A lithium ion battery high cycle life negative electrode material and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion battery materials, and discloses a lithium ion battery high-cycle-life negative electrode material and a preparation method thereof, which comprises the following steps: S1, porous carbon is subjected to lithium evaporation to obtain a first dopant; the surface of the first dopant is deposited with amorphous carbon to obtain a lithium supplement agent; S2, in an inert atmosphere, after oxidation coal-based graphite, a liquid-phase coating agent, the lithium supplement agent and a solvent are blended, a composite material is obtained through carbonization. Through surface coating of the coal-based graphite with metallic lithium, lithium ions are released in the charging and discharging process, and the cycle performance is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, and more specifically, to a high cycle life negative electrode material for lithium-ion batteries and its preparation method. Background Technology

[0002] As market demands for lithium-ion battery energy storage increase, the anode materials used in lithium-ion batteries require excellent cycle performance. Many factors influence the cycle performance of anode materials, such as material isotropy, expansion, surface defects, and side reactions. The main reason for anode material loss is that during lithium-ion charging and discharging, the expansion of the anode material causes SEI recombination, consuming lithium ions and resulting in battery loss. Lithium replenishment at the anode can not only compensate for lithium ion loss during charging and discharging, improving initial efficiency and reducing lithium ion loss, but also enhance cycle performance.

[0003] For example, patent CN105702943A discloses a method for replenishing lithium in a negative electrode material of a lithium-ion battery. The preparation process is as follows: (1) Take the negative electrode material and conductive agent and mix them evenly to obtain a mixed powder; (2) Using a lithium replenishment device, in an inert atmosphere, drip electrolyte into the mixed powder until the electrolyte wets the mixed powder, and use a stainless steel gasket to compact the powder. Then, lay a separator and a lithium sheet on the mixed powder, and use a battery testing system to form the lithium replenishment device. In this technical solution, the preparation process is complex and difficult to industrialize. Moreover, the lithium replenishment process is difficult to control precisely and is prone to lithium plating. Summary of the Invention

[0004] The technical problem solved by this invention:

[0005] This is intended to address the problem of uncontrollable lithium replenishment processes in current anode materials, which easily leads to lithium plating.

[0006] The technical solution adopted in this invention is as follows:

[0007] To address the aforementioned technical problems, the present invention aims to provide a high-cycle-life negative electrode material for lithium-ion batteries and its preparation method. By coating the surface of coal-based graphite with metallic lithium, lithium ions are released during charging and discharging, thereby improving cycle performance.

[0008] The details are as follows:

[0009] First, the present invention provides a method for preparing a high cycle life negative electrode material for lithium-ion batteries, comprising the following steps:

[0010] S1 porous carbon is used to deposit lithium strips to obtain the first dopant; amorphous carbon is deposited on the surface of the first dopant to obtain a lithium replenishing agent; wherein:

[0011] The porous carbon parameters are: pore size 10–30 nm, pore volume 1–5 cm³. 3 / g, specific surface area 50-500m² 2 / g.

[0012] The vapor deposition process parameters are as follows: vapor deposition is carried out in a vacuum environment; deposition voltage is 10–20V; conveyor speed is 10–100 mm / min; vacuum degree is 5 × 10⁻⁶. -4 ~5×10 -2 MBA; Temperature 100~300℃; Operating speed 1-10m / s;

[0013] Surface deposition is performed by introducing a carbon source gas; the carbon source gas includes at least one of methane, acetylene, and ethylene; the temperature is 700–1000℃, and the time is 1–6 h.

[0014] S2, in an inert atmosphere, is mixed with coal-based graphite oxide, a liquid-phase coating agent, a lithium supplement, and a solvent, and then carbonized to obtain a composite material; wherein:

[0015] The mass ratio of coal oxide-based graphite, liquid phase coating agent, lithium supplement agent, and solvent is 100:5~10:0.5~2:100~500;

[0016] The solvent includes at least one of xylene, toluene, cyclohexane, and tetrahydrofuran;

[0017] Liquid phase coating agents include at least one of petroleum asphalt and coal tar pitch, with a softening point of 50-80℃;

[0018] Preparation of coal-based graphite: Anthracite, concentrated sulfuric acid, and potassium permanganate were blended, heated, and then post-treated. The mass ratio of anthracite, concentrated sulfuric acid, and potassium permanganate was 1-5:10-50:1-5. Heating was carried out at 20-50℃ for 10-60 minutes. Post-treatment involved washing and drying the filter residue after the reaction was stopped.

[0019] Carbonization includes primary carbonization and secondary carbonization; the temperature of primary carbonization is lower than that of secondary carbonization; secondary carbonization is carried out under a halogen mixed gas.

[0020] Primary carbonization: carbonization at 200-300℃ for 1-6 hours; Secondary carbonization: carbonization at 700-1200℃ for 1-6 hours;

[0021] Halogen mixed gas is a mixture of halogen gas and argon gas. The halogen gas includes at least one of fluorine, chlorine and bromine gas. The volume ratio of halogen gas to argon gas is 1 to 5:10, and the flow rate is 10 to 100 ml / min.

[0022] Second, the present invention provides a high cycle life anode material for lithium-ion batteries obtained by the aforementioned preparation method.

[0023] The technical effects achieved by this invention are as follows:

[0024] (1) The present invention improves the lithium ion insertion and extraction channels by oxidizing coal-based graphite to form micropores, thereby improving the rate performance of the material during charging and discharging; forming micropores improves the insertion and extraction channels.

[0025] (2) The present invention coats the surface of its material with metallic lithium, which releases lithium ions during charging and discharging, thereby increasing the lithium ion insertion and extraction rate and reducing the irreversible capacity of the material, improving the first efficiency and cycle performance, and using the high specific area of ​​porous carbon in the lithium replenishment agent to improve the liquid retention performance of the material and further improve the cycle performance.

[0026] (3) The present invention modifies the surface of the material by using a mixture of halogen gases. The halogen and carbon materials are modified to form an -RC- structure, which improves the structural stability of the material and improves the cycle performance. Attached Figure Description

[0027] Figure 1 The image shows a SEM image of the graphite composite material prepared in Example 1. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] <Example>

[0030] Preparation method of coal oxide-based graphite: 3g of anthracite, 20g of concentrated sulfuric acid and 3g of potassium permanganate are mixed evenly, then transferred to a water bath at 30℃ and reacted for 30min. After the reaction is stopped, the mixture is filtered, the filter residue is deionized and washed, and then vacuum dried at 80℃ for 24h to obtain coal oxide-based graphite.

[0031] Example 1

[0032] This embodiment provides a high cycle life negative electrode material for lithium-ion batteries, comprising the following steps:

[0033] Step S1: Prepare porous carbon (pore size 20 nm, pore volume 3 cm³). 3 / g, specific surface area 100m² 2 / g) is placed in a vacuum environment and vapor deposition is performed according to the following parameters: deposition voltage 15V, conveyor speed 50mm / min, vacuum degree 5×10 -3In an MBA process at 200℃ and a speed of 5m / s, lithium strips are vapor-deposited onto the surface of porous carbon to form lithium-doped porous carbon. The carbon is then transferred to a tube furnace and methane gas is introduced. Amorphous carbon is deposited on the surface at 900℃ for 3 hours to obtain a lithium replenishing agent.

[0034] Step S2: Under an inert argon atmosphere, 100g of coal-based graphite oxide, 8g of petroleum pitch, 1g of lithium supplement and 300g of xylene organic solvent are mixed evenly. Then, the mixture is first heated to 250℃ for 3h and then carbonized at 900℃ for 3h under a halogen mixed gas (volume ratio, chlorine:argon = 3:10, flow rate 50ml / min) to obtain the graphite composite material.

[0035] Example 2

[0036] This embodiment provides a high cycle life negative electrode material for lithium-ion batteries, comprising the following steps:

[0037] Step S1: Prepare porous carbon (pore size 10 nm, pore volume 5 cm³). 3 / g, specific surface area 500m² 2 / g) is placed in a vacuum environment and subjected to the following parameters: deposition voltage 10V, conveying speed 10mm / min, vacuum degree 5×10 -4 In an MBA process at 300℃ and 1 m / s, lithium strips are vapor-deposited onto the surface of porous carbon to form lithium-doped porous carbon. The carbon is then transferred to a tube furnace and acetylene gas is introduced. Amorphous carbon is deposited on the surface at 700℃ for 6 hours to obtain a lithium replenishing agent.

[0038] Step S2: Under an inert atmosphere, 100g of coal oxide-based graphite, 5g of coal tar pitch, 0.5g of lithium supplement and 100g of toluene organic solvent are mixed evenly. Then, the mixture is first heated to 200℃ for 6h and then heated to 700℃ for 6h under a halogen mixed gas (volume ratio, fluorine:argon = 1:10, flow rate 10ml / min) to obtain graphite composite material.

[0039] Example 3

[0040] This embodiment provides a high cycle life negative electrode material for lithium-ion batteries, comprising the following steps:

[0041] Step S1: Prepare porous carbon (pore size 30 nm, pore volume 1 cm³). 3 / g, specific surface area 50m² 2 / g) is placed in a vacuum environment and subjected to the following parameters: deposition voltage 20V, conveying speed 100mm / min, vacuum degree 5×10 -2In an MBA process at 300℃ and 10m / s, lithium strips are vapor-deposited onto the surface of porous carbon to form lithium-doped porous carbon. The carbon strips are then transferred to a tube furnace, and ethylene carbon source gas is introduced. Amorphous carbon is deposited on the surface at 1000℃ for 1 hour to obtain a lithium replenishing agent.

[0042] Step S2: Under an inert atmosphere, 100g of coal-based graphite oxide, 10g of coal tar pitch, 2g of lithium supplement and 500g of cyclohexane organic solvent are mixed evenly. Then, the mixture is first heated to 300℃ for 1h for carbonization, and then heated to 1200℃ for 1h under a halogen mixed gas (volume ratio, bromine:argon = 5:10, flow rate 100ml / min) to obtain graphite composite material.

[0043] <Comparative Example>

[0044] Comparative Example 1

[0045] Unlike Example 1, no lithium supplement was added; otherwise, it was the same as Example 1.

[0046] <Experimental Example>

[0047] SEM test

[0048] The graphite composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 As shown.

[0049] Depend on Figure 1 As can be seen, the material exhibits a spherical structure, and the particle size is between (8-18) μm.

[0050] Physicochemical testing and its button cell testing

[0051] Methods for testing the electrical conductivity of powder:

[0052] The powder (Examples 1-3, Comparative Example 1) was pressed into a block structure using a powder compaction density meter under a pressure of 2T. The powder conductivity was then tested using a four-probe tester. The test results are shown in Table 1. Specific surface area, particle size, and tap density were tested according to GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0053] Table 1

[0054]

[0055] As can be seen from Table 1, the specific surface area of ​​the materials in the examples is significantly higher than that in the comparative examples. This is because the specific surface area of ​​the materials in the examples contains porous carbon, which increases the specific surface area of ​​the materials, thereby increasing the specific surface area of ​​the graphite composite material.

[0056] Button cell battery test

[0057] The graphite materials from Examples 1-3 and Comparative Example 1 were assembled into coin cells. The assembly method was as follows: a binder, conductive agent, and solvent were added to the negative electrode material, stirred to form a slurry, coated onto copper foil, and then dried and rolled to obtain the negative electrode sheet. The binder used was LA132 binder, the conductive agent was SP, the negative electrode material was the graphite composite material from Examples 1-3 and Comparative Example 1, and the solvent was double-distilled water. The ratio of each component was: negative electrode material: SP: LA132: double-distilled water = 95g: 1g: 4g: 220mL; the electrolyte was LiPF6 / EC+DEC (LiPF6 concentration was 1.2mol / L, EC and DEC volume ratio was 1:1), the lithium metal sheet was used as the counter electrode, and the separator was a polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membrane. The button cell assembly was carried out in a hydrogen-filled glove box. Electrochemical performance testing was conducted using a Wuhan Landian CT2001A battery tester, with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The material's discharge coefficient (DCR) was also tested. The test results are shown in Table 2.

[0058] Table 2

[0059]

[0060] As can be seen from Table 2, the first discharge capacity and first charge-discharge efficiency of the lithium-ion battery using the composite negative electrode materials obtained in Examples 1-3 are significantly higher than those of Comparative Example 1. The reason is that the graphite surface is coated with metallic lithium, which releases lithium ions during the charge-discharge process, increasing the lithium ion insertion and extraction rate and reducing the irreversible capacity of the material, thereby improving the first efficiency and reducing the impedance.

[0061] Soft-pack battery testing

[0062] Anode sheets were prepared using the graphite composite materials from Examples 1-3 and Comparative Example 1 as the anode material. Ternary materials (LiNi) were also used. 1 / 3 Co 1 / 3 Mn 1 / 3 Using O2 as the positive electrode, LiPF6 solution (solvent: EC+DEC, volume ratio 1:1, LiPF6 concentration 1.3 mol / L) as the electrolyte, and Celegard 2400 as the separator, 5 Ah pouch cells were prepared. The cycle performance and rate performance of the pouch cells were then tested.

[0063] Cyclic performance test conditions: charge / discharge current 1C / 1C, voltage range 2.8-4.2V, number of cycles 500. Test results are shown in Table 3.

[0064] Table 3

[0065]

[0066] As can be seen from Table 3, the graphite composite materials prepared in Examples 1-3 exhibit better cycle performance as negative electrodes for pouch batteries than Comparative Example 1. This is because, in terms of 1C / 1C rate cycle performance, the release of lithium ions during charging and discharging increases the lithium ion insertion / extraction rate and reduces the irreversible capacity of the material, thereby improving cycle performance. Furthermore, the high specific area of ​​porous carbon in the lithium replenishment agent enhances the liquid retention performance of the material, further improving cycle performance. Simultaneously, the surface modification of the material by a halogen mixed gas, with the halogen and carbon materials forming an -RC- structure, improves the structural stability of the material and enhances cycle performance.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-cycle-life negative electrode material for lithium-ion batteries, characterized in that, Includes the following steps: S1 porous carbon is vapor-deposited with lithium strips to obtain the first dopant; amorphous carbon is deposited on the surface of the first dopant to obtain a lithium replenishing agent; S2 is a composite material obtained by carbonization after blending coal-based graphite oxide, liquid phase coating agent, lithium supplement agent and solvent in an inert atmosphere; the carbonization includes primary carbonization and secondary carbonization; the temperature of primary carbonization is lower than that of secondary carbonization; the secondary carbonization is carried out under a halogen mixed gas; the liquid phase coating agent includes at least one of petroleum pitch and coal pitch, with a softening point of 50~80℃.

2. The method for preparing the high cycle life negative electrode material for lithium-ion batteries according to claim 1, characterized in that, The porous carbon parameters are: pore size 10~30nm, pore volume 1-5cm³. 3 / g, specific surface area 50~500m² 2 / g.

3. The method for preparing the high cycle life negative electrode material for lithium-ion batteries according to claim 2, characterized in that, The solvent includes at least one of xylene, toluene, cyclohexane, and tetrahydrofuran.

4. The method for preparing a high cycle life negative electrode material for lithium-ion batteries according to any one of claims 1 to 3, characterized in that, S1 includes at least one of features (A1)-(A2): (A1) Evaporation process parameters are as follows: evaporation is performed in a vacuum environment; deposition voltage 10~20V; conveyor speed 10~100mm / min; vacuum degree: 5×10 -4 ~ 5×10 -2 MBA; Temperature 100~300℃; Operating speed 1-10m / s; (A2) Surface deposition is performed by introducing carbon source gas.

5. The method for preparing the high cycle life negative electrode material for lithium-ion batteries according to claim 4, characterized in that, S1 includes at least one of features (A2-1) to (A2-2): (A2-1) The carbon source gas includes at least one of methane, acetylene, and ethylene; (A2-2) Temperature is 700~1000℃, time is 1~6h.

6. The method for preparing a high cycle life negative electrode material for lithium-ion batteries according to any one of claims 1 to 3, characterized in that, S2 includes at least one of features (B1) to (B2): (B1) Preparation of coal-based graphite oxide: Anthracite, concentrated sulfuric acid and potassium permanganate are mixed and then heated and post-treated to obtain the graphite oxide. (B2) The mass ratio of oxidized coal-based graphite, liquid phase coating agent, lithium supplement agent and solvent is 100:5~10:0.5~2:100~500.

7. The method for preparing the high cycle life negative electrode material for lithium-ion batteries according to claim 1, characterized in that, S2 includes at least one of features (B3-1) to (B3-3): (B3-1) Primary carbonization: Carbonization at 200~300℃ for 1~6 hours; (B3-2) Secondary carbonization: Carbonization at 700~1200℃ for 1~6 hours; (B3-3) Halogen mixed gas is a mixture of halogen gas and argon gas. The halogen gas includes at least one of fluorine, chlorine and bromine gas. By volume ratio, halogen gas:argon gas = 1~5:10, and the flow rate is 10~100 ml / min.

8. The high cycle life negative electrode material for lithium-ion batteries obtained by the preparation method according to any one of claims 1 to 7.

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