Preparation method of high-safety artificial graphite negative electrode composite material and lithium ion battery

Abstract

The invention discloses a preparation method of a high-safety artificial graphite negative electrode composite material and a lithium ion battery. The preparation method comprises the following steps: adding the organic aluminum polymer, the aluminum-based coupling agent and the phosphorus-based flame retardant into an organic solvent, uniformly dispersing to obtain a mixed solution, then adding the artificial graphite, and carrying out spray drying to obtain an artificial graphite precursor; and mixing the artificial graphite precursor, asphalt and a catalyst, and carbonizing at a high temperature of 800-1200 DEG C for 1-6 hours to obtain the phosphorus-containing porous alumina coated artificial graphite composite material. When the composite material is subjected to thermal runaway, the impedance of aluminum oxide is sharply increased, the risk of thermal runaway is reduced, and the safety performance of the material is improved by virtue of the flame-retardant characteristic of the phosphorus compound; meanwhile, in the first charging and discharging process, porous aluminum oxide reacts with lithium to generate lithium metaaluminate, so that the conduction rate of lithium ions is increased, and the rate capability of the material is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a method for preparing a high-safety artificial graphite anode composite material and a lithium-ion battery thereof. Background Technology

[0002] Lithium-ion batteries are widely used in power batteries and other fields due to their advantages such as good reversibility, long cycle life, and high energy density. With the increasing demand for pure electric vehicles, higher requirements have been placed on the safety technology of lithium-ion batteries, such as rapid charging and discharging, and the ability to withstand harsh operating conditions like collisions, compression, short circuits, and overcharging. The negative electrode material is one of the key factors affecting battery safety performance. Research has found that at the onset of battery abuse, the negative electrode, especially in the charged state, has very high chemical activity. The SEI film decomposes at high temperatures, and the reaction between the negative electrode and the electrolyte generates heat, further pushing up the battery temperature and exacerbating various side reactions. When the battery temperature reaches above 200°C, the SEI film formed by the negative electrode material begins to decompose, releasing oxygen and generating a large amount of heat, causing large-scale internal short circuits, electrolyte combustion, and ultimately thermal runaway and explosion. Therefore, controlling the source of negative electrode runaway is crucial. Current negative electrode materials, especially artificial graphite, have an outer shell coated with amorphous carbon, which, at excessively high temperatures, results in an unstable SEI film that can easily cause safety hazards. One way to improve the safety of anode materials is to coat the surface of artificial graphite with materials that have good thermal stability or flame retardant materials to reduce thermal runaway and improve safety performance. Summary of the Invention

[0003] To improve the safety performance of artificial graphite, this invention provides a method for preparing a high-safety artificial graphite anode composite material.

[0004] A method for preparing a high-safety artificial graphite anode composite material, characterized by comprising the following steps:

[0005] Step S1:

[0006] According to the mass ratio of organoaluminum polymer: aluminum-based coupling agent: phosphorus-based flame retardant: organic solvent: artificial graphite = 1-10: 1-5: 1-5: 500-1000: 100, the organoaluminum polymer, aluminum-based coupling agent, and phosphorus-based flame retardant are added to the organic solvent and dispersed evenly to obtain a uniformly dispersed mixture. Then, artificial graphite is added and reacted at a temperature of 50-100℃ for 1-3 hours. After spray drying (inlet temperature 180-220℃, outlet temperature 80-120℃, flow rate 0.1kg / h, 5 hours), the artificial graphite precursor is obtained.

[0007] Step S2:

[0008] According to the mass ratio of artificial graphite precursor: asphalt: catalyst = 100:5-15:1-5, artificial graphite precursor, asphalt and catalyst are added to a ball mill and mixed evenly, and then carbonized at a high temperature of 800-1200℃ for 1-6 hours to obtain a phosphorus-containing amorphous carbon porous alumina-coated artificial graphite composite material.

[0009] In step S1, the phosphorus-based flame retardant is one of melamine pyrophosphate, ammonium polyphosphate, melamine polyphosphate, triphenylphosphine, phenylphosphine diamide, and diphenylphosphine; the organic solvent is one of N-methylpyrrolidone, cyclohexane, carbon tetrachloride, and xylene.

[0010] In step S1, the organoaluminum polymer is one of methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, isobutylaluminoxane, methylethylaluminoxane, or methylbutylaluminoxane.

[0011] In step S1, the aluminum-based coupling agent is one of distearyloxyisopropoxyaluminate and isopropyl dioleoyloxyaluminate;

[0012] The catalyst in step S2 is one of Na2CO3, K2CO3, NaHCO3, NH4F, H3BO3, B2O3, and KClO4.

[0013] A lithium-ion battery includes a positive electrode, a negative electrode, and a separator, wherein the negative electrode of the lithium-ion battery is coated with a high-safety artificial graphite negative electrode composite material.

[0014] Beneficial effects:

[0015] This invention utilizes a liquid-phase method to deposit an organoaluminum polymer on the surface of artificial graphite. Due to the coupling effect of the aluminum-based coupling agent's own chemical groups, the chemical groups on the surface of the organoaluminum compound are connected, resulting in a network structure through carbonization. This carbonization process yields porous alumina and a phosphorus-containing amorphous carbon coating layer. The large pore structure of the porous alumina enhances the material's liquid retention performance and reduces the rapid increase in impedance during battery thermal runaway, thus lowering the risk of thermal runaway and improving safety. Furthermore, compared to inorganic aluminum compounds, the organoaluminum compound exhibits milder reaction conditions, lower dispersion uniformity, and relies on the reaction between the -O-AL-O chemical groups on the material surface and the small amount of -COOH / -OH chemical groups on the asphalt surface to enhance the bonding force between materials, reducing impedance and improving processing performance. Simultaneously, during the first charge-discharge process, the porous alumina reacts with lithium to form lithium aluminate, increasing the lithium-ion conductivity and improving the material's rate performance. Phosphorus-based flame retardants are formed through the interaction between organic compounds and organoaluminum polymers. The high specific capacity of the phosphorus-based materials enhances the specific capacity and safety performance, while the high thermal runaway temperature of the alumina generated by the organoaluminum compounds improves the safety level. Attached Figure Description

[0016] Figure 1 The image shows a SEM image of the high-safety artificial graphite anode composite material prepared in Example 1. Detailed Implementation

[0017] Example 1

[0018] A method for preparing a high-safety artificial graphite anode composite material includes the following steps: Step S1:

[0019] 5g of methylaluminoxane, 3g of distearate, and 3g of melamine pyrophosphate were added to 800g of N-methylpyrrolidone and dispersed evenly to obtain a mixture. Then, 100g of artificial graphite was added and dispersed evenly. The mixture was reacted at 80℃ for 2h and then spray-dried (inlet temperature 200℃, outlet temperature 100℃, flow rate 0.1kg / h, 5h) to obtain the artificial graphite precursor.

[0020] Step S2:

[0021] 100g of artificial graphite precursor, 10g of pitch and 3g of Na2CO3 were added to a ball mill and mixed evenly. Then the mixture was transferred to a tube furnace and heated to 900℃ for 3 hours under a nitrogen atmosphere to obtain a phosphorus-containing amorphous carbon porous alumina-coated artificial graphite composite material (abbreviated as: high safety artificial graphite anode composite material).

[0022] Example 2

[0023] A method for preparing a high-safety artificial graphite anode composite material includes the following steps: Step S1:

[0024] 1g of ethylaluminoxane, 1g of isopropyl dioleoyloxyaluminate, and 1g of ammonium polyphosphate were added to 500g of N-methylpyrrolidone and dispersed evenly to obtain a mixture. Then, 100g of artificial graphite was added and dispersed evenly. The mixture was reacted at 50℃ for 3h and spray-dried (inlet temperature 180℃, outlet temperature 80℃, flow rate 0.1kg / h, 5h) to obtain the artificial graphite precursor.

[0025] Step S2:

[0026] 100g of artificial graphite precursor, 5g of pitch and 1g of K2CO3 were added to a ball mill and mixed evenly. Then the mixture was transferred to a tube furnace and heated to 800℃ for 6 hours under a nitrogen atmosphere to obtain a phosphorus-containing amorphous carbon porous alumina-coated artificial graphite composite material (abbreviated as: high safety artificial graphite anode composite material).

[0027] Example 3

[0028] A method for preparing a high-safety artificial graphite anode composite material includes the following steps: Step S1:

[0029] 10g of propylaluminoxane, 5g of distearate, and 5g of melamine polyphosphate were added to 1000g of N-methylpyrrolidone and dispersed evenly to obtain a mixture. Then, 100g of artificial graphite was added and dispersed evenly. The mixture was reacted at 100℃ for 1h and spray-dried (inlet temperature 220℃, outlet temperature 120℃, flow rate 0.1kg / h, 5h) to obtain the artificial graphite precursor.

[0030] Step S2:

[0031] 100g of artificial graphite precursor, 15g of pitch and 5g of NH4F were added to a ball mill and mixed evenly. Then the mixture was transferred to a tube furnace and heated to 1200℃ for 1 hour under a nitrogen atmosphere to obtain a phosphorus-containing amorphous carbon porous alumina-coated artificial graphite composite material (abbreviated as: high safety artificial graphite anode composite material).

[0032] Comparative Example 1:

[0033] Unlike Example 1, aluminum chloride and ammonia were used to replace the organoaluminum polymer and aluminum-based coupling agent.

[0034] Add 10g aluminum chloride and 30g ammonia water to 100g deionized water, then add 100g artificial graphite, mix well, heat to 80℃ and react for 3h, then vacuum dry at 80℃ for 24h to obtain aluminum hydroxide coated artificial graphite precursor material.

[0035] 100g of aluminum hydroxide-coated artificial graphite precursor material, 10g of asphalt, and 3g of Na2CO3 were added to a ball mill and mixed evenly. The mixture was then carbonized at 900℃ for 3 hours to obtain a porous alumina-coated artificial graphite composite material.

[0036] Comparative Example 2:

[0037] 100g of the artificial graphite precursor from step S2 in Example 1 was added to a ball mill and mixed evenly, and then carbonized at 900℃ for 3h to obtain a phosphorus-containing amorphous carbon porous alumina-coated artificial graphite composite material.

[0038] 1) SEM testing

[0039] Figure 1 The image shows a SEM image of the artificial graphite composite material prepared in Example 1. As can be seen from the image, the material exhibits a granular structure with a porous surface and a particle size between 15 and 20 μm.

[0040] 2) Physicochemical properties and button cell testing:

[0041] In this experiment, the specific surface area and tap density of the anode materials of Examples 1-3 and Comparative Examples 1-2 were determined according to the method specified in GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The OI value of the powder material was tested by XRD and the resistivity of the powder was tested by a four-probe tester.

[0042] 9g of the negative electrode material from each of Examples 1-3 and Comparative Examples 1-2, 0.5g of conductive agent SP, and 0.5g of LA132 binder were weighed and added to 220mL of deionized water. After stirring evenly, the mixture was coated onto copper foil to form a membrane. Then, using lithium foil as the negative electrode, Celegard 2400 as the separator, and a 1mol / L LiPF6 solution (the solvent was a mixture of EC and DMC in a volume ratio of 1:1) as the electrolyte, coin cells were assembled in a glove box with oxygen and water content both below 0.1ppm. The initial discharge capacity and initial efficiency of each coin cell were then tested on a blue electric tester. During the test, the cells were charged and discharged at a rate of 0.1C within a voltage range of 0.05V to 2.0V for 3 cycles. The test results are shown in Table 1.

[0043] Table 1

[0044]

[0045] As shown in Table 1, the anode material of the embodiment has better first-time efficiency and first-time discharge capacity than the comparative example. This is because the porous alumina is coated on the surface of the material. The porous alumina does not react with lithium ions and does not form an SEI film, thus reducing the consumption of lithium ions and improving the first-time efficiency. At the same time, the catalyst participates in the reaction to form a dense carbon structure and the amorphous carbon formed by the carbonization of pitch reduces the resistivity of the powder.

[0046] 3) Soft-pack batteries

[0047] Anode sheets were prepared using the artificial graphite composite materials from Examples 1-3 and Comparative Examples 1-2 as the anode material, and ternary materials (Li(Ni)) were used. 0.8 Co 0.1 Mn 0.1 LiPF6 was used as the positive electrode material; a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 was used as the electrolyte; and a 5Ah soft-pack battery was prepared using a Celgard 2400 membrane as the separator, labeled C1, C2, C3, D1, and D2.

[0048] 3.1 Acupuncture test

[0049] Take 10 batteries each from Examples 1-3 and Comparative Examples 1-2. After the batteries are fully charged, insert a nail with a diameter of 5 mm through the center of the battery and install a temperature tester at the battery terminal. Leave the nail inside the battery and observe the battery condition and measure the battery temperature, as shown in Table 2 below.

[0050] Table 2

[0051] Example Temperature (°C) Is it on fire? Example 1 106 no Example 2 109 no Example 3 112 no Comparative Example 1 204 yes Comparative Example 2 213 yes

[0052] As can be seen from Table 2, the artificial graphite composite material in Examples 1 to 3 improves the safety factor because the local temperature of the battery is too high when the battery is used abnormally such as during a short circuit. The impedance of the porous alumina in the examples increases sharply, which avoids thermal runaway of the battery. At the same time, the phosphorus-containing compound, as a flame retardant, can improve the safety performance of the battery.

[0053] 3.2 Impact Test:

[0054] Take 10 batteries each from Examples 1-3 and Comparative Examples 1-2, fully charge them, place a rigid rod with a diameter of 16.0 mm horizontally on the batteries, and drop a 20-pound weight from a height of 610 mm onto the rigid rod. Observe the condition of the batteries. The test results are detailed in Table 3.

[0055] Table 3

[0056]

[0057]

[0058] As can be seen from Table 3, the lithium-ion battery prepared in the example is significantly better than the comparative example in the impact test. The reason is that the phosphorus-based flame retardant is an interaction between organic compounds and organoaluminum polymers, which brings out the high specific capacity of the phosphorus-based material itself to improve the specific capacity and safety performance. The organoaluminum compound generates alumina with a high thermal runaway temperature, which improves the safety performance.

[0059] 3.3 Cyclic Performance

[0060] The cycle performance of the battery was tested at a charge / discharge rate of 1C / 1C and a voltage range of 2.8V-4.2V at a temperature of 25±3℃; the test results are shown in Table 4.

[0061] 3.4x performance:

[0062] The battery was charged to 100% SOC using a constant current + constant voltage mode at a 2C rate. The constant current ratio was then calculated as constant current capacity / (constant current capacity + constant voltage capacity). The test results are shown in Table 4.

[0063] Table 4

[0064]

[0065] As shown in Table 4, the cycle performance and rate performance of the pouch batteries prepared using the artificial graphite composite materials of Examples 1-3 are significantly higher than those of Comparative Examples 1-2. This is because the graphite composite materials of the examples have a high specific surface area, which can improve the liquid absorption capacity of the material and enhance the cycle performance. Meanwhile, the rate performance of the artificial graphite prepared in Examples 1-3 is better than that of the comparative examples. This is because the porous alumina forms lithium aluminate during charge and discharge, which has high lithium-ion conductivity, thus improving the rate performance of the material.

Claims

1. A method for preparing a high-safety artificial graphite anode composite material, characterized in that, Includes the following steps: Step S1: According to the mass ratio of organoaluminum polymer: aluminum-based coupling agent: phosphorus-based flame retardant: organic solvent: artificial graphite = 1-10: 1-5: 1-5: 500-1000: 100, the organoaluminum polymer, aluminum-based coupling agent, and phosphorus-based flame retardant are added to the organic solvent and dispersed evenly to obtain a mixture. Then, artificial graphite is added and spray-dried to obtain the artificial graphite precursor. Step S2: According to the mass ratio of artificial graphite precursor: asphalt: catalyst = 100:5-15:1-5, artificial graphite precursor, asphalt, and catalyst are added to a ball mill and mixed evenly, and then carbonized at a high temperature of 800-1200℃ for 1-6 hours to obtain a high-safety artificial graphite anode composite material.

2. The method for preparing a high-safety artificial graphite anode composite material according to claim 1, characterized in that, In step S1, the phosphorus-based flame retardant is one of melamine pyrophosphate, ammonium polyphosphate, melamine polyphosphate, triphenylphosphine, phenylphosphine diamide, and diphenylphosphine.

3. The method for preparing a high-safety artificial graphite anode composite material according to claim 1, characterized in that, In step S1, the organoaluminum polymer is one of methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, isobutylaluminoxane, methylethylaluminoxane, or methylbutylaluminoxane.

4. The method for preparing a high-safety artificial graphite anode composite material according to claim 1, characterized in that, In step S1, the aluminum-based coupling agent is one of distearyloxyisopropoxyaluminate and isopropyl dioleoyloxyaluminate.

5. The method for preparing a high-safety artificial graphite anode composite material according to claim 1, characterized in that, The catalyst in step S2 is one of Na2CO3, K2CO3, NaHCO3, NH4F, H3BO3, B2O3, and KClO4.

6. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator, wherein the negative electrode of the lithium-ion battery is coated with a high-safety artificial graphite negative electrode composite material prepared by the method described in claim 1.

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