CN107742694B

CN107742694B - Silicon-based negative electrode plate, silicon-doped composite current collector and lithium ion battery

Info

Publication number: CN107742694B
Application number: CN201711123398.8A
Authority: CN
Inventors: 赵晓锋; 张要军; 怀永建; 郭建峰
Original assignee: China Aviation Lithium Battery Co Ltd; China Aviation Lithium Battery Research Institute Co Ltd
Current assignee: Avic Innovation Technology Research Institute Jiangsu Co ltd; China Aviation Lithium Battery Co Ltd; CALB Technology Co Ltd
Priority date: 2017-11-14
Filing date: 2017-11-14
Publication date: 2020-04-10
Anticipated expiration: 2037-11-14
Also published as: CN107742694A

Abstract

The invention relates to a silicon-based negative electrode plate, a silicon-doped composite current collector and a lithium ion battery. The silicon-based negative pole piece comprises a current collector and an electrode material layer attached to the current collector, wherein the current collector is a silicon-doped composite current collector which is formed by doping silicon into the current collector by adopting an ion injection method. According to the silicon-based negative electrode plate provided by the invention, silicon is doped into the current collector in an ion injection mode to form a silicon-doped current collector, and an electrode material is coated on the silicon-doped current collector to prepare the silicon-based negative electrode. Defects, dislocation or damage are generated in the current collector in the ion injection process, the expansion rate of silicon in the current collector under charge and discharge is small, and the silicon expansion rate is changed within a controllable range, so that the problem that the expansion rate of the silicon-based negative electrode is large and uncontrollable in the circulation process is greatly improved.

Description

Silicon-based negative electrode plate, silicon-doped composite current collector and lithium ion battery

Technical Field

The invention belongs to the field of lithium ion batteries, and particularly relates to a silicon-based negative electrode plate, a silicon-doped composite current collector and a lithium ion battery.

Background

The rapid development of electric vehicles has increasingly stringent requirements on high-specific-capacity, long-cycle-life and high-safety power lithium ion batteries. In the lithium ion battery cathode material, the capacity advantage (the theoretical specific capacity is up to 4200mAh/g) which is incomparable with other materials and high safety of silicon are widely concerned by researchers. However, the volume expansion of the silicon-based negative electrode in the circulation process is as high as 300%, so that the material is easily pulverized, and the electrical contact with a current collector is lost, so that the circulation performance of the silicon-based negative electrode is rapidly reduced.

Patent application publication No. CN107293700A discloses a silicon-based negative electrode sheet, which is improved by using a silicon-carbon composite material having a three-layer composite structure including silicon-carbon composite particles located in an inner core, a porous carbon layer located in a middle layer and a dense carbon layer located in an outer layer. Although the silicon-carbon composite material improves the first charge-discharge efficiency of the battery, the problem of large expansion rate of the silicon-carbon composite material still cannot be improved after multiple cycles, so that the cycle performance and the rate performance of the lithium ion battery still need to be further improved.

Disclosure of Invention

The invention aims to provide a silicon-based negative electrode plate, so that the problem of high expansion rate of the conventional silicon-based negative electrode is solved. The invention also provides a silicon-doped composite current collector and a lithium ion battery.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a silicon-based negative pole piece comprises a current collector and an electrode material layer attached to the current collector, wherein the current collector is a silicon-doped composite current collector which is formed by doping silicon into the current collector by adopting an ion injection method.

According to the silicon-based negative electrode plate provided by the invention, silicon is doped into the current collector in an ion injection mode to form a silicon-doped current collector, and an electrode material is coated on the silicon-doped current collector to prepare the silicon-based negative electrode. Defects, dislocation or damage are generated in the current collector in the ion injection process, the expansion rate of silicon in the current collector under charge and discharge is small, and the silicon expansion rate is changed within a controllable range, so that the problem that the expansion rate of the silicon-based negative electrode is large and uncontrollable in the circulation process is greatly improved.

Meanwhile, the internal resistance between silicon and a current collector is reduced, and the conductivity is improved. On the premise of improving the expansion rate and the conductivity, the cycle performance and the rate performance of the silicon-based negative electrode can be obviously improved.

The ion injection method is to inject the high-energy ions accelerated by the extraction electrode into the solid target material, transfer the energy to the target material atoms and make them dislocate, to generate a large amount of dislocated atoms and vacancies, and the injected ions stay in the target due to the energy loss to become impurity atoms, and combine with the matrix elements to realize doping. By adjusting the energy and the dose of the implanted ions, the ion implantation method can control the depth distribution and the doping concentration of the incident ions, thereby calculating the chemical content of the doping elements in the matrix.

The process of ion implantation into the surface of material is the process of interaction between implanted ions and base atoms, the process of sputtering and precipitated phase formation is generated on the surface of material, and the process of point defect, dislocation and irradiation damage is generated in the internal structure of material. The invention utilizes the action process to combine silicon with elements contained in the current collector, thereby reducing the expansion rate of silicon in the circulation process while exerting high specific capacity of silicon.

In the ion implantation process, the implantation energy is 100-300 kev, and the implantation dose is (1-3) × 10¹⁵cm^-2。Si²⁺The implantation depth of (A) is 10 to 1000 nm. The ion implantation process under the above preferred parameters has better silicon doping effect.

During the ion implantation process, polysilicon can be used as the implantation source. The injection process is preferably carried out under a protective atmosphere. And annealing treatment is carried out after ion implantation to eliminate implantation damage. The annealing treatment is carried out in a protective atmosphere, the temperature of the annealing treatment is 90-100 ℃, and the time is 1-2 hours. And annealing to obtain the silicon-doped composite current collector.

The negative electrode current collector is generally made of copper foil, and metal foil such as nickel foil or aluminum foil may be selected according to the kind of the negative electrode material and the needs of application.

The current collector is an etched current collector subjected to etching treatment. The etching treatment is acid etching. Specifically, the current collector is soaked in an acid solution, washed by secondary distilled water and dried. The concentration of the acid solution is (0.01-0.1) mol/L, and the soaking time is (1-24) hours. The acid can be one of hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid. The current collector can remove the surface oxide layer and form a rough surface after chemical etching, so that preparation can be made for ion implantation, and a better ion implantation effect can be obtained. The current collector after chemical etching treatment can also provide larger contact area, thereby facilitating the adhesion of electrode material layers, reducing contact internal resistance and improving the energy density of the pole piece.

The electrode material layer can meet the requirements by adopting conventional cathode materials such as graphite and the like. Preferably, the electrode material layer comprises a silane coupling agent and a conductive agent, and the weight ratio of the silane coupling agent to the conductive agent is (50-70): (10-30). Preferably, the electrode material layer consists of a silane coupling agent, a conductive agent and a binder, and the weight ratio of the silane coupling agent to the conductive agent is (50-70): (10-30): (5-10). By adopting the electrode material layer with the composition, the silane coupling agent can connect the current collector and the conductive agent on one hand, so that the conductivity of the pole piece is further improved; on the other hand, the silane coupling agent can react with lithium ions, the lithium storage reaction of silicon doped into the current collector is not influenced, and meanwhile, a protective layer can be formed, so that the direct contact between the silicon and the electrolyte is reduced, and the occurrence probability of side reaction of the silicon is reduced. The conductive agent can further improve the capacity and conductivity of the negative electrode.

The electrode material layer is prepared by preparing electrode material layer slurry and then utilizing a coating technology. The coating technology can adopt the existing gravure printing, spraying and other technologies. The electrode material layer slurry is formed by mixing a silane coupling agent, a conductive agent, a binder and a solvent. Preferably, the weight ratio of the silane coupling agent to the conductive agent to the binder to the solvent is: (50-70): (10-30): (5-10): 500. the binder can be polyvinylidene fluoride binder, and the corresponding solvent can be N-methyl pyrrolidone. Other types of binders and solvents can be used without affecting the physical and chemical properties of the electrode material.

The silane coupling agent is gamma-aminopropyltriethoxysilane, gamma- (2, 3-epoxypropoxy) propyltrimethoxysilane, gamma- (methacryloyloxy) propyltrimethoxysilane, octyltriethoxysilane, dimethyldimethoxysilane, methyltributanoxime silane or isocyanatopropyltriethoxysilane. The conductive agent is one or a combination of more of nitrogen-doped graphene, boron-doped graphene and graphene.

By adopting the optimized electrode material layer, the conductivity, the cycle performance and the rate performance of the silicon-based negative electrode plate can be further improved, so that the defects of low energy density and poor cycle performance of the conventional lithium ion battery are overcome.

The technical scheme adopted by the silicon-doped composite current collector is as follows:

a silicon-doped composite current collector is obtained by doping silicon into the current collector by adopting an ion implantation method.

The preferred technical solution of the silicon-doped composite current collector can refer to the preferred technical solution of the silicon-based negative electrode, and is not described in detail herein.

The silicon-doped composite current collector is very suitable for preparing a silicon-based negative electrode plate, has the characteristics of small silicon expansion and high energy density, and can remarkably improve the conductivity and the cycle performance of a silicon-based negative electrode.

The lithium ion battery adopting the silicon-based negative electrode pole piece has good cycle performance and rate performance due to the improvement of conductivity and structural stability, and the electrochemical performance of the conventional lithium ion battery adopting the silicon-based negative electrode is obviously improved.

Drawings

Fig. 1 is an SEM image of a silicon-based negative electrode tab of example 1.

Detailed Description

The following examples are provided to further illustrate the practice of the invention. The nitrogen-doped graphene is purchased from Nanjing GmbH nanotechnology Co., Ltd, and has the model of JCG-2-3-N; boron-doped graphene is purchased from Nanjing GmbH nanotechnology, Inc., model JCG-2-3-B.

Example 1

The silicon-based negative electrode plate comprises a silicon-doped composite current collector and electrode material layers attached to the surfaces of two sides of the silicon-doped composite current collector, and is prepared by the following steps:

1) immersing a copper foil with the thickness of 15 mu m into 0.1mol/L hydrochloric acid solution, treating for 12 hours, and then cleaning and drying by adopting secondary distilled water to obtain an etched copper foil; placing the etched copper foil into ion implantation equipment, and performing ion implantation on the etched copper foil under the protection of argon by taking polycrystalline silicon as an implantation source; the implantation time is 10min, the implantation energy is 200kev, and the implantation dose is 2 × 10¹⁵cm^-2The injection depth reaches 500nm, and then thermal annealing is carried out under the protection of argon, the annealing temperature is 90 ℃, and the time is 2 hours; obtaining a silicon-doped composite current collector;

2) uniformly mixing 60g of gamma-aminopropyltriethoxysilane, 20g of nitrogen-doped graphene conductive agent, 8g of polyvinylidene fluoride binder and 500g N-methyl pyrrolidone to prepare electrode material layer slurry; and coating the electrode material layer slurry on the surfaces of two sides of the silicon-doped composite current collector by using a gravure printing technology, and drying to obtain the silicon-based negative pole piece.

The lithium ion battery of this embodiment adopts the silicon-based negative electrode plate of this embodiment, and the positive electrode is made of a lithium iron phosphate material, and the LiPF with a concentration of 1mol/L is used₆The solution (solvent is formed by mixing EC and DEC in a volume ratio of 1: 1) is used as electrolyte, Celgard 2400 membrane is used as a diaphragm, and the 5Ah soft package battery is assembled according to the prior art.

Example 2

1) immersing a copper foil with the thickness of 15 mu m into a nitric acid solution of 0.1mol/L, treating for 1h, and then cleaning and drying by adopting secondary distilled water to obtain an etched copper foil; placing the etched copper foil into ion implantation equipment, and performing ion implantation on the etched copper foil under the protection of argon by taking polycrystalline silicon as an implantation source; the implantation time was 5min, the implantation energy was 100kev, and the implantation dose was 1 × 10¹⁵cm^-2The injection depth reaches 10nm, and then thermal annealing is carried out under the protection of argon, the annealing temperature is 100 ℃, and the time is 1 h; obtaining a silicon-doped composite current collector;

2) uniformly mixing 50g of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane, 30g of boron-doped graphene conductive agent, 5g of polyvinylidene fluoride binder and 500g N-methyl pyrrolidone, and preparing electrode material layer slurry; and coating the electrode material layer slurry on the surfaces of two sides of the silicon-doped composite current collector by using a gravure printing technology, and drying to obtain the silicon-based negative pole piece.

The lithium ion battery of this embodiment adopts the silicon-based negative electrode sheet of this embodiment, and the preparation method is the same as that of embodiment 1.

Example 3

1) soaking a copper foil with the thickness of 15 mu m into a 1mol/L phosphoric acid solution, and treating for 24 hours to obtain an etched copper foil; placing the etched copper foil into ion implantation equipment, and performing ion implantation on the etched copper foil under the protection of nitrogen by taking polycrystalline silicon as an implantation source; the implantation time was 20min, the implantation energy was 300kev, and the implantation dose was 3 × 10¹⁵cm^-2The injection depth reaches 1000nm, and then thermal annealing is carried out under the protection of argon, the annealing temperature is 100 ℃, and the time is 1 h; obtaining a silicon-doped composite current collector;

2) uniformly mixing 70g of octyl triethoxysilane, 30g of graphene conductive agent, 10g of polyvinylidene fluoride binder and 500g N-methyl pyrrolidone to prepare electrode material layer slurry; and coating the electrode material layer slurry on the surfaces of two sides of the silicon-doped composite current collector by using a gravure printing technology, and drying to obtain the silicon-based negative pole piece.

In other embodiments of the silicon-based negative electrode plate of the present invention, the method in example 1 may be referred to replace the silane coupling agent with γ - (methacryloyloxy) propyl trimethoxysilane, dimethyl dimethoxysilane, methyl tributyrinoxime silane or isocyanatopropyl triethoxysilane by an equivalent amount, so as to obtain a silicon-based negative electrode plate with a comparable effect.

Comparative example

According to the negative pole piece of the comparative example, a silicon-carbon material is used as a negative pole material, 95g of the silicon-carbon material, 4g of LA132 binder, 1gSP conductive agent and 200ml of secondary distilled water are mixed to prepare negative pole material slurry, the negative pole material slurry is coated on copper foil, and the negative pole piece is prepared through drying and rolling. Lithium iron phosphate is adopted as a positive electrode material. The silicon-carbon material is purchased from Shenzhen fibrate rui new energy science and technology Limited and has the model number of S400. A 5Ah pouch cell was prepared as in example 1.

Test example 1

In this test example, the microscopic morphology of the silicon-based negative electrode plate of example 1 is observed, and the SEM image thereof is shown in fig. 1. As can be seen from fig. 1, the silicon-based negative electrode of example 1 has uniform wrinkles on the surface thereof and has a plurality of pore structures.

Test example 2

In the test example, the negative electrode plates of examples 1 to 3 and comparative example were used as negative electrodes, and LiPF with a concentration of 1mol/L was used₆The solution (the solvent is formed by mixing EC and DEC in a volume ratio of 1: 1) is used as electrolyte, the metal lithium sheet is used as a counter electrode, the polyethylene film is used as a diaphragm, and the button cell is assembled in a glove box filled with hydrogen. Electrochemical performance of each button cell was measured on a wuhan blue CT2001A type cell tester, the charging and discharging voltage range was 0.005V to 2.0V, the charging and discharging rate was 0.1C, and the test results are shown in table 1.

Table 1 comparison of test results of button cells of each example and comparative example

Item	Example 1	Example 2	Example 3	Comparative example
					First discharge capacity (mAh/g)	555.5	536.6	527.1	412
First efficiency (%)	94.1	94.3	93.1	91.4
					Compacted density (g/cm)³)	1.81	1.76	1.75	1.54

As can be seen from the test results in Table 1, the button cells of examples 1-3 had first discharge capacities of 555.5mAh/g, 536.6mAh/g, 527.1mAh/g, respectively, which were much higher than the first discharge capacity of the comparative example, 412 mAh/g. Meanwhile, the compaction density of the silicon-based negative electrode of the embodiment 1-3 reaches (1.75-1.81) g/cm³The cathode pole piece prepared by the method has the characteristics of high gram volume and large compaction density, and is suitable for preparing a high-energy-density lithium ion battery.

Test example 3

The test examples examine the liquid-absorbing and liquid-retaining ability and the pole piece rebound of the negative pole piece of each example and comparative example, and the results are shown in tables 2 and 3. The rebound of the pole piece is detected by adopting the following method: the average thickness of the pole piece was first tested with a micrometer (D1), then the pole piece was placed in a 45 ℃ oven to dry for 24h, and then the thickness of the pole piece was tested (D2), with the rebound rate of the pole piece being (D2-D1)/D1 x 100%.

Table 2 liquid-absorbing and liquid-retaining ability test results of negative electrode sheets of each example and comparative example

The test results in table 2 show that the liquid absorption speed and the liquid retention performance of the negative electrode plate in examples 1 to 3 are significantly better than those of the comparative example, and the rough surface formed in the etching process and the hole structure formed in the ion implantation process are beneficial to improving the liquid absorption and retention capability of the negative electrode plate.

TABLE 3 comparative table of the rebound ratios of the negative electrode sheets of the respective examples and comparative examples

Numbering	Rebound Rate (%) of Pole piece
		Example 1	4.8
Example 2	5.6
		Example 3	5.1
Comparative example	19.6

The test results in table 3 show that the negative electrode sheets of examples 1 to 3 exhibit a low rebound rate, which indicates that silicon is doped into the current collector in an ion implantation manner, and the expansion rate of the silicon material can be significantly reduced.

Test example 4

The test example inspects the cycle performance of the soft package lithium ion battery of each embodiment and comparative example, and the specific detection conditions are as follows: the charge and discharge multiplying power is 1.0C/1.0C, the voltage range is 3.0-4.2V, the temperature is 23 +/-5 ℃, and the detection results are shown in Table 4.

Table 4 comparison of the cycling performance of soft-packed lithium ion batteries of each example and comparative example

Numbering	Capacity retention (%) after 500 cycles
		Example 1	92.62
Example 2	91.78
		Example 3	90.39
Comparative example	85.55

As can be seen from the results in table 4, the lithium ion batteries of examples 1 to 3 have improved conductivity and structural stability of the negative electrode, reduced probability of side reaction between silicon and the electrolyte, and improved cycle performance by designing the silicon-doped electrode material layer.

Claims

1. A silicon-based negative pole piece comprises a current collector and an electrode material layer attached to the current collector, and is characterized in that the current collector is a silicon-doped composite current collector which is formed by doping silicon into the current collector by adopting an ion injection method;

the electrode material layer consists of a silane coupling agent, a conductive agent and a binder, and the weight ratio of the silane coupling agent to the conductive agent is (50-70): (10-30): (5-10).

2. The silicon-based negative electrode plate of claim 1, wherein during the ion implantation, the implantation energy is 100 to 300kev, and the implantation dose is (1 to 3) × 10¹⁵cm^-2。

3. The silicon-based negative electrode tab of claim 1, wherein during the ion implantation, Si is present²⁺The implantation depth of (A) is 10 to 1000 nm.

4. The silicon-based negative electrode plate according to claim 2 or 3, wherein annealing treatment is performed after ion implantation.

5. The silicon-based negative electrode plate according to claim 1, wherein the current collector is an etched current collector subjected to etching treatment.

6. The silicon-based negative electrode plate of claim 1, wherein the silane coupling agent is γ -aminopropyltriethoxysilane, γ - (2, 3-epoxypropoxy) propyltrimethoxysilane, γ - (methacryloyloxy) propyltrimethoxysilane, octyltriethoxysilane, dimethyldimethoxysilane, methyltributanoxime silane, or isocyanatopropyltriethoxysilane.

7. The silicon-based negative electrode plate of claim 1, wherein the conductive agent is one or more of nitrogen-doped graphene, boron-doped graphene and graphene.

8. A silicon-doped composite current collector is characterized in that silicon is doped into the current collector by adopting an ion implantation method.

9. A lithium ion battery using the silicon-based negative electrode plate of claim 1.