CN102694165A - High-capacity lithium-rich layered crystalline structured lithium battery cathode material and preparation thereof - Google Patents

Abstract

The invention discloses a high-capacity lithium-rich layered crystalline structured lithium battery cathode material, which is characterized in that a layer of LiNbO3 coats the particle surfaces of a powdery lithium-rich layered crystalline structured material, and the powdery lithium-rich layered crystalline structured material has a chemical formula xLi2MnO3.(1-x)LiNimConMn1-m-nO2, wherein x is more than or equal to 0.2 and less than or equal to 0.9, m is more than or equal to 0.1 and less than 1, and n is more than or equal to 0 and less than or equal to 0.5. A preparation method comprises the following steps of: first preparing a lithium-rich layered precursor, then preparing lithium-rich layered crystalline structured particles, and finally coating the particles by using the LiNbO3. The invention has the advantages that 1) the cathode material has high specific capacity, and the maximum specific capacity can reach 280mAh/g; 2) compared with an uncoated lithium-rich layered crystalline structured material, the lithium-rich layered crystalline structured material coated with the LiNbO3 has higher charge and discharge specific capacity and longer cycle life; and 3) the cathode material has high electrochemical performance under high voltage and high current density.

Description

A high-capacity lithium-rich layered crystal structure lithium battery cathode material and its preparation

technical field

The invention relates to the technical field of lithium-ion battery cathode materials, in particular to a high-capacity lithium-rich layered crystal structure lithium battery cathode material and its preparation.

Background technique

Since the first commercialization of Sony in 1991, lithium batteries have been widely used in 3C products such as mobile phones, digital cameras, and notebook computers, and play an important role in people's daily lives. Due to the advantages of high power density, high energy density, and high cycle performance, lithium batteries have become the preferred battery for electric vehicles. With the continuous reduction of international non-renewable energy reserves and the deepening of environmental pollution, the research on batteries for electric vehicles, especially lithium batteries, has attracted much attention. As far as the current situation is concerned, the research on anode materials for lithium batteries lags behind that of anode materials. Both in theory and in practical applications, the capacity of anode materials used is lower than that of anode materials, and the power batteries required for electric vehicles Both power density and energy density are required, so the research and development of high-performance lithium battery cathode materials has become the key to the development of power batteries. Among them, the earliest commercialized lithium cobalt oxide has the most mature production process and good cycle life, but the tetravalent cobalt formed after charging has strong oxidative properties, which has potential safety hazards, and the actual capacity of lithium cobalt oxide is only 148mA/g. Battery demand is low. And cobalt resources are scarce, expensive and toxic. In recent years, ternary materials based on Ni, Co, and Mn and spinel materials represented by LiMn ₂ O ₄ have been widely studied, but their development is restricted due to their respective defects. Recently, the solid solution mainly formed by Li ₂ MnO ₃ and the layered material LiMO ₂ (M=Mn, Ni, Co, etc., one or more of them) has high theoretical capacity and high working voltage as the lithium-rich layered cathode material for lithium batteries. High, low cost, good safety performance and other advantages, it is expected to become a new generation of high energy density lithium battery cathode material. However, the reported lithium-rich materials have poor cycle performance and unsatisfactory rate performance, which limits their competitive advantage and wide application.

Contents of the invention

The purpose of the present invention is to solve the above existing problems and provide a high-capacity lithium-rich layered crystal structure lithium battery cathode material with high energy density, good rate performance, low cost, good safety and long service life and its preparation.

Technical scheme of the present invention:

A high-capacity lithium-rich layered crystal structure lithium battery cathode material, the structure is that a layer of LiNbO ₃ is coated on the particle surface of the powdery lithium-rich layered crystal material, wherein the chemical formula of the powdered lithium-rich layered crystal material is xLi ₂ MnO ₃ ·(1-x)Li Ni _m Co _n Mn _1-mn O ₂ , where: 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5.

The mass of LiNbO ₃ accounts for 1-10% of the total mass of the material.

The thickness of the cladding layer LiNbO ₃ is less than 1 μm.

A preparation method of the high-capacity lithium-rich layered crystal structure lithium battery positive electrode material, the steps are as follows:

(1) Preparation of Li-rich layered [xMn·(1-x)Ni _m Co _n Mn _1-mn ][OH] ₂ precursor:

1) Prepare nickel-cobalt-manganese sulfate solution at the ratio of molar ratio Ni:Co:Mn=(1-x)m:(1-x)n:[(1-x)(1-m-n)+x], wherein 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5; 0<m+n<1;

2) Add the prepared above-mentioned salt solution into the reaction kettle at a uniform speed at a rate of 1L/h, and carry out a co-precipitation reaction with a sodium hydroxide solution with a concentration of 2-10M at a pH value of 10-12 to obtain a precursor solid liquid mixture;

3) Stop the reaction after all the salt solution is completely injected into the reactor, the solid-liquid mixture is separated by centrifugal filtration, washed with deionized water until neutral, and dried at 80-200°C for 4-10h to obtain the molecular formula [xMn· (1-x)Ni _m Co _n Mn _1-mn ][OH] ₂ , where 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5, 0<m+n<1 is a precursor;

(2) Preparation of lithium-rich layered crystal structure xLi ₂ MnO ₃ ·(1-x)Li Ni _m Co _n Mn _1-mn O ₂ particles by high-temperature solid-state method:

1) Mix the above precursor and lithium carbonate powder evenly at a molar ratio of 1:1-2;

2) Put the above mixture in a muffle furnace for multi-stage calcination, the calcination temperature is 300-1200 ℃, the calcination time is 8-30h, and then the powder with lithium-rich layered crystal structure to be coated is obtained by cooling, crushing and sieving Bulk particles xLi ₂ MnO ₃ ·(1-x)Li Ni _m Co _n Mn _1-mn O ₂ , where 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5, 0<m+n<1;

( ₃ ) Coating xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles with LiNbO 3 :

1) Put the powder particles of the lithium-rich layered crystal structure obtained by the above roasting and ethanol in a mass ratio of 1:5-20 into a stirrer to suspend the powder particles at a stirring speed of 50-500 revolutions per minute;

2) Weigh a certain amount of niobium ethoxide and pour it into the stirrer. The amount of niobium ethoxide is calculated based on the ratio of the final LiNbO ₃ to the total mass of the product. Niobium ethoxide is evenly hydrolyzed in the lithium-rich layer in the rotating ethanol Surface of powder particles with crystal structure;

3) Weigh lithium carbonate with the same stoichiometric ratio as niobium ethoxide and add it to the agitator to disperse it evenly;

4) Heat to 80°C during the stirring process, stir until the ethanol is completely volatilized, then place it in an oven and dry at 100°C for 5 hours to obtain a lump;

5) Put the above block in a muffle furnace and bake it at 500-800°C for 10 hours to get LiNbO ₃ coated xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ Granular high-capacity lithium-rich layered crystal structure lithium battery cathode material.

The advantages of the present invention are: compared with traditional lithium battery positive electrode materials, the lithium battery positive electrode material has the following advantages: 1) High specific capacity, the highest specific capacity can reach 280mAh/g; 2) Lithium-rich layer coated with LiNbO ₃ Compared with uncoated materials, the material with the shape structure exhibits higher charge-discharge specific capacity and cycle life; 3) it has better electrochemical performance at high voltage and high current density.

Description of drawings

FIG. 1 is the XRD pattern of Example 1 before and after coating lithium-rich layered crystal particles.

FIG. 2 is a scanning electron micrograph of Example 1 before and after coating lithium-rich layered crystal particles.

Fig. 3 is a graph of 300 1C cycles before and after coating the lithium-rich layered crystal particles in Example 1.

FIG. 4 is the first charge and discharge curves before and after coating the lithium-rich layered crystal particles in Example 1. FIG.

Fig. 5 is the first charge and discharge curves under high current charge and discharge conditions before and after coating the lithium-rich layered crystal particles in Example 5.

Fig. 6 is a graph of 20 cycles at 0.1C before and after coating the lithium-rich layered crystal particles in Example 6.

Detailed ways

Example 1:

A preparation method of a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material:

1) Preparation of xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles without _LiNbO 3 coating:

With 2767g of nickel sulfate, 2924g of cobalt sulfate and 7044g of manganese sulfate, 25L of salt solution with a concentration of 2.5M was prepared. Inject the prepared solution at a rate of 1L/h into the reaction kettle with a rotation speed of 200rps, and inject 10M NaOH solution at the same time, pay attention to adjusting the flow rate of the alkali solution, and keep the pH value between 10-11 until the salt solution is completely injected into the reaction kettle , the precursor preparation reaction is complete. After the reaction, the solid-liquid mixture was separated by centrifugation, washed to neutrality and then dried at 120°C for 6 hours. Mix the dried precursor and lithium carbonate uniformly at a molar ratio of 1:1.5, and then roast in a muffle furnace at 950°C for 16 hours. The roasted material is crushed and sieved to obtain a uniform lithium-rich layered crystal structure powder. Material 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

2) Preparation of xLi ₂ MnO ₃ ·(1-x) _{LiNi m Co n} Mn _1-mn O ₂ particles coated with LiNbO 3 :

Take out 9.6 grams of the above-prepared spherical lithium-rich layered crystal powder granular material and place an appropriate amount of ethanol in a stirrer for rapid stirring to suspend. Weigh 0.8609 g of niobium ethoxide and pour it into a stirrer, and the niobium ethoxide is uniformly degraded on the surface of the powder particles with spherical lithium-rich layered crystal structure in the high-speed rotating ethanol. Then weigh 0.1 gram of lithium carbonate and add it to the stirrer to disperse it evenly. During the stirring process, the whole system was heated to 80° C., stirred until the ethanol was completely volatilized, and then dried in an oven at 100° C. for 5 hours to obtain a lump. The above mixed block is placed in a muffle furnace and calcined at 700°C for 10 hours to obtain a LiNbO ₃ coating to increase the 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ particle product. The final mass of LiNbO ₃ accounts for 4% of the total product, and the thickness of the cladding layer LiNbO ₃ is 20-100nm.

The two materials before and after coating were made into 2032 button batteries, and the first discharge specific capacity at 2.0-4.8V 0.1C was 265mAh/g and 261mAh/g respectively, as shown in Figure 3, 2.0-4.8V 1C 300 cycles The post-capacity retention rates were 37.7% and 53.6%, respectively, as shown in Figure 4; the capacity retention rates were 79% and 88% after 50 cycles of 2.0-4.8V 1C at a high temperature of 55°C.

Example 2:

A preparation method of a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material:

1) Preparation of xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles without _LiNbO 3 coating:

With 2767g of nickel sulfate, 2924g of cobalt sulfate and 7044g of manganese sulfate, 25L of salt solution with a concentration of 2.5M was prepared. Inject the prepared solution at a rate of 1L/h into the reaction kettle with a rotation speed of 200rps, and inject 10M NaOH solution at the same time, pay attention to adjusting the flow rate of the alkali solution, and keep the pH value between 10-11 until the salt solution is completely injected into the reaction kettle , the precursor preparation reaction is complete. After the reaction, the solid-liquid mixture was separated by centrifugation, washed to neutrality and then dried at 120°C for 6 hours. Mix the dried precursor and lithium carbonate uniformly at a molar ratio of 1:1.5, and then roast in a muffle furnace at 950°C for 16 hours. The roasted material is crushed and sieved to obtain a uniform lithium-rich layered crystal structure powder. Material 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

2) Preparation of xLi ₂ MnO ₃ ·(1-x) _{LiNi m Co n} Mn _1-mn O ₂ particles coated with LiNbO 3 :

Take out 9.2 grams of the above-prepared spherical lithium-rich layered crystal powder granular material and put an appropriate amount of ethanol in a stirrer for rapid stirring to suspend. Weigh 1.7219 g of niobium ethoxide and pour it into a stirrer, and the niobium ethoxide is uniformly degraded on the surface of the powder particles with a spherical lithium-rich layered crystal structure in ethanol rotating at high speed. Then weigh 0.2 g of lithium carbonate and add it to the stirrer to make it evenly dispersed. During the stirring process, the whole system was heated to 80° C., stirred until the ethanol was completely volatilized, and then dried in an oven at 100° C. for 5 hours to obtain a lump. The above mixed block is placed in a muffle furnace and calcined at 700°C for 10 hours to obtain a LiNbO ₃ coating to increase the 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ particle product. The final mass of LiNbO ₃ accounts for 8% of the total product, and the thickness of the cladding layer LiNbO ₃ is 30-150nm.

The two materials before and after coating were made into 2032 button batteries, and the first discharge specific capacity at 2.0-4.8V 0.1C was 262.3mAh/g and 243.2mAh/g respectively; the capacity retention rate after 100 cycles at 2.0-4.8V 1C They are 77% and 89%, respectively; after 50 cycles of 2.0-4.8V 1C at a high temperature of 55 °C, the capacity retention rates are 79% and 90%, respectively.

Example 3:

A preparation method of a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material:

1) Preparation of xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles without _LiNbO 3 coating:

With 2767g of nickel sulfate, 2924g of cobalt sulfate and 7044g of manganese sulfate, 25L of salt solution with a concentration of 2.5M was prepared. Inject the prepared solution at a rate of 1L/h into the reaction kettle with a rotation speed of 200rps, and inject 10M NaOH solution at the same time, pay attention to adjusting the flow rate of the alkali solution, and keep the pH value between 10-11 until the salt solution is completely injected into the reaction kettle , the precursor preparation reaction is complete. After the reaction, the solid-liquid mixture was separated by centrifugation, washed to neutrality and then dried at 120°C for 6 hours. Mix the dried precursor and lithium carbonate uniformly at a molar ratio of 1:1.5, and then roast in a muffle furnace at 950°C for 16 hours. The roasted material is crushed and sieved to obtain a uniform lithium-rich layered crystal structure powder. Material 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

2) Preparation of xLi ₂ MnO ₃ ·(1-x) _{LiNi m Co n} Mn _1-mn O ₂ particles coated with LiNbO 3 :

Take out 9.6 grams of the above-prepared spherical lithium-rich layered crystal powder granular material and place an appropriate amount of ethanol in a stirrer for rapid stirring to suspend. Weigh 0.4305 g of niobium ethoxide and pour it into a stirrer, and the niobium ethoxide is uniformly degraded on the surface of the powder particles with spherical lithium-rich layered crystal structure in the high-speed rotating ethanol. Then weigh 0.05 gram of lithium carbonate and add it into the stirrer to make it disperse evenly. During the stirring process, the whole system was heated to 80° C., stirred until the ethanol was completely volatilized, and then dried in an oven at 100° C. for 5 hours to obtain a lump. The above mixed block is placed in a muffle furnace and calcined at 700°C for 10 hours to obtain a LiNbO ₃ coating to increase the 0.5Li ₂ MnO ₃ ·0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ particle product. The final mass of LiNbO ₃ accounts for 2% of the total product, and the thickness of the cladding layer LiNbO ₃ is 150-80nm.

The two materials before and after coating were made into 2032 button batteries, and the first discharge specific capacity at 2.0-4.8V 0.1C was 262.3mAh/g and 257.6mAh/g respectively; the capacity retention rate after 100 cycles at 2.0-4.8V 1C They are 77% and 83%, respectively; after 50 cycles of 2.0-4.8V 1C at a high temperature of 55 °C, the capacity retention rates are 79% and 85%, respectively.

Example 4:

A preparation method of a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material:

1) Preparation of xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles without _LiNbO 3 coating:

25L of salt solution with a concentration of 2.5M was prepared with 3873g of nickel sulfate, 4192g of cobalt sulfate and 5635g of manganese sulfate. Inject the prepared solution at a rate of 1L/h into the reaction kettle with a rotation speed of 200rps, and inject 10M NaOH solution at the same time, pay attention to adjusting the flow rate of the alkali solution, and keep the pH value between 10-11 until the salt solution is completely injected into the reaction kettle , the precursor preparation reaction is complete. After the reaction, the solid-liquid mixture was separated by centrifugation, washed to neutrality and then dried at 120°C for 6 hours. Mix the dried precursor and lithium carbonate uniformly at a molar ratio of 1:1.3, and then roast in a muffle furnace at 950°C for 16 hours. The roasted material is crushed and sieved to obtain a uniform lithium-rich layered crystal structure powder. Material 0.3Li ₂ MnO ₃ ·0.7LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

2) Preparation of xLi ₂ MnO ₃ ·(1-x) _{LiNi m Co n} Mn _1-mn O ₂ particles coated with LiNbO 3 :

Take out 9.6 grams of the above-prepared spherical lithium-rich layered crystal powder granular material and place an appropriate amount of ethanol in a stirrer for rapid stirring to suspend. Weigh 0.8609 g of niobium ethoxide and pour it into a stirrer, and the niobium ethoxide is uniformly degraded on the surface of the powder particles with spherical lithium-rich layered crystal structure in the high-speed rotating ethanol. Then weigh 0.1 gram of lithium carbonate and add it to the stirrer to disperse it evenly. During the stirring process, the whole system was heated to 80° C., stirred until the ethanol was completely volatilized, and then dried in an oven at 100° C. for 5 hours to obtain a lump. The above mixed block is placed in a muffle furnace and calcined at 700°C for 10 hours to obtain a LiNbO ₃ coating to increase the 0.3Li ₂ MnO ₃ ·0.7LiNi _1/3 Co _1/3 Mn _1/3 O ₂ particle product. The final mass of LiNbO ₃ accounts for 4% of the total product, and the thickness of the cladding layer LiNbO ₃ is 20-100nm.

The two materials before and after coating were made into 2032 button batteries, and the specific capacities of the first discharge at 2.0-4.8V 0.1C were 285.7mAh/g and 271.9mAh/g respectively; the capacity retention rate after 100 cycles at 2.0-4.8V 1C They were 73% and 86%, respectively; the capacity retention rates were 75% and 84% after 50 cycles at 2.0-4.8V 1C at a high temperature of 55°C.

Example 5:

A preparation method of a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material:

1) Preparation of xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles without _LiNbO 3 coating:

Prepare 25L of salt solution with a concentration of 2.5M with 1660g of nickel sulfate, 1797g of cobalt sulfate and 8452g of manganese sulfate. Inject the prepared solution at a rate of 1L/h into the reaction kettle with a rotation speed of 200rps, and inject 10M NaOH solution at the same time, pay attention to adjusting the flow rate of the alkali solution, and keep the pH value between 10-11 until the salt solution is completely injected into the reaction kettle , the precursor preparation reaction is complete. After the reaction, the solid-liquid mixture was separated by centrifugation, washed to neutrality and then dried at 120°C for 6 hours. Mix the dried precursor and lithium carbonate uniformly at a molar ratio of 1:1.7, and then roast in a muffle furnace at 950°C for 16 hours. The roasted material is crushed and sieved to obtain a uniform lithium-rich layered crystal structure powder. Material 0.7Li ₂ MnO ₃ ·0.3LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .

2) Preparation of xLi ₂ MnO ₃ ·(1-x) _{LiNi m Co n} Mn _1-mn O ₂ particles coated with LiNbO 3 :

Take out 9.6 grams of the above-prepared spherical lithium-rich layered crystal powder granular material and place an appropriate amount of ethanol in a stirrer for rapid stirring to suspend. Weigh 0.8609 g of niobium ethoxide and pour it into a stirrer, and the niobium ethoxide is uniformly degraded on the surface of the powder particles with spherical lithium-rich layered crystal structure in the high-speed rotating ethanol. Then weigh 0.1 gram of lithium carbonate and add it to the stirrer to disperse it evenly. During the stirring process, the whole system was heated to 80° C., stirred until the ethanol was completely volatilized, and then dried in an oven at 100° C. for 5 hours to obtain a lump. Put the above mixed block in a muffle furnace and bake at 700°C for 10 hours to obtain LiNbO ₃ coating to increase the 0.7Li ₂ MnO ₃ ·0.3LiNi _1/3 Co _1/3 Mn _1/3 O ₂ particle product. The final mass of LiNbO ₃ accounts for 4% of the total product, and the thickness of the cladding layer LiNbO ₃ is 20-100nm.

After the two materials before and after coating were made into 2032 button batteries, the first discharge specific capacities at 2.0-4.8V 0.1C were 252.3mAh/g and 247.6mAh/g respectively; the capacity retention rates after 100 cycles at 2.0-4.8V 1C were respectively 81% and 87%; 2.0-4.8V 3C first discharge specific capacity is 159.3mAh/g and 178.6mAh/g respectively, as shown in Figure 5, the rate performance is significantly improved; 3.0-4.3V 1C at a high temperature of 55°C The capacity retention rates after 50 cycles were 83% and 90%, respectively.

Embodiment 6:

A preparation method of a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material:

1) Preparation of xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles without _LiNbO 3 coating:

Use 5809g of nickel sulfate and 6868g of manganese sulfate to prepare 25L of salt solution with a concentration of 2.5M. Inject the prepared solution at a rate of 1L/h into the reaction kettle with a rotation speed of 200rps, and inject 10M NaOH solution at the same time, pay attention to adjusting the flow rate of the alkali solution, and keep the pH value between 10-11 until the salt solution is completely injected into the reaction kettle , the precursor preparation reaction is complete. After the reaction, the solid-liquid mixture was separated by centrifugation, washed to neutrality and then dried at 120°C for 6 hours. Mix the dried precursor and lithium carbonate uniformly at a molar ratio of 1:1.3, and then roast in a muffle furnace at 950°C for 16 hours. The roasted material is crushed and sieved to obtain a uniform lithium-rich layered crystal structure powder. Material 0.3Li ₂ MnO ₃ ·0.7LiNi _0.5 Mn _0.5 O ₂ .

2) Preparation of xLi ₂ MnO ₃ ·(1-x) _{LiNi m Co n} Mn _1-mn O ₂ particles coated with LiNbO 3 :

Take out 9.6 grams of the above-prepared spherical lithium-rich layered crystal powder granular material and place an appropriate amount of ethanol in a stirrer for rapid stirring to suspend. Weigh 0.8609 g of niobium ethoxide and pour it into a stirrer, and the niobium ethoxide is uniformly degraded on the surface of the powder particles with spherical lithium-rich layered crystal structure in the high-speed rotating ethanol. Then weigh 0.1 gram of lithium carbonate and add it to the stirrer to disperse it evenly. During the stirring process, the whole system was heated to 80° C., stirred until the ethanol was completely volatilized, and then dried in an oven at 100° C. for 5 hours to obtain a lump. The above mixed block is placed in a muffle furnace and calcined at 700°C for 10 hours to obtain a LiNbO ₃ coating to increase the 0.3Li ₂ MnO ₃ ·0.7LiNi _0.5 Mn _0.5 O ₂ particle product. The final mass of LiNbO ₃ accounts for 4% of the total product, and the thickness of the cladding layer LiNbO ₃ is 20-100nm.

The two materials before and after coating were made into 2032 button batteries, and the specific capacities of the first discharge at 2.0-4.8V 0.1C were 244.5mAh/g and 239.6mAh/g respectively; the capacity was maintained after 20 cycles at 2.0-4.8V 0.1C The rates are 88.1% and 94.5%, respectively. As shown in Figure 6, the cycle performance is significantly improved; after 20 cycles of 3.0-4.3V 1C at a high temperature of 55 °C, the capacity retention rates are 83% and 90%, respectively.

To sum up, compared with LiNbO ₃ coated materials, cycle stability, high temperature cycle performance and thermal stability have obvious performance improvements in many aspects.

Although the present invention has been described above in conjunction with the drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the inspiration, many modifications can be made without departing from the gist of the present invention, and these all belong to the protection of the present invention.

Claims (4)

1. A high-capacity lithium-rich layered crystal structure lithium battery positive electrode material, characterized in that: the structure is to coat a layer of LiNbO ₃ on the particle surface of the powdery lithium-rich layered crystal material, wherein the powdered lithium-rich layered crystal The chemical formula of the material is xLi ₂ MnO ₃ ·(1-x)Li Ni _m Co _n Mn _1-mn O ₂ , where: 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5. 2. The anode material for a high-capacity lithium-rich layered crystal structure lithium battery according to claim 1, wherein the mass of the LiNbO ₃ accounts for 1-10% of the total mass of the material. 3. The anode material for a high-capacity lithium-rich layered crystal structure lithium battery according to claim 1, wherein the thickness of the coating layer LiNbO ₃ is less than 1 μm. 4. A method for preparing a high-capacity lithium-rich layered crystal structure lithium battery positive electrode material as claimed in claim 1, characterized in that the steps are as follows: (1) Preparation of Li-rich layered [xMn·(1-x)Ni _m Co _n Mn _1-mn ][OH] ₂ precursor: 1) Prepare nickel-cobalt-manganese sulfate solution at the ratio of molar ratio Ni:Co:Mn=(1-x)m:(1-x)n:[(1-x)(1-m-n)+x], wherein 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5; 0<m+n<1; 2) Add the prepared above-mentioned salt solution into the reaction kettle at a uniform speed at a rate of 1L/h, and carry out a co-precipitation reaction with a sodium hydroxide solution with a concentration of 2-10M at a pH value of 10-12 to obtain a precursor solid liquid mixture; 3) Stop the reaction after all the salt solution is completely injected into the reactor, the solid-liquid mixture is separated by centrifugal filtration, washed with deionized water until neutral, and dried at 80-200°C for 4-10h to obtain the molecular formula [xMn· (1-x)Ni _m Co _n Mn _1-mn ][OH] ₂ , where 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5, 0<m+n<1 is a precursor; (2) Preparation of lithium-rich layered crystal structure xLi ₂ MnO ₃ ·(1-x)Li Ni _m Co _n Mn _1-mn O ₂ particles by high-temperature solid-state method: 1) Mix the above precursor and lithium carbonate powder evenly at a molar ratio of 1:1-2; 2) Put the above mixture in a muffle furnace for multi-stage calcination, the calcination temperature is 300-1200 ℃, the calcination time is 8-30h, and then the powder with lithium-rich layered crystal structure to be coated is obtained by cooling, crushing and sieving Bulk particles xLi ₂ MnO ₃ ·(1-x)Li Ni _m Co _n Mn _1-mn O ₂ , where 0.2≤x≤0.9, 0.1≤m<1, 0≤n≤0.5, 0<m+n<1; ( ₃ ) Coating xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ particles with LiNbO 3 : 1) Put the powder particles of the lithium-rich layered crystal structure obtained by the above roasting and ethanol in a mass ratio of 1:5-20 into a stirrer to suspend the powder particles at a stirring speed of 50-500 revolutions per minute; 2) Weigh a certain amount of niobium ethoxide and pour it into the stirrer. The amount of niobium ethoxide is calculated based on the ratio of the final LiNbO ₃ to the total mass of the product. Niobium ethoxide is evenly hydrolyzed in the lithium-rich layer in the rotating ethanol Surface of powder particles with crystal structure; 3) Weigh lithium carbonate with the same stoichiometric ratio as niobium ethoxide and add it to the stirrer to disperse it evenly; 4) Heat to 80°C during the stirring process, stir until the ethanol is completely volatilized, then place it in an oven and dry it at 100°C for 5 hours to obtain a lump; 5) Put the above block in a muffle furnace and bake it at 500-800°C for 10 hours to get LiNbO ₃ coated xLi ₂ MnO ₃ ·(1-x)LiNi _m Co _n Mn _1-mn O ₂ Granular high-capacity lithium-rich layered crystal structure lithium battery cathode material.

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