Lithium manganate positive electrode material and preparation method and application thereof

Abstract

This invention discloses a lithium manganese oxide cathode material, its preparation method, and its applications, relating to the field of lithium-ion battery technology. The invention involves sequentially coating a lithium manganese oxide substrate with a phosphate ester coating layer and a hafnium oxide surface layer. The phosphate ester coating layer is grafted using phosphate ester bonds (P-O-Mn), and the hafnium oxide surface layer is bonded via covalent bonds (Hf-O-Mn), significantly improving interfacial adhesion and eliminating the risk of detachment. Furthermore, hafnium oxide (HfO2) exhibits high ionic conductivity (approximately 10). ‑6 S / cm), does not hinder Li + Therefore, the coating structure provided by this invention can effectively suppress the dissolution of Mn and improve the cycling stability of the material while ensuring material capacity.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a lithium manganese oxide cathode material, its preparation method, and its application. Background Technology

[0002] Lithium spinel manganese oxide (LiMn2O4) is an important research direction for lithium-ion battery cathode materials due to its low raw material cost, environmental friendliness, high theoretical capacity (148 mAh / g), and compatibility with commercial electrolytes at its operating voltage. It is widely used in power tools, energy storage batteries, and other fields. However, three core problems exist in its practical applications, severely limiting its performance:

[0003] (1) Mn dissolution problem: Mn dissolution during charging and discharging 3+ It is prone to disproportionation reaction (Mn) 3+ →Mn 2+ +Mn 4+ ), generating Mn 2+ Dissolving in the electrolyte leads to the destruction of the crystal lattice structure; at the same time, trace amounts of HF in the electrolyte will accelerate the dissolution of Mn, further reducing cycle stability.

[0004] (2) Low ion transport efficiency: Traditional LiMn2O4 particles are micron-sized, while Li + Long-distance migration is required, and capacity decay is severe at high rates (such as 5C and 10C). The capacity retention rate at 10C is usually less than 30%.

[0005] (3) Poor structural stability: There is a volume change of about 4% in the lattice during charging and discharging. Long-term cycling can easily lead to particle breakage and electrode pulverization. The capacity retention rate after 100 cycles is mostly less than 70%, and the performance degradation is more significant under high temperature (55℃) environment.

[0006] To suppress Mn leaching, traditional coating modification methods typically employ physical coatings with inorganic materials such as Al2O3 and LiPO3, or carbon materials. However, these methods suffer from poor interfacial compatibility and the coating layer is prone to detachment. Furthermore, some coating layers (such as Al2O3) have low ionic conductivity, which can hinder the dissolution of Li. + Migration severely affects the rate performance of materials.

[0007] Therefore, there is an urgent need to optimize lithium manganese oxide cathode materials to achieve the goal of inhibiting Mn dissolution without hindering Li. + Transmission, improving the cyclic stability of materials while ensuring capacity.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a lithium manganese oxide cathode material, its preparation method, and its application, thereby improving the cycle stability of the material while ensuring capacity.

[0010] This invention is implemented as follows:

[0011] In a first aspect, the present invention provides a lithium manganese oxide cathode material, comprising a lithium manganese oxide substrate, wherein a phosphate ester coating layer and a hafnium oxide surface layer are formed on the lithium manganese oxide substrate, and the phosphate ester coating layer is located between the lithium manganese oxide substrate and the hafnium oxide surface layer.

[0012] In an optional embodiment, the thickness of the phosphate ester coating layer is 5nm-10nm, and the thickness of the hafnium oxide surface layer is 1nm-3nm;

[0013] And / or, in lithium manganese oxide cathode materials, the mass percentage of phosphate ester is 0.5%-1.0%, and the mass percentage of HfO2 is 1.0%-2.0%;

[0014] And / or, the lithium manganese oxide matrix is ​​a porous microsphere with a particle size of 1μm-5μm and a porosity of 10%-20%.

[0015] Secondly, the present invention provides a method for preparing any of the lithium manganese oxide cathode materials in the foregoing embodiments, comprising:

[0016] Provide lithium manganese oxide matrix;

[0017] A lithium manganese oxide matrix was subjected to plasma treatment to obtain an oxygen vacancy-modified substrate.

[0018] The oxygen vacancy-modified substrate was placed in a sol formed by manganese and lithium salts and dried to obtain a pre-coated sample.

[0019] The pre-coated sample and the phosphate compound were mixed and reacted to obtain a sample grafted with phosphate ester.

[0020] Hafnium oxide was deposited on the surface of the grafted phosphate sample.

[0021] In an optional embodiment, the preparation process of the sol used in the preparation of the pre-coated sample includes: mixing manganese salt, lithium salt and alcohol solvent, reacting at 20℃-30℃ for 2h-4h, and controlling the molar ratio of lithium to manganese to be (3.5-4.5):5;

[0022] Preferably, the manganese salt is manganese nitrate and the lithium salt is lithium nitrate;

[0023] Preferably, the oxygen vacancy-modified substrate is ultrasonically dispersed in a sol for 20-60 minutes, and then dried at 70-90°C.

[0024] In an optional embodiment, the phosphate compound used in the preparation of the grafted phosphate sample is selected from at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

[0025] Preferably, the mass ratio of the pre-coated sample to the phosphate compound is (8-12):1;

[0026] Preferably, the pre-coated sample and the phosphate compound are reacted under an inert atmosphere, with the reaction temperature controlled at 150℃-200℃ and the reaction time at 2h-4h.

[0027] In an optional implementation, hafnium oxide is deposited on the surface of the grafted phosphate sample using atomic layer deposition.

[0028] Preferably, during the deposition of hafnium oxide, HfCl4 and H2O are used as precursors, the deposition temperature is set to 200℃-250℃, the deposition cycle is 5-20 cycles, and the deposition thickness is 1nm-3nm.

[0029] In an optional embodiment, during plasma treatment, a mixture of argon and oxygen is introduced, wherein the volume fraction of oxygen in the mixture is 5%-15%.

[0030] Preferably, the mixed gas flow rate is controlled at 10 sccm-20 sccm, the power is set at 100W-300W, and the processing time is 5min-15min.

[0031] In an optional embodiment, the preparation process of the lithium manganese oxide matrix includes:

[0032] A mixed solution was obtained by mixing lithium source, manganese source and solvent. The substrate was placed in the mixed solution and reacted at 180℃-220℃ for 12h-24h to grow two-dimensional lithium manganese oxide nanosheets on the substrate surface.

[0033] Two-dimensional lithium manganese oxide nanosheets were peeled off from the substrate and dispersed in water to form a suspension. The suspension was then spray-dried to obtain porous microspheres with a particle size of 1μm-5μm.

[0034] The porous microspheres were calcined at 500℃-600℃ for 4-6 hours.

[0035] Preferably, the molar ratio of lithium to manganese in the mixed solution is (1.03-1.07):2, and the total concentration of lithium and manganese in the mixed solution is 0.5 mol / L-1.0 mol / L;

[0036] Preferably, during the spray drying process, the inlet temperature is controlled at 200℃-250℃ and the outlet temperature is controlled at 80℃-100℃;

[0037] Preferably, the substrate is a metal foil; more preferably, the metal foil is selected from at least one of Ti foil, Cu foil, and Ni foil.

[0038] Thirdly, the present invention provides a positive electrode sheet, comprising any of the lithium manganese oxide positive electrode materials in the foregoing embodiments or lithium manganese oxide positive electrode materials prepared by any of the preparation methods in the foregoing embodiments.

[0039] Fourthly, the present invention provides a lithium battery, including the positive electrode sheet described in the foregoing embodiments.

[0040] This invention has the following beneficial effects: In this invention, a phosphate ester coating layer and a hafnium oxide surface layer are sequentially coated onto a lithium manganese oxide substrate. The phosphate ester coating layer is grafted using phosphate ester bonds (PO-Mn), and the hafnium oxide surface layer is bonded via covalent bonds (Hf-O-Mn), significantly improving interfacial adhesion and eliminating the risk of detachment; furthermore, hafnium oxide (HfO2) has a high ionic conductivity (approximately 10). -6 (S / cm), does not hinder Li + Therefore, the coating structure provided by this invention can effectively suppress the dissolution of Mn and improve the cycling stability of the material while ensuring material capacity. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The flowchart illustrates the preparation process of the lithium manganese oxide cathode material provided by this invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0044] To address the Mn leaching problem in lithium manganese oxide cathode materials, traditional coating modification methods typically employ physical coatings such as Al2O3 and LiPO3. However, these methods suffer from poor interfacial compatibility, easy detachment of the coating layer, and hindering Li... + Migration can affect rate performance and other issues. This invention optimizes the coating layer structure, constructs an interface layer through chemical bonding, and selects materials that facilitate lithium-ion transport, effectively solving the above problems.

[0045] This invention provides a lithium manganese oxide cathode material, comprising a lithium manganese oxide substrate, a phosphate ester coating layer and a hafnium oxide surface layer formed on the lithium manganese oxide substrate, wherein the phosphate ester coating layer is located between the lithium manganese oxide substrate and the hafnium oxide surface layer.

[0046] It should be noted that this invention overcomes the limitation of "interface instability," abandons physical coating, and constructs the interface layer through two chemical bonding methods: phosphate ester bonds (PO-Mn) grafting combined with ALD HfO2 covalent bonds (Hf-O-Mn) connection, increasing the interfacial bonding force by more than 300% and eliminating the risk of detachment; moreover, HfO2 has high ionic conductivity (10). -6 (S / cm), does not hinder Li + Transmission helps ensure the rate performance of materials.

[0047] In some embodiments, the lithium manganese oxide matrix is ​​a porous microsphere with a particle size of 1μm-5μm, such as 1μm, 2μm, 3μm, 4μm, 5μm, etc.; the porosity is 10%-20%, such as 10%, 13%, 15%, 18%, 20%, etc.

[0048] In some embodiments, the thickness of the phosphate ester coating layer is 5nm-10nm (e.g., 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc.); the thickness of the hafnium oxide surface layer is 1nm-3nm (e.g., 1.0nm, 1.5nm, 2.0nm, 2.5nm, 3.0nm, etc.). In the lithium manganese oxide cathode material, the mass percentage of phosphate ester is 0.5%-1.0% (e.g., 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.), and the mass percentage of HfO2 is 1.0%-2.0% (e.g., 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc.). By controlling the coating amount, Mn dissolution can be better suppressed without affecting the capacity of the material.

[0049] This invention provides a method for preparing lithium manganese oxide cathode material, such as... Figure 1 As shown, the steps are as follows:

[0050] S1, providing lithium manganese oxide matrix

[0051] The lithium manganese oxide matrix can be a commercially available material. To further improve the electrochemical performance of the material, the synthesis steps of the lithium manganese oxide matrix were optimized, as follows: steps (a)-(d) are as follows:

[0052] (a) Preparation of two-dimensional hierarchical porous LiMn2O4 matrix

[0053] The lithium source, manganese source and solvent are mixed and stirred to dissolve, resulting in a mixed solution for later use.

[0054] In some embodiments, the molar ratio of lithium to manganese in the mixed solution is (1.03-1.07):2, such as 1.03:2, 1.04:2, 1.05:2, 1.06:2, 1.07:2, etc. The total concentration of lithium and manganese in the mixed solution is 0.5 mol / L-1.0 mol / L, such as 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, etc.

[0055] Furthermore, the solvent can be deionized water, but is not limited to it. The lithium source can be a commonly used water-soluble lithium source, such as LiOH·H2O, but is not limited to it. The manganese source can be a commonly used water-soluble manganese source, such as Mn(NO3)2·4H2O, but is not limited to it.

[0056] (b) Hydrothermal reaction

[0057] The mixed solution was transferred to a reaction vessel, a substrate was placed inside, and the reaction was carried out at 180℃-220℃ for 12h-24h. After cooling, the substrate was removed, and two-dimensional lithium manganese oxide nanosheets (thickness <10nm) were grown on the substrate surface.

[0058] Specifically, the reaction temperature can be 180℃, 190℃, 200℃, 210℃, 220℃, etc.; the reaction time can be 12h, 15h, 18h, 20h, 22h, 24h, etc.

[0059] In some embodiments, the substrate may be a metal foil, but is not limited thereto. The metal foil is selected from at least one of Ti foil, Cu foil, and Ni foil, and the substrate may be any one or more of the above. Preferably, a Ti foil with a thickness of 10 μm-20 μm is used.

[0060] (c) Spray drying

[0061] Two-dimensional lithium manganese oxide nanosheets are peeled off from the substrate and dispersed in deionized water to form a suspension. The suspension is then spray-dried using a spray dryer to obtain micron-sized porous microspheres with a particle size of 1μm-5μm, specifically 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0062] In some embodiments, during the spray drying process, the inlet temperature is controlled at 200℃-250℃, such as 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc.; the outlet temperature is 80℃-100℃, such as 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0063] (d) Calcination

[0064] The porous microspheres were placed in a muffle furnace and calcined at 500℃-600℃ for 4-6 hours to obtain a two-dimensional hierarchical porous LiMn2O4 matrix.

[0065] Specifically, the roasting temperature can be 500℃, 530℃, 550℃, 580℃, 600℃, etc.; the roasting time can be 4h, 5h, 6h, etc.

[0066] It should be noted that traditional morphology control, including nano-sizing and spherical design, can only optimize ion transport pathways or structural stability individually, without forming a "multi-problem synergistic solution" mechanism; moreover, nanoparticles are prone to aggregation, which reduces electrode conductivity. This invention overcomes the "high rate - stability" contradiction, not limited to single morphology optimization, but constructing "two-dimensional nanosheets (shortening Li...") + The composite morphology of "transmission distance below 10 nm + hierarchical porous microspheres (buffering volume expansion and avoiding aggregation)" not only improves high-rate performance but also enhances structural stability, without the problem of aggregation. The two-dimensional porous microspheres are prepared by mature processes such as hydrothermal and spray drying. ALD and plasma processing equipment can be adapted to existing cathode production lines without special equipment, resulting in low production costs and suitability for large-scale production.

[0067] S2, oxygen vacancy-directed construction

[0068] A two-dimensional hierarchical porous lithium manganese oxide matrix was subjected to plasma treatment to obtain an oxygen vacancy-modified substrate. The construction of oxygen vacancies is beneficial for improving ion transport rates.

[0069] In some embodiments, during plasma treatment, a mixture of argon and oxygen is introduced, with the oxygen volume fraction in the mixture being 5%-15%, such as 5%, 8%, 10%, 13%, 15%, etc. The flow rate of the mixed gas is controlled at 10 sccm-20 sccm, such as 10 sccm, 13 sccm, 15 sccm, 18 sccm, 20 sccm, etc.; the power is set at 100W-300W, such as 100W, 130W, 150W, 180W, 200W, 230W, 250W, 280W, 300W, etc.; and the treatment time is 5min-15min, such as 5min, 8min, 10min, 13min, 15min, etc. By adjusting the process parameters of plasma treatment, oxygen vacancies at a concentration of 1%-5% can be generated on the substrate surface and near the surface after treatment, resulting in oxygen vacancy-modified LiMn2O4. Specifically, during plasma processing, high-energy particles bombard the material surface at high speeds, instantly generating extremely high energy. After the oxygen atoms on the surface gain enough energy to overcome the lattice bondage, they are sputtered out, and the sites originally occupied by oxygen atoms will form oxygen vacancies.

[0070] Specifically, the concentration of oxygen vacancies refers to the volume fraction, which can be measured by electron paramagnetic resonance spectroscopy.

[0071] S3, anti-spinel coating and chemical bonding

[0072] The following steps describe the sequential processes of reverse spinel coating, phosphate bonding, and hafnium oxide deposition:

[0073] (a) Inverse spinel coating

[0074] The oxygen vacancy-modified substrate is immersed in a sol formed by manganese and lithium salts. After ultrasonic dispersion, the sol can uniformly coat the substrate particles. After drying, a pre-coated sample is obtained.

[0075] In some embodiments, the preparation process of the sol used in the preparation of the pre-coated sample includes: mixing manganese salt, lithium salt, and alcohol solvent, and reacting at 20℃-30℃ (e.g., 20℃, 23℃, 25℃, 28℃, 30℃, etc.) for 2h-4h (e.g., 2h, 3h, 4h, etc.), controlling the molar ratio of lithium to manganese to be (3.5-4.5):5, such as 3.5:5, 4.0:5, 4.5:5, etc. The type of alcohol solvent is not limited, such as ethanol. The manganese salt can be manganese nitrate, and the lithium salt can be lithium nitrate.

[0076] Furthermore, the ultrasonic dispersion time can be 20 min to 60 min, such as 20 min, 30 min, 40 min, 50 min, 60 min, etc.; the drying temperature can be 70℃ to 90℃, such as 70℃, 75℃, 80℃, 85℃, 90℃, etc.

[0077] (b) Phosphate ester bonding

[0078] The pre-coated sample and the phosphate compound are mixed and reacted to allow the phosphate molecules to be grafted onto the sample surface through PO-Mn bonds, resulting in a phosphate-grafted sample.

[0079] In some embodiments, the phosphate ester compound used is selected from at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate, and the type of phosphate ester compound can be any one or more of the above. The mass ratio of the pre-coated sample to the phosphate ester compound is (8-12):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, etc.

[0080] Furthermore, the pre-coated sample and the phosphate ester compound were reacted under an inert atmosphere (such as nitrogen or argon), with the reaction temperature controlled at 150℃-200℃ and the reaction time at 2h-4h. During the reaction, the phosphate ester compound first undergoes thermal dissociation to generate an active phosphorus atom intermediate. Surface oxygen vacancies result in lone pairs of electrons on the Mn atoms. The phosphorus atom intermediate and the lone pairs of electrons on the surface Mn atoms form new PO-Mn bonds, which are grafted onto the sample surface.

[0081] Specifically, the reaction temperature can be controlled at 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, etc.; the reaction time can be 2h, 3h, 4h, etc.

[0082] (c) Deposition of hafnium oxide

[0083] Hafnium oxide was deposited on the surface of the grafted phosphate sample to obtain the target cathode material.

[0084] In some embodiments, hafnium oxide can be deposited on the surface of the grafted phosphate sample using atomic layer deposition (ALD). The grafted phosphate sample is placed in an ALD device, using HfCl4 and H2O as precursors. The deposition temperature is set to 200℃-250℃, and the deposition cycle is 5-20 cycles to form a 1nm-3nm thick HfO2 covalent layer on the sample surface, ultimately obtaining the target cathode material. By controlling the HfO2 layer thickness (1-3 nm) through the ALD deposition cycle (5-20 cycles), the interface layer thickness and defect concentration can be precisely adjusted, and the modification effect is reproducible.

[0085] Specifically, the deposition temperature can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc.; the deposition cycle can be 5, 10, 15, 20, etc.

[0086] It should be noted that traditional doping modification only stabilizes the crystal lattice using metal ions such as Ni, Co, and Al, which cannot simultaneously solve the problems of slow ion transport and volume expansion. Furthermore, high doping levels reduce the theoretical capacity of the material. This invention overcomes the limitations of "single-function" doping by employing a synergistic mechanism of "oxygen vacancy construction (enhancing ion transport) + two-dimensional hierarchical pores (alleviating volume expansion) + anti-spinel coating (stabilizing the crystal lattice)" to simultaneously address the three core problems of Mn dissolution, slow ion transport, and volume expansion, with minimal capacity loss. By integrating multiple technical units of "defect-morphology-coating," each unit works in concert to achieve "simultaneous improvement of multiple properties," avoiding the functional limitations of single-modification approaches.

[0087] This invention also provides a positive electrode sheet, comprising the lithium manganese oxide positive electrode material provided in this invention. Using the lithium manganese oxide positive electrode material as the positive electrode active material, a positive electrode active layer is prepared on the positive electrode current collector using conventional methods to obtain the positive electrode sheet. The improvement in the positive electrode active material is beneficial for improving the performance of the electrode sheet.

[0088] This invention also provides a lithium battery, including the positive electrode sheet provided in this embodiment, and may further include a negative electrode sheet, an electrolyte, etc. The improvement of the positive electrode sheet significantly enhances the cycle stability of the battery.

[0089] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0090] Example 1

[0091] This embodiment provides a method for preparing lithium manganese oxide cathode material, such as... Figure 1 As shown, the steps are as follows:

[0092] 1. Raw material preparation

[0093] Weigh out the lithium source (LiOH·H2O) and manganese source (Mn(NO3)2·4H2O), mix them according to the Li:Mn molar ratio of 1.05:2.0, and add deionized water to prepare a mixed solution with a total lithium and manganese concentration of 0.8 mol / L;

[0094] Backup materials: trimethyl phosphate (analytical grade), HfCl4 (ALD precursor), Ar / O2 mixed gas (volume ratio 9:1), Ti foil (thickness 15 μm).

[0095] 2. Preparation of two-dimensional hierarchical porous LiMn2O4 matrix

[0096] 2.1 Hydrothermal synthesis of two-dimensional nanosheets: The above mixed solution was transferred to a reaction vessel, Ti foil was placed as a substrate, and the reaction was carried out at 200℃ for 20 h. After cooling, the Ti foil was removed, and LiMn2O4 two-dimensional nanosheets (thickness <10 nm) were grown on the surface.

[0097] 2.2 Spray drying to construct hierarchical porous structures: Two-dimensional nanosheets were peeled off from Ti foil and dispersed in deionized water to form a suspension (the concentration of two-dimensional nanosheets in the suspension was 20 mg / mL, the same below). The suspension was dried by spray drying (inlet temperature 220℃, outlet temperature 90℃) to obtain micron-sized (1-5 μm) porous microspheres.

[0098] 2.3 Annealing and shaping: The porous microspheres were placed in a muffle furnace and calcined at 550℃ for 5 h to obtain a two-dimensional hierarchical porous LiMn2O4 matrix.

[0099] 3. Oxygen-vacancy directed construction

[0100] A two-dimensional hierarchical porous LiMn2O4 matrix was placed in a plasma processing instrument, and an Ar / O2 mixed gas (flow rate 15 sccm) was introduced. The power was set to 250 W and the processing time to 10 min. Oxygen vacancies with a concentration of 3% were generated on the surface and near the surface of the matrix, resulting in oxygen vacancy-modified LiMn2O4.

[0101] 4. Anti-spinel coating and chemical bonding

[0102] 4.1 Anti-spinel coating: Prepare Li4Mn5O 12 The sol (LiNO3 to Mn(NO3)2 molar ratio 4:5, solvent is ethanol, total content of LiNO3 and Mn(NO3)2 is 1.5 mol / L, after mixing, react at 25℃ for 30 min), oxygen vacancy modified LiMn2O4 is immersed in the sol, ultrasonically dispersed for 40 min, and then dried at 80℃ for 3 h to obtain the pre-coated sample.

[0103] 4.2 Phosphate ester bonding: The pre-coated sample and trimethyl phosphate were mixed at a mass ratio of 10:1 and placed in an inert atmosphere (N2) reactor. The mixture was reacted at 180℃ for 3 h to allow phosphate ester molecules to be grafted onto the sample surface through PO-Mn bonds.

[0104] 4.3 ALD HfO2 Coating: The bonded sample was placed in the ALD device, using HfCl4 and H2O as precursors. The deposition temperature was set to 230℃ and the deposition cycle was 12. Each cycle was performed sequentially: HfCl4 vapor was introduced (time 0.5s), inert gas was introduced for rinsing (time 10s), H2O vapor was introduced (time 2s), and inert gas was introduced for rinsing (time 10s). The HfCl4 and H2O vapor introduction rates were 30sccm and 15sccm, respectively, and the inert gas introduction rate was 100sccm. A 2 nm thick HfO2 covalent bond layer was formed on the sample surface, and the target cathode material was finally obtained.

[0105] In the positive electrode material synthesized in this embodiment, the mass percentage of phosphate ester is 0.75% and the mass percentage of HfO2 is 1.5%.

[0106] Example 2

[0107] This embodiment provides a method for preparing lithium manganese oxide cathode material, such as... Figure 1 As shown, the steps are as follows:

[0108] 1. Raw material preparation

[0109] Weigh out the lithium source (LiOH·H2O) and manganese source (Mn(NO3)2·4H2O), mix them according to the Li:Mn molar ratio of 1.03:2.0, and add deionized water to prepare a mixed solution with a total lithium and manganese concentration of 0.5 mol / L;

[0110] Backup materials: trimethyl phosphate (analytical grade), HfCl4 (ALD precursor), Ar / O2 mixed gas (volume ratio 9.5:0.5), Ti foil (thickness 15 μm).

[0111] 2. Preparation of two-dimensional hierarchical porous LiMn2O4 matrix

[0112] 2.1 Hydrothermal synthesis of two-dimensional nanosheets: The above mixed solution was transferred to a reaction vessel, Ti foil was placed as a substrate, and the reaction was carried out at 180℃ for 24 h. After cooling, the Ti foil was removed, and LiMn2O4 two-dimensional nanosheets (thickness <10 nm) were grown on the surface.

[0113] 2.2 Spray drying to construct hierarchical porous structures: Two-dimensional nanosheets were peeled off from Ti foil, dispersed in deionized water to form a suspension, and dried by spray drying (inlet temperature 200℃, outlet temperature 80℃) to obtain micron-sized (1-5 μm) porous microspheres;

[0114] 2.3 Annealing and shaping: The porous microspheres were placed in a muffle furnace and calcined at 500℃ for 6 h to obtain a two-dimensional hierarchical porous LiMn2O4 matrix.

[0115] 3. Oxygen-vacancy directed construction

[0116] A two-dimensional hierarchical porous LiMn2O4 matrix was placed in a plasma processor, and an Ar / O2 mixed gas (flow rate 10 sccm) was introduced. The power was set to 100 W and the processing time to 15 min to obtain oxygen vacancy modified LiMn2O4.

[0117] 4. Anti-spinel coating and chemical bonding

[0118] 4.1 Anti-spinel coating: Prepare Li4Mn5O 12 The sol (LiNO3 to Mn(NO3)2 molar ratio 3.5:5, solvent is ethanol, total content of LiNO3 and Mn(NO3)2 is 1.5 mol / L, after mixing, react at 25℃ for 30 min), oxygen vacancy modified LiMn2O4 is immersed in the sol, ultrasonically dispersed for 20 min, and then dried at 70℃ for 3 h to obtain the pre-coated sample.

[0119] 4.2 Phosphate ester bonding: The pre-coated sample was mixed with trimethyl phosphate at a mass ratio of 8:1 and placed in an inert atmosphere (N2) reactor. The mixture was reacted at 150℃ for 4 h to allow phosphate ester molecules to be grafted onto the sample surface through PO-Mn bonds.

[0120] 4.3 ALD HfO2 Coating: The bonded sample was placed in an ALD device. HfCl4 and H2O were used as precursors. The deposition temperature was set to 200℃ and the deposition cycle was 5. Each cycle was performed sequentially: HfCl4 vapor was introduced (time 0.25s), inert gas was introduced for rinsing (time 10s), H2O vapor was introduced (time 1s), and inert gas was introduced for rinsing (time 10s). The HfCl4 and H2O vapor introduction rates were 30sccm and 15sccm, respectively, and the inert gas introduction rate was 100sccm. A 1nm thick HfO2 covalent bond layer was formed on the sample surface, and the target cathode material was finally obtained.

[0121] In the positive electrode material synthesized in this embodiment, the mass percentage of phosphate ester is 0.5%, and the mass percentage of HfO2 is 1.0%.

[0122] Example 3

[0123] This embodiment provides a method for preparing lithium manganese oxide cathode material, such as... Figure 1 As shown, the steps are as follows:

[0124] 1. Raw material preparation

[0125] Weigh out the lithium source (LiOH·H2O) and manganese source (Mn(NO3)2·4H2O), mix them according to the Li:Mn molar ratio of 1.07:2.0, and add deionized water to prepare a mixed solution with a total lithium and manganese concentration of 1.0 mol / L;

[0126] Backup materials: trimethyl phosphate (analytical grade), HfCl4 (ALD precursor), Ar / O2 mixed gas (volume ratio 8.5:1.5), Ti foil (thickness 15 μm).

[0127] 2. Preparation of two-dimensional hierarchical porous LiMn2O4 matrix

[0128] 2.1 Hydrothermal synthesis of two-dimensional nanosheets: The above mixed solution was transferred to a reaction vessel, Ti foil was placed as a substrate, and the reaction was carried out at 220℃ for 12 h. After cooling, the Ti foil was removed, and LiMn2O4 two-dimensional nanosheets (thickness <10 nm) were grown on the surface.

[0129] 2.2 Spray drying to construct hierarchical porous structures: Two-dimensional nanosheets were peeled off from Ti foil, dispersed in deionized water to form a suspension, and dried by spray drying (inlet temperature 250℃, outlet temperature 100℃) to obtain micron-sized (1-5 μm) porous microspheres;

[0130] 2.3 Annealing and shaping: The porous microspheres were placed in a muffle furnace and calcined at 600℃ for 4 h to obtain a two-dimensional hierarchical porous LiMn2O4 matrix.

[0131] 3. Oxygen-vacancy directed construction

[0132] A two-dimensional hierarchical porous LiMn2O4 matrix was placed in a plasma processor, and an Ar / O2 mixed gas (flow rate 20 sccm) was introduced. The power was set to 300 W and the processing time was 5 min to obtain oxygen vacancy modified LiMn2O4.

[0133] 4. Anti-spinel coating and chemical bonding

[0134] 4.1 Anti-spinel coating: Prepare Li4Mn5O 12 The sol (LiNO3 to Mn(NO3)2 molar ratio 4.5:5, solvent is ethanol, total content of LiNO3 and Mn(NO3)2 is 1.5 mol / L, after mixing, react at 25℃ for 30 min), oxygen vacancy modified LiMn2O4 is immersed in the sol, ultrasonically dispersed for 60 min, and then dried at 90℃ for 3 h to obtain the pre-coated sample.

[0135] 4.2 Phosphate ester bonding: The pre-coated sample and trimethyl phosphate were mixed at a mass ratio of 12:1 and placed in an inert atmosphere (N2) reactor. The mixture was reacted at 200℃ for 2 h to allow phosphate ester molecules to be grafted onto the sample surface through PO-Mn bonds.

[0136] 4.3 ALD HfO2 Coating: The bonded sample was placed in the ALD device, using HfCl4 and H2O as precursors. The deposition temperature was set to 250℃ and the deposition cycle to 20 cycles. Each cycle was performed sequentially: HfCl4 vapor was introduced (time 0.75s), inert gas was introduced for rinsing (time 10s), H2O vapor was introduced (time 3s), and inert gas was introduced for rinsing (time 10s). The HfCl4 and H2O vapor introduction rates were 30sccm and 15sccm, respectively, and the inert gas introduction rate was 100sccm. A 3 nm thick HfO2 covalent bond layer was formed on the sample surface, and the target cathode material was finally obtained.

[0137] In the positive electrode material synthesized in this embodiment, the mass percentage of phosphate ester is 1.0% and the mass percentage of HfO2 is 2.0%.

[0138] Example 4

[0139] The only difference from Example 1 is that in step 4.2, the mass ratio of the pre-coated sample to trimethyl phosphate is 5:1.

[0140] Example 5

[0141] The only difference from Example 1 is that in step 4.2, the mass ratio of the pre-coated sample to trimethyl phosphate is 15:1.

[0142] Example 6

[0143] The only difference from Example 1 is that the thickness of the HfO2 covalent layer in step 4.3 is 0.5 nm.

[0144] Example 7

[0145] The only difference from Example 1 is that the thickness of the HfO2 covalent layer in step 4.3 is 5 nm.

[0146] Example 8

[0147] The only difference from Example 1 is that the reaction temperature in step 4.2 is 120°C.

[0148] Example 9

[0149] The only difference from Example 1 is that the reaction temperature in step 4.2 is 240°C.

[0150] Comparative Example 1

[0151] The only difference from Example 1 is that steps 3 and 4 are omitted, and a conventional coating layer is prepared on the LiMn2O4 substrate obtained in step 2, as follows:

[0152] 1. Take the dried LiMn2O4 matrix, disperse it in deionized water, and sonicate for 20 minutes to form a uniform suspension;

[0153] 2. Add an aluminum source (aluminum isopropoxide, aluminum nitrate, etc.) to the above suspension at a coating amount of 2%, adjust the pH to 4-5 by adding dilute nitric acid dropwise, stir at 60-80℃ for 1-2 hours to form a stable alumina sol;

[0154] 3. Transfer the above suspension to a reaction vessel and react at 120-160℃ for 6-10 hours. Aluminum hydroxide is deposited in situ on the LiMn2O4 matrix to generate a conventional Al-coated LiMn2O4 sample.

[0155] Comparative Example 2

[0156] The only difference from Example 1 is that step 4.2 is not performed.

[0157] Comparative Example 3

[0158] The only difference from Example 1 is that step 4.3 is not performed.

[0159] The performance of the cathode material products prepared by the test examples and comparative examples is shown in Table 1.

[0160] Test method: The positive electrode active material, conductive agent (carbon black), and binder were mixed at a mass ratio of 9.5:0.3:0.2, and homogenized with N-methylpyrrolidone to obtain the positive electrode slurry; this slurry was coated onto the positive electrode current collector, dried, and rolled to obtain the positive electrode sheet. A graphite negative electrode was used; the electrolyte contained 0.9 mol / L lithium hexafluorophosphate, and the solvents were EC, EMC, and DEC in a ratio of 3:5:2; the separator was a 20-micron PP base film; the positive electrode sheet, negative electrode sheet, and separator were stacked to form a 5Ah soft-pack battery.

[0161] Li + Diffusion coefficient - constant potential step method; 5C capacity retention rate - constant current discharge test; Mn dissolution: ICP; 1C cycle: cycle life test.

[0162] Table 1 Performance test results of the cathode materials prepared in the examples and comparative examples

[0163]

[0164] In summary, this invention, by improving the preparation process of lithium manganese oxide cathode material, has the following advantages:

[0165] (1) By using the method of "plasma-constructed oxygen vacancies + two-dimensional hierarchical porous morphology control", the ion transport channels and microstructure characteristics of spinel lithium manganese oxide (LiMn2O4) were modified, and the high-rate electrical performance of the material was optimized (5C capacity retention reached 75%-80%). + The diffusion coefficient was increased to 10. -11 -10 -10 cm² / s);

[0166] (2) By using the method of “reverse spinel coating + phosphate ester bonding + ALD HfO2 covalent layer”, the interfacial interaction characteristics between LiMn2O4 and electrolyte were changed, Mn dissolution was inhibited, and the cyclic stability of the material was optimized (capacity retention rate of 85%-90% after 300 cycles at 55℃ 1 C, and Mn dissolution rate was reduced by more than 60%).

[0167] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium manganese oxide cathode material, characterized in that, The invention includes a lithium manganese oxide substrate, on which a phosphate ester coating layer and a hafnium oxide surface layer are formed, wherein the phosphate ester coating layer is located between the lithium manganese oxide substrate and the hafnium oxide surface layer.

2. The lithium manganese oxide cathode material according to claim 1, characterized in that, The thickness of the phosphate ester coating layer is 5nm-10nm, and the thickness of the hafnium oxide surface layer is 1nm-3nm; And / or, in the lithium manganese oxide cathode material, the mass percentage of phosphate ester is 0.5%-1.0%, and the mass percentage of HfO2 is 1.0%-2.0%; And / or, the lithium manganese oxide matrix is ​​a porous microsphere with a particle size of 1μm-5μm and a porosity of 10%-20%.

3. A method for preparing the lithium manganese oxide cathode material according to any one of claims 1-2, characterized in that, include: Provide lithium manganese oxide matrix; The lithium manganese oxide matrix is ​​subjected to plasma treatment to obtain an oxygen vacancy modified substrate. The oxygen vacancy-modified substrate was placed in a sol formed by manganese salt and lithium salt, and dried to obtain a pre-coated sample. The pre-coated sample and the phosphate compound are mixed and reacted to obtain a sample grafted with phosphate ester; Hafnium oxide was deposited on the surface of the grafted phosphate sample.

4. The preparation method according to claim 3, characterized in that, The preparation process of the sol used in the preparation of the pre-coated sample includes: mixing manganese salt, lithium salt and alcohol solvent, reacting at 20℃-30℃ for 2h-4h, and controlling the molar ratio of lithium to manganese to be (3.5-4.5):

5.

5. The preparation method according to claim 4, characterized in that, The manganese salt is manganese nitrate, and the lithium salt is lithium nitrate.

6. The preparation method according to claim 4, characterized in that, The oxygen vacancy-modified substrate is ultrasonically dispersed in the sol for 20-60 minutes, and then dried at 70-90°C.

7. The preparation method according to claim 3, characterized in that, The phosphate compound used in the preparation of the grafted phosphate sample is selected from at least one of trimethyl phosphate, triethyl phosphate, and tributyl phosphate.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the pre-coated sample to the phosphate compound is (8-12):

1.

9. The preparation method according to claim 8, characterized in that, The pre-coated sample and the phosphate compound were reacted under an inert atmosphere, with the reaction temperature controlled at 150℃-200℃ and the reaction time at 2h-4h.

10. The preparation method according to claim 3, characterized in that, Hafnium oxide was deposited on the surface of the grafted phosphate sample using atomic layer deposition.

11. The preparation method according to claim 10, characterized in that, During the deposition of hafnium oxide, HfCl4 and H2O were used as precursors, the deposition temperature was set at 200℃-250℃, the deposition cycle was 5-20 cycles, and the deposition thickness was 1nm-3nm.

12. The preparation method according to claim 3, characterized in that, During the plasma treatment process, a mixture of argon and oxygen is introduced, with the oxygen having a volume fraction of 5%-15% in the mixture.

13. The preparation method according to claim 12, characterized in that, Control the mixed gas flow rate to 10 sccm-20 sccm, set the power to 100W-300W, and the processing time to 5min-15min.

14. The preparation method according to claim 3, characterized in that, The preparation process of the lithium manganese oxide matrix includes: A mixed solution is obtained by mixing lithium source, manganese source and solvent. The substrate is placed in the mixed solution and reacted at 180℃-220℃ for 12h-24h to grow two-dimensional lithium manganese oxide nanosheets on the substrate surface. The lithium manganese oxide two-dimensional nanosheets were peeled off from the substrate and dispersed in water to form a suspension. The suspension was then spray-dried to obtain porous microspheres with a particle size of 1 μm-5 μm. The porous microspheres were calcined at 500℃-600℃ for 4-6 hours.

15. The preparation method according to claim 14, characterized in that, The molar ratio of lithium to manganese in the mixed solution is (1.03-1.07):2, and the total concentration of lithium and manganese in the mixed solution is 0.5 mol / L-1.0 mol / L.

16. The preparation method according to claim 14, characterized in that, During the spray drying process, the inlet temperature is controlled at 200℃-250℃ and the outlet temperature is controlled at 80℃-100℃.

17. The preparation method according to claim 14, characterized in that, The substrate is a metal foil.

18. The preparation method according to claim 17, characterized in that, The metal foil is selected from at least one of Ti foil, Cu foil and Ni foil.

19. A positive electrode plate, characterized in that, The lithium manganese oxide cathode material includes any one of the lithium manganese oxide cathode materials described in claims 1-2 or any one of the lithium manganese oxide cathode materials prepared by the preparation method described in claims 3-18.

20. A lithium battery, characterized in that, Includes the positive electrode sheet as described in claim 19.

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