ratio of boric acid to the single-crystal lithium-rich manganese-based material is 1:0.005~0.

1.

20. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 19, characterized in that, The weight ratio of boric acid to the single-crystal lithium-rich manganese-based material is 1:0.01~0.

05.

21. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 20, characterized in that, The weight ratio of boric acid to the single-crystal lithium-rich manganese-based material is 1:0.03~0.

05.

22. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material according to any one of claims 2 to 21, characterized in that, The temperature during the roasting stage is 300~600℃; The heat preservation time during the roasting stage is 4~10 hours.

23. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 22, characterized in that, The roasting process includes a first stage of heat preservation roasting and a second stage of heat preservation roasting, wherein the temperature of the first stage of heat preservation roasting is 300~400℃; and the temperature of the second stage of heat preservation roasting is 450~600℃.

24. The method for preparing boron gradient doped single-crystal lithium-rich manganese-based @Li3BO3 composite material as described in claim 23, characterized in that, The first stage of heat preservation and roasting takes 1 to 4 hours; the second stage of heat preservation takes 3 to 6 hours.

25. A positive electrode material for a lithium-ion battery, characterized in that, The composite material includes the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material as described in claim 1, or the boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material prepared by any one of the preparation methods of claims 2 to 24.

26. The positive electrode material of the lithium-ion battery as described in claim 25, characterized in that, It also contains conductive agents and adhesives.

27. The positive electrode material of the lithium-ion battery as described in claim 26, characterized in that, The boron gradient doped single-crystal lithium-rich manganese-based material @Li3BO3 composite material has a content of 60~90wt.%, a binder content of ≤15wt%, and a conductive agent content of ≤15wt%.

28. A positive electrode for a lithium-ion battery, comprising a current collector and a positive electrode material composited thereon, characterized in that, The cathode material is the cathode material according to any one of claims 25 to 27.

29. A lithium-ion battery, characterized in that, The positive electrode described herein is the positive electrode as described in claim 28.

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