A lithium battery for electric vehicles

Abstract

The present invention discloses a lithium battery for electric vehicles. It includes a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet is coated with a positive electrode active material; the negative electrode sheet is coated with a negative electrode active material and a protective layer; the negative electrode active material includes silicon dioxide, modified carbon black, a binder and an additive in a weight ratio of 0.1 to 0.5: 2 to 5: 0.01 to 0.1: 0.1 to 0.5. The present invention can significantly improve the uniformity and specific capacity of the negative electrode material, effectively improve the cycle performance of the battery, and thus extend the service life of the battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium batteries, and in particular relates to a lithium battery for electric vehicles. Background Art

[0002] Energy shortages and climate change have attracted global attention to electric vehicles, which have the advantages of energy conservation and environmental protection. Electric vehicles use electricity to replace fossil fuels such as oil as power, and are the only long-term solution for future transportation. Lithium-ion batteries have the advantages of high operating voltage, wide operating temperature range, high energy density, high output power, no memory effect and long cycle life. They are not only widely used in 3C digital products such as mobile phones and laptops, but also have a broad application market in new energy vehicles and large-scale energy storage.

[0003] However, most lithium-ion batteries currently still use lithium iron phosphate batteries. When this type of battery is used for a long time, or when it is cycled more than 2,000 times at room temperature, it will experience accelerated attenuation, which will affect the battery's service life. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a lithium battery for electric vehicles, which can effectively improve the service life of the lithium battery.

[0005] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0006] A lithium battery for electric vehicles, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet is coated with a positive electrode active material; the negative electrode sheet is coated with a negative electrode active material and a protective layer;

[0007] The negative electrode active material includes silicon dioxide, modified carbon black, a binder and an additive in a weight ratio of 0.1-0.5:2-5:0.01-0.1:0.1-0.5.

[0008] Further, the negative electrode active material includes silicon dioxide, modified carbon black, a binder and an additive in a weight ratio of 0.5:3:0.5:0.1.

[0009] Further, the preparation method of modified carbon black is as follows:

[0010] (1) immersing carbon black in an aqueous solution containing 0.1 to 5 wt% lithium chloride, then adding barium chloride, stirring and dissolving, adjusting the pH of the solution to 9 to 11, filtering, and collecting a solid phase product;

[0011] (2) Heat the solid product at 600-800°C for 5-10 minutes, take it out and grind it.

[0012] Furthermore, the binder is at least one of acrylic acid, lithium-substituted acrylic acid, sodium alginate, polyhydroxy compounds, polyacrylates and silane coupling agents.

[0013] Furthermore, the binder includes sodium alginate and acrylic acid in a weight ratio of 0.5-1:1-2.

[0014] Furthermore, the additive is at least one of lithium nitrate, rubidium nitrate, indium nitride, phosphorus pentasulfide and lithium sulfate.

[0015] Furthermore, the preparation method of the protective layer is as follows:

[0016] Molybdenum disulfide and lithium salt are mixed in a weight ratio of 0.5 to 1:3 to 5 and then cured to form a film to form a protective layer.

[0017] Furthermore, the lithium salt is one or more of lithium ethoxide, lithium formate, lithium oxalate and lithium stearate.

[0018] Furthermore, the positive electrode sheet is aluminum foil, and the positive electrode active material is lithium iron phosphate.

[0019] Furthermore, the negative electrode sheet is a copper foil, and a separator is provided between the positive electrode sheet and the negative electrode sheet.

[0020] Furthermore, the electrolyte includes a lithium salt and a solvent.

[0021] Furthermore, the lithium salt is at least one of LiPF6, LiBOB, LiFSI, LiTFSI, and LiPO2F2, and its concentration is 1.0 to 1.5 mol / L.

[0022] Furthermore, at least one of the solvents EC, DMC, EMC, PA, MB, and EB.

[0023] Beneficial effects of the present invention:

[0024] 1. The present invention uses lithium chloride and barium chloride as raw materials, and forms barium hydroxide and lithium hydroxide in the matrix of carbon black through the precipitation effect of sodium hydroxide. At high temperature, the two react with carbon dioxide to form lithium carbonate and barium carbonate. Under the action of barium carbonate, the specific capacitance of lithium carbonate in the negative electrode material is improved. At the same time, barium carbonate and lithium carbonate are loaded into the interlayer of carbon black, avoiding the problem that barium carbonate and lithium carbonate have poor compatibility with carbon black and are difficult to mix evenly, and at the same time, the conductivity of carbon black will not be significantly reduced.

[0025] 2. The present invention uses modified carbon black in the negative electrode material so that lithium carbonate and barium carbonate can be fully and evenly mixed with the carbon black, thereby improving the uniformity and specific capacity of the negative electrode material, and effectively improving the cycle performance of the battery.

[0026] 3. The present invention also adds silicon dioxide to the negative electrode active material to improve the cycle life of the battery. However, the battery performance will be greatly reduced due to the large difference in silicon / carbon expansion coefficients. Therefore, the present application uses a compound of sodium alginate and acrylic acid as a binder. The carboxyl group can effectively promote the formation of the SEI film and improve the cycle performance of the silicon-containing negative electrode. The ions formed by the ionization of sodium alginate can further promote the process, thereby effectively solving the problem of battery performance degradation caused by the large difference in silicon / carbon expansion coefficients.

[0027] 4. Binders can promote the formation of SEI films, but may cause uneven or excessive growth of negative electrode SEI. Therefore, the present application further adds additives that enhance battery stability to the negative electrode active material to avoid uneven or excessive growth of negative electrode SEI. DETAILED DESCRIPTION

[0028] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0029] Example 1

[0030] A lithium battery for electric vehicles, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; wherein:

[0031] The electrolyte consists of solvent EC and LiFSI, and the final concentration of LiFSI is 1.5 mol / L;

[0032] The positive electrode is aluminum foil with a pressure of 120 mg / cm 2 It is coated with lithium iron phosphate active material, then rolled, die-cut and baked;

[0033] The negative electrode sheet is a copper foil, which is coated with negative electrode active material and then dried. Then, a protective layer is coated on the negative electrode active material and then dried. The negative electrode active material is 135 mg / cm 2 The protective layer is coated at 40 mg / cm 2 The protective layer is formed by mixing molybdenum disulfide and lithium formate in a weight ratio of 1:3 and then curing to form a film.

[0034] The negative electrode active material includes silicon dioxide, modified carbon black, a binder and lithium nitrate in a weight ratio of 0.1-2:0.5:0.1. The binder includes sodium alginate and acrylic acid in a weight ratio of 0.5:1.

[0035] The preparation method of modified carbon black is as follows:

[0036] (1) immersing carbon black in an aqueous solution containing 1.5 wt% lithium chloride, then adding barium chloride, stirring and dissolving, adding sodium hydroxide to adjust the pH of the solution to 10, filtering, and collecting a solid phase product;

[0037] (2) The solid phase product is heated at 800°C for 6 minutes, then taken out and ground.

[0038] Example 2

[0039] A lithium battery for electric vehicles, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; wherein:

[0040] The electrolyte consists of solvent DMC and LiPF6, and the final concentration of LiPF6 is 1.5 mol / L;

[0041] The positive electrode is aluminum foil with a thickness of 100 mg / cm 2 It is coated with lithium iron phosphate active material, then rolled, die-cut and baked;

[0042] The negative electrode sheet is a copper foil, which is coated with a negative electrode active material and then dried. A protective layer is then coated on the negative electrode active material and then dried. The negative electrode active material is 130 mg / cm 2 The protective layer is coated at 45 mg / cm 2 The protective layer is formed by mixing molybdenum disulfide and lithium formate in a weight ratio of 0.5:3 and then curing to form a film.

[0043] The negative electrode active material includes silicon dioxide, modified carbon black, a binder and lithium nitrate in a weight ratio of 0.5:3:0.5:0.1. The binder includes sodium alginate and acrylic acid in a weight ratio of 0.5:2.

[0044] The preparation method of modified carbon black is as follows:

[0045] (1) immersing carbon black in an aqueous solution containing 0.5 wt% lithium chloride, then adding barium chloride, stirring and dissolving, adding sodium hydroxide to adjust the pH of the solution to 10, filtering, and collecting a solid phase product;

[0046] (2) Heat the solid product at 800°C for 10 min, take it out and grind it.

[0047] Example 3

[0048] A lithium battery for electric vehicles, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; wherein:

[0049] The electrolyte consists of solvent PA and LiPF6, and the final concentration of LiPF6 is 1.5 mol / L;

[0050] The positive electrode is aluminum foil with a pressure of 125 mg / cm 2 It is coated with lithium iron phosphate active material, then rolled, die-cut and baked;

[0051] The negative electrode sheet is a copper foil, which is coated with negative electrode active material and then dried. Then, a protective layer is coated on the negative electrode active material and then dried. The negative electrode active material is 125 mg / cm 2 The protective layer is coated with 50mg / cm 2 The protective layer is formed by mixing molybdenum disulfide and lithium formate in a weight ratio of 1:3.5 and then curing to form a film.

[0052] The negative electrode active material includes silicon dioxide, modified carbon black, a binder and lithium nitrate in a weight ratio of 0.5:3:0.5:0.5. The binder includes sodium alginate and acrylic acid in a weight ratio of 1:1.

[0053] The preparation method of modified carbon black is as follows:

[0054] (1) immersing carbon black in an aqueous solution containing 1.0 wt% lithium chloride, then adding barium chloride, stirring and dissolving, adding sodium hydroxide to adjust the pH of the solution to 10, filtering, and collecting a solid phase product;

[0055] (2) The solid phase product is heated at 800°C for 8 minutes, then taken out and ground.

[0056] Comparative Example 1

[0057] Compared with Example 2, graphite is used in the negative electrode active material to replace the modified carbon black, and the rest of the process is the same as Example 2.

[0058] Comparative Example 2

[0059] Compared with Example 2, CMC is used in the adhesive to replace acrylic acid, and the rest of the process is the same as Example 2.

[0060] Comparative Example 3

[0061] Compared with Example 2, only CMC is used as the binder, and the rest of the process is the same as Example 2.

[0062] Comparative Example 4

[0063] Compared with Example 2, the amount of additive in the negative electrode is 0, and the rest of the process is the same as Example 2.

[0064] The lithium batteries of Examples 1-3 and Comparative Examples 1-4 were subjected to charge and discharge tests, charged to a voltage of 3.6V at different current rates, constant voltage to 0.1C, left for 10 minutes, and then discharged to a cut-off voltage of 2.0V at different current rates; the lithium batteries of Examples 1-3 and Comparative Examples 1-4 were subjected to long cycle tests at a charge and discharge rate of 1C, with a cycle number of 3000 times. The results are shown in Table 1:

[0065] Table 1 Lithium battery performance

[0066]

[0067] As can be seen from the data in Table 1, the performance of the lithium-ion batteries prepared in Examples 1 to 3 of the present application is significantly better than that of Comparative Examples 1 to 4. Among them, Comparative Example 1 uses graphite to replace modified carbon black as the negative electrode active material, and it can be seen that its performance has declined. Comparative Examples 2 and 3 replaced the acrylic acid in the binder, resulting in a significant decline in the prepared batteries, reflecting the impact of the binder used in this application on the battery performance. Comparative Example 4 does not use additives in the negative electrode active material. From the results, it can be seen that not using additives will have a certain impact on battery performance, but it is not the main factor affecting battery performance.

Claims

1. A lithium battery for electric vehicles, characterized in that: It includes a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet is coated with a positive electrode active material; the negative electrode sheet is coated with a negative electrode active material and a protective layer; The negative electrode active material includes silicon dioxide, modified carbon black, a binder and an additive in a weight ratio of 0.1-0.5:2-5:0.5-1:0.1-0.5; The preparation method of the modified carbon black is as follows: (1) Immerse the carbon black in an aqueous solution containing 0.1-5 wt% lithium chloride, then add barium chloride, stir and dissolve, adjust the pH of the solution to 9-11, filter and collect the solid phase product; (2) Heat the solid product at 600-800°C for 5-10 minutes, take it out and grind it; The binder comprises sodium alginate and acrylic acid in a weight ratio of 0.5-1:1-2.

2. The lithium battery for electric vehicles according to claim 1, characterized in that: The negative electrode active material includes silicon dioxide, modified carbon black, a binder and an additive in a weight ratio of 0.5:3:0.5:0.

1.

3. The lithium battery for electric vehicles according to claim 1 or 2, characterized in that: The additive is at least one of lithium nitrate, rubidium nitrate, indium nitride, phosphorus pentasulfide and lithium sulfate.

4. The lithium battery for electric vehicles according to claim 1, characterized in that: The preparation method of the protective layer is as follows: Molybdenum disulfide and lithium salt are mixed in a weight ratio of 0.5-1:3-5 and then cured into a film to form a protective layer.

5. The lithium battery for electric vehicles according to claim 1, characterized in that: The positive electrode sheet is aluminum foil, and the positive electrode active material is lithium iron phosphate.

6. The lithium battery for electric vehicles according to claim 1, characterized in that: The negative electrode sheet is a copper foil, and a separation film is arranged between the positive electrode sheet and the negative electrode sheet.

7. The lithium battery for electric vehicles according to claim 1, characterized in that: The electrolyte includes a lithium salt and a solvent.

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