Lithium ion cell with ultrahigh energy density and preparation method thereof

Abstract

The invention discloses a lithium ion battery cell with ultrahigh energy density and a preparation method thereof. The negative electrode of the battery cell is prepared from the following raw materials: graphite, silicon carbon, conductive carbon black, polyacrylic acid, butadiene styrene rubber and single-walled carbon nanotubes. According to the battery cell negative electrode disclosed by the invention, a silicon-carbon material is used as a novel gas-phase silicon-carbon material, so that a silicon-based material can be reduced to a nanometer level, and more gaps can be formed for buffering stress and deformation generated by silicon in a lithium ion de-intercalation process; a porous carbon skeleton structure is adopted, a silicon expansion space is fully reserved, in addition, a double-layer carbon coating technology can inhibit silicon expansion, and the conductivity of the material is improved; the single-walled carbon nanotubes can inhibit the expansion of the silicon material and improve the conductivity by forming a reticular conductive network; polyacrylic acid can be combined with graphite and silicon carbon surface functional groups through carboxyl to promote the formation of an SEI film, so that the cycle performance is improved, and the negative electrode expansion is reduced. The gram capacity of the prepared battery negative electrode can reach 400 mAh / g or above, the first efficiency reaches 93%, and the battery negative electrode has high energy density and good cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery cell with ultra-high energy density and a preparation method thereof. Background Art

[0002] Since the commercialization of lithium-ion batteries in 1991, they have been used in all aspects of human life. With the popularization of mobile phones and electric vehicles, people have put forward higher demands on the energy density of lithium-ion batteries.

[0003] The theoretical gram capacity of lithium cobalt oxide is 274mAh / g, and the theoretical gram capacity of graphite is 372mAh / g. The gram capacity and compaction density of graphite on the market are close to the theoretical limit. It is difficult to improve the energy density of graphite. High-voltage lithium cobalt oxide is limited by the high temperature and high pressure stability of the electrolyte, and progress is slow. In addition, silicon is the material with the highest theoretical gram capacity known for negative electrode materials. The gram capacity can reach 4200mAh / g, which is more than 10 times that of graphite. It can greatly improve the energy density of the battery, but silicon negative electrodes have problems such as large expansion after cycling and poor conductivity. How to solve the expansion and poor conductivity of silicon materials has become a major problem in the commercial application of silicon negative electrodes. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides a lithium-ion battery cell with ultra-high energy density and a preparation method thereof, which can solve the above-mentioned technical problems.

[0006] (II) Technical solution

[0007] To solve the above technical problems, the present invention provides the following technical solution: a lithium-ion battery cell with ultra-high energy density, wherein the negative electrode of the lithium-ion battery cell with ultra-high energy density adopts the following raw material formula with the following mass fraction: 90-95% graphite, 2-7% silicon carbon, 0.5-1.5% conductive carbon black, 1.0-2.5% polyacrylic acid, 1.0-2.5% styrene-butadiene rubber and 0.02-0.15% single-walled carbon nanotubes.

[0008] Preferably, the silicon-carbon is a nano-scale silicon-carbon composite material.

[0009] Preferably, the silicon carbon comprises a nano silicon core, a carbon coating layer and a graphene coating layer, wherein the carbon coating layer is coated on the surface of the nano silicon core, and the graphene coating layer is coated on the surface of the carbon coating layer.

[0010] Preferably, the carbon coating layer is a porous structure.

[0011] Preferably, the electrolyte of the ultra-high energy density lithium-ion battery cell is added with fluoroethylene carbonate.

[0012] In order to solve the above technical problems, the present invention provides another technical solution as follows: a method for preparing a lithium-ion battery cell with ultra-high energy density, wherein the negative electrode of the lithium-ion battery cell with ultra-high energy density adopts the following raw material formula by mass fraction: 90-95% graphite, 2-7% silicon carbon, 0.5-1.5% conductive carbon black, 1.0-2.5% polyacrylic acid, 1.0-2.5% styrene-butadiene rubber and 0.02-0.15% single-walled carbon nanotubes; the preparation method is specifically a negative electrode homogenization method, and the preparation method comprises the following steps:

[0013] S1: dry-mixing graphite, silicon carbon and conductive carbon black powder to obtain a first mixed powder, and at the same time, dispersing carboxymethyl cellulose powder at a high speed by deionized water;

[0014] S2: Wetting the first mixed powder with deionized water to obtain a second mixed powder, and at the same time, dispersing the carboxymethyl cellulose powder and polyacrylic acid at a high speed to obtain a third mixed powder;

[0015] S3: dispersing the third mixed powder and the single-walled carbon nanotubes at high speed to obtain a fourth mixed powder, and further kneading a portion of the fourth mixed powder and the second mixed powder to obtain a fifth mixed powder;

[0016] S4: homogenizing and stirring the remaining part of the fourth mixed powder and the fifth mixed powder with deionized water to obtain a first slurry;

[0017] S5: adjusting the viscosity of the first slurry by using deionized water to obtain a second slurry;

[0018] S6: Adding styrene-butadiene rubber to the second slurry to obtain a third slurry.

[0019] Preferably, step S6 further comprises: performing vacuum defoaming on the third slurry.

[0020] Preferably, a portion of the fourth mixed powder specifically accounts for 35-55% of the total amount of the fourth mixed powder, and the remaining portion of the fourth mixed powder specifically accounts for 45-65% of the total amount of the fourth mixed powder.

[0021] (III) Beneficial effects

[0022] Compared with the prior art, the present invention provides a lithium-ion battery cell with ultra-high energy density and a preparation method thereof, which has the following beneficial effects: (1) By adding silicon carbon to graphite, the lithium-ion battery cell of the present invention has the advantages of graphite negative electrode batteries such as strong stability, good wear resistance, and a wide operating temperature range, while the silicon carbon can greatly improve the energy density of the lithium-ion battery cell of the present invention. In addition, the silicon carbon also has the advantages of low expansion and good cycle performance; (2) By adding polyacrylic acid to the raw material formula of the negative electrode, the polyacrylic acid binder has a large number of carboxyl groups. These carboxyl groups combine with graphite and silicon carbon surface functional groups through hydrogen bonds to promote the formation of the negative electrode SEI film, which can greatly improve the cycle performance and bonding performance of the silicon negative electrode and reduce the expansion of the negative electrode; (3) Single-walled carbon nanotubes have excellent conductivity. The single-walled carbon nanotubes dispersed in the negative electrode can form a mesh conductive network to inhibit the expansion and cracking of the silicon material, improve the conductivity of the silicon material, and improve the cycle performance of the silicon negative electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The first schematic diagram of a method for preparing a lithium-ion battery cell with ultra-high energy density according to the present invention;

[0024] Figure 2 This is a second schematic diagram of a method for preparing a lithium-ion battery cell with ultra-high energy density according to the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The invention provides a lithium ion battery cell with ultra-high energy density. The negative electrode of the lithium ion battery cell with ultra-high energy density adopts the following raw material formula with mass fraction: 90-95% of graphite, 2-7% of silicon carbon, 0.5-1.5% of conductive carbon black (SP), 1.0-2.5% of polyacrylic acid (PAA), 1.0-2.5% of styrene-butadiene rubber (SBR) and 0.02-0.15% of single-walled carbon nanotubes (CNTs).

[0027] The first embodiment of the negative electrode of the ultra-high energy density lithium-ion battery cell adopts the following raw material formula in mass fraction: 90% graphite, 6% silicon carbon, 1.0% conductive carbon black, 1.5% polyacrylic acid, 1.35% styrene-butadiene rubber and 0.15% single-walled carbon nanotubes.

[0028] The second embodiment of the negative electrode of the ultra-high energy density lithium-ion battery cell adopts the following raw material formula in mass fraction: 92% graphite, 4% silicon carbon, 1.5% conductive carbon black, 1.0% polyacrylic acid, 1.4% styrene-butadiene rubber and 0.1% single-walled carbon nanotubes.

[0029] It should be understood that silicon-carbon refers to a composite material of silicon and carbon. The silicon material has a high specific capacity, and the carbon material has good stability, small volume change, and excellent conductivity. The silicon-carbon material formed by the combination of the two can effectively improve the specific capacity of the negative electrode of the lithium-ion battery cell and also improve the conductive performance of the battery cell.

[0030] Preferably, the silicon-carbon is a nanoscale silicon-carbon composite material, that is, the silicon-carbon material is reduced to the nanoscale, so that there can be more gaps for buffering the stress and deformation generated by silicon during the lithium ion insertion and extraction process; further, the silicon-carbon is preferably a vapor-deposited silicon-carbon material.

[0031] Preferably, silicon carbon includes a nano silicon core, a carbon coating layer and a graphene coating layer, wherein the carbon coating layer is coated on the surface of the nano silicon core, and the graphene coating layer is coated on the surface of the carbon coating layer, that is, a double-layer carbon is used to coat the nano silicon core. By adopting the above double-layer carbon coating technology, the expansion of silicon can be suppressed and the electrical conductivity of the material can be improved. Furthermore, the above carbon coating layer is preferably a porous structure, that is, a porous carbon skeleton structure is adopted to fully reserve silicon expansion space to better solve the expansion problem of silicon materials. In addition, silicon carbon can also be used: artificial graphite or natural graphite is used as the substrate, a layer of silicon nanoparticles is pinned on the graphite surface, and then a layer of graphene is coated on the surface of the silicon nanoparticles; other types of silicon carbon composite materials in the prior art can also be used.

[0032] Preferably, the electrolyte of the ultra-high energy density lithium-ion battery cell is added with fluoroethylene carbonate (FEC), so that the SEI film (solid electrolyte interface film) generated by the lithium-ion battery cell is more dense and stable, and can repair the rupture of the SEI film caused by the volume expansion of the silicon negative electrode during the cycle, further improving the battery cell cycle performance.

[0033] The present invention also provides a method for preparing a lithium-ion battery cell with ultra-high energy density, wherein the negative electrode of the lithium-ion battery cell with ultra-high energy density also adopts the following raw material formula by mass fraction: 90-95% graphite, 2-7% silicon carbon, 0.5-1.5% conductive carbon black, 1.0-2.5% polyacrylic acid, 1.0-2.5% styrene-butadiene rubber and 0.02-0.15% single-walled carbon nanotubes. The above-mentioned preparation method is specifically a method for homogenizing the negative electrode, and the preparation method comprises the following steps:

[0034] S1: Graphite, silicon carbon and conductive carbon black (SP) are dry-mixed to obtain a first mixed powder. At the same time, carboxymethyl cellulose (CMC) powder is dispersed at a high speed by deionized water, wherein the added amount of carboxymethyl cellulose powder can be the same as that of the conductive carbon black, and the added amount of deionized water can be half of the added amount of carboxymethyl cellulose powder.

[0035] S2: The first mixed powder is wetted with deionized water to obtain a second mixed powder, and the amount of deionized water added can be specifically one-third of the mass of the first mixed powder; at the same time, carboxymethyl cellulose powder and polyacrylic acid (PAA) are dispersed at a high speed to obtain a third mixed powder.

[0036] S3: The third mixed powder and single-walled carbon nanotubes (CNTs) are dispersed at high speed to obtain a fourth mixed powder, and further, a part of the fourth mixed powder and the second mixed powder are kneaded to obtain a fifth mixed powder.

[0037] S4: The remaining part of the fourth mixed powder and the fifth mixed powder are homogenized and stirred with deionized water to obtain a first slurry, and the amount of deionized water added is such that the fourth mixed powder and the fifth mixed powder are in a slurry state after stirring. The part of the fourth mixed powder may specifically account for 35-55% of the total amount of the fourth mixed powder, and the remaining part of the fourth mixed powder may specifically account for 45-65% of the total amount of the fourth mixed powder.

[0038] S5: The viscosity of the first slurry is adjusted by deionized water to obtain a second slurry. The amount of deionized water added can be one third of the mass of the first slurry. Of course, the amount of deionized water added can also be adjusted accordingly according to different viscosity requirements of the slurry. No excessive restrictions are made here.

[0039] S6: adding styrene-butadiene rubber to the second slurry to obtain a third slurry; further, vacuum defoaming the third slurry. It should be understood that the third slurry is further coated on a metal foil, and then dried, rolled, slit, etc. to obtain the negative electrode of the lithium-ion battery cell.

[0040] The preparation method of the present invention can achieve better negative electrode homogenization effect by combining the steps of powder dry mixing, wetting, multiple high-speed dispersion, kneading, homogenization and stirring, so as to better ensure the negative electrode performance of the lithium ion battery cell.

[0041] The performance of the lithium-ion battery cell of the present invention was tested, and the results were as follows: (1) Fully charged: the negative electrode interface was golden yellow, without black spots or watermarks, and no material fell off; (2) Half-charged negative electrode expansion: 18.5-20.5%; (3) Nominal voltage was 3.83V; (4) Cycle performance: standard 1C / 0.5C, 800-week retention rate was 83.2%, and the thickness expansion rate was 10.78%; (5) High and low temperature performance: after 7 days of storage at 70°C, the discharge performance retention rate was 71.9%, the recovery rate was 84.1%, and the thickness expansion rate was 4.6%; the retention rate of -20°C 0.2C discharge was 51.8%.

[0042] Compared with the prior art, the present invention provides a lithium-ion battery cell with ultra-high energy density and a preparation method thereof, which has the following beneficial effects: (1) By adding silicon carbon to graphite, the lithium-ion battery cell of the present invention has the advantages of graphite negative electrode batteries such as strong stability, good wear resistance, and a wide operating temperature range, while the silicon carbon can greatly improve the energy density of the lithium-ion battery cell of the present invention. In addition, the silicon carbon also has the advantages of low expansion and good cycle performance; (2) By adding polyacrylic acid to the raw material formula of the negative electrode, the polyacrylic acid binder has a large number of carboxyl groups. These carboxyl groups combine with graphite and silicon carbon surface functional groups through hydrogen bonds to promote the formation of the negative electrode SEI film, which can greatly improve the cycle performance and bonding performance of the silicon negative electrode and reduce the expansion of the negative electrode; (3) Single-walled carbon nanotubes have excellent conductivity. The single-walled carbon nanotubes dispersed in the negative electrode can form a mesh conductive network to inhibit the expansion and cracking of the silicon material, improve the conductivity of the silicon material, and improve the cycle performance of the silicon negative electrode. The negative electrode gram capacity of the lithium-ion battery cell of the present invention can reach more than 400 mAh / g, the first efficiency reaches 93%, the negative electrode does not fall off when fully charged and the energy density can be increased by about 5% compared with the pure graphite battery cell, and the energy density can reach 770Wh / L, taking into account both high energy density and good cycle performance.

[0043] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0044] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium-ion battery cell with ultra-high energy density, It is characterized in that The negative electrode of the ultra-high energy density lithium-ion battery cell adopts the following raw material formula by mass fraction: 90-95% graphite, 2-7% silicon carbon, 0.5-1.5% conductive carbon black, 1.0-2.5% polyacrylic acid, 1.0-2.5% styrene-butadiene rubber and 0.02-0.15% single-walled carbon nanotubes.

2. The ultra-high energy density lithium-ion battery cell according to claim 1, Features: The silicon-carbon is a nanometer-level silicon-carbon composite material.

3. The ultra-high energy density lithium-ion battery cell according to claim 1, Features: The silicon carbon comprises a nano silicon core, a carbon coating layer and a graphene coating layer, wherein the carbon coating layer is coated on the surface of the nano silicon core, and the graphene coating layer is coated on the surface of the carbon coating layer.

4. The ultra-high energy density lithium-ion battery cell according to claim 3, Features: The carbon coating layer is a porous structure.

5. The ultra-high energy density lithium-ion battery cell according to claim 1, Features: The electrolyte of the ultra-high energy density lithium-ion battery cell is added with fluoroethylene carbonate.

6. A method for preparing a lithium-ion battery cell with ultra-high energy density, Features: The negative electrode of the ultra-high energy density lithium-ion battery cell adopts the following raw material formula by mass fraction: 90-95% graphite, 2-7% silicon carbon, 0.5-1.5% conductive carbon black, 1.0-2.5% polyacrylic acid, 1.0-2.5% styrene-butadiene rubber and 0.02-0.15% single-walled carbon nanotubes; the preparation method is specifically a homogenization method of the negative electrode, and the preparation method comprises the following steps: S1: dry-mixing the graphite, the silicon carbon and the conductive carbon black to obtain a first mixed powder, and at the same time, dispersing the carboxymethyl cellulose powder at a high speed by deionized water; S2: Wetting the first mixed powder with deionized water to obtain a second mixed powder, and at the same time, dispersing the carboxymethyl cellulose powder and the polyacrylic acid at a high speed to obtain a third mixed powder; S3: dispersing the third mixed powder and the single-walled carbon nanotubes at high speed to obtain a fourth mixed powder, and further kneading a portion of the fourth mixed powder and the second mixed powder to obtain a fifth mixed powder; S4: homogenizing and stirring the remaining part of the fourth mixed powder and the fifth mixed powder with deionized water to obtain a first slurry; S5: adjusting the viscosity of the first slurry with deionized water to obtain a second slurry; S6: adding the styrene-butadiene rubber to the second slurry to obtain a third slurry.

7. The method for preparing a lithium-ion battery cell with ultra-high energy density according to claim 6, It is characterized in that The step S6 also includes: performing vacuum defoaming on the third slurry.

8. The method for preparing a lithium-ion battery cell with ultra-high energy density according to claim 6, Features: A portion of the fourth mixed powder specifically accounts for 35-55% of the total amount of the fourth mixed powder, and the remaining portion of the fourth mixed powder specifically accounts for 45-65% of the total amount of the fourth mixed powder.

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