A biomass-based aqueous binder for lithium ion battery silicon negative electrode and a preparation method and application thereof

Abstract

The application discloses a biomass-based aqueous binder for a lithium ion battery silicon negative electrode and a preparation method and application thereof. The preparation method of the binder comprises the following steps: adding carboxymethyl cellulose into water, stirring and uniformly mixing, then adding caffeic acid monomer, and then adding an initiator hydrogen peroxide and ferrous sulfate, and stirring and reacting under heating, and then adding a LiOH solution to adjust a pH value to 6-8 after the reaction is completed, so that the biomass-based aqueous binder for the lithium ion battery silicon negative electrode is obtained. The binder prepared in the application can be applied to the silicon negative electrode of a lithium ion battery, and can effectively enhance mechanical properties, cycle performance and capacity retention of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery electrode material and biomass binder synthesis, in particular to a biomass-based aqueous binder for lithium ion battery silicon negative electrode and its preparation method and application. BACKGROUND

[0002] The traditional lithium ion battery negative electrode is generally graphite, which has a low theoretical specific capacity and is difficult to meet the increasing requirement of energy density of lithium ion batteries.

[0003] Compared with the graphite negative electrode, the theoretical specific capacity of the silicon negative electrode is several times that of the commercial graphite electrode. However, the silicon-based material will undergo a severe volume change (> 400%) during the intercalation and deintercalation of lithium ions. On the one hand, the commonly used electrode material binders such as polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) have poor deformation stability and are difficult to inhibit the volume expansion of the silicon-based negative electrode, which leads to the destruction of the electrode structure, the collapse and shedding of the material, and further causes the performance degradation and failure of the battery, seriously affecting the service life of the battery. On the other hand, the use of these commonly used binders requires the use of organic solvents such as N-methyl pyrrolidone (NMP), which has environmental pollution and safety problems and does not meet the green development concept.

[0004] Therefore, it is necessary to develop a high-elasticity aqueous binder with strong binding performance and mechanical strength and capable of being applied to the silicon negative electrode, so as to prevent or reduce the breakage and peeling of the silicon negative electrode material during the charging and discharging process, buffer the deformation stress caused by the volume expansion, and reduce the use of organic solvents. SUMMARY

[0005] The primary purpose of the present application is to overcome the shortcomings and deficiencies of the prior art and provide a preparation method of a biomass-based aqueous binder for a lithium ion battery silicon negative electrode.

[0006] Another purpose of the present application is to provide a biomass-based aqueous binder for a lithium ion battery silicon negative electrode prepared by the method.

[0007] Still another purpose of the present application is to provide the application of the biomass-based aqueous binder for a lithium ion battery silicon negative electrode.

[0008] The purposes of the present application are achieved by the following technical solutions:

[0009] A preparation method of a biomass-based aqueous binder for a lithium ion battery silicon negative electrode, comprising the following steps:

[0010] (1) Carboxymethyl cellulose (CMC) is added to water, heated and stirred to mix uniformly to obtain a gel solution;

[0011] (2) adding caffeic acid (CA) into the colloidal solution obtained in step (1) and mixing uniformly by heating and stirring to obtain a mixed solution;

[0012] (3) adding hydrogen peroxide (H2O2) and ferrous sulfate (FeSO4) into the mixed solution obtained in step (2) and reacting (to make the reaction complete) by heating and stirring to obtain a CMC-PCA colloidal solution;

[0013] (4) adding a LiOH solution into the CMC-PCA colloidal solution obtained in step (3) to adjust the pH value to 6-8 to obtain the biomass-based aqueous binder for a silicon anode of a lithium ion battery.

[0014] The water in step (1) is preferably deionized water.

[0015] The mass ratio of carboxymethyl cellulose (CMC) to water in step (1) is (0.02-0.05):1; preferably 0.04:1.

[0016] The mass ratio of carboxymethyl cellulose (CMC) to caffeic acid (CA) in step (1) is 1:(0.05-0.15); preferably 1:0.1.

[0017] In steps (1), (2) and (3), a magnetic stirrer is used for heating and stirring.

[0018] The temperature of heating and stirring in steps (1), (2) and (3) is 55-60℃; preferably 55℃.

[0019] The rotation speed of heating and stirring in steps (1), (2) and (3) is 250-300 rpm; preferably 250 rpm.

[0020] The time of heating and stirring in steps (1) and (2) is 20-30 min; preferably 30 min.

[0021] The mass ratio of hydrogen peroxide (H2O2) to ferrous sulfate (FeSO4) in step (3) is (0.1-0.2):1; preferably 0.1:1.

[0022] The mass ratio of hydrogen peroxide (H2O2) to caffeic acid (CA) in step (3) is 1:(100-150); preferably 1:100.

[0023] The time of heating and stirring reaction in step (3) is 1.5-2 h; preferably 1.5 h.

[0024] The concentration of the LiOH solution in step (4) is 20%-30% by mass; preferably 30% by mass.

[0025] The adjusting pH value in step (4) is preferably adjusting pH value to 6-7.

[0026] A biomass-based aqueous binder for silicon anode of lithium ion battery is prepared by the method of any one of the above.

[0027] The biomass-based aqueous binder for silicon anode of lithium ion battery is applied to the preparation of lithium ion battery anode material or lithium ion battery.

[0028] The lithium ion battery anode material is a silicon anode material of lithium ion battery.

[0029] A lithium ion battery anode material comprises active material silicon, conductive agent and the biomass-based aqueous binder for silicon anode of lithium ion battery.

[0030] The active material silicon is preferably silicon powder; more preferably silicon powder with a particle size of about 100 nm.

[0031] The conductive agent can be selected according to actual needs; preferably carbon black; more preferably carbon black with a particle size of about 100 nm.

[0032] In the lithium ion battery anode material, the amount of biomass-based aqueous binder for silicon anode of lithium ion battery accounts for 5-10% of the mass of lithium ion battery anode material.

[0033] The preparation method of the lithium ion battery anode material comprises the following steps: mixing and stirring the active material silicon, conductive agent and the biomass-based aqueous binder for silicon anode of lithium ion battery to obtain uniformly dispersed electrode slurry; then coating the electrode slurry on a copper foil, drying, rolling with a rolling machine, cutting to obtain an electrode wafer, i.e. the lithium ion battery anode material.

[0034] The mass ratio of the active material silicon, conductive agent and biomass-based aqueous binder for silicon anode of lithium ion battery is (7-8.5):(1-2):(0.5-1); preferably 8:1:1.

[0035] The stirring time is 5-6 h; preferably 6 h.

[0036] The drying condition is vacuum drying at 60±5℃ for 12-15 h; preferably vacuum drying at 60℃ for 12 h.

[0037] The thickness of the lithium ion battery anode material is 3-5 µm.

[0038] A lithium ion battery comprises a positive electrode material, the lithium ion battery anode material, a separator and an electrolyte.

[0039] The lithium ion battery is preferably a CR2032 button cell (if a half cell is made, a lithium sheet can be used as a counter electrode).

[0040] The positive electrode material is preferably LiFePO4.

[0041] The separator is preferably a commercial PE membrane.

[0042] The electrolyte is preferably a LiPF6 solution; more preferably a LiPF6 solution with a concentration of 1 mol / L.

[0043] The caffeic acid used in the application contains a catechol group, a carboxylic acid group and a carbon-carbon double bond. Under the action of an initiator (H2O2 / FeSO4), polymerization is initiated to form a CMC-PCA binder. On the one hand, the caffeic acid monomer forms ester bonds and hydrogen bonds with the CMC network, and the carboxylic acid groups and hydroxyl groups of the two can also form stable ester bonds and hydrogen bonds with the Si surface oxidation groups, which reflects the binding capacity of the binder to the active material; on the other hand, the caffeic acid monomer self-polymerizes and crosslinks with the CMC network, making the mechanical strength of the binder higher, and the catechol group can realize adhesion through chemical actions such as hydrogen bonds, metal chelation coordination, π-π stacking and covalent bonding. The composite binder can be used to enhance the cycle performance and capacity retention rate of a silicon-based negative electrode of a lithium ion battery. The silicon-based negative electrode using the composite binder can maintain good cycle performance and capacity retention rate under the condition of a low binder content (5-10 wt%).

[0044] The application has the following advantages and effects relative to the prior art:

[0045] (1) The application provides a preparation method of a biomass-based water-based binder with high elasticity applied to a silicon negative electrode of a lithium ion battery, aiming at the problems of weak binding capacity, poor mechanical strength and serious environmental pollution of traditional binders. Carboxymethyl cellulose (CMC) and caffeic acid (CA) are used as raw materials, and under the action of an initiator hydrogen peroxide / ferrous sulfate, polymerization is rapidly initiated to form a CMC-PCA binder. Finally, LiOH is used for neutralization to enhance the viscosity and Li + conductivity of the binder. Due to the combined action of the network structure of the binder and the mimic mussel structure, the mechanical strength and the binding capacity to the active material and the current collector are extremely excellent.

[0046] (2) The main raw materials used in the application are from plants, which are abundant in source, high in safety, renewable and degradable. The solvent is water, which is pollution-free to the environment and green and environmentally friendly, and has the potential for large-scale commercial application.

[0047] (3) The high-elasticity biomass-based water-based binder of the present application is polymerized under the action of an initiator, and due to the network structure of the CMC binder and the chemical action of the catechol group of the caffeic acid monomer on CMC, Si particles and current collector metal, the composite binder has excellent binder strength and mechanical properties.

[0048] (4) The high-elasticity biomass-based water-based binder of the present application effectively enhances the cycle performance and capacity retention rate of the silicon negative electrode of a lithium ion battery. The cycle performance of the silicon negative electrode is tested by using the binder CMC-PCA of the present application and PVDF, CMC and simply blended CMC-CA binders. Under a constant current charge-discharge of 1 C, the initial specific discharge capacity of the CMC-PCA prepared by the present application is 3868 mAh·g -1 , the initial coulombic efficiency is 92.09%, and after 100 cycles, the specific discharge capacity is maintained at 2476 mAh·g -1 , and the capacity retention rate is 64.01%; the initial specific discharge capacity of PVDF is 3000 mAh·g -1 , the initial coulombic efficiency is 71.43%, and after 20 cycles, there is basically no discharge capacity; the initial specific discharge capacity of CMC is 3525 mAh·g -1 , the initial coulombic efficiency is 83.93%, and after 100 cycles, the specific discharge capacity is only 1722 mAh·g -1 , and the capacity retention rate is 48.85%; the initial specific discharge capacity of simply blended CMC-CA is 3214 mAh·g -1 , the initial coulombic efficiency is 76.52%, and after 100 cycles, the specific discharge capacity is only 1320 mAh·g -1 , and the capacity retention rate is 41.07%. It is shown that after the binder of the present application is applied to the silicon negative electrode of a lithium ion battery, the performance of the battery can be obviously improved. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a cycle performance diagram of a full cell assembled by using the silicon negative electrode prepared by using the high-elasticity biomass-based water-based binder in Example 1, the PVDF binder in Comparative Example 1 and the CMC binder in Comparative Example 2 under 1 C. DETAILED DESCRIPTION

[0050] The present application will be further described in detail below in conjunction with examples, but the embodiments of the present application are not limited thereto. The battery electrochemical performance detection method in the following examples is a general detection method for lithium ion battery electrochemical performance. Unless otherwise specified, each raw material and reagent used in the following examples can be obtained from the market.

[0051] In the present application, all percentages (%) are mass percentages, unless otherwise specified.

[0052] The carboxymethyl cellulose (CMC) powder and the caffeic acid (CA) involved in the examples and comparative examples of the present application are all analytically pure; the effective content of ferrous sulfate is not less than 90%; the particle size of silicon powder is 100 nm, and the effective content is not less than 99.99%; the particle size of carbon black is 100 nm, and the effective content is not less than 99.5%; the above raw materials and reagents are purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.

[0053] The hydrogen peroxide involved in the examples and comparative examples of the present application has an effective content of not less than 99.99%, and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; the lithium hydroxide (LiOH) has an effective content of not less than 99.9%, and is purchased from Shanghai Bangcheng Chemical Co., Ltd.

[0054] In the examples and comparative examples of the present application, LiFePO4 is used as the positive electrode, a commercial PE film is used as the separator, and the electrolyte is a 1 M LiPF6 solution, and a full battery (CR2032 button cell) is assembled for cycle performance test. The above battery materials are all commercial products, and are purchased from Keluode New Energy Technology Co., Ltd.

[0055] Example 1

[0056] (1) 24 g of deionized water was taken into a 50 mL pressure-resistant bottle;

[0057] (2) 1 g of carboxymethyl cellulose (CMC) powder was added into the pressure-resistant bottle in step (1), and stirred at 55°C and 250 rpm for 30 min to obtain a colloidal solution with certain viscosity;

[0058] (3) 0.1 g of caffeic acid monomer (CA) was added into the colloidal solution prepared in step (2), and continued to be stirred at 55°C and 250 rpm for 30 min to obtain a mixed solution with certain viscosity;

[0059] (4) 0.001 g of hydrogen peroxide and 0.01 g of ferrous sulfate were sequentially added into the mixed solution prepared in step (3), and continued to be stirred at 55°C and 250 rpm for 1.5 h to obtain a CMC-PCA colloidal solution with certain viscosity;

[0060] (5) A 30% LiOH solution was slowly added into the colloidal solution prepared in step (4) to adjust the pH to 6-7, and a high-elasticity biomass-based aqueous binder for silicon negative electrode was obtained;

[0061] (6) The active material Si (silicon powder), conductive agent carbon black and the binder prepared in step (5) in a mass ratio of 8:1:1 were mixed and stirred for 6 h to obtain a uniformly dispersed electrode slurry. The obtained slurry was coated onto a copper foil using a doctor blade coater, and the electrode slurry was dried in a vacuum drying oven at 60°C for 12 h. The dried electrode slurry was then rolled to a thickness of 3 μm using a rolling machine, and electrode discs with a diameter of 12 mm were cut out.

[0062] (7) The dried electrode discs in step (6) (as anodes) were transferred to an argon-filled glove box for battery assembly. A commercial LiFePO4 electrode was used as a cathode, 1 M LiPF6 solution was used as an electrolyte, a commercial PE membrane was used as a separator, and a CR2032 button cell was used for assembly to prepare a full cell for cycle performance testing.

[0063] Example 2

[0064] The difference from Example 1 is that the mass of the caffeic acid monomer added in step (3) was adjusted to 0.05 g, and the other step parameters were the same as in Example 1.

[0065] Example 3

[0066] The difference from Example 1 is that the mass of the caffeic acid monomer added in step (3) was adjusted to 0.15 g, and the other step parameters were the same as in Example 1.

[0067] Comparative Example 1

[0068] (1) 2 g of polyvinylidene fluoride (PVDF) powder was dissolved in 8 g of N-methyl pyrrolidone (NMP) to obtain a PVDF binder with a mass concentration of 20%;

[0069] (2) The active material Si (silicon powder), conductive agent carbon black and the PVDF binder prepared in step (1) in a mass ratio of 8:1:1 were mixed and stirred for 6 h to obtain a uniformly dispersed electrode slurry. The obtained slurry was coated onto a copper foil using a doctor blade coater, and the electrode slurry was dried in a vacuum drying oven at 60°C for 12 h. The dried electrode slurry was then rolled to a thickness of 3 μm using a rolling machine, and electrode discs with a diameter of 12 mm were cut out.

[0070] (3) The dried electrode discs in step (2) (as anodes) were transferred to an argon-filled glove box for battery assembly. A commercial LiFePO4 electrode was used as a cathode, 1 M LiPF6 solution was used as an electrolyte, a commercial PE membrane was used as a separator, and a CR2032 button cell was used for assembly to prepare a full cell for cycle performance testing.

[0071] Comparative Example 2

[0072] (1) 0.4 g CMC powder was dissolved in 9.6 g deionized water to obtain a CMC binder with a mass concentration of 4%;

[0073] (2) The active material Si (silicon powder), the conductive agent carbon black and the CMC binder prepared in step (1) were mixed in a mass ratio of 8:1:1 and stirred for 6 h to obtain a uniformly dispersed electrode slurry. The obtained slurry was coated on a copper foil using a doctor blade coater, and the electrode slurry was dried in a vacuum drying oven at 60°C for 12 h. The dried electrode slurry was then rolled to 3 µm using a roller press, and the electrode slurry was cut into electrode discs with a diameter of 12 mm.

[0074] (3) The dried electrode disc in step (2) (as a negative electrode) was transferred to an argon-filled glove box for battery assembly. A commercial LiFePO4 electrode was used as a positive electrode, a 1 M LiPF6 solution was used as an electrolyte, and a commercial PE membrane was used as a separator. The CR2032 button cell was assembled to prepare a full battery for cycle performance testing.

[0075] Comparative Example 3

[0076] (1) 1 g CMC powder was dissolved in 24 g deionized water to obtain a colloidal solution with a certain concentration.

[0077] (2) 0.1 g CA was directly dissolved in the colloidal solution prepared in step (1) and heated and stirred to obtain a uniformly mixed CMC-CA binder.

[0078] (3) The active material Si (silicon powder), the conductive agent carbon black and the CMC-CA binder prepared in step (2) were mixed in a mass ratio of 8:1:1 and stirred for 6 h to obtain a uniformly dispersed electrode slurry. The obtained slurry was coated on a copper foil using a doctor blade coater, and the electrode slurry was dried in a vacuum drying oven at 60°C for 12 h. The dried electrode slurry was then rolled to 3 µm using a roller press, and the electrode slurry was cut into electrode discs with a diameter of 12 mm.

[0079] (3) The dried electrode disc in step (3) (as a negative electrode) was transferred to an argon-filled glove box for battery assembly. A commercial LiFePO4 electrode was used as a positive electrode, a 1 M LiPF6 solution was used as an electrolyte, and a commercial PE membrane was used as a separator. The CR2032 button cell was assembled to prepare a full battery for cycle performance testing.

[0080] Effect Implementation Example

[0081] 1. The thickness and loading of the electrode discs (silicon anodes) prepared in Examples 1-3 and Comparative Examples 1-3 were tested in accordance with GB / T 20220-2006. The silicon anodes prepared using different binders in Examples 1-3 and Comparative Examples 1-3 were then assembled into full cells. The lithium-ion batteries were tested for initial charge and discharge and 100 cycles at a constant current of 1 C. The initial discharge capacity and 100-cycle discharge capacity were tested in accordance with GB / T 31467.2-2015. The results are shown in Table 1 below.

[0082] Table 1 Performance comparison of various binders in Examples and Comparative Examples

[0083]

[0084] The assembled batteries were tested for cycling performance using a battery cycling system. Figure 1 The figure shows the cycle performance of a full battery assembled with the highly elastic biomass-based aqueous adhesive in Example 1, the PVDF adhesive in Comparative Example 1, and the CMC adhesive in Comparative Example 2 as the adhesive for the Si electrode. It can be seen that the adhesive prepared by the present invention is significantly superior to the PVDF adhesive and the CMC adhesive. In addition, when CMC-CA is simply blended (Comparative Example 3), the viscosity of the adhesive decreases, and the prepared electrode will show obvious shedding and powdering. As can be seen from the data in Table 1, its first coulombic efficiency and capacity retention rate are also low. It can be seen that when the adhesive of the present invention is applied to the silicon negative electrode of a lithium-ion battery, the performance of the battery is significantly improved.

[0085] 2. The binders prepared in Examples 1-3 and Comparative Examples 1-3 were formed into films by filtration, and their quantitative properties, tensile strength, and elongation were tested. The quantitative properties were tested in accordance with GB / T451.2-2002, and the tensile strength and elongation were tested in accordance with GB / T12914-2018. The results are shown in Table 2 below.

[0086] Table 2 Comparison of mechanical properties of adhesive films in Examples and Comparative Examples

[0087]

[0088] It can be seen from the data in Table 2 that after the adhesives of the embodiments and comparative examples are made into films, the tensile strength and elongation of the CMC-PCA film made from the adhesive of the present invention are significantly improved, reflecting its excellent mechanical properties, namely elasticity.

[0089] In summary, the composite binder of the present invention is primarily derived from abundant, renewable, and biodegradable plant materials, and the solvent, water, is environmentally friendly. Silicon-based anodes employing this composite binder can maintain excellent cycling performance and capacity retention at relatively low binder contents (5-10 wt%), demonstrating its potential for applications in resisting electrode deformation.

[0090] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a biomass-based aqueous binder for a lithium-ion battery silicon negative electrode, characterized in that: The steps include: (1) Add carboxymethyl cellulose to water, heat and stir to mix evenly to obtain a colloidal solution; (2) adding caffeic acid to the colloidal solution obtained in step (1), heating and stirring to mix uniformly, to obtain a mixed solution; (3) adding hydrogen peroxide and ferrous sulfate to the mixed solution obtained in step (2), heating and stirring to react, and obtaining a CMC-PCA colloidal solution; (4) Adding LiOH solution to the CMC-PCA colloidal solution obtained in step (3) to adjust the pH value to 6-8, thereby obtaining the biomass-based aqueous binder for the silicon negative electrode of lithium-ion batteries.

2. The method according to claim 1, wherein: The mass ratio of carboxymethyl cellulose to water in step (1) is 0.02-0.05:1; The mass ratio of the carboxymethyl cellulose to the caffeic acid in step (1) is 1:0.05-0.15; The mass ratio of hydrogen peroxide to ferrous sulfate in step (3) is 0.1-0.2:1; The mass ratio of hydrogen peroxide to caffeic acid in step (3) is 1:100-150.

3. The method according to claim 2, wherein: The mass ratio of carboxymethyl cellulose to water in step (1) is 0.04:1; The mass ratio of the carboxymethyl cellulose to the caffeic acid in step (1) is 1:0.1; The mass ratio of hydrogen peroxide to ferrous sulfate in step (3) is 0.1:1; The mass ratio of the hydrogen peroxide to the caffeic acid in step (3) is 1:

100.

4. The method according to claim 1, wherein: The concentration of the LiOH solution in step (4) is 20% to 30% by mass; The pH value adjustment in step (4) is to adjust the pH value to 6-7.

5. The method according to claim 1, wherein: The temperature of the heating and stirring in steps (1), (2) and (3) is 55-60°C; The heating and stirring in steps (1), (2) and (3) are performed at a speed of 250 to 300 rpm; The heating and stirring time in steps (1) and (2) is 20 to 30 minutes; The heating and stirring reaction time in step (3) is 1.5 to 2 hours.

6. A biomass-based aqueous binder for lithium-ion battery silicon negative electrode, characterized in that: It is prepared by the method according to any one of claims 1 to 5.

7. Use of the biomass-based aqueous binder for lithium-ion battery silicon negative electrode according to claim 6 in the preparation of lithium-ion battery negative electrode materials or lithium-ion batteries.

8. A negative electrode material for a lithium-ion battery, characterized in that: The invention comprises active material silicon, a conductive agent and the biomass-based aqueous binder for lithium-ion battery silicon negative electrode according to claim 6.

9. The lithium-ion battery negative electrode material according to claim 8, characterized in that: The active material silicon is silicon powder; The conductive agent is carbon black; The amount of the biomass-based aqueous binder used for the lithium-ion battery silicon negative electrode accounts for 5-10% of the mass of the lithium-ion battery negative electrode material.

10. A lithium-ion battery, characterized in that: Comprising a positive electrode material, the negative electrode material of the lithium-ion battery according to claim 8 or 9, a separator and an electrolyte; The positive electrode material is LiFePO4; The diaphragm is a PE film; The electrolyte is LiPF6 solution.

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