Homologous cellulose material for solid-state lithium ion battery as well as preparation method and application of homologous cellulose material

Abstract

The invention discloses a homologous cellulose material for a solid-state lithium ion battery as well as a preparation method and application of the homologous cellulose material. The homologous cellulose material is composed of cellulose nanocrystals, a polymer film-forming agent and a lithium salt. According to the homologous cellulose material, cellulose nanocrystals are bonded together through a polymer film-forming agent, a continuous ion transmission channel is constructed while a high-toughness film is formed, and the homologous cellulose material can be used as a good lithium ion battery solid electrolyte. Meanwhile, the polymer film-forming agent and the cellulose nanocrystal can form a high-strength network structure by virtue of chain segment interlocking, so that the polymer film-forming agent can also be used as an electrode binder. When the battery is prepared, the solid electrolyte and the electrode binder both use the homologous cellulose material, so that the electrode-electrolyte interface is effectively improved, and the purposes of reducing ion transmission hindrance, reducing interface side reaction, simplifying battery preparation and the like are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and more specifically, relates to a homogenized cellulose material for solid-state lithium ion batteries and a preparation method and application thereof. Background Art

[0002] With the rapid growth in demand for lithium-ion batteries in consumer electronics, energy storage, and electric vehicles, how to further improve the energy density, stability, and safety of batteries has become a key research topic. Traditional liquid lithium-ion batteries cannot meet the higher requirements for lithium-ion batteries at this stage due to the flammability of liquid electrolytes and their instability under high / low temperature conditions. In this context, solid-state electrolytes, as an innovative alternative to liquid electrolytes due to their excellent stability and safety, are leading lithium-ion battery technology into a new generation. However, existing solid-state electrolyte materials usually have problems such as low conductivity and poor electrode-electrolyte interface, which limits their application in high-performance lithium-ion batteries. Summary of the invention

[0003] In order to solve the above-mentioned deficiencies and shortcomings of the prior art, the purpose of the present invention is to provide a homologous cellulose material, which can be used as an electrode binder and a solid electrolyte in a solid-state lithium-ion battery at the same time, so as to solve the problems of complex process, high cost, poor interface, etc. in solid-state lithium-ion batteries.

[0004] Another object of the present invention is to provide a method for preparing the above homologous cellulose material.

[0005] Another object of the present invention is to provide applications of the homogenized cellulose material.

[0006] The purpose of the present invention is achieved through the following technical solutions: A homologous cellulose material for solid-state lithium-ion batteries consists of cellulose nanocrystals, a polymer film-forming agent and a lithium salt.

[0007] Preferably, in the above-mentioned homologous cellulose material for solid-state lithium-ion batteries, the mass ratio of the cellulose nanocrystals to the polymer film-forming agent is 3-10:1, and the mass ratio of the cellulose nanocrystals to the lithium salt is 5-10:1.

[0008] Preferably, in the above-mentioned homologous cellulose material for solid-state lithium-ion batteries, the polymer film-forming agent is any one of polyethylene oxide (PEO), polyvinyl alcohol (PVA, 1799 type), polyurethane (PU, polyether type), and polyvinyl pyrrolidone (PVP), and the molecular weight is 100,000~800,000 Da.

[0009] Preferably, in the above homologated cellulose material for solid-state lithium-ion batteries, the lithium salt is any one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), and lithium nitrate (LiNO3).

[0010] Preferably, in the above-mentioned homologous cellulose material for solid-state lithium-ion batteries, the length of the cellulose nanocrystals is 5 to 50 nm.

[0011] A method for preparing a homogenized cellulose material for a solid-state lithium-ion battery comprises the following steps: S1. Add cellulose nanocrystals into water and stir to form a uniform dispersion; S2. The polymer film-forming agent is added to the uniform dispersion, and the viscosity of the solution is adjusted by controlling the amount added; S3. Add lithium salt to the solution obtained in step S2, and continue stirring to dissolve it to obtain a binder, namely, the homologous cellulose material.

[0012] A solid electrolyte membrane is prepared by the following method: casting the homologated cellulose material into a polytetrafluoroethylene mold, and evaporating the solvent to prepare the solid electrolyte membrane.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses cellulose nanocrystals and polymer film-forming agents as two major substrates. The former has abundant lithium ion complexing sites (electronegative oxygen atoms), which is conducive to the rapid transfer of lithium ions; the latter, as a high molecular polymer, can contribute excellent adhesion through mechanical entanglement and chain segment interlocking. The combination of the two can simultaneously meet the material requirements of solid electrolytes and electrode binders.

[0014] 2. The present invention innovatively uses one material as both a solid electrolyte and an electrode binder (completely replacing traditional electrode binders). When preparing batteries, both solid electrolytes and electrode binders use homologous cellulose materials, which greatly improves the electrode-electrolyte interface problem and simplifies the battery preparation process, helping to reduce the transmission barriers of lithium ions at the interface while reducing interface side reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The figure is a comparison chart of the battery cycle performance prepared in Examples 1 and 2 and Comparative Example 1; Figure 2 This is a schematic diagram of the battery assembly of Example 1. DETAILED DESCRIPTION

[0016] The content of the present invention is further described below in conjunction with specific examples, but it should not be construed as limiting the present invention. If not specifically indicated, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0017] A homologous cellulose material for solid-state lithium-ion batteries, the homologous cellulose material comprising cellulose nanocrystals, a polymer film-forming agent, and a lithium salt Preparation of homologous cellulose material: Add cellulose nanocrystals into water and stir to form a uniform dispersion; add a polymer film-forming agent to the above solution and stir to dissolve it; add lithium salt to the above solution and continue to stir to dissolve it to obtain a binder (homologous cellulose material A); cast the above solution into a polytetrafluoroethylene mold, and then evaporate the solvent at 80°C to obtain a solid electrolyte membrane (homologous cellulose material B).

[0018] The homologous cellulose materials A and B are used in a lithium ion battery, which comprises a lithium iron phosphate positive electrode, a solid electrolyte (homologous cellulose material B) and a lithium metal negative electrode. The lithium iron phosphate positive electrode comprises a lithium iron phosphate active material, a conductive agent and a binder (homologous cellulose material A).

[0019] Embodiment 1: 1. Add cellulose nanocrystals and polymer film-forming agent (PEO) to water in turn and stir to form a uniform dispersion; add LiTFSI to the above solution and continue stirring to dissolve it to obtain a binder (homologous cellulose material A).

[0020] 2. The above solution was cast into a polytetrafluoroethylene mold, and then transferred to an oven at 80°C to evaporate the solvent to obtain a solid electrolyte membrane (homologous cellulose material B).

[0021] 3. Mix the lithium iron phosphate active material, the conductive agent and the binder (homologated cellulose material A) in water at a mass ratio of 8:1:1 to obtain a positive electrode slurry. Scrape the slurry onto a carbon-coated aluminum foil, dry it, and cut it into a circular electrode with a diameter of 12 mm to obtain a positive electrode.

[0022] 4. Lithium-ion batteries are assembled in a glove box. The assembly sequence is positive battery shell, lithium iron phosphate positive electrode sheet, solid electrolyte, plasticizer, lithium sheet, gasket, spring, negative battery shell. After packaging, lithium-ion batteries are obtained. The battery assembly diagram is shown in the figure. Figure 2 The amount of plasticizer added is 10% of the total mass of the electrolyte, the solute is 1 mol / L LiTFSI, and the solvent is a DME / DOL mixed solvent with a volume ratio of 1:1.

[0023] Embodiment 2: 1. Add cellulose nanocrystals and polyvinyl pyrrolidone (PVP) to water in turn and stir to form a uniform dispersion; add lithium nitrate (LiNO3) to the above solution and continue stirring to dissolve it to obtain a binder (homologous cellulose material A).

[0024] 2. The above solution was cast into a polytetrafluoroethylene mold, and then transferred to an oven at 80°C to evaporate the solvent to obtain a solid electrolyte membrane (homologous cellulose material B).

[0025] 3. Mix the lithium iron phosphate active material, the conductive agent and the binder (homologated cellulose material A) in water at a mass ratio of 8:1:1 to obtain a positive electrode slurry. Scrape the slurry onto a carbon-coated aluminum foil, dry it, and cut it into a circular electrode with a diameter of 12 mm to obtain a positive electrode.

[0026] 4. Lithium-ion batteries were assembled in a glove box in the order of positive battery shell, lithium iron phosphate positive electrode sheet, solid electrolyte, plasticizer, lithium sheet, gasket, spring, negative battery shell, and the lithium-ion battery was obtained after packaging. The amount of plasticizer added accounted for 10% of the total mass of the electrolyte, the solute was 1 mol / L LiNO3, and the solvent was a DME / DOL mixed solvent with a volume ratio of 1:1.

[0027] Comparative Example 1: 1. Mix the lithium iron phosphate active material, conductive agent and binder (PVDF) in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a positive electrode slurry. Scrape the slurry onto a carbon-coated aluminum foil, and cut it into a circular electrode with a diameter of 12 mm after drying to obtain a positive electrode.

[0028] 2. The lithium-ion battery was assembled in a glove box in the order of positive electrode battery shell, lithium iron phosphate positive electrode sheet, electrolyte, diaphragm, lithium sheet, negative electrode battery shell, and the lithium-ion battery was obtained after packaging, wherein the electrolyte solute was 1 mol / L LiTFSI, and the solvent was a DME / DOL mixed solvent with a volume ratio of 1:1.

[0029] The lithium ion batteries assembled in Examples 1 and 2 and Comparative Example 1 were placed at 28°C for 5 hours before charge and discharge cycle tests. The above Examples 1 and 2 and Comparative Example 1 show that the homogenized cellulose material of the present invention has good electrochemical properties, and the prepared batteries exhibit higher discharge capacity and better cycle stability. After 100 cycles, the discharge capacity can reach 151 mAh g -1 The cycle retention rate is 92.6%, and the discharge capacity of Example 2 is 147 mAh g -1 The cycle retention rate is 91.0%. In contrast, the discharge capacity of comparative example 1 is only 122 mAh g-1 , the retention rate is 85.1%.

Claims

1. A homogenized cellulose material for solid-state lithium-ion batteries, characterized in that: The homologous cellulose material consists of cellulose nanocrystals, a polymer film-forming agent and a lithium salt.

2. The homogenized cellulose material for solid-state lithium-ion batteries according to claim 1, characterized in that: The mass ratio of the cellulose nanocrystals to the polymer film-forming agent is 3-10:1, and the mass ratio of the cellulose nanocrystals to the lithium salt is 5-10:

1.

3. The homogenized cellulose material for solid-state lithium-ion batteries according to claim 1, characterized in that: The polymer film-forming agent is any one of polyethylene oxide, polyvinyl alcohol, polyurethane, and polyvinyl pyrrolidone, and has a molecular weight of 100,000 to 800,000 Da.

4. The homogenized cellulose material for solid-state lithium-ion batteries according to claim 1, characterized in that: The lithium salt is any one of lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate and lithium nitrate.

5. The homogenized cellulose material for solid-state lithium-ion batteries according to claim 1, characterized in that: The length of the cellulose nanocrystals is 5 to 50 nm.

6. A method for preparing a homogenized cellulose material for solid-state lithium-ion batteries according to claim 1, characterized in that The following steps are involved: S1. Add cellulose nanocrystals into water and stir to form a uniform dispersion; S2. The polymer film-forming agent is added to the uniform dispersion, and the viscosity of the solution is adjusted by controlling the amount added; S3. Add lithium salt to the solution obtained in step S2, and continue stirring to dissolve it to obtain a homologous cellulose material.

7. A solid electrolyte membrane, characterized in that The method is as follows: the homologous cellulose material obtained in claim 6 is cast into a polytetrafluoroethylene mold, and the solvent is evaporated to obtain a solid electrolyte membrane.

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