CN112803002B - Lithium-rich manganese-based positive electrode material with surface coated by mixed ion conductor and electronic conductor, and preparation method and application thereof - Google Patents

Abstract

The invention provides a lithium-rich manganese-based positive electrode material with an ion conductor-electron conductor mixed coating structure on the surface, and a preparation method and application thereof, wherein the lithium-rich manganese-based positive electrode material comprises a lithium-rich manganese-based positive electrode material core and an ion conductor-electron conductor mixed coating layer; the ion conductor-electron conductor mixed coating layer is a surface modification layer formed by mixing and crosslinking an ion conductor and an electron conductor, wherein the ion conductor is a fluorine-based polyanion compound, and the electron conductor is cyclized polyacrylonitrile. The preparation method is simple in preparation process and easy to operate, the heterostructure with the lithium-embedded active substance is cooperatively constructed by coating, the interface between the lithium-rich material and the electrolyte can be stabilized under high voltage, the side reaction between the electrolyte and the lithium-rich material is inhibited, the cycling stability and the rate capability of the material are improved, and the electrochemical performance is obviously improved.

Description

Lithium-rich manganese-based cathode material with surface-structured ionic conductor-electronic conductor mixed coating and preparation method and application thereof

technical field

The present invention relates to the technical field of lithium ion battery materials, in particular to a lithium-rich manganese-based positive electrode material with a mixed coating of an ion conductor and an electronic conductor on the surface, and a preparation method and application thereof.

Background technique

Environmental pollution and energy crisis are two hot issues in recent years, which have aroused widespread concern. The problem of the reserves of fossil energy and the pollution caused by its use has become imminent. In order to respond to the country's call for carbon emission reduction, it is imperative to vigorously develop new energy and its storage technology. Among them, lithium-ion batteries, as the representative of new energy energy storage technology, play an important role in the fields of 3C, energy storage and power batteries, and cathode materials, as the core part of lithium-ion batteries, play a vital role in the performance of lithium-ion batteries effect. Therefore, it is necessary to prepare cathode materials for lithium ion batteries with good performance.

The current commercial lithium-ion battery cathode materials are basically LiCoO ₂ (LCO), LiNi _x Co _y Mn _1-xy O ₂ (NCM), LiNi _x Co _y Al _1-xy O ₂ (NCA), LiFePO ₄ (LFP) ) and LiMn ₂ O ₄ (LMO), but LCO, NCM and NCA have high cost and poor safety performance, and LFP and LMO have low volumetric energy density, which cannot meet the development requirements of the new energy industry. Therefore, it is necessary to develop cathode materials with higher energy density, lower cost and higher safety. The lithium-rich manganese-based cathode material xLi ₂ MnO ₃ ·(1-x)LiMO ₂ (M=Ni, Co, Mn0<x<1) has ultra-high energy density (theoretical specific capacity>250mAhg ^-1 ), high The advantages of operating voltage, low cost, high safety and low pollution are regarded as the ideal choice for next-generation lithium-ion battery cathode materials. Although lithium-rich materials have ultra-high capacity, they also have extremely serious problems, such as low first efficiency, severe capacity fading, poor rate performance, and voltage drop, which limit the practical production and application of lithium-rich materials.

The high capacity of Li-rich is mainly due to the redox of oxygen anions in the Li ₂ MnO ₃ phase. The irreversible extraction of oxygen anions leads to the migration of transition metal ions, which destroys the crystal structure and occurs from layered to spinel phase and disordered rock salt phase. irreversible transformation. In addition, the interface between the lithium-rich and the electrolyte under high voltage is unstable, and side reactions are prone to occur, which will cause the electrolyte to deteriorate and produce HF and other substances, destroy the lithium-rich surface structure, and lead to the dissolution of transition metals. Therefore, it is necessary to improve its structural stability and electrochemical performance, and modify the material to make it have good cycle stability. Surface modification is currently the easiest and most effective means to improve the electrochemical performance of Li-rich manganese-based cathode materials. Traditional surface coating materials, such as metal oxides, are electrochemically inert materials, which only serve as physical barriers and also lose some lithium-rich capacity; phosphate or organic matter coating can only conduct single ions or electrons. It only plays a role in one aspect, and some organic coatings are not stable under high voltage, and the improvement effect is limited.

SUMMARY OF THE INVENTION

In view of the deficiencies of the existing surface modification technology, the purpose of the present invention is to provide a lithium-rich manganese-based positive electrode material with a mixed coating of ion conductor-electronic conductor on the surface and a preparation method thereof, including a lithium-rich manganese-based positive electrode material core and ions Conductor-electronic conductor mixed cladding layer; the ionic conductor-electronic conductor mixed cladding layer is a surface modification layer in which ionic conductors and electronic conductors are mixed and cross-linked, wherein the ionic conductors are fluorine-based polyanion compounds, and the electronic conductors are It is a cyclized polyacrylonitrile, the preparation process is simple, the operation is easy, the electrochemical performance of the modified lithium-rich manganese-based cathode material is obviously improved, and the invention has a broad development prospect.

In order to achieve the above object, the present invention provides the following technical solutions:

A lithium-rich manganese-based positive electrode material whose surface is constructed with ion conductor-electronic conductor mixed coating, comprising a lithium-rich manganese-based positive electrode material core and an ion conductor-electronic conductor mixed coating layer; the ionic conductor-electronic conductor mixed coating layer It is a surface modification layer in which ion conductors and electronic conductors are mixed and cross-linked, wherein the ion conductors are fluorine-based polyanion compounds, and the electron conductors are cyclized polyacrylonitrile.

In a preferred solution, the chemical formula of the lithium-rich manganese-based cathode material core is xLi ₂ MnO ₃ ·(1-x)LiTMO ₂ , where 0.2≤x≤0.8, and TM is at least one of Ni, Co, and Mn.

In a preferred solution, in the lithium-rich manganese-based positive electrode material, the mass ratio of the inner core of the lithium-rich manganese-based positive electrode material to the ion conductor-electronic conductor mixed coating layer is 1:0.005-0.05; more preferably 1:0.02-0.03.

In a preferred solution, in the ion conductor-electronic conductor mixed coating layer, the mass ratio of the ion conductor and the electron conductor is 0.5-2:1.

The present invention also provides a method for preparing the above-mentioned surface-structured ion conductor-electronic conductor mixed-coated lithium-rich manganese-based positive electrode material, comprising the following steps:

1) adding polyacrylonitrile to the solvent, ultrasonicating for several times and heating and stirring to obtain a uniform solution; then adding a fluorine-based polyanion compound to the uniform solution, and continuing to stir to obtain a uniform mixed solution;

2) then adding the lithium-rich manganese-based positive electrode material to the homogeneous mixed solution in step 1), stirring and evaporating to dryness, and grinding to obtain a lithium-rich manganese-based positive electrode material coated with polyacrylonitrile and a fluorine-based polyanion compound;

3) Perform low temperature sintering on the coated lithium-rich manganese-based positive electrode material obtained in step 2) to obtain a lithium-rich manganese-based positive electrode material with an ion conductor-electronic conductor mixed coating on the surface.

In a preferred solution, in step 1), the solvent is one of N-methylpyrrolidone, anhydrous ethanol, dimethylformamide, and dimethylsulfoxide; the concentration fraction of polyacrylonitrile is 0.00167-0.05 g/ml; the concentration fraction of the fluorine-based polyanion compound is 0.00167～0.05g/ml.

In a preferred solution, in step 1), the ultrasonic time is 10-30 min, the ultrasonic frequency is 1-3 times, and the temperature is 30-70°C.

A preferred solution, in step 1), the fluorine-based polyanion compound is one of sodium vanadium fluorophosphate (Na ₃ V ₂ (PO ₄ ) ₂ F ₃ ), lithium vanadium fluorophosphate (LiVPO ₄ F) or variety.

In a preferred solution, in step 2), the evaporation temperature is 80-150°C.

In a preferred solution, in step 3), the temperature of the low-temperature sintering is 200-350° C., the sintering time is 0.5-5 h, and the sintering atmosphere is vacuum, nitrogen or argon atmosphere. In the present invention, through low-temperature sintering, the dehydrocyclization of polyacrylonitrile obtains good electronic conductivity, and at the same time, the fluorine-based polyanion active material and the lithium-rich manganese-based material form a good interface contact, so that the surface is constructed with ionic conductor-electron Lithium-rich manganese-based cathode material mixed with conductors.

The invention also provides the application of the above-mentioned lithium-rich manganese-based positive electrode material whose surface is constructed with ion conductor-electronic conductor mixed coating, which is used as the positive electrode material of lithium ion battery for preparing lithium ion battery.

The fluorine-based polyanion compound in the present invention has good ionic conductivity and three-dimensional ion channel, which can make lithium ion transfer faster, effectively improve the rate performance of lithium-rich, and more stable in structure. It has certain resistance to harmful substances such as HF generated in the electrolyte, and can protect the surface of lithium-rich materials cycled under high voltage from damage; the cyclized polyacrylonitrile synergistic coating can significantly improve the electronic conductivity, At the same time, after thermal cyclization, it is cross-linked with a fluorine-based polyanion compound to coat the lithium-rich surface, which can have good tolerance under high charging voltage, improve the interface stability between the material and the electrolyte, and improve the cycle performance.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The present invention constructs a heterostructure with lithium intercalation dual active material through the synergistic coating of fluorine-based polyanion compound and cyclized polyacrylonitrile, which can stabilize the interface between the lithium-rich material and the electrolyte under high voltage, The side reaction between the electrolyte and the lithium-rich solution is inhibited, the cycle stability and rate performance of the material are improved, and the electrochemical performance is significantly improved.

(2) The present invention prepares a lithium-rich manganese-based positive electrode material with surface-structured ionic conductor-electronic conductor mixed coating by a simple liquid phase method supplemented by low-temperature sintering, the preparation process is simple, the operation is easy, and the coated lithium-rich material is coordinated The electrochemical performance has been significantly improved, and it has broad development prospects.

Description of drawings

Figure 1 is a SEM image of the lithium-rich material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ in Comparative Example 1;

FIG. 2 is a SEM image of the lithium-rich material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ , the surface of which is constructed with ionic conductor-electronic conductor mixed coating prepared in Example 1;

3 is a 100-cycle cycle-capacity curve diagram of Example 1, Comparative Example 1, and Comparative Example 3 at 1C magnification;

Fig. 4 is the magnification performance diagram of embodiment 1 and comparative example 1, comparative example 3;

Fig. 5 is the first circle charge-discharge curve diagram of Example 1 and Comparative Example 1;

6 is a 100-cycle cycle-capacity curve diagram of Example 2 and Comparative Example 2 at a 1C rate;

Detailed ways

Example 1

Weigh 0.10g of polyacrylonitrile and dissolve it in 15ml of dimethylformamide, ultrasonically stir for 10min for 10min alternately three times, then heat up to 50°C and continue to stir until it is completely dissolved to form a solution, add 0.10g of sodium vanadium fluorophosphate to the solution (Na ₃ V ₂ (PO ₄ ) ₂ F ₃ ), continue to stir for 20 min, then add 10 g of lithium-rich material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ into it, keep stirring at 90°C until the solvent becomes dry , vacuum-dried at 120°C to obtain the mixture, and after grinding, treated in argon atmosphere at 250°C for 1 h to obtain lithium-rich Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ with a mixed coating of ionic conductor and electronic conductor on the surface. The experimental design coating amount is 2.0 wt%, and the mass ratio of the fluorine-based polyanion compound to the cyclized polyacrylonitrile is 1:1. As shown in Fig. 2, a mixed coating of ionic conductor and electronic conductor is attached to its surface.

Weigh the modified lithium-rich material, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. After grinding evenly, add an appropriate amount of NMP dropwise to make a mixed slurry, and then use a scraper to remove the slurry. The material was evenly coated on aluminum foil, and then placed in a vacuum drying box at 120 °C for 8 hours, then the pole piece was rolled and punched to obtain a 14mm pole piece, and finally a 2025 button half-cell was assembled in a super clean glove box. = 250mAg ^-1 is the nominal specific capacity, and the charge-discharge cycle test is carried out in the voltage range of 2-4.8V, as shown in Figure 3, and the capacity retention rate is 82.58% after 100 cycles at 1C.

Example 2

Weigh 0.20 g of polyacrylonitrile and dissolve it in 20 ml of N-methylpyrrolidone and 5 ml of absolute ethanol, ultrasonically stir for 10 min for 10 min alternately for three times, then heat up to 60 ° C and continue to stir until it is completely dissolved to form a solution, add 0.10 g to the solution Lithium vanadium fluorophosphate (LiVPO ₄ F), continue to stir for 20 min, then add 10 g of lithium-rich material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ into it, keep stirring at 100 ° C until the solvent becomes dry, at 120 ° C The mixture was obtained by vacuum drying. After grinding, the mixture was treated in a vacuum environment at 290° C. for 1 h to obtain a lithium-rich Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ with a mixed coating of ionic conductor and electronic conductor on the surface. The experimental design coating amount is 3.0wt%, and the mass ratio of the fluorine-based polyanion compound to the cyclized polyacrylonitrile is 1:2.

Weigh the modified lithium-rich, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. After grinding evenly, add an appropriate amount of NMP dropwise to make a mixed slurry, and then use a scraper to remove the slurry. It was evenly coated on aluminum foil, then placed in a vacuum drying box at 120°C for 8 hours, and then the pole piece was rolled and punched to obtain a 14mm pole piece. 250mAg ^-1 is the nominal specific capacity, and the charge-discharge cycle test is carried out in the voltage range of 2-4.8V. As shown in Figure 6, it is measured that the capacity retention rate is 86.41% after 100 cycles at 1C.

Example 3

Weigh 0.20 g of polyacrylonitrile and dissolve it in 15 ml of a mixed solvent of dimethyl sulfoxide and 5 ml of ethanol, ultrasonically stir for 20 min for 15 min alternately three times, then heat up to 50 ° C and continue to stir to obtain a uniform dispersion, add 0.10 g sodium vanadium fluorophosphate (Na ₃ V ₂ (PO ₄ ) ₂ F ₃ ), continue to stir for 30 min, then add 10 g of lithium-rich material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ into it, keep stirring at 80° C., After the solvent dries, the mixture is obtained by vacuum drying at 120 °C. After grinding, the mixture is treated in a vacuum environment at 300 °C for 30 minutes to obtain a lithium-rich Li _1.2 Ni _0.13 Co _0.13 Mn with a mixed coating of ionic conductor and electronic conductor on the surface. _0.54 O ₂ . The experimental design coating amount is 3.0wt%, and the mass ratio of the fluorine-based polyanion compound to the cyclized polyacrylonitrile is 2:1.

Weigh the modified lithium-rich, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. After grinding evenly, add an appropriate amount of NMP dropwise to make a mixed slurry, and then use a scraper to remove the slurry. It was evenly coated on aluminum foil, then placed in a vacuum drying box at 120°C for 8 hours, and then the pole piece was rolled and punched to obtain a 14mm pole piece. 250mAg ^-1 is the nominal specific capacity, and the charge-discharge cycle test was carried out in the voltage range of 2 to 4.8V, and the capacity retention rate was 83.62% after 100 cycles at 1C.

Example 4

Weigh 0.10g of polyacrylonitrile and dissolve it in 15ml of dimethylamide, ultrasonically stir for 20min and 15min alternately for three times, then heat up to 50 ° C and continue to stir to obtain a uniform dispersion, add 0.20g of sodium vanadium fluorophosphate (Na ₃ V ₂ (PO ₄ ) ₂ F ₃ ), continue to stir for 30 min, then add 10 g of lithium-rich material Li _1.2 Ni _0.2 Mn _0.6 O ₂ into it, keep stirring at 90 ° C until the solvent dries, at 120 ° C The mixture was obtained by vacuum drying, and after grinding, the mixture was treated in a muffle furnace at 250° C. for 2 hours to obtain a lithium-rich Li _1.2 Ni _0.2 Mn _0.6 O ₂ with a mixed coating of ionic conductor and electronic conductor on the surface. The experimental design coating amount is 3.0wt%, and the mass ratio of the fluorine-based polyanion compound to the cyclized polyacrylonitrile is 1:2.

Weigh the modified lithium-rich, acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. After grinding evenly, add an appropriate amount of NMP dropwise to make a mixed slurry, and then use a scraper to remove the slurry. It was evenly coated on aluminum foil, then placed in a vacuum drying box at 120°C for 8 hours, and then the pole piece was rolled and punched to obtain a 14mm pole piece. 250mAg ^-1 is the nominal specific capacity, and the charge-discharge cycle test is carried out in the voltage range of 2 to 4.8V. It is measured that the capacity retention rate is 85.19% after 100 cycles at 1C.

Comparative Example 1

In contrast to Example 1, the only difference is that the lithium-rich bare material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ is not treated, and the battery assembly and electrochemical performance test are directly performed. As shown in Figure 1, the surface is smooth and free of attachments. It was measured, as shown in Figure 3, that the capacity retention rate was only 65.68% after 100 cycles at 1C rate.

Comparative Example 2

Compared with Example 2, the only difference is that only lithium-vanadium fluorophosphate is used to coat the lithium-rich bare material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ , and the designed coating amount is 3.0 wt %. The coating method is the same as that in Example 2. Example 2 is completely consistent, and battery assembly and electrochemical performance tests are performed on the coated lithium-rich. It was measured, as shown in Figure 6, that the capacity retention rate was 80.26% after 100 cycles at 1C rate.

Comparative Example 3

Compared with Example 1, the only difference is that only the cyclized polyacrylonitrile is used to coat the lithium-rich bare material Li _1.2 Ni _0.13 Co _0.13 Mn _0.54 O ₂ , and the designed coating amount is 2.0wt%, The coating method is completely the same as that in Example 1, and the battery assembly and electrochemical performance test are carried out on the coated lithium-rich. It was measured that the capacity retention rate was only 75.63% after 100 cycles at 1C rate.

Claims (6)

1. a lithium-rich manganese-based positive electrode material of surface construction ion conductor-electronic conductor mixed coating, is characterized in that: comprise lithium-rich manganese-based positive electrode material core and ion conductor-electronic conductor mixed coating; Described ion conductor- The electronic conductor mixed coating layer is a surface modification layer in which ionic conductors and electronic conductors are mixed and cross-linked, wherein the ionic conductors are fluorine-based polyanion compounds, and the electronic conductors are cyclized polyacrylonitrile; The chemical formula of the core of the lithium-rich manganese-based cathode material is xLi ₂ MnO ₃ ·(1-x)LiTMO ₂ , wherein 0.2≤x≤0.8, and TM is at least one of Ni, Co, and Mn; The preparation method of the lithium-rich manganese-based positive electrode material comprises the following steps: 1) adding polyacrylonitrile to the solvent, ultrasonicating for several times and heating and stirring to obtain a uniform solution; then adding a fluorine-based polyanion compound to the uniform solution, and continuing to stir to obtain a uniform mixed solution; 2) then adding the lithium-rich manganese-based positive electrode material to the homogeneous mixed solution in step 1), stirring and evaporating to dryness, and grinding to obtain a lithium-rich manganese-based positive electrode material coated with polyacrylonitrile and a fluorine-based polyanion compound; 3) sintering the coated lithium-rich manganese-based positive electrode material obtained in step 2) at a low temperature to obtain a lithium-rich manganese-based positive electrode material with an ionic conductor-electronic conductor mixed coating on the surface; In step 1), the ultrasonic time is 10 to 30 min, the ultrasonic frequency is 1 to 3 times, and the temperature is 30 to 70 °C; one or more; In step 3), the temperature of the low-temperature sintering is 200-350° C., the sintering time is 0.5-5 h, and the sintering atmosphere is vacuum, nitrogen or argon atmosphere; In step 1), the fluorine-based polyanion compound is one or more of Na ₃ V ₂ (PO ₄ ) ₂ F ₃ and LiVPO ₄ F. 2. The lithium-rich manganese-based positive electrode material with a surface-structured ion conductor-electronic conductor mixed coating according to claim 1, characterized in that: in the lithium-rich manganese-based positive electrode material, the lithium-rich manganese-based positive electrode material has an inner core. The mass ratio to the ion-electron mixed coating layer is 1:0.005-0.05. 3. A lithium-rich manganese-based positive electrode material with surface-structured ion conductor-electronic conductor mixed coating according to claim 1, characterized in that: in the ion conductor-electronic conductor mixed coating layer, the ionic conductor and The mass ratio of the electronic conductors is 0.5 to 2:1. 4. The lithium-rich manganese-based positive electrode material with surface-structured ionic conductor-electronic conductor mixed coating according to claim 1, characterized in that: in step 1), the solvent is N-methylpyrrolidone, no One of water ethanol, dimethylformamide and dimethyl sulfoxide; the concentration fraction of polyacrylonitrile is 0.00167～0.05g/ml; the concentration fraction of fluorine-based polyanion compound is 0.00167～0.05g/ml. 5 . The lithium-rich manganese-based positive electrode material with surface-structured ion conductor-electronic conductor mixed coating according to claim 1 , wherein in step 2), the evaporation temperature is 80-150° C. 6 . 6. The application of the lithium-rich manganese-based positive electrode material of the surface structure ion conductor-electronic conductor mixed coating described in any one of claims 1-5, characterized in that: it is used as a positive electrode material for lithium ion batteries for preparing lithium ions Battery.

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