Lithium-rich manganese-based positive electrode material, preparation method thereof and solid-state battery

Abstract

The invention provides a lithium-rich manganese-based positive electrode material, a preparation method thereof and a solid-state battery. The lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based core, and a composite oxide layer, a nitrogen-doped carbon nanotube layer and a solid-state electrolyte nanoparticle layer which sequentially coat the surface of the lithium-rich manganese-based core. By arranging multiple coating layers on the surface of the lithium-rich manganese-based inner core, the obtained lithium-rich manganese-based positive electrode material not only has the characteristics of low interface impedance, good structural stability and perfect electron / ion conduction network, but also can avoid the problem of mechanical contact failure; the electrochemical performance and the cycling stability of the material in a solid-state battery system are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, and relates to a lithium-rich manganese-based cathode material, its preparation method, and a solid-state battery. Background Technology

[0002] The demand for high-safety, high-energy-density energy storage systems is growing rapidly in emerging fields such as new energy vehicles, electric VTOL (electric vehicle-to-everything) aircraft, and smart grids. All-solid-state batteries (ASSBs) use non-flammable solid electrolytes to replace traditional liquid electrolytes, fundamentally solving the risk of thermal runaway. At the same time, by being compatible with lithium metal anode and high-voltage cathode materials, they are expected to achieve energy densities of over 500Wh / kg, and are regarded as the core direction of next-generation power battery technology.

[0003] In solid-state battery systems, the cathode material is a key factor limiting the improvement of battery energy density, accounting for more than 30% of the total cost of battery materials. Currently, the most researched cathode materials for solid-state batteries mainly include high-nickel ternary materials (such as NCM and NCA), lithium-rich manganese-based materials (xLi2MnO3·(1-x)LiMO2), and high-voltage nickel-manganese spinel (LiNi). 0.5 Mn 1.5 O4), etc. Among them, lithium-rich manganese-based cathode materials are considered ideal cathode materials for all-solid-state batteries due to their inherent advantages of high theoretical capacity (up to 320mAh / g) and high operating voltage (3.7-4.6V). Compared with high-nickel ternary materials, lithium-rich manganese-based materials are mainly composed of cheaper manganese and contain less precious metals, resulting in lower costs (unit cost can be reduced by nearly 20%) and better safety.

[0004] CN118156486A describes a method for constructing a specific ionic conductivity (0.5 × 10⁻⁶) on the surface of a lithium-rich manganese-based material. -3 ~5×10 - 3 (S / cm) and low electronic conductivity (≤10) -9 A coating layer with a capacitance of S / cm improves interfacial ion migration efficiency and material stability. The "dual-phase composite ultra-high nickel cathode material" developed by Dangsheng Technology employs ultra-stable fast ion conductor modification technology to solve the problems of high interfacial impedance and severe side reactions. However, these methods still have shortcomings in long-term cycle stability and high-rate performance, and the processes are complex and costly.

[0005] CN117751471A proposes using residual lithium (content exceeding 2000ppm) on the surface of the positive electrode active material to reduce the interfacial resistance between the solid electrolyte and the active material, but this method has extremely high requirements for material purity and process control.

[0006] The above-mentioned methods are costly and difficult to prepare, and the resulting materials have poor stability and ionic / electronic conductivity. Summary of the Invention

[0007] The purpose of this invention is to provide a lithium-rich manganese-based cathode material, its preparation method, and a solid-state battery. By setting multiple coating layers on the surface of the lithium-rich manganese-based core, this invention obtains a lithium-rich manganese-based cathode material that not only has the characteristics of low interfacial impedance, good structural stability, and perfect electron / ion conduction network, but also avoids the problem of mechanical contact failure, thus significantly improving the electrochemical performance and cycle stability of the material in the solid-state battery system.

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

[0009] In a first aspect, the present invention provides a lithium-rich manganese-based cathode material, the lithium-rich manganese-based cathode material comprising a lithium-rich manganese-based core and a composite oxide layer, a nitrogen-doped carbon nanotube layer, and a solid electrolyte nanoparticle layer sequentially coated on the surface of the lithium-rich manganese-based core.

[0010] The lithium-rich manganese-based cathode material of this invention employs multiple coatings. The inner composite oxide layer provides high ionic conductivity and interfacial stability, the middle nitrogen-doped carbon nanotubes construct a three-dimensional electron network, and the outer solid electrolyte nanoparticles pre-construct ion channels, reducing the interfacial impedance from the traditional >1000 Ω·cm. 2 Reduced to <200Ω·cm 2 .

[0011] Preferably, the lithium-rich manganese-based core has the chemical formula Li. 1.2+α Ni x Co y Mn z O 2+δ , where 0≤α≤0.3, 0.1≤x≤0.3, 0≤y≤0.2, 0.5≤z≤0.7, -0.1≤δ≤0.1, and x+y+z=1.

[0012] Preferably, the median particle size D50 of the lithium-rich manganese-based core is 3μm to 8μm, for example: 3μm, 4μm, 5μm, 6μm, 7μm or 8μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] Preferably, the specific surface area of ​​the lithium-rich manganese-based core is 1 m². 2 / g~3m 2 / g, for example: 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g or 3m 2 / g, etc., are not limited to the listed values; other unlisted values ​​within this range also apply.

[0014] Preferably, the composite oxide layer is made of Li3NbO4 and Li5TaO5.

[0015] This invention uses a composite oxide layer of Li3NbO4 and Li5TaO5. By forming a strong Nb / Ta-O bond (bond energy > 532 kJ / mol), the two inhibit oxygen loss under high voltage, reducing the oxygen release at 4.6V from 0.28 mol to 0.05 mol.

[0016] Preferably, the molar ratio of Li3NbO4 to Li5TaO5 in the composite oxide layer is 1:(0.5~2), for example: 1:0.5, 1:0.8, 1:1, 1:1.5 or 1:2, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, the thickness of the composite oxide layer is 5nm to 15nm, for example: 5nm, 8nm, 10nm, 12nm or 15nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the ionic conductivity of the composite oxide layer is ≥1×10⁻⁶. -3 S / cm.

[0019] Preferably, the electronic conductivity of the composite oxide layer is ≤1×10⁻⁶. -10 S / cm.

[0020] Preferably, the diameter of the carbon nanotubes in the nitrogen-doped carbon nanotube layer is 10nm~30nm, for example: 10nm, 15nm, 20nm, 25nm or 30nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] The nitrogen in the nitrogen-doped carbon nanotube layer of the present invention is mainly in the form of pyridine nitrogen, with the proportion of pyridine nitrogen >60%, which provides more lithium adsorption sites and reduces the electron transfer resistance by 58%.

[0022] Preferably, the aspect ratio of the carbon nanotubes in the nitrogen-doped carbon nanotube layer is >1000.

[0023] Preferably, with the total number of atoms in the nitrogen-doped carbon nanotube layer being 100%, the percentage of nitrogen atoms is 1% to 5%, for example: 1%, 2%, 3%, 4% or 5%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the defect density of the nitrogen-doped carbon nanotube layer is 0.2 defects / nm. 2 ~0.8 per nm 2 For example: 0.2 per nm 2 0.4 units / nm 2 0.5 units / nm 2 0.6 units / nm 2 Or 0.8 per nm 2 The term "etc." is not limited to the listed values; it also applies to other unlisted values ​​within the range.

[0025] Preferably, based on the mass of the lithium-rich manganese-based cathode material as 100%, the mass fraction of the nitrogen-doped carbon nanotube layer is 1% to 3%, for example: 1%, 1.5%, 2%, 2.5% or 3%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] Preferably, the material of the solid electrolyte nanoparticle layer includes Li. 6.5 La3Zr 1.5 Ta 0.5 O 12 (LLZTO).

[0027] Preferably, the median particle size D50 of the solid electrolyte nanoparticles in the solid electrolyte nanoparticle layer is 20nm~50nm, for example: 20nm, 25nm, 30nm, 40nm or 50nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, based on the mass of the lithium-rich manganese-based cathode material as 100%, the mass fraction of the solid electrolyte nanoparticle layer is 5% to 10%, for example: 5%, 6%, 7%, 8%, 9% or 10%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] Preferably, a lithium vacancy buffer layer is further provided between the lithium-rich manganese-based core and the composite oxide layer.

[0030] This invention forms a lithium vacancy buffer layer by precisely controlling the lithium vacancy concentration (5%~10%) between the core and the composite oxide layer, which can absorb volumetric strain during cycling and reduce the contact loss rate from 30% to <5%.

[0031] Preferably, the material of the lithium vacancy buffer layer includes Li 1-x Al x O2 and / or Li 3-y La y NbO4, where 0.05≤x≤0.15, 0.02≤y≤0.08;

[0032] Preferably, the lithium vacancy concentration of the lithium vacancy buffer layer is 2% to 15%, for example: 2%, 5%, 10%, 12% or 15%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the thickness of the lithium vacancy buffer layer is 1nm to 3nm, for example: 1nm, 1.5nm, 2nm, 2.5nm or 3nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] In a second aspect, the present invention provides a method for preparing a lithium-rich manganese-based cathode material as described in the first aspect, the method comprising the following steps:

[0035] A lithium-rich manganese-based precursor is mixed with a lithium source and subjected to a first sintering treatment to obtain a sintered material.

[0036] The first-burned material, niobium source, and tantalum source are mixed and subjected to a second sintering process to obtain the second-burned material;

[0037] The sintered material, nitrogen-doped carbon nanotubes, conductive carbon black and binder solution are mixed and spray-dried. The resulting spray-dried material is mixed with solid electrolyte and pressed into shape. The lithium-rich manganese-based cathode material is obtained by a third sintering process.

[0038] The lithium-rich manganese-based precursor of the present invention is prepared by coprecipitation-redox method.

[0039] The method described in this invention can generate, in situ, a Li-Nb / Ta-O interface phase on the surface of a lithium-rich manganese-based core, which can suppress the interaction between LRM and sulfide electrolytes (such as Li). 10 GeP2S 12 The side reactions were minimized, and after 200 cycles, the interface thickness increased by only about 2.8 nm, far lower than the >15 nm increase of traditional materials. Dry ball milling enabled the solid electrolyte nanoparticles to be uniformly embedded in the conductive network, avoiding the uneven contact problem in traditional dry electrode processes.

[0040] The present invention incorporates conductive carbon black, which plays a role in inhibiting particle agglomeration and promoting uniform sintering during the sintering process. The carbon black doping does indeed play some other roles during the sintering process, such as buffering volume strain during charging and discharging, protecting surface active sites, and changing interfacial impedance and conductivity. After sintering, the conductive carbon black and nitrogen-doped carbon nanotubes form a composite conductive layer.

[0041] Preferably, the total molar ratio of metal ions in the lithium-rich manganese-based precursor to the molar ratio of lithium in the lithium source is 1:(1.45~1.55), for example: 1:1.45, 1:1.48, 1:1.5, 1:1.52 or 1:1.55, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the atmosphere of the first sintering treatment includes oxygen.

[0043] Preferably, the first sintering process includes a first-stage calcination and a second-stage calcination.

[0044] Preferably, the calcination temperature is 500℃~600℃, for example: 500℃, 520℃, 550℃, 580℃ or 600℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the calcination time is 4h to 6h, for example: 4h, 4.5h, 5h, 5.5h or 6h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the temperature of the second-stage calcination is 800℃~900℃, for example: 800℃, 820℃, 850℃, 880℃ or 900℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Preferably, the calcination time for the second stage is 10h to 15h, for example: 10h, 11h, 12h, 13h, 14h or 15h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] Preferably, the niobium source includes niobium pentaethoxy.

[0049] Preferably, the tantalum source includes pentaethoxytantalum.

[0050] Preferably, based on the mass of the calcined material as 100%, the total addition amount of the niobium source and tantalum source is 0.75% to 2.5%, for example: 0.75%, 1%, 1.5%, 2% or 2.5%, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0051] Preferably, ethanol is added during the ball milling process of mixing the sintered material, niobium source, and tantalum source.

[0052] Preferably, the atmosphere for the second sintering treatment includes argon.

[0053] Preferably, the temperature of the second sintering treatment is 400℃~500℃, for example: 400℃, 420℃, 450℃, 480℃ or 500℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the second sintering treatment time is 4h to 8h, for example: 4h, 5h, 6h, 7h or 8h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0055] Preferably, the nitrogen-doped carbon nanotubes are prepared by treating carbon nanotubes with ammonia plasma.

[0056] Preferably, the mass ratio of the nitrogen-doped carbon nanotubes to the conductive carbon black is (1.5~2.5):1, for example: 1.5:1, 1.8:1, 2:1, 2.2:1 or 2.5:1, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the adhesive solution comprises a polyvinylidene fluoride (PVDF) N-methylpyrrolidone (NMP) solution with a mass percentage concentration of 2% to 4%.

[0058] Preferably, the method of mixing the obtained spray-dried material with the solid electrolyte includes dry ball milling.

[0059] Preferably, the grinding speed of the dry ball mill is 200 rpm to 400 rpm, for example: 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0060] Preferably, the dry ball milling time is 2h to 6h, for example: 2h, 3h, 4h, 5h or 6h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0061] Preferably, the pressing pressure is 200MPa~400MPa, for example: 200MPa, 250MPa, 300MPa, 350MPa or 400MPa, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0062] Preferably, the temperature of the third sintering treatment is 200℃~300℃, for example: 200℃, 220℃, 250℃, 280℃ or 300℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] Preferably, the time for the third sintering treatment is 1h to 3h, for example: 1h, 1.5h, 2h, 2.5h or 3h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] Thirdly, the present invention provides a positive electrode sheet comprising the lithium-rich manganese-based positive electrode material as described in the first aspect.

[0065] Fourthly, the present invention provides a solid-state battery comprising a positive electrode as described in the third aspect.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) By setting multiple coating layers on the surface of the lithium-rich manganese-based core, the present invention obtains a lithium-rich manganese-based cathode material that not only has the characteristics of low interfacial impedance, good structural stability and perfect electronic / ion conduction network, but also avoids the problem of mechanical contact failure, and significantly improves the electrochemical performance and cycle stability of the material in the solid-state battery system.

[0068] (2) The solid-state battery made from the lithium-rich manganese-based cathode material of the present invention can achieve a first discharge capacity of 258 mAh / g or more at 0.1C, a first coulombic efficiency of 84.2% or more, a capacity retention rate of 77.5% or more after 1000 cycles at 1C, a 5C capacity / 0.1C capacity ratio of 75.8% or more, and a cathode-electrolyte interface impedance of 512 Ω·cm. 2 Within 7 days of storage at 60℃, the capacity loss can be less than 8.8%. Detailed Implementation

[0069] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0070] The lithium-rich manganese-based precursors used in the embodiments and comparative examples of this invention were prepared by the following method:

[0071] According to Ni 0.2 Co 0.1 Mn 0.7 The chemical formula of (OH)2 was used to prepare a mixed salt solution. Under nitrogen atmosphere and stirring at 1000 rpm, the mixed salt solution, ammonia and sodium hydroxide solution were introduced into the bottom liquid. The mixture was then subjected to a process at 50°C and pH 11 for 18 hours to obtain the lithium-rich manganese-based precursor.

[0072] The nitrogen-doped carbon nanotubes used were prepared by the following method:

[0073] Multi-walled carbon nanotubes (MWCNTs) undergo three pretreatment steps followed by controlled nitrogen-doped plasma modification:

[0074] 1. Pre-processing:

[0075] (1) Acid washing and purification: MWCNTs were placed in 3MHNO3 solution and ultrasonically treated (40kHz, 300W, 2h) to remove metal catalyst residues;

[0076] (2) Water washing and neutralization: Wash with deionized water until pH=6.5±0.5 (conductivity≤5μS / cm);

[0077] (3) Vacuum drying: Dry at 80℃ for 12 hours to ensure moisture content <0.1wt%.

[0078] 2. Plasma treatment:

[0079] (1) Equipment configuration: The pretreated MWCNTs were placed in a quartz reaction chamber (100 mm in diameter) and the plasma was excited by radio frequency (13.56 MHz) parallel plate electrodes;

[0080] (2) Process conditions:

[0081] Gas ratio: NH3 / Ar = 1:4 (volume ratio), flow rate controlled at 80 ± 5 sccm;

[0082] Key parameters: Power 150W, Pressure 80Pa, Temperature 700℃, Processing time 60min (heating rate 5℃ / min);

[0083] (3) Operating steps

[0084] 1. Sample loading: Spread the pretreated carbon nanotubes evenly on the quartz sample boat (thickness ≤2mm, avoid particle stacking), place it in the center of the reaction chamber, and seal the reaction chamber.

[0085] 2. Vacuuming: Activate the vacuum system and evacuate the reaction chamber to a vacuum level of 5 × 10⁻⁶. -2 Below Pa.

[0086] 3. Gas introduction: Introduce NH3 and Ar at a volume ratio of 1:4, and control the total flow rate at 80±5 sccm; maintain the gas flow rate stable for 30 minutes to ensure a uniform atmosphere in the reaction chamber.

[0087] 4. Heating and Plasma Excitation

[0088] Heating: The temperature was increased to 700℃ at a rate of 5℃ / min, and the sample temperature was monitored in real time using an infrared thermometer.

[0089] Plasma stimulation: After heating to the target temperature, turn on the radio frequency power supply, adjust the power to 150W, and maintain the reaction chamber pressure at 80Pa; monitor the characteristic peaks (N atom characteristic peak at 337.1nm, NH radical characteristic peak at 336.0nm) using an OES spectrometer to ensure plasma stability.

[0090] (5) Doping reaction: Maintain the above conditions for 60 min, and continuously monitor the plasma spectrum during the period to avoid power fluctuations that could lead to uneven doping.

[0091] (6) In-situ annealing: After the reaction is completed, turn off the radio frequency power supply, maintain the NH3 atmosphere, and cool down to 300℃ at a rate of 2℃ / min, and keep warm for 30min.

[0092] Real-time monitoring: Plasma stability is ensured by using an infrared thermometer (±2℃ accuracy) and an OES spectrometer.

[0093] 3. Post-processing and storage:

[0094] (1) In-situ annealing: After the treatment, the nitrogen-doped structure was slowly cooled to 300℃ in an NH3 atmosphere (cooling rate 2℃ / min) to stabilize the nitrogen-doped structure.

[0095] (2) Passivation treatment: 5% H2 / Ar mixed gas was introduced for 30 min to eliminate surface dangling bonds;

[0096] (3) Inert storage: Quickly transfer to an argon-filled glove box (H2O<0.1ppm, O2<0.1ppm) for later use, and avoid exposure to the atmosphere.

[0097] Example 1

[0098] This embodiment provides a lithium-rich manganese-based cathode material, which includes a lithium-rich manganese-based core and a Li3NbO4-Li5TaO5 composite oxide layer, a nitrogen-doped carbon nanotube layer, and an LLZTO solid electrolyte nanoparticle layer sequentially coated on the surface of the lithium-rich manganese-based core.

[0099] The chemical formula of the lithium-rich manganese-based core is Li 1.4 Ni 0.2 Co 0.1 Mn 0.7 O2, the median particle size D50 of the lithium-rich manganese-based core is 5 μm, and the specific surface area of ​​the lithium-rich manganese-based core is 2 m². 2 / g, a lithium vacancy buffer layer is provided before the lithium-rich manganese-based core and the Li3NbO4-Li5TaO5 composite oxide layer, and the material of the lithium vacancy buffer layer includes Li 2.95 La 0.05 NbO4, wherein the thickness of the lithium vacancy buffer layer is 2 nm;

[0100] The molar ratio of Li3NbO4 to Li5TaO5 in the Li3NbO4-Li5TaO5 composite oxide layer is 1:1, the thickness of the composite oxide layer is 10 nm, and the ionic conductivity of the Li3NbO4-Li5TaO5 composite oxide layer is ≥1×10⁻⁶. -3 The electronic conductivity of the Li3NbO4-Li5TaO5 composite oxide layer is ≤1×10⁻⁶ S / cm. -10 S / cm;

[0101] In the nitrogen-doped carbon nanotube layer, the aspect ratio of the carbon nanotubes is >1000, the diameter of the carbon nanotubes is 20 nm, the atomic percentage of nitrogen atoms in the nitrogen-doped carbon nanotube layer is 3%, and the defect density of the nitrogen-doped carbon nanotube layer is 0.5 atoms / nm. 2 In the lithium-rich manganese-based cathode material, the mass fraction of the nitrogen-doped carbon nanotube layer is 2%.

[0102] In the LLZTO solid electrolyte nanoparticle layer, the median particle size D50 of the solid electrolyte nanoparticles is 35 nm, and in the lithium-rich manganese-based cathode material, the mass fraction of the LLZTO solid electrolyte nanoparticle layer is 8%.

[0103] The lithium-rich manganese-based cathode material is prepared by the following method:

[0104] The lithium-rich manganese-based precursor was mixed at a molar ratio of Li / (Ni+Co+Mn)=1.5:1, heated at a rate of 2℃ / min in an O2 atmosphere, calcined at 550℃ for 5h, and then calcined at 850℃ for 12h to obtain a calcined material.

[0105] The first-calcined material was mixed with Nb(OC2H5)5 and Ta(OC2H5)5, wherein the total mass ratio of Nb(OC2H5)5 and Ta(OC2H5)5 to the first-calcined material was 1.5:100, and the molar ratio of Nb(OC2H5)5 to Ta(OC2H5)5 was 1:1. Ethanol was added and the mixture was wet-milled for 4 hours. The mixture was then sintered at 450°C for 6 hours under an argon atmosphere to obtain the second-calcined material.

[0106] Nitrogen-doped carbon nanotubes and conductive carbon black were mixed at a mass ratio of 2:1. The resulting mixture was then ball-milled with a 3% PVDF NMP solution for 6 hours and spray-dried. The dried material was then mixed with LLZTO solid electrolyte nanoparticles and dry-milled at 300 rpm for 4 hours. The mixture was then cold isostatically pressed at 300 MPa and sintered at 250 °C for 2 hours to obtain the lithium-rich manganese-based cathode material.

[0107] Example 2

[0108] This embodiment provides a lithium-rich manganese-based cathode material, which includes a lithium-rich manganese-based core and a Li3NbO4-Li5TaO5 composite oxide layer, a nitrogen-doped carbon nanotube layer, and an LLZTO solid electrolyte nanoparticle layer sequentially coated on the surface of the lithium-rich manganese-based core.

[0109] The chemical formula of the lithium-rich manganese-based core is Li 1.2 Ni 0.2 Co 0.1 Mn 0.7 O2, the median particle size D50 of the lithium-rich manganese-based core is 8 μm, and the specific surface area of ​​the lithium-rich manganese-based core is 1 m². 2 / g, a lithium vacancy buffer layer is provided before the lithium-rich manganese-based core and the Li3NbO4-Li5TaO5 composite oxide layer, and the material of the lithium vacancy buffer layer is Li 2.95 La 0.05 NbO4, wherein the thickness of the lithium vacancy buffer layer is 3 nm;

[0110] The molar ratio of Li3NbO4 to Li5TaO5 in the Li3NbO4-Li5TaO5 composite oxide layer is 1:0.5, the thickness of the composite oxide layer is 5 nm, and the ionic conductivity of the Li3NbO4-Li5TaO5 composite oxide layer is ≥1×10⁻⁶. -3 The electronic conductivity of the Li3NbO4-Li5TaO5 composite oxide layer is ≤1×10⁻⁶ S / cm. -10 S / cm;

[0111] In the nitrogen-doped carbon nanotube layer, the aspect ratio of the carbon nanotubes is >1000, the diameter of the carbon nanotubes is 30 nm, the atomic percentage of nitrogen atoms in the nitrogen-doped carbon nanotube layer is 5%, and the defect density of the nitrogen-doped carbon nanotube layer is 0.8 atoms / nm. 2 In the lithium-rich manganese-based cathode material, the mass fraction of the nitrogen-doped carbon nanotube layer is 1%.

[0112] In the LLZTO solid electrolyte nanoparticle layer, the median particle size D50 of the solid electrolyte nanoparticles is 50 nm, and in the lithium-rich manganese-based cathode material, the mass fraction of the LLZTO solid electrolyte nanoparticle layer is 5%.

[0113] The lithium-rich manganese-based cathode material is prepared by the following method:

[0114] The lithium-rich manganese-based precursors were mixed at a molar ratio of Li / (Ni+Co+Mn)=1.45:1, heated at a rate of 2℃ / min in an O2 atmosphere, calcined at 500℃ for 6h, and then calcined at 800℃ for 15h to obtain a calcined material.

[0115] The first-burned material was mixed with Nb(OC2H5)5 and Ta(OC2H5)5, wherein the total mass ratio of Nb(OC2H5)5 and Ta(OC2H5)5 to the first-burned material was 0.75:100, and the molar ratio of Nb(OC2H5)5 to Ta(OC2H5)5 was 1:0.5. Ethanol was added and wet-milled for 4 hours, and then sintered at 400℃ for 8 hours under an argon atmosphere to obtain the second-burned material.

[0116] Nitrogen-doped carbon nanotubes and conductive carbon black were mixed at a mass ratio of 1.5:1. The resulting mixture was then ball-milled with a 2% PVDF NMP solution for 6 hours and spray-dried. The dried material was then mixed with LLZTO solid electrolyte nanoparticles and dry-milled at 200 rpm for 6 hours. The mixture was then cold isostatically pressed at 200 MPa and sintered at 200 °C for 3 hours to obtain the lithium-rich manganese-based cathode material.

[0117] Example 3

[0118] This embodiment provides a lithium-rich manganese-based cathode material, which includes a lithium-rich manganese-based core and a Li3NbO4-Li5TaO5 composite oxide layer, a nitrogen-doped carbon nanotube layer, and an LLZTO solid electrolyte nanoparticle layer sequentially coated on the surface of the lithium-rich manganese-based core.

[0119] The chemical formula of the lithium-rich manganese-based core is Li 1.5 Ni 0.2 Co 0.1 Mn 0.7 O2, the median particle size D50 of the lithium-rich manganese-based core is 3 μm, and the specific surface area of ​​the lithium-rich manganese-based core is 3 m². 2 / g, a lithium vacancy buffer layer is provided before the lithium-rich manganese-based core and the Li3NbO4-Li5TaO5 composite oxide layer, and the material of the lithium vacancy buffer layer is Li 2.95 La 0.05 NbO4, wherein the thickness of the lithium vacancy buffer layer is 1 nm;

[0120] The molar ratio of Li3NbO4 to Li5TaO5 in the Li3NbO4-Li5TaO5 composite oxide layer is 1:2, the thickness of the composite oxide layer is 15 nm, and the ionic conductivity of the Li3NbO4-Li5TaO5 composite oxide layer is ≥1×10⁻⁶. -3 The electronic conductivity of the Li3NbO4-Li5TaO5 composite oxide layer is ≤1×10⁻⁶ S / cm. -10 S / cm;

[0121] In the nitrogen-doped carbon nanotube layer, the aspect ratio of the carbon nanotubes is >1000, the diameter of the carbon nanotubes is 10 nm, the atomic percentage of nitrogen atoms in the nitrogen-doped carbon nanotube layer is 1%, and the defect density of the nitrogen-doped carbon nanotube layer is 0.2 atoms / nm. 2 In the lithium-rich manganese-based cathode material, the mass fraction of the nitrogen-doped carbon nanotube layer is 3%.

[0122] In the LLZTO solid electrolyte nanoparticle layer, the median particle size D50 of the solid electrolyte nanoparticles is 20 nm, and in the lithium-rich manganese-based cathode material, the mass fraction of the LLZTO solid electrolyte nanoparticle layer is 10%.

[0123] The lithium-rich manganese-based cathode material is prepared by the following method:

[0124] The lithium-rich manganese-based precursor was mixed at a molar ratio of Li / (Ni+Co+Mn)=1.55:1, heated at a rate of 2℃ / min in an O2 atmosphere, calcined at 600℃ for 4h, and then calcined at 900℃ for 10h to obtain a calcined material.

[0125] The first-calcined material was mixed with Nb(OC2H5)5 and Ta(OC2H5)5, wherein the total mass ratio of Nb(OC2H5)5 and Ta(OC2H5)5 to the first-calcined material was 2.5:100, and the molar ratio of Nb(OC2H5)5 to Ta(OC2H5)5 was 1:2. Ethanol was added and the mixture was wet-milled for 4 hours. The mixture was then sintered at 500°C for 4 hours under an argon atmosphere to obtain the second-calcined material.

[0126] Nitrogen-doped carbon nanotubes and conductive carbon black were mixed at a mass ratio of 2.5:1. The resulting mixture was then ball-milled with a 4% PVDF NMP solution for 6 hours and spray-dried. The dried material was then mixed with LLZTO solid electrolyte nanoparticles and dry-milled at 400 rpm for 2 hours. The mixture was then cold isostatically pressed at 400 MPa and sintered at 300 °C for 1 hour to obtain the lithium-rich manganese-based cathode material.

[0127] Example 4

[0128] The only difference between this embodiment and Embodiment 1 is that the molar ratio of Li3NbO4 to Li5TaO5 in the composite oxide layer is controlled to be 1:0.3. All other conditions and parameters are exactly the same as in Embodiment 1.

[0129] Example 5

[0130] The only difference between this embodiment and Embodiment 1 is that the molar ratio of Li3NbO4 to Li5TaO5 in the composite oxide layer is controlled to be 1:3. All other conditions and parameters are exactly the same as in Embodiment 1.

[0131] Example 6

[0132] The only difference between this embodiment and Embodiment 1 is that the thickness of the composite oxide layer is controlled to be 2 nm, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0133] Example 7

[0134] The only difference between this embodiment and Embodiment 1 is that the thickness of the composite oxide layer is controlled to be 20 nm, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0135] Example 8

[0136] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the nitrogen-doped carbon nanotube layer is controlled at 0.5%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0137] Example 9

[0138] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the nitrogen-doped carbon nanotube layer is controlled at 5%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0139] Example 10

[0140] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the solid electrolyte nanoparticle layer is controlled at 2%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0141] Example 11

[0142] The only difference between this embodiment and Embodiment 1 is that the mass fraction of the solid electrolyte nanoparticle layer is controlled at 15%, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0143] Comparative Example 1

[0144] The only difference between this comparative example and Example 1 is that the composite oxide layer is replaced with Li3NbO4, while the other conditions and parameters are exactly the same as in Example 1.

[0145] Comparative Example 2

[0146] The only difference between this comparative example and Example 1 is that the composite oxide layer is replaced with a Li5TaO5 layer; all other conditions and parameters are exactly the same as in Example 1.

[0147] Comparative Example 3

[0148] The only difference between this comparative example and Example 1 is that the nitrogen-doped carbon nanotube layer is replaced with a conventional carbon nanotube layer; all other conditions and parameters are exactly the same as in Example 1.

[0149] Performance testing:

[0150] Solid-state battery fabrication and performance testing

[0151] 1. Battery manufacturing

[0152] The lithium-rich manganese-based cathode materials of the examples and comparative examples were placed in solid-state battery molds respectively; then a certain amount of electrolyte was weighed into the solid-state battery mold containing the cathode; then, using a lithium metal electrode sheet as the cathode, a 50μm thick lithium metal strip was die-cut to obtain a cathode electrode sheet, which was placed in the solid-state battery mold containing the cathode and sulfide electrolyte; finally, the cathode, solid electrolyte membrane, and cathode were stacked, and the battery mold was pressurized with 4t pressure to assemble an all-solid-state battery.

[0153] 2. Performance Testing

[0154] The performance of the prepared solid-state battery was tested:

[0155] (a) Initial discharge capacity, initial efficiency and rate capability: The solid-state batteries of the examples and comparative examples were clamped on the Blue Electric Charge-Discharge Tester and constant current charge-discharge test was performed. The charge-discharge voltage was 2.5-4.8V and the current density was 0.1C to obtain the initial discharge capacity and initial efficiency. Then, the charge-discharge test was performed at a current density of 5C to obtain the discharge capacity ratio of 5C / 0.1C.

[0156] (b) Cyclic performance: The solid-state batteries of the examples and comparative examples were clamped on the Blue Electric Charge-Discharge Tester and constant current charge-discharge test was performed. The charge-discharge voltage was 2.5-4.8V and the current density was 1C / 5C. The capacity retention rate and voltage decay value after 500 cycles were obtained.

[0157] (c) Storage: The solid-state batteries of the examples and comparative examples were stored at 60°C for 7 days, and the capacity loss rate was calculated.

[0158] (d) Interface impedance and internal resistance: The battery interface impedance and internal resistance are obtained using the AC impedance method (EIS) and the DC internal resistance method (DCR).

[0159] The test results are shown in Table 1:

[0160] Table 1

[0161]

[0162] As shown in Table 1, and based on Examples 1-11, the solid-state battery prepared from the lithium-rich manganese-based cathode material of this invention exhibits a first discharge capacity of over 258 mAh / g at 0.1C, a first coulombic efficiency of over 84.2%, a capacity retention rate of over 77.5% after 1000 cycles at 1C, a 5C capacity / 0.1C capacity ratio of over 75.8%, and a cathode-electrolyte interface impedance of over 512 Ω·cm. 2Within this range, the capacity loss after 7 days of storage at 60℃ can be less than 8.8%. The parameters of each coating layer need to find a balance between "performance improvement" and "active material ratio". For example, when the mass fraction of the LLZTO layer is increased from 8% to 15%, although the interfacial impedance is slightly reduced, the reduction in the proportion of active material leads to a decrease in the first discharge capacity, which is not conducive to improving the battery energy density. Similarly, when the mass fraction of the nitrogen-doped carbon nanotube layer is too high, the capacity performance will also be sacrificed due to the reduction in the proportion of active material.

[0163] A comparison of Examples 1 and 4-5 shows that the molar ratio of Li3NbO4 to Li5TaO5 in the composite oxide layer of the lithium-rich manganese-based cathode material of the present invention affects its performance. When the molar ratio of Li3NbO4 to Li5TaO5 in the composite oxide layer is controlled at 1:(0.5~2), the performance of the lithium-rich manganese-based cathode material is better. If the proportion of Li3NbO4 is too high, the content of Li5TaO5 is insufficient, the synergistic effect of the Nb / Ta-O bonds formed by the two is significantly weakened, the ability to inhibit oxygen loss from the lithium-rich manganese-based core decreases, and the side reactions at the cathode-electrolyte interface are aggravated, resulting in an interface impedance that decreases from 182 Ω / cm in Example 1. 2 Increased to 265Ω / cm 2 After 1000 cycles at 1C, the capacity retention rate decreases by 3.3 percentage points, and the rate performance also degrades. If the proportion of Li3NbO4 is too low, the effect is essentially the same as if the proportion of Li3NbO4 is too high. The ionic conductivity of the composite oxide layer decreases, the transport of lithium ions at the interface is hindered, and the cycle stability and rate performance of the battery both deteriorate significantly.

[0164] A comparison of Examples 1 and 6-7 shows that the thickness of the composite oxide layer in the lithium-rich manganese-based cathode material of the present invention affects its performance. When the thickness of the composite oxide layer is controlled between 5 nm and 15 nm, the performance of the lithium-rich manganese-based cathode material is better. If the thickness of the composite oxide layer is too thick (e.g., 20 nm in Example 7), the transport path of lithium ions inside the cathode material is prolonged, increasing the charge transfer resistance and causing the cathode-electrolyte interface impedance to decrease from 182 Ω / cm in Example 1. 2 Increased to 356Ω / cm 2 Meanwhile, the thick coating layer will reduce the space occupied by the active material, causing the 5C / 0.1C capacity ratio to drop to 78.3%, and the capacity retention rate after 1000 cycles at 1C to decrease by 6.4 percentage points. If the thickness of the composite oxide layer is too thin (such as 2nm in Example 6), the coating layer will be difficult to form a continuous and dense protective film. The lithium-rich manganese-based core will directly contact the subsequent coating layer and the solid electrolyte, causing interfacial side reactions and accelerating oxygen loss, resulting in an interfacial impedance of 298Ω / cm. 2 During the cycle, the risk of particle cracking increases, and both capacity retention and rate performance deteriorate significantly.

[0165] A comparison of Examples 1 and 8-9 shows that the mass percentage of nitrogen-doped carbon nanotubes in the lithium-rich manganese-based cathode material of the present invention affects its performance. When the mass percentage of nitrogen-doped carbon nanotubes is controlled at 1%~3%, the performance of the lithium-rich manganese-based cathode material is better. If the mass fraction of nitrogen-doped carbon nanotubes is too high (e.g., 5% in Example 9), it will significantly reduce the space occupied by the lithium-rich manganese-based active material, causing the 0.1C initial discharge capacity to decrease from 296 mAh / g in Example 1 to 262 mAh / g, and the initial coulombic efficiency to decrease by 5.9 percentage points. Simultaneously, excessive carbon nanotubes will increase interfacial side reaction sites, negating the improvement in cycle stability. If the mass fraction of nitrogen-doped carbon nanotubes is too low (e.g., 0.5% in Example 8), a continuous electron conduction network cannot be constructed on the cathode material surface, resulting in a sharp increase in electron transfer resistance and a cathode-electrolyte interface impedance rising to 421 Ω / cm. 2 The 5C / 0.1C capacity ratio dropped to 75.8%, and the rate performance deteriorated significantly.

[0166] A comparison of Examples 1 and 10-11 shows that the mass percentage of the solid electrolyte nanoparticle layer in the lithium-rich manganese-based cathode material of the present invention affects its performance. Controlling the mass percentage of the nitrogen-doped carbon nanotube layer to 5%~10% results in better performance of the lithium-rich manganese-based cathode material. If the mass percentage of the solid electrolyte nanoparticle layer is too high (e.g., 15% in Example 11), it significantly compresses the space for the lithium-rich manganese-based active material, causing the 0.1C initial discharge capacity to decrease from 296 mAh / g in Example 1 to 258 mAh / g, the initial coulombic efficiency to decrease by 7.0 percentage points, and the battery energy density to decrease accordingly. If the mass percentage of the solid electrolyte nanoparticle layer is too low (e.g., 2% in Example 10), a continuous and dense ion transport channel cannot be formed on the surface of the cathode material, hindering the migration of lithium ions at the cathode-electrolyte interface, causing the cathode-electrolyte interface impedance to surge to 512 Ω / cm. 2 After 7 days of storage at 60℃, the capacity loss rate increased to 8.8%, and both cycle stability and high-temperature storage performance showed significant deterioration.

[0167] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, the present invention uses a composite oxide layer of Li3NbO4 and Li5TaO5. Through the formation of strong Nb / Ta-O bonds (bond energy > 532 kJ / mol), Li3NbO4 and Li5TaO5 can synergistically enhance the Li... + Improve the transport efficiency at the cathode / electrolyte interface, reduce interfacial impedance, enhance cycle stability, and suppress oxygen loss under high voltage.

[0168] As can be seen from the comparison between Example 1 and Comparative Example 3, the present invention uses nitrogen-doped carbon nanotubes. The nitrogen element in the nitrogen-doped carbon nanotube layer is mainly in the form of pyridine nitrogen, with the proportion of pyridine nitrogen >60%. Pyridine nitrogen sites provide more lithium adsorption sites, thereby reducing electron transfer resistance, improving the rate performance of the cathode, enhancing structural integrity, and reducing particle cracking.

[0169] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, The lithium-rich manganese-based cathode material comprises a lithium-rich manganese-based core and a composite oxide layer, a nitrogen-doped carbon nanotube layer, and a solid electrolyte nanoparticle layer sequentially coated on the surface of the lithium-rich manganese-based core.

2. The lithium-rich manganese-based cathode material as described in claim 1, characterized in that, The chemical formula of the lithium-rich manganese-based core is Li 1.2+α Ni x Co y Mn z O 2+δ , where 0≤α≤0.3, 0.1≤x≤0.3, 0≤y≤0.2, 0.5≤z≤0.7, -0.1≤δ≤0.1, and x+y+z=1; Preferably, the median particle size D50 of the lithium-rich manganese-based core is 3 μm to 8 μm; Preferably, the specific surface area of ​​the lithium-rich manganese-based core is 1 m². 2 / g~3m 2 / g.

3. The lithium-rich manganese-based cathode material as described in claim 1 or 2, characterized in that, The materials of the composite oxide layer include Li3NbO4 and Li5TaO5; Preferably, the molar ratio of Li3NbO4 to Li5TaO5 in the composite oxide layer is 1:(0.5~2); Preferably, the thickness of the composite oxide layer is 5 nm to 15 nm.

4. The lithium-rich manganese-based cathode material according to any one of claims 1-3, characterized in that, The diameter of the carbon nanotubes in the nitrogen-doped carbon nanotube layer is 10 nm to 30 nm. Preferably, with the total number of atoms in the nitrogen-doped carbon nanotube layer being 100%, the percentage of nitrogen atoms is 1% to 5%. Preferably, the defect density of the nitrogen-doped carbon nanotube layer is 0.2 defects / nm. 2 ~0.8 per nm 2 ; Preferably, based on the mass of the lithium-rich manganese-based cathode material as 100%, the mass fraction of the nitrogen-doped carbon nanotube layer is 1% to 3%.

5. The lithium-rich manganese-based cathode material according to any one of claims 1-4, characterized in that, The material of the solid electrolyte nanoparticle layer includes LLZTO; Preferably, the median particle size D50 of the solid electrolyte nanoparticles in the solid electrolyte nanoparticle layer is 20 nm to 50 nm. Preferably, based on the mass of the lithium-rich manganese-based cathode material as 100%, the mass fraction of the solid electrolyte nanoparticle layer is 5% to 10%.

6. The lithium-rich manganese-based cathode material according to any one of claims 1-5, characterized in that, A lithium vacancy buffer layer is also provided between the lithium-rich manganese-based core and the composite oxide layer. Preferably, the material of the lithium vacancy buffer layer includes Li 1-x Al x O2 and / or Li 3-y La y NbO4, where 0.05≤x≤0.15, 0.02≤y≤0.08; Preferably, the lithium vacancy concentration of the lithium vacancy buffer layer is 2% to 15%; Preferably, the thickness of the lithium vacancy buffer layer is 1 nm to 3 nm.

7. A method for preparing a lithium-rich manganese-based cathode material as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: A lithium-rich manganese-based precursor is mixed with a lithium source and subjected to a first sintering treatment to obtain a sintered material. The first-burned material, niobium source, and tantalum source are mixed and subjected to a second sintering process to obtain the second-burned material; The sintered material, nitrogen-doped carbon nanotubes, conductive carbon black and binder solution are mixed and spray-dried. The resulting spray-dried material is mixed with solid electrolyte and pressed into shape. The lithium-rich manganese-based cathode material is obtained by a third sintering process.

8. The preparation method according to claim 7, characterized in that, The total molar amount of metal ions in the lithium-rich manganese-based precursor and the molar ratio of lithium in the lithium source are 1:(1.45~1.55). Preferably, the atmosphere of the first sintering treatment includes oxygen; Preferably, the first sintering process includes a first-stage calcination and a second-stage calcination; Preferably, the calcination temperature of the first stage is 500℃~600℃; Preferably, the calcination time is 4h to 6h; Preferably, the temperature of the second-stage calcination is 800℃~900℃; Preferably, the calcination time for the two stages is 10h to 15h; Preferably, the niobium source comprises niobium pentaethoxy; Preferably, the tantalum source comprises tantalum pentaethoxylate; Preferably, based on the mass of the sintered material as 100%, the total addition amount of the niobium source and tantalum source is 0.75%~2.5%; Preferably, ethanol is added during the ball milling process of mixing the calcined material, niobium source, and tantalum source; Preferably, the atmosphere for the second sintering treatment includes argon; Preferably, the temperature of the second sintering treatment is 400℃~500℃; Preferably, the second sintering treatment time is 4h~8h; Preferably, the nitrogen-doped carbon nanotubes are prepared by treating carbon nanotubes with ammonia plasma. Preferably, the mass ratio of the nitrogen-doped carbon nanotubes to the conductive carbon black is (1.5~2.5):1; Preferably, the adhesive solution comprises a PVDF NMP solution with a mass percentage concentration of 2% to 4%; Preferably, the method of mixing the obtained spray-dried material with the solid electrolyte includes dry ball milling; Preferably, the grinding speed of the dry ball mill is 200 rpm to 400 rpm; Preferably, the dry ball milling time is 2h to 6h; Preferably, the pressing pressure is 200MPa~400MPa; Preferably, the temperature of the third sintering treatment is 200℃~300℃; Preferably, the third sintering treatment takes 1 to 3 hours.

9. A positive electrode sheet, characterized in that, The positive electrode comprises the lithium-rich manganese-based positive electrode material as described in any one of the claims.

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

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