Carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface and preparation method thereof

Abstract

The present invention aims to provide a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on its surface and a preparation method thereof. The chemical formula of the carbon-coated lithium-rich manganese-based cathode material is: (1-b)Li 1+(1‑2x) / 3 Ni x‑2 / yCoyMn(2‑x) / 3‑2 / y O 2 •bC. Using carbon materials as crystal seeds and manganese and nickel salt solutions as the bottom liquid, it includes the preparation of the precursor and the preparation of the carbon-coated lithium-rich manganese-based cathode material. The prepared carbon-coated lithium-rich manganese-based cathode material has a high discharge specific capacity, and the cycle capacity retention rate reaches over 90%. The material exhibits excellent capacity performance and stable cycle performance, improving the market competitiveness of the product.

Description

Technical Field:

[0002] The present invention relates to the field of new lithium - ion energy materials, mainly to lithium - rich manganese - based cathode materials and their preparation methods, especially a carbon - coated lithium - rich manganese - based cathode material with a spinel phase on the surface and its preparation method. Background Art:

[0004] As countries increase their efforts in the development of new energy; in response to the current requirements of "carbon peak and carbon neutrality", it is of great significance to promote the development of energy to rapidly transition from fossil energy to new energy, get rid of the excessive dependence on petrochemical energy, alleviate energy crises and environmental protection problems, and ensure energy security.

[0005] Lithium manganate has advantages such as high voltage, good safety, rich resources, and low pollution, and is one of the most promising cathode materials. However, lithium manganate or spinel lithium manganate has a rapid capacity decay at high temperatures, severely limiting its practical applications in new - energy vehicle power batteries and other fields. Existing technologies generally improve the high - temperature cycle performance of spinel lithium manganate by doping to stabilize the crystal structure of lithium manganate and surface coating to inhibit the dissolution of manganese on the crystal surface. When the doping amount of the doping element is low, the improvement of the high - temperature cycle performance is limited, while a higher doping amount will reduce its specific capacity.

[0006] For example, Chinese Patent Publication No. CN102583565A, "A Preparation Method of Spinel - Type Lithium Manganate", includes: a) providing a roasting promoter loaded with a lithium - source compound and a manganese - source compound; b) placing the roasting promoter on a hearth plate and feeding it into a roller hearth kiln for roasting; the roller hearth kiln at least includes: a heating cavity and a roller hearth arranged below the heating cavity; the roller hearth consists of a number of heating rollers driven by motors; the roller hearth and the heating cavity are divided into a pre - heating zone, a heating zone, and a cooling zone. The preparation method provided by the present invention can carry out continuous reactions for a long time, improve production efficiency, and at the same time, improve the performance of spinel lithium manganate.

[0007] Chinese Patent Publication No. CN101807682A discloses "A Power - Type Spinel Lithium Manganate Cathode Material and Its Preparation Method", which specifically discloses a power - type spinel lithium manganate cathode material and its preparation method. The power - type spinel lithium manganate cathode material is composed of power - type spinel lithium manganate Li a Mn 2-x-z Nb x Al y M z O 4It consists of a lithium source, a manganese source, a niobium source, an aluminum source, a doping element M and a coating layer on its surface. The preparation method is to ball-mill and mix the treated lithium source, manganese source, niobium source, aluminum source and doping element M, and then calcine at a temperature of 550-900 °C; after the calcined preliminary product is crushed and classified, a coating material is added and secondary calcination is carried out at a temperature of 750-950 °C, and the power-type spinel lithium manganate cathode material is obtained after crushing and classification. The spinel lithium manganate material provided by the present invention has a very high tap density and specific capacity, and has good cycle performance in both normal temperature and high temperature environments, with stable performance and good consistency.

[0008] Another example is the "A Coated Lithium Manganate Cathode Material, Its Preparation Method and Lithium Ion Battery" disclosed in Chinese Patent Publication No. CNCN110137457A. The specific coated lithium manganate cathode material includes LiMn 2 O 4 and a coating layer with the chemical formula AB 2 O 4 . AB 2 O 4 is an inverse spinel material, A is a divalent metal element, and B is a trivalent metal element. The present invention also provides a preparation method for the cathode material, including the following steps: mixing, sintering and cooling a compound of transition metal Mn and a lithium-containing compound to obtain LiMn 2 O 4 , and then mixing, roasting and cooling with an additive containing element A and element B to obtain a coated spinel lithium manganate cathode material. The coated lithium manganate cathode material provided by the present invention has a stable inverse spinel coating layer, which can improve the structural stability of the material, inhibit the dissolution of manganese in the electrolyte and the Jahn-Teller effect of the material during charge and discharge, and can significantly improve the cycle performance of lithium ion batteries. It can be seen from the above disclosed technical solutions that none of them are carbon-coated lithium manganate products, and their performance still has deficiencies.

[0009] Another example is the "A Carbon-Coated Spinel Lithium Manganate Nanocomposite and Its Preparation Method" disclosed in Chinese Patent Publication CN107275606A. Specifically, through a one-step high-energy ball milling method, micron-scale spinel lithium manganate is crushed into nanoscale while the carbon material is uniformly coated on the surface of the nanoparticles. The application of nanoparticles shortens the ion diffusion and transmission path during charge and discharge of the material; while carbon coating improves the conductivity of the active material, it can also prevent direct contact between the lithium manganate cathode and the electrolyte, and can greatly improve the rate performance and cycle performance of lithium ion batteries and hybrid supercapacitors; since the coating layer has formed a conductive network, there is no need to additionally add a conductive agent in subsequent applications. However, this method only coats a layer of carbon material on its periphery, and there are still deficiencies in the performance modification of lithium manganate. At the same time, it uses a ball milling method, so its preparation method is still relatively complicated, and the raw materials used are required to be nanoscale. Therefore, the production cost of its products is higher, and so on.

[0010] Therefore, in view of the deficiencies in the prior art, how to provide a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface and a preparation method; using ordinary carbon materials as seeds and manganese, nickel salts, etc. as reaction solutions, so as to realize the synthesis of spinel lithium manganate that overcomes the problem of poor cycling performance under high-temperature environmental conditions, and realizes a large discharge specific capacity of lithium battery materials under high-temperature conditions, such as greater than 120 mAh / g, a cycle capacity retention rate of greater than 90% after 100 cycles, stable cycling performance, and the synthesis method has the advantages of carbon coating on both the precursor and the prepared carbon-coated lithium-rich manganese-based cathode material, convenient synthesis, and suitability for industrial production. Summary of the Invention:

[0012] The object of the present invention is to provide a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface and a preparation method. The chemical formula of the carbon-coated lithium-rich manganese-based cathode material is: (1 - b)Li 1+(1-2x) / 3 Ni x-2 / yCoyMn(2-x) / 3-2 / y O 2 •bC; using carbon materials as seeds and manganese, nickel salt solutions as the bottom liquid, including the preparation of the precursor and the preparation of the carbon-coated lithium-rich manganese-based cathode material. The prepared carbon-coated lithium-rich manganese-based cathode material has a high discharge specific capacity and a cycle capacity retention rate of more than 90%, excellent capacity performance of the material, and stable cycling performance; improving the market competitiveness of the product.

[0013] One object of the present invention is to provide a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface, and its chemical formula is: (1 - b)Li 1+(1-2x) / 3 Ni x-2 / yCoyMn(2-x) / 3-2 / y O 2 •bC;

[0014] wherein, x = 0 - 0.5, y = 0 - 1, b = 0.005 - 0.05.

[0015] For the carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface described in the present invention, the chemical formula of the precursor of the carbon-coated lithium-rich manganese-based cathode material is (1 - a)Ni x Co 1-x-y Mn y (OH) 2 •aC; controlling the content a value of carbon in the precursor to be 0.5% - 5.0%, wherein, x = 0 - 0.5, y = 0 - 1.

[0016] Another object of the present invention is to provide a preparation method of a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface, which specifically includes the following method steps:

[0017] 1) Preparation of the precursor,

[0018] a) Dispersion: Using carbon materials as seeds and manganese and nickel salt solutions as the base solution, place the base solution of manganese and nickel salt solutions in a reaction device, and evenly disperse the carbon material seeds in the reaction base solution to obtain a carbon material seed dispersion. b) Heating: Conduct a low-temperature heating reaction on the carbon material seed dispersion to obtain a heated seed dispersion. c) Preparation of the precursor: Drop nickel, cobalt, and manganese salt solutions and an alkali solution into the heated seed dispersion simultaneously, and continuously stir. Control the reaction under alkaline reaction solution conditions so that nickel cobalt manganese hydroxide formed during the reaction wraps the carbon materials in the reaction solution, forming a lithium-rich manganese-based material precursor with carbon in the particle center; the chemical formula of the lithium-rich manganese-based material precursor is (1 - a)Ni x Co 1-x-y Mn y (OH) 2 •aC;

[0019] 2) Preparation of the carbon-coated lithium-rich manganese-based cathode material

[0020] (1) Stirring and mixing for loading into a box: Place the lithium-rich manganese-based precursor with carbon in the particle center and lithium carbonate in a high-speed mixer according to the ratio for stirring and mixing to obtain a mixed ingredient, and load the material of the mixed ingredient into a box to obtain the box-loaded ingredient. (2) Roasting in a roller hearth kiln: Place the box-loaded ingredient in a roller hearth kiln for high-temperature roasting, control the roasting temperature at 850 - 1100 °C and keep it warm to obtain a lithium-rich manganese-based material, and then crush it to obtain a lithium-rich manganese-based powder material. (3) Carbon material coating: Add carbon materials to the lithium-rich manganese-based powder material for carbon material coating treatment to obtain a carbon material-coated material. (4) Secondary roasting: Place the carbon material-coated material obtained in step (3) in a roasting device furnace for roasting, control the roasting atmosphere in the roasting device furnace under reducing atmosphere conditions for roasting to form a small amount of spinel phase cathode material on the surface of the lithium-rich manganese-based material, and there is residual carbon material coated on the surface. After treatment, a lithium-rich manganese-based cathode material with carbon inside, carbon coating on the surface and spinel phase on the surface is prepared; the chemical formula of the lithium-rich manganese-based material is: (1 - b)Li 1+(1-2x) / 3 Ni x-2 / yCoyMn(2-x) / 3-2 / y O 2 •bC.

[0021] In the preparation method of a carbon-coated lithium-rich manganese-based cathode material with spinel phase on the surface according to the present invention, in step 1) the preparation of the precursor, in step a), the manganese and nickel salt solutions are manganese sulfate or nickel sulfate solutions or hydrated manganese sulfate or hydrated nickel sulfate solutions; the carbon material seeds are carbon black or conductive carbon black.

[0022] In the preparation method of a carbon-coated lithium-rich manganese-based cathode material with spinel phase on the surface, preferably, in step 1) the preparation of the precursor, in step b), control the low-temperature heating reaction temperature at 45 - 60 °C.

[0023] The preparation method of a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to the present invention, in step 1) of the preparation of the precursor, the chemical formula of the lithium-rich manganese-based material precursor in step c) is (1-a)Ni x Co 1-x-y Mn y (OH) 2 •aC; control the carbon content in the chemical formula of the precursor to be 0.5% - 5.0%; the alkaline reaction solution is a mixture of liquid caustic soda with a mass concentration of 25 - 35 wt% and ammonia water with a mass concentration of 15 - 25 wt%; under the condition of the alkaline reaction solution, control the pH value = 11.0 - 11.5.

[0024] For the preparation method of a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface, in step (1) of the preparation of the carbon-coated lithium-rich manganese-based cathode material, control the stirring and mixing time to be 20 - 35 minutes; in step (2), the roller hearth kiln roasting and firing is to control the heat preservation time to be 10 - 25 hours.

[0025] For the preparation method of a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface, in step (3) of carbon material coating, place the lithium-rich manganese-based powder material in a coating device, add carbon material, and then add pure water for coating treatment. Control the carbon material coating amount to be 0.5% - 5.0%. After the coating is completed, perform filtration and dehydration treatment, and then perform roasting after dehydration.

[0026] For the preparation method of a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface, in step (4), the reducing atmosphere condition is that when performing secondary roasting in the roasting device furnace, fill the roasting device furnace with nitrogen or inert gas and control the oxygen content during roasting, so that roasting is carried out under the reducing atmosphere condition, and ensure that the manganese on the surface layer of the lithium-rich manganese-based powder material is reduced to trivalent manganese by the carbon material coated on the surface.

[0027] A carbon-coated lithium-rich manganese-based cathode material and a preparation method disclosed by the present invention have the following outstanding advantages compared with the prior art processes:

[0028] The carbon-coated lithium-rich manganese-based cathode material prepared by the method of the present invention uses ordinary carbon materials such as conductive carbon black as seeds, and two or three of nickel, cobalt, and manganese salt solutions as reaction solutions for reaction. It includes the preparation of a lithium-rich manganese-based precursor with carbon in the particle center and the preparation of a carbon-coated lithium-rich manganese-based cathode material by controlling the reduction inside and outside the particles. The prepared carbon-coated lithium-rich manganese-based cathode material has a structure with carbon inside and carbon coating on the surface layer, thus greatly improving the performance of the carbon-coated lithium-rich manganese-based cathode material. When it is applied to a button battery assembled with a cathode material, under the charge and discharge conditions of 2.0 - 4.8V and 0.1C, the discharge specific capacity is 252 mAh / g. Under the charge and discharge conditions of 2.0 - 4.7V and 1C, the discharge gram capacity is 210 mAh / g, and the capacity retention rate after 200 cycles is 92.3%. The cathode material prepared by the present invention has excellent gram capacity performance and stable cycle performance. Compared with the carbon-free coated lithium battery cathode material of the prior art, its capacity retention rate is nearly 20% higher. Moreover, the preparation process is simple and the production cost is low.

[0029] Detected by relevant departments, when the carbon-coated lithium-rich manganese-based cathode material prepared by the method of the present invention is applied to a button battery assembled with a cathode material and tested in the voltage range of 2.5 - 4.8V, the performance is as follows:

[0030] Total charge capacity: 361.5 mAh / g;

[0031] Initial efficiency: 69.7%;

[0032] Discharge gram capacity at 0.1C: 252.1 mAh / g;

[0033] Discharge gram capacity at 0.33C: 230.1 mAh / g;

[0034] D50: 6.9 μm;

[0035] D90: 12.9 μm;

[0036] Ambient temperature: 26.8 °C;

[0037] Capacity retention rate after 200 cycles: 92.3%.

[0038] Storage and transportation conditions of the product prepared by the present invention: cool, dry, moisture-proof, and humidity-proof. Description of the drawings:

[0040] Figure 1 As shown, it is an electron microscope image of the carbon-coated lithium-rich manganese-based cathode material prepared by the present invention with WD = 8.5 mm and Mag = 15.0KX;

[0041] Figure 2 As shown, it is an electron microscope image of the carbon-coated lithium-rich manganese-based cathode material prepared by the present invention with WD = 8.5 mm and Mag = 5.0KX;

[0042] Figure 3 As shown, it is the electron microscope image of the carbon-coated lithium-rich manganese-based cathode material WD8.5mm prepared by the present invention at Mag = 10.0KX;

[0043] Figure 4 As shown, it is the XRD pattern of the carbon-coated lithium-rich manganese-based cathode material prepared by the present invention;

[0044] Figure 5 As shown, it is the first charge-discharge curve of the button cell made of the carbon-coated lithium-rich manganese-based cathode material prepared by the invention. Specific embodiments:

[0046] The following further details the present invention according to a specific corresponding embodiment and the accompanying drawings, by mass ratio or parts by mass.

[0047] A carbon-coated lithium-rich manganese-based cathode material and a preparation method thereof disclosed by the present invention, the prepared carbon-coated lithium-rich manganese-based cathode material has the chemical formula: (1 - b)Li 1+(1-2x) / 3 Ni x-2 / yCoyMn(2-x) / 3-2 / y O 2 •bC;

[0048] wherein, x = 0 - 0.5, y = 0 - 1, b = 0.005 - 0.05;

[0049] For a carbon-coated lithium-rich manganese-based cathode material of the present invention, the chemical formula of the precursor of the carbon-coated lithium-rich manganese-based cathode material is (1 - a)Ni x Co 1-x-y Mn y (OH) 2 •aC; controlling the content a value of carbon in the precursor to be 0.5% - 5.0%,

[0050] wherein, x = 0 - 0.5, y = 0 - 1.

[0051] Another object of the present invention is a preparation method of the carbon-coated lithium-rich manganese-based cathode material, which includes the following method steps:

[0052] 1) Preparation of the precursor,

[0053] a) Dispersion: Using carbon materials as seeds and manganese and nickel salt solutions as the bottom liquid. Place the bottom liquid of the manganese and nickel salt solutions in a reaction device, and evenly disperse the carbon material seeds in the reaction bottom liquid. The manganese and nickel salt solutions are manganese sulfate or nickel sulfate solutions, or hydrated manganese sulfate or hydrated nickel sulfate solutions. The carbon material seeds are carbon black or conductive carbon black, forming a carbon material seed dispersion liquid. b) Heating: Conduct a low-temperature heating reaction on the carbon material seed dispersion liquid, controlling the low-temperature heating reaction temperature at 45 - 60 °C to heat the seed dispersion liquid. c) Preparation of the precursor: Simultaneously drop nickel, cobalt, and manganese salt solutions and an alkali solution into the heated seed dispersion liquid, and continuously stir. Control the reaction to occur under alkaline reaction liquid conditions, so that nickel cobalt manganese hydroxide formed during the reaction wraps the carbon materials in the reaction liquid, forming a lithium-rich manganese-based material precursor with carbon in the center of the particles. The chemical formula of the lithium-rich manganese-based material precursor is (1 - a)Ni x Co 1-x-y Mn y (OH) 2 •aC; Control the carbon content in the chemical formula of this precursor to be 0.5% - 5.0%. The alkaline reaction liquid is a mixture of liquid caustic soda with a mass concentration of 25 - 35 wt% and ammonia water with a mass concentration of 15 - 25 wt%. The alkaline reaction liquid has a controlled pH value of 11.0 - 11.5;

[0054] 2) Preparation of the carbon-coated lithium-rich manganese-based cathode material

[0055] (1) Stir and mix for potting. Place the lithium-rich manganese-based precursor with carbon in the center of the particles and lithium carbonate in proportion in a high-speed mixer for stirring and mixing to obtain a mixed ingredient. Control the stirring and mixing time for 20 - 35 minutes. Load the material of the mixed ingredient into a sagger to obtain the sagger-loaded ingredient. (2) Roast in a roller hearth kiln. Place the material about to be sagger-loaded ingredient in a roller hearth kiln for high-temperature roasting. Control the roasting temperature in the roller hearth kiln to be 850 - 1100 °C and the heat preservation time to be 10 - 25 hours to obtain a lithium-rich manganese-based material. After pulverization, obtain a lithium-rich manganese-based powder material. (3) Coating with carbon material. Add carbon material to the lithium-rich manganese-based powder material for coating treatment with carbon material. Place the lithium-rich manganese-based powder material in a coating device, add carbon material, and then add pure water for coating treatment. Control the carbon material coating amount to be 0.5% - 5.0%. After coating, perform filtration and dehydration treatment. After dehydration, perform roasting to obtain the carbon material-coated material. (4) Secondary firing. Place the carbon material-coated material obtained in step (3) in a roasting device furnace for roasting. Control the roasting atmosphere in the roasting device furnace to perform roasting under a reducing atmosphere condition. The reducing atmosphere condition is that when performing secondary roasting in the roasting device furnace, fill nitrogen (or other inert gases) into the roasting device furnace or control the oxygen content during baking to a certain value to perform roasting under a reducing atmosphere condition, and ensure that the manganese on the surface layer of the lithium-rich manganese-based powder material is reduced to trivalent manganese by the carbon material coated on the surface, forming a small part of spinel phase cathode material on the surface of the lithium-rich manganese-based material, and there is residual carbon material coated on the surface. After treatment, prepare a lithium-rich manganese-based cathode material with carbon inside, carbon-coated on the surface, and containing spinel phase on the surface. The chemical formula of the lithium-rich manganese-based material is: (1 - b)Li 1+(1-2x) / 3 Ni x-2 / yCoyMn(2-x) / 3-2 / y O 2 •bC.

[0056] Example 1

[0057] (1) Weigh 3862.8 g of manganese sulfate monohydrate (MnSO 4 •H 2 O) and 2000.8 g of nickel sulfate hexahydrate (Ni SO 4 •6H2O), dissolve them in pure water, and prepare a 20 L sulfate mixed solution with a concentration of 1.5 mol / L. Add 40 L of pure water and 54 g of conductive carbon black to a 50 L reaction kettle as the reaction bottom liquid. Heat the reaction kettle bottom liquid to 50 °C and stir it. Add the sulfate mixed solution, NaOH with a mass concentration of 32% of liquid alkali, and 20% ammonia water solution simultaneously into the reaction kettle at a certain feeding rate, and control the reaction pH value to be 11.2 to form a lithium-rich manganese-based material precursor with carbon material in the center. The obtained precursor is treated through processes such as washing, filtering, drying, sieving, and iron removal to obtain the required lithium-rich manganese-based material precursor. The chemical formula of this lithium-rich manganese-based material precursor is 0.98Ni0.25 Mn 0.75 (OH) 2 • 0.02C. Control the carbon content in the precursor to be 2%;

[0058] (2) Weigh 2000 grams of the precursor of the lithium-rich manganese-based material and 1472 grams of battery-grade lithium hydroxide, add them to a mixer, mix for 30 minutes. After mixing evenly, load the material into a sagger and place it in a kiln for firing. The firing temperature is 850 °C and the holding time is 20 hours. The fired material is processed through processes such as jaw crushing, pulverizing, and sieving to obtain 0.984Li of the lithium-rich manganese-based cathode material 1.2 Ni 0.2 Mn 0.6 O 2 • 0.016C. Weigh 2000 grams of the lithium-rich manganese-based cathode material and 20 grams of acetylene black material, add the materials to a coater, and add 20 L of pure water to make a slurry for coating treatment. The acetylene black material is evenly coated on the surface of the cathode material. After coating, filter and dehydrate the slurry, and place the material in a kiln for firing. Control the atmosphere and temperature to reduce the manganese on the surface layer of the lithium-rich manganese-based material to trivalent manganese, form a small part of spinel-phase cathode material on the surface of the lithium-rich manganese-based material, and there is residual carbon material coated on the surface. After the fired material is processed through processes such as crushing, sieving, and iron removal, a carbon-coated lithium-rich manganese-based cathode material containing carbon inside, coated with carbon on the surface, and containing spinel phase on the surface is finally prepared;

[0059] (3) Assemble the prepared cathode material into a coin cell. Under the charge and discharge conditions of 2.0 - 4.8V and 0.1C, the discharge specific capacity is 252 mAh / g, and under the conditions of 2.0 - 4.7V and 1C discharge, the gram capacity is 210 mAh / g, and the capacity retention rate after 200 cycles is 92.8%; the material has excellent capacity performance and stable cycle performance.

[0060] Example 2

[0061] (1) Weigh 3862.8 g of manganese sulfate monohydrate (MnSO 4 •H 2 O), nickel sulfate hexahydrate (Ni SO 4•2000.8 g of (6H₂O) is dissolved in pure water to prepare 20 L of a 1.5 mol / L mixed sulfate solution. 40 L of pure water and 27 g of conductive carbon black are added to a 50 L reactor as the reaction bottom liquid. The bottom liquid of the reactor is heated to 50 °C and stirred. The mixed sulfate solution, liquid alkali (32% NaOH content), and ammonia water (20%) are simultaneously added to the reactor at a certain feeding rate, and the reaction pH value is controlled at 11.2 to form a lithium-rich manganese-based material precursor with a carbon material in the center. The precursor meeting the indicators is treated through processes such as washing, filtering, drying, sieving, and iron removal to obtain the required lithium-rich manganese-based material precursor. The chemical formula of this lithium-rich manganese-based material precursor is 0.99Ni 0.25 Mn 0.75 (OH) 2 •0.01C. The carbon content in this precursor is 1%;

[0062] (2) Weigh 2000 g of the lithium-rich manganese-based material precursor and 1291 g of battery-grade lithium carbonate, add them to a mixer, mix for 30 minutes. After mixing evenly, load the material into a crucible and place it in a kiln for firing. The firing temperature is 850 °C and the heat preservation time is 20 hours. The fired material is processed through processes such as jaw crushing, pulverizing, and sieving to obtain a lithium-rich manganese-based cathode material 0.992Li 1.2 Ni 0.2 Mn 0.6 O 2 •0.008C. Weigh 2000 g of the lithium-rich manganese-based cathode material and 40 g of acetylene black material, add the materials to a coater, and add 20 L of pure water to make a slurry for coating treatment. The acetylene black material is evenly coated on the surface of the cathode material. After coating is completed, the slurry is filtered and dehydrated, and the material is placed in a kiln for firing. Control the atmosphere and temperature well to reduce the manganese on the surface layer of the lithium-rich manganese-based material to trivalent manganese, form a small part of spinel-phase cathode material on the surface of the lithium-rich manganese-based material, and there is residual carbon material on the surface. After the fired material is processed through processes such as crushing, sieving, and iron removal, a carbon-coated lithium-rich manganese-based cathode material with carbon inside, carbon-coated on the surface, and spinel phase on the surface is finally prepared, which has high-performance characteristics;

[0063] (3) Assemble the prepared cathode material into a coin cell. Under the charge-discharge conditions of 2.0 - 4.8 V and 0.1C, the discharge specific capacity is 248 mAh / g. Under the conditions of 2.0 - 4.7 V and 1C discharge, the gram capacity is 202 mAh / g, and the capacity retention rate after 200 cycles is 91.9%. The material has excellent capacity performance and stable cycling performance.

[0064] Compared with the lithium-rich manganese-based material without carbon coating, the performance of this material has been significantly improved. The specific capacity has increased by 28 mAh / g, the rate performance has been significantly improved, the specific capacity at 1C discharge has increased by 43 mAh / g, and the cycling performance has also been significantly improved, with the capacity retention rate increasing by 20.7% after 200 cycles.

[0065] Comparative Example 1

[0066] This comparative example is to prepare the cathode material Li of the carbon-free lithium-rich manganese-based material 1.2 Ni 0.2 Mn 0.6 O 2 ;

[0067] (1) Weigh 3862.8 g of manganese sulfate monohydrate (MnSO 4 •H 2 O) and 2000.8 g of nickel sulfate hexahydrate (Ni SO 4 •6H2O), dissolve them in pure water, and prepare a 20 L sulfate mixed solution with a concentration of 1.5 mol / L. Add 40 L of pure water to a 50 L reaction kettle as the reaction bottom liquid. Heat the reaction kettle bottom liquid to 50 °C and stir it. Add the sulfate mixed solution, liquid alkali (32% NaOH content), and ammonia water (20%) into the reaction kettle simultaneously at a certain feeding rate, and control the reaction pH value to be 11.2. The obtained precursor is treated through washing, filtering, drying, sieving, iron removal and other processes to obtain the required lithium-rich manganese-based material precursor. The chemical formula of this lithium-rich manganese-based material precursor is Ni 0.25 Mn 0.75 (OH) 2 . There is no carbon in this precursor.

[0068] (2) Weigh 2000 g of the lithium-rich manganese-based material precursor and 1291 g of battery-grade lithium carbonate, add them to a mixer, mix for 30 minutes. After mixing evenly, load the material into a crucible and place it in a kiln for firing. The firing temperature is 850 °C and the holding time is 20 hours. The fired material is treated through jaw crushing, pulverizing, sieving and other processes to obtain the cathode material Li of the lithium-rich manganese-based material 1.2 Ni 0.2 Mn 0.6 O 2 .

[0069] (3) Assemble the prepared cathode material into a coin cell. Under the charge-discharge conditions of 2.0 - 4.8 V and 0.1C, the discharge specific capacity is 220 mAh / g. Under the charge-discharge conditions of 2.0 - 4.7 V and 1C, the specific capacity at discharge is 159 mAh / g, and the capacity retention rate after 200 cycles is 70.3%.

[0070] Comparative Example 2

[0071] This comparative example is to prepare a lithium-rich manganese-based cathode material with carbon in the center of the particles and without carbon coating on the surface;

[0072] (1)Weigh 3862.8 g of manganese sulfate monohydrate (MnSO 4 •H 2 O) and 2000.8 g of nickel sulfate hexahydrate (NiSO 4 •6H2O), dissolve them in pure water, and prepare a 20 L sulfate mixed solution with a concentration of 1.5 mol / L. Add 40 L of pure water and 27 g of conductive carbon black to a 50 L reactor as the reaction bottom liquid. Heat the reactor bottom liquid to 50 °C and stir it. Add the sulfate mixed solution, liquid alkali (with 32% NaOH content), and ammonia water (20%) into the reactor simultaneously at a certain feeding rate, and control the reaction pH value to 11.2 to form a lithium-rich manganese-based material precursor with carbon in the center. The obtained precursor meeting the requirements is processed through washing, filtering, drying, sieving, iron removal and other processes to obtain the required lithium-rich manganese-based material precursor. The chemical formula of this lithium-rich manganese-based material precursor is 0.99Ni 0.25 Mn 0.75 (OH) 2 •0.01C. The carbon content in this precursor is 1%.

[0073] (2)Weigh 2000 g of the lithium-rich manganese-based material precursor and 1291 g of battery-grade lithium carbonate, add them to a mixer, mix for 30 minutes. After mixing evenly, load the material into a crucible and place it in a kiln for firing. The firing temperature is 850 °C and the holding time is 20 hours. The fired material is processed through jaw crushing, pulverizing, sieving and other processes to obtain the lithium-rich manganese-based cathode material 0.992Li 1.2 Ni 0.2 Mn 0.6 O 2 •0.008C.

[0074] (3)Assemble the prepared cathode material into a coin cell. Under the charge-discharge conditions of 2.0 - 4.8 V and 0.1C, the discharge specific capacity is 228 mAh / g. Under the conditions of 2.0 - 4.7 V and 1C discharge, the discharge gram capacity is 175 mAh / g, and the capacity retention rate after 200 cycles is 79.6%. Compared with the lithium-rich manganese-based material without carbon coating, the gram capacity is increased by 8 mAh / g, the rate performance is significantly improved, the 1C discharge gram capacity is increased by 16 mAh / g, and the cycling performance is also significantly improved. The 200-cycle capacity retention rate is increased by 9.3%; there is still a certain gap compared with the material in Example 2.

[0075] Comparative Example 3

[0076] (1)Weigh manganese sulfate monohydrate (MnSO 4 •H2 O) 3862.8 g of nickel sulfate hexahydrate (NiSO 4 •6H 2 O) 2000.8 g was dissolved in pure water to prepare 20 L of a 1.5 mol / L sulfate mixed solution. 40 L of pure water was added to a 50 L reactor as the reaction bottom liquid. The reaction bottom liquid in the reactor was heated to 50 °C and stirred. The sulfate mixed solution, liquid alkali (32% NaOH content), and ammonia water (20%) were simultaneously added to the reactor at a certain feeding rate, and the reaction pH value was controlled at 11.2. The precursor that met the index was treated through processes such as washing, filtering, drying, sieving, and iron removal to obtain the required lithium-rich manganese-based material precursor. The chemical formula of this lithium-rich manganese-based material precursor is Ni 0.25 Mn 0.75 (OH) 2 . There is no carbon in this precursor.

[0077] (2) Weigh 2000 grams of the lithium-rich manganese-based material precursor and 1291 grams of battery-grade lithium carbonate, add them to a mixer, and mix for 30 minutes. After mixing evenly, load the material into a crucible and place it in a kiln for firing. The firing temperature is 850 °C, and the holding time is 20 hours. The fired material is processed through processes such as jaw crushing, pulverizing, and sieving to obtain the lithium-rich manganese-based cathode material Li 1.2 Ni 0.2 Mn 0.6 O 2 . Weigh 2000 grams of the lithium-rich manganese-based cathode material and 40 grams of acetylene black material, add the materials to a coater, and add 20 L of pure water to make a slurry for coating treatment. The acetylene black material is evenly coated on the surface of the cathode material. After coating is completed, the slurry is filtered and dehydrated, and the material is placed in a kiln for firing. Control the atmosphere and temperature well to reduce the manganese on the surface layer of the lithium-rich manganese-based material to trivalent manganese, form a small part of spinel-phase cathode material on the surface of the lithium-rich manganese-based material, and there is residual carbon material coated on the surface. After the fired material is processed through processes such as crushing, sieving, and iron removal, a high-performance lithium-rich manganese-based cathode material with a carbon-coated surface and containing spinel phase on the surface is finally prepared.

[0078] (3) Assemble the prepared cathode material into a coin cell. Under the charge-discharge conditions of 2.0 - 4.8V and 0.1C, the discharge specific capacity is 231 mAh / g. Under the charge-discharge conditions of 2.0 - 4.7V and 1C, the discharge gram capacity is 182 mAh / g, and the capacity retention rate after 200 cycles is 81.5%. The material has excellent capacity performance and stable cycling performance. Compared with the lithium-rich manganese-based material without carbon coating, the performance is significantly improved. The gram capacity increases by 11 mAh / g, the rate performance is significantly improved, the discharge gram capacity at 1C increases by 23 mAh / g, and the cycling performance is also significantly improved. The capacity retention rate after 200 cycles increases by 11.2%. There is still a certain gap compared with the material in Example 2;

[0079] It can be seen from the comparison of the above examples with Comparative Documents 1 - 3 that the carbon-coated lithium-rich manganese-based cathode material has significantly better cycling performance than the uncoated carbon one.

[0080] The description is only an overview of the technical solution of the present invention and can be implemented according to the content of the specification. It is only a preferred embodiment and does not impose any formal limitation on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention or modify it into an equivalent embodiment with equivalent changes without departing from the scope of the technical solution of the present invention. Therefore, any changes, modifications, equivalent changes, and modifications made to the above embodiments based on the technology of the present invention without departing from the content of the technical solution of the present invention all fall within the protection scope of this technical solution.

Claims

1. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface, and its chemical formula is: ； Among them, x = 0 - 0.5, y = 0 - 1, b = 0.005 - 0.05; It is prepared according to the following method steps: 1) Preparation of the precursor, a) Dispersion: Using carbon materials as seeds and manganese and nickel salt solutions as the base solution. Place the base solution of manganese and nickel salt solutions in a reaction device, and uniformly disperse the carbon material seeds in the reaction base solution to obtain a carbon material seed dispersion liquid. b) Heating: Conduct a low-temperature heating reaction on the carbon material seed dispersion liquid to obtain a heated seed dispersion liquid. c) Preparation of precursor: Simultaneously drip nickel, cobalt, and manganese salt solutions and an alkali solution into the heated seed dispersion liquid, continuously stir, and control the reaction under alkaline reaction solution conditions, so that nickel cobalt manganese hydroxide formed during the reaction wraps the carbon materials in the reaction solution to form a lithium-rich manganese-based material precursor with carbon in the particle center; the chemical formula of the lithium-rich manganese-based material precursor is (1-a)Ni x Co 1-x-y Mn y (OH) 2 •aC; 2) Preparation of the carbon-coated lithium-rich manganese-based cathode material, (1) Stirring and mixing and loading into the sagger, placing the lithium-rich manganese-based precursor with carbon in the center of the particles and lithium carbonate according to the ratio in a high-speed mixer for stirring and mixing to form a mixed ingredient, and loading the material of the mixed ingredient into the sagger, which is the sagger-loading ingredient. (2) Roasting in a roller hearth kiln, placing the sagger-loading ingredient in the roller hearth kiln for high-temperature roasting, controlling the roasting temperature at 850 - 1100 °C and holding the temperature to obtain the lithium-rich manganese-based material, and pulverizing it to obtain the lithium-rich manganese-based powder material; (3) Carbon material coating: Add carbon material to the lithium-rich manganese-based powder material for carbon material coating treatment to obtain carbon material coated material; (4) Secondary firing: Place the carbon material coated material obtained in step (3) in the kiln of the roasting device for roasting, and control the roasting atmosphere in the roasting device furnace to carry out roasting under reducing atmosphere conditions, so as to form a small part of spinel phase cathode material on the surface of the lithium-rich manganese-based material, and there is residual carbon material coated on the surface. After treatment, a lithium-rich manganese-based cathode material with carbon inside, carbon coated on the surface and spinel phase on the surface is prepared; The chemical formula of the lithium-rich manganese-based cathode material is: (1-b)Li 1+(1-2x) / 3 Ni x-2 / y Co y Mn (2-x) / 3-2 / y O 2 •bC.

2. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are The precursor chemical formula of the carbon-coated lithium-rich manganese-based cathode material is (1-a)Ni x Co 1-x-y Mn y (OH) 2 •aC; the value of a, which controls the carbon content in the precursor, is 0.5% - 5.0%, where x = 0 - 0.5 and y = 0 - 1.

3. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are The manganese and nickel salt solutions in step 1) a) of the preparation of the precursor are manganese sulfate or nickel sulfate solution or hydrated manganese sulfate or hydrated nickel sulfate solution; the carbon material seed crystal is carbon black or conductive carbon black.

4. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are In step 1) b) of the preparation of the precursor, the low-temperature heating reaction temperature is controlled at 45 - 60 °C.

5. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are Step 1) The chemical formula of the lithium-rich manganese-based material precursor described in step c) of the preparation of the precursor is (1-a)Ni x Co 1-x-y Mn y (OH) 2 •aC; controlling the carbon content in the chemical formula of the precursor to be 0.5% - 5.0%; the basic reaction solution is a mixture of caustic soda with a mass concentration of 25 - 35 Wt% and ammonia water with a mass concentration of 15 - 25 Wt%; the pH value is controlled to be 11.0 - 11.5 under the conditions of the basic reaction solution.

6. A preparation method of a carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are In step (1) stirring and mixing and loading into the sagger, the stirring and mixing time is controlled at 20 - 35 minutes; in step (2) roasting in a roller hearth kiln, the holding time is controlled at 10 - 25 hours.

7. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are In step (3) carbon material coating, the lithium-rich manganese-based powder material is placed in a coating device, after adding the carbon material, pure water is added for coating treatment, the carbon material coating amount is controlled at 0.5% - 5.0%, after coating is completed, filtration and dehydration treatment are carried out, and after dehydration, roasting is carried out.

8. A carbon-coated lithium-rich manganese-based cathode material with a spinel phase on the surface according to claim 1, The characteristics are The reduction atmosphere condition in step (4) is that when secondary roasting is carried out in the roasting device furnace, nitrogen or inert gas is filled into the roasting device furnace and the oxygen content during roasting is controlled, so that roasting is carried out under the reduction atmosphere condition, and it is ensured that the manganese on the surface layer of the lithium-rich manganese-based powder material is reduced to trivalent manganese by the carbon material coated on the surface.

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