Preparation method of silicon negative electrode of conductive binder containing side-chain-free n-type high-conductivity polymer material PBFDO

Abstract

The invention provides a preparation method of a silicon negative electrode of a conductive binder containing a side-chain-free n-type high-conductivity polymer material PBFDO, and the preparation method comprises the following steps: S1, blending organic acid, alcohol, salt and PBFDO, and carrying out heating and stirring reaction to obtain a binder precursor solution; and S2, blending and stirring the binder precursor solution and an active substance, coating a substrate with the mixture, and drying to obtain the silicon negative electrode, wherein the active substance is selected from one or more of nano silicon, micron silicon and silicon carbon. According to the invention, organic acid, alcohol, salt and PBFDO are mutually crosslinked to obtain the binder, and the binder forms a three-dimensional elastic structure on the surface of silicon particles in situ, so that the volume change of the silicon negative electrode in the cycle process can be effectively accommodated, the structural damage caused by the volume change is effectively relieved, and the cycle stability of the battery is improved; and meanwhile, the conductivity of the silicon-based negative electrode is effectively improved by the PBFDO, and the practical application of the PBFDO in the lithium ion battery is realized.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery materials, and mainly to a method for preparing a silicon negative electrode containing a conductive binder of an n-type high-conductivity polymer material PBFDO without a side chain. Background Art

[0002] With the continuous development of society, people have higher requirements for the battery life of portable electronic devices and power batteries. At present, with the continuous optimization of material processes, the lithium-ion battery system has gradually approached its theoretical energy density. Therefore, in the development of high-energy-density systems, it is necessary to develop negative electrode materials with higher theoretical energy density.

[0003] Silicon, as the negative electrode material of lithium-ion batteries, has a low lithium desorption potential (about 0.2-0.5V, vs. Li / Li + ) and a higher theoretical capacity (4200mAh g -1 ), is considered to be a suitable negative electrode material for the new generation of high energy density lithium-ion batteries. However, silicon particles will produce huge volume deformation (about 300%) during the charge and discharge process, causing damage to the negative electrode structure, and ultimately leading to a significant reduction in cycle life, which greatly limits the use of silicon negative electrodes.

[0004] Optimizing and improving silicon-based negative electrode binders is a very effective and promising way to solve the problems of silicon-based active materials. However, some current binders are very brittle when used independently and are difficult to resist the repeated large volume expansion of silicon particles. At the same time, the point contact between the conductive agent particles and silicon is difficult to provide sufficient electron transmission efficiency, which leads to large polarization of the battery during use and difficulty in fully releasing the capacity.

[0005] In summary, it is necessary to develop a new technical solution to solve the defects and shortcomings in the existing technology. Summary of the invention

[0006] The present invention provides a method for preparing a silicon negative electrode with a conductive binder containing a side chain-free n-type high-conductivity polymer material PBFDO (poly(benzodifurandione)). The method for preparing a silicon negative electrode with a conductive binder containing a side chain-free n-type high-conductivity polymer material PBFDO in situ constructs a functional surface coating layer on the surface of silicon negative electrode particles, forms an interface layer with certain elasticity through mutual bonding between functional groups, and has excellent mechanical properties. Then, a conductive network is constructed by introducing a conductive polymer, thereby effectively improving the conductivity of the silicon electrode and the cycle performance of the silicon negative electrode, and has good application prospects.

[0007] One object of the present invention is to provide a method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without a side chain, characterized in that the method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without a side chain comprises the following steps:

[0008] S1, mixing organic acid, alcohol, salt and PBFDO, heating and stirring to react, and obtaining a binder precursor solution;

[0009] S2, mixing the binder precursor solution and the active material, coating the mixture on a substrate, and drying the mixture to obtain a silicon negative electrode;

[0010] Wherein, the active material is selected from one or more of nano silicon, micro silicon, and silicon carbon.

[0011] Furthermore, the organic acid is selected from one or more of ferulic acid, itaconic acid, citric acid, phytic acid and malic acid.

[0012] Furthermore, the alcohol is selected from one or more of glycerol, ethylene glycol, isopropanol and polyethylene glycol.

[0013] Furthermore, the salt is selected from one or more of sodium styrene sulfonate and sodium lignin sulfonate.

[0014] Furthermore, the mass ratio of the organic acid, alcohol, salt, PBFDO and active substance is (5-20):(5-20):(1-5):(1-5):(60-80).

[0015] Furthermore, in step S1, the temperature of the heating and stirring reaction is 60-120° C. and the time is 10-15 h.

[0016] Furthermore, in step S2, the stirring time is 0.5-2h.

[0017] Furthermore, in step S2, the drying temperature is 60-120° C. and the drying time is 16-24 hours.

[0018] The present invention has the following beneficial effects:

[0019] The present invention provides a method for preparing a silicon negative electrode with a conductive binder containing a side chain-free n-type high-conductivity polymer material PBFDO, wherein an organic acid, alcohol, salt, and PBFDO are cross-linked to obtain a binder, and then the binder reacts with silicon to obtain a silicon negative electrode, and the reaction process between the binder and silicon is an esterification reaction between the sulfonic acid groups in the salt molecules provided by the present invention, the hydroxyl groups carried by the natural oxide on the surface of the silicon particles, and the abundant carboxyl groups contained in the organic acid, and cross-links with each other. The binder forms a three-dimensional elastic structure in situ on the surface of the silicon particles, which can effectively accommodate the volume change of the silicon negative electrode during the cycle, thereby effectively alleviating the structural damage caused by the volume change of the silicon negative electrode during the cycle, and improving the cycle stability of the silicon-based negative electrode lithium ion battery; at the same time, the n-type conductive polymer PBFDO is introduced into the binder, which can effectively improve the conductivity of the silicon-based negative electrode, and realize the practical application of the n-type conductive polymer in lithium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The silicon-based negative electrode obtained in Example 1 shows the -1 CV curve of.

[0021] Figure 2 The graph shows the cycle performance of the silicon-based negative electrode material obtained in Example 1 when used as a negative electrode material for a lithium-ion battery.

[0022] Figure 3 The graph shows the cycle performance of the silicon-based negative electrode material obtained in Example 2 when used as a negative electrode material for a lithium-ion battery.

[0023] Figure 4 The graph shows the cycle performance of the silicon-based negative electrode material obtained in Comparative Example 1 when used as a negative electrode material for a lithium-ion battery. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the technical solution of the present invention, the following examples are listed. Unless otherwise stated, the raw materials, reactions and post-treatment methods shown in the examples are common raw materials on the market and technical methods well known to those skilled in the art.

[0025] The words "preferred", "preferably", "more preferably", etc. in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same circumstances or other circumstances. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0026] It should be understood that, except in any operating examples, or where otherwise indicated, all numbers indicating, for example, the amounts of ingredients used in the specification and claims should be understood to be modified in all cases by the term "about". Therefore, unless indicated to the contrary, the numerical parameters set forth in the following specification and the appended claims are approximate values ​​that vary depending on the desired properties to be obtained by the present invention.

[0027] The present invention adopts the following raw materials:

[0028] PBFDO was published in Nature by Professor Huang Fei, Academician Cao Yong, and Academician Ma Yuguang from the State Key Laboratory of Luminescent Materials and Devices of South China University of Technology in an article titled "A solution-processed n-type conducting polymer with ultrahigh conductivity";

[0029] Polyethylene glycol, molecular weight 20,000, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0030] Nanosilicon, particle size 100-200 nm, purchased from Alfa Aesar (China) Chemical Co., Ltd.;

[0031] Sodium carboxymethyl cellulose, molecular weight 700,000, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0032] Carbon nanotubes, outer diameter 10-20 nm, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0033] Polyvinylidene fluoride, molecular weight 400,000, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0034] Styrene butadiene rubber, model L-SBR-822, was purchased from Aladdin Biochemical Technology Co., Ltd.

[0035] Example 1

[0036] A method for preparing a silicon negative electrode containing a conductive binder of an n-type high-conductivity polymer material PBFDO without a side chain, comprising the following steps:

[0037] S1, 0.15g itaconic acid, 0.1g polyethylene glycol, 0.02g sodium lignin sulfonate, and 0.03g PBFDO were mixed, heated to 80°C and stirred for 10h to obtain a binder precursor solution;

[0038] S2. Blend the binder precursor solution and 0.7 g of nano-silicon, stir for 0.5 h, apply it on the current collector copper foil, and dry it at 80° C. for 16 h to obtain a silicon negative electrode sheet.

[0039] Example 2

[0040] A method for preparing a silicon negative electrode containing a conductive binder of an n-type high-conductivity polymer material PBFDO without a side chain, comprising the following steps:

[0041] S1, 0.2 g itaconic acid, 0.05 g polyethylene glycol, 0.01 g sodium lignin sulfonate, and 0.04 g PBFDO were mixed, heated to 80° C. and stirred for 10 h to obtain a binder precursor solution;

[0042] S2. Blend the binder precursor solution and 0.7 g of nano-silicon, stir for 0.5 h, apply it on the current collector copper foil, and dry it at 80° C. for 16 h to obtain a silicon negative electrode sheet.

[0043] Example 3

[0044] A method for preparing a silicon negative electrode containing a conductive binder of an n-type high-conductivity polymer material PBFDO without a side chain, comprising the following steps:

[0045] S1, 0.2g phytic acid, 0.05g polyethylene glycol, 0.01g sodium lignin sulfonate, and 0.04g PBFDO were mixed, heated to 80°C and stirred for 10h to obtain a binder precursor solution;

[0046] S2. Blend the binder precursor solution and 0.7 g of nano-silicon, stir for 0.5 h, apply it on the current collector copper foil, and dry it at 80° C. for 16 h to obtain a silicon negative electrode sheet.

[0047] Example 4

[0048] A method for preparing a silicon negative electrode containing a conductive binder of an n-type high-conductivity polymer material PBFDO without a side chain, comprising the following steps:

[0049] S1, 0.15g itaconic acid, 0.1g polyethylene glycol, 0.02g sodium lignin sulfonate, and 0.03g PBFDO were mixed, heated to 80°C and stirred for 10h to obtain a binder precursor solution;

[0050] S2. Blend the binder precursor solution and 0.7 g of nano-silicon, stir for 0.5 h, apply it on the current collector copper foil, and dry it at 60° C. for 16 h to obtain a silicon negative electrode sheet.

[0051] Comparative Example 1

[0052] A method for preparing a silicon negative electrode comprises the following steps:

[0053] Sodium carboxymethyl cellulose, carbon nanotubes and nano-silicon were mixed in a mass ratio of 1:2:7, that is, 0.05g sodium carboxymethyl cellulose, 0.1g carbon nanotubes and 0.35g nano-silicon were mixed and stirred for 0.5h, then coated on the current collector copper foil and dried at 80°C for 16h to obtain a silicon negative electrode sheet.

[0054] Comparative Example 2

[0055] A method for preparing a silicon negative electrode comprises the following steps:

[0056] Polyvinylidene fluoride, carbon nanotubes and nano-silicon were mixed in a mass ratio of 1:2:7, that is, 0.05g polyvinylidene fluoride, 0.1g carbon nanotubes and 0.35g nano-silicon were mixed and stirred for 2.5h, coated on the current collector copper foil, and dried at 80°C for 16h to obtain a silicon negative electrode sheet.

[0057] Comparative Example 3

[0058] A method for preparing a silicon negative electrode comprises the following steps:

[0059] Sodium carboxymethyl cellulose, styrene butadiene rubber, carbon nanotubes and nano-silicon are mixed in a mass ratio of 0.5:0.5:2:7, i.e., 0.025g sodium carboxymethyl cellulose, 0.025g styrene butadiene rubber, 0.1g carbon nanotubes and 0.35g nano-silicon are mixed and stirred for 0.5h, coated on the current collector copper foil, and dried at 80°C for 16h to obtain a silicon negative electrode sheet.

[0060] Comparative Example 4

[0061] The preparation method of Comparative Example 4 is the same as that of Example 1, except that:

[0062] Step S1 was modified as follows: 0.15 g of itaconic acid, 0.1 g of polyethylene glycol, 0.02 g of sodium lignin sulfonate, and 0.03 g of PBFDO were blended and stirred for 10 h to obtain a binder precursor solution.

[0063] Test Example 1

[0064] The performance tests were performed on the silicon negative electrodes of Examples 1-4 and Comparative Examples 1-4.

[0065] Test Method

[0066] The prepared silicon negative electrode was transferred to an argon glove box, and a button cell was assembled using metallic lithium as the positive electrode. The diaphragm was Celgard 2325 and the electrolyte was 1.0 M LiPF 6in ECD:EC=1:1Vol%with 5%FEC. The battery was assembled in a glove box and sealed, and then left to stand for 12 hours. The battery was then tested for constant current electrochemical performance on a charge and discharge battery test system. The cycle test was performed at 0.2Ag -1 The current density was 0.01-1.5V.

[0067] Test Results

[0068] Figure 1 The silicon-based negative electrode obtained in Example 1 shows the -1 CV curve of.

[0069] Figure 2 The graph shows the cycle performance of the silicon-based negative electrode material obtained in Example 1 when used as a negative electrode material for a lithium-ion battery.

[0070] Figure 3 The graph shows the cycle performance of the silicon-based negative electrode material obtained in Example 2 when used as a negative electrode material for a lithium-ion battery.

[0071] Figure 4 The graph shows the cycle performance of the silicon-based negative electrode material obtained in Comparative Example 1 when used as a negative electrode material for a lithium-ion battery.

[0072] Table 1 shows the cycle performance of the silicon-based negative electrode materials obtained in Examples 1-4 and Comparative Examples 1-4 when used as negative electrode materials for lithium-ion batteries.

[0073] Table 1 Cyclic performance test results of the silicon-based negative electrode materials obtained in Examples 1-4 and Comparative Examples 1-4 when used as negative electrode materials for lithium-ion batteries

[0074] project <![CDATA[Specific capacity (mAh g -1 )]]> Coulomb efficiency (%) Example 1 2032 58.66 Example 2 2016 57.45 Example 3 2011 53.45 Example 4 2019 57.95 Comparative Example 1 1409 38.24 Comparative Example 2 1699 55.44 Comparative Example 3 1912 53.79 Comparative Example 4 1458 32.78

[0075] From Table 1, Figure 1 , Figure 2 , Figure 3 It can be seen that the specific capacity of Example 1-2 is 2000 mAh g -1 In the silicon negative electrode preparation method provided by the present invention, a three-dimensional elastic structure is formed in situ on the surface of silicon particles to construct an ester bond network with high elastic modulus and a stable SEI layer, thereby alleviating the problem of separation of the silicon negative electrode active material and the current collector due to volume expansion during the cycle of the silicon-based battery, thereby achieving high coulombic efficiency and stable operation of the silicon negative electrode, which has practical significance and effect on improving the cycle performance of the silicon negative electrode.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0077] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without a side chain, characterized in that: The method for preparing the silicon negative electrode containing the conductive binder of the n-type high conductivity polymer material PBFDO without side chains comprises the following steps: S1, mixing organic acid, alcohol, salt and PBFDO, heating and stirring to react, and obtaining a binder precursor solution; S2, mixing the binder precursor solution and the active material, coating the mixture on a substrate, and drying the mixture to obtain a silicon negative electrode; Wherein, the active material is selected from one or more of nano silicon, micro silicon, and silicon carbon.

2. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: The organic acid is selected from one or more of ferulic acid, itaconic acid, citric acid, phytic acid and malic acid.

3. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: The alcohol is selected from one or more of glycerol, ethylene glycol, isopropanol and polyethylene glycol.

4. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: The salt is selected from one or more of sodium styrene sulfonate and sodium lignin sulfonate.

5. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: The mass ratio of the organic acid, alcohol, salt, PBFDO and active substance is (5-20):(5-20):(1-5):(1-5):(60-80).

6. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: In step S1, the temperature of the heating and stirring reaction is 60-120° C. and the time is 10-15 h.

7. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: In step S2, the stirring time is 0.5-2h.

8. The method for preparing a silicon negative electrode containing a conductive binder of an n-type high conductivity polymer material PBFDO without side chains according to claim 1, characterized in that: In step S2, the drying temperature is 60-120°C and the drying time is 16-24 hours.

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