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CN-121748715-B - Nanocellulose-based lithium ion battery diaphragm, preparation method thereof and secondary battery

CN121748715BCN 121748715 BCN121748715 BCN 121748715BCN-121748715-B

Abstract

The invention discloses a nanocellulose-based lithium ion battery diaphragm, a preparation method thereof and a secondary battery, and relates to the technical field of battery diaphragms. According to the invention, the branched chitosan is prepared by performing grafting reaction on chitosan and branched chain monomers containing a plurality of amino groups, and then grafted on the surface of the nano-cellulose, and the branched chain of the chitosan is led in to extend the chain and then graft the branched chain to the nano-cellulose, so that the branched chain which is extended outwards and rich in the amino groups is led in while the nano-cellulose is not damaged excessively, namely, higher effective group is led in with lower modification degree, the migration number of lithium ions is obviously improved, and the pore structure of a diaphragm is optimized. The nitrogen content of the prepared lithium ion battery diaphragm reaches 0.6-1.5%, the porosity is 65-70%, the tensile strength is greater than 12 MPa, the ionic conductivity is greater than 1.8 mS cm ‑1 , and the migration number of lithium ions is greater than 0.6.

Inventors

  • SHENG JIE
  • Zou Tengyan
  • ZHOU RONGFU

Assignees

  • 佛山大学

Dates

Publication Date
20260508
Application Date
20260227

Claims (13)

  1. 1. The preparation method of the nanocellulose-based lithium ion battery diaphragm is characterized by comprising the following steps of: The preparation method comprises the steps of carrying out grafting reaction on chitosan and a branched monomer containing a plurality of amino groups to obtain branched chitosan, wherein the branched chitosan is provided with a branched structure which extends outwards from a main chain and is rich in amino groups, the branched monomer is at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine and low molecular weight polyethyleneimine, the weight average molecular weight of the low molecular weight polyethyleneimine is 300-1200, and the molar ratio of a repeating unit of the chitosan to the branched monomer is 1 (1-5); Grafting the branched chitosan onto the surface of nano cellulose to form a composite material with a three-dimensional amino functional layer; And preparing a battery diaphragm by using the composite material.
  2. 2. The preparation method of the branched chitosan according to claim 1, wherein the preparation process of the branched chitosan comprises the steps of mixing chitosan, the branched monomer and the coupling agent, and reacting at the pH value of 5-6 and the temperature of 35-45 ℃ for 4-12 hours.
  3. 3. The method according to claim 2, wherein the coupling agent is at least one selected from glutaraldehyde and dialdehyde xylose.
  4. 4. The method according to claim 3, wherein the molar ratio of the repeating unit of chitosan to the coupling agent is 1 (0.2-0.7).
  5. 5. The method according to claim 3, wherein the preparation of the branched chitosan comprises the steps of adjusting the pH value of a chitosan acetic acid solution to 5-6, mixing the chitosan acetic acid solution with the branched monomer, dripping the coupling agent, reacting under an inert atmosphere, quenching unreacted aldehyde groups after the reaction, pouring the reaction solution into an alcohol solvent for precipitation, collecting the precipitate for washing, redissolving the precipitate in the acetic acid solution, dialyzing with water, and drying.
  6. 6. The method of claim 1, wherein the branched chitosan is grafted to the surface of the nanocellulose by covalent bonds; The nanocellulose is oxidized nanocellulose with aldehyde groups on the surface; The covalent bond is a Schiff base bond and is formed by the reaction of aldehyde groups on the surface of activated nanocellulose and amino groups of branched chitosan.
  7. 7. The method of preparing the composite material according to claim 6, wherein the process of preparing the composite material from the branched chitosan comprises: Mixing and reacting the nano cellulose suspension with the mass fraction of 0.5% -2.0% with an oxidant, terminating the reaction, dialyzing and purifying, and then performing ultrasonic dispersion to obtain an oxidized nano cellulose suspension; After dissolving the branched chitosan in a buffer solution, dropwise adding the buffer solution into the oxidized nanocellulose suspension, reacting under an inert atmosphere, controlling the reaction temperature to be 30-40 ℃, the reaction time to be 3-10 h, and the reaction pH value to be 5.0-6.0; after the reaction is finished, the reaction mixture is washed by water to obtain a composite material suspension with a three-dimensional amino functional layer.
  8. 8. The preparation method according to claim 7, wherein the oxidizing agent is NaIO 4 , the reaction is carried out under the condition of light shielding in the reaction process with the oxidizing agent, the reaction temperature is 40-50 ℃, the reaction time is 3-10 h, then ethylene glycol is added for continuous reaction for 20-40 min to terminate the reaction, and the reaction mixture is filled into a dialysis bag, dialyzed with water and then dispersed by ultrasonic.
  9. 9. The method of claim 7, wherein the buffer is an acetate buffer.
  10. 10. The method according to claim 7, wherein the ratio of the amount of the nanocellulose to the branched chitosan is controlled to be 1 (0.7-1.1).
  11. 11. The method according to claim 7, wherein the composite suspension is diluted with water, vacuum-filtered to form a wet film, and then transferred to absolute ethanol for solvent displacement, and then dried.
  12. 12. A nanocellulose-based lithium ion battery separator, characterized in that it is prepared by the preparation method of any one of claims 1-11; The nanocellulose-based lithium ion battery separator has at least one of the following features 1 to 5: the nitrogen content reaches 0.6 to 1.5 percent; the porosity is 65-70%; characterized by a tensile strength greater than 12 MPa; Characteristic 4, ionic conductivity is greater than 1.8 mS cm -1 ; and 5, the migration number of lithium ions is more than 0.6.
  13. 13. A secondary battery comprising the nanocellulose-based lithium ion battery separator of claim 12.

Description

Nanocellulose-based lithium ion battery diaphragm, preparation method thereof and secondary battery Technical Field The invention relates to the technical field of battery diaphragms, in particular to a nanocellulose-based lithium ion battery diaphragm, a preparation method thereof and a secondary battery. Background The separator is used as a key component of the lithium ion battery, and largely determines the performance of the lithium ion battery. In recent years, nanocellulose-based lithium ion battery separators have been receiving attention because of their excellent mechanical strength, thermal stability, electrolyte wettability, and other characteristics. In order to improve the performance of the separator, graft modification of nanocellulose is a common option. For example, researchers graft chitosan onto nanocellulose surfaces, and utilize the interaction of amino groups on the chitosan molecular chain with anions in the electrolyte (such as PF 6-) to inhibit anion migration, so as to increase the membrane lithium ion migration number (t +), and improve battery performance. However, there are significant limitations to the prior art. On one hand, since the chitosan and the cellulose are long-chain molecules, the steric hindrance is large during direct grafting, so that the grafting degree is low, and the quantity of the introduced amino groups is small. And the grafting degree is forcedly improved, the nano cellulose structure is often damaged, and the mechanical strength of the diaphragm is obviously reduced. On the other hand, the grafted chitosan molecule chain and the cellulose chain are approximately arranged in parallel, so that the grafting chitosan molecule chain is difficult to penetrate into the electrolyte phase, and the effective regulation and control of anion migration are limited. Therefore, development of a novel structural design strategy is needed to realize high-density three-dimensional extending amino functionalization without damaging the strength of the nanocellulose skeleton, so that the ion selectivity and electrochemical performance of the diaphragm are remarkably improved. In view of this, the present invention has been made. Disclosure of Invention The invention aims to provide a nanocellulose-based lithium ion battery diaphragm, a preparation method thereof and a secondary battery, which can realize high-density three-dimensional extending amino functionalization on the premise of not excessively damaging the strength of a nanocellulose skeleton, thereby remarkably improving the ion selectivity and electrochemical performance of the diaphragm. The invention is realized in the following way: In a first aspect, the invention provides a method for preparing a nanocellulose-based lithium ion battery separator, which comprises the following steps: The method comprises the steps of carrying out grafting reaction on chitosan and a branched monomer containing a plurality of amino groups to obtain branched chitosan, wherein the branched chitosan has a branched structure which extends outwards from a main chain and is rich in amino groups; Grafting branched chitosan onto the surface of nano cellulose to form a composite material with a three-dimensional amino functional layer; and preparing a battery diaphragm by using the composite material. In an alternative embodiment, the branched monomer is selected from at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine and low molecular weight polyethyleneimine, wherein the weight average molecular weight of the low molecular weight polyethyleneimine is 300-1200; and/or the molar ratio of the repeating unit of chitosan to the branched monomer is 1 (1-5). In an alternative embodiment, the branched chitosan is prepared by mixing chitosan, branched monomer and coupling agent, and reacting at pH 5-6 and temperature 35-45deg.C for 4-12 hr. In an alternative embodiment, the coupling agent is selected from at least one of glutaraldehyde and dialdehyde xylose; And/or the molar ratio of the repeating unit of chitosan to the coupling agent is 1 (0.2-0.7); and/or the preparation process of the branched chitosan comprises the steps of regulating the pH value of chitosan acetic acid solution to 5-6, mixing with branched monomers, dripping a coupling agent, reacting in an inert atmosphere, quenching unreacted aldehyde groups after the reaction is finished, pouring the reaction solution into an alcohol solvent for precipitation, collecting the precipitate for washing, redissolving in the acetic acid solution, dialyzing with water, and drying. In an alternative embodiment, the branched chitosan is grafted to the surface of the nanocellulose by covalent bonds; preferably, the nanocellulose is oxidized nanocellulose with aldehyde groups on the surface; preferably, the covalent bond is a schiff base bond formed by the reaction of aldehyde groups on the surface of the activated nanocellulose with amino groups of the branched ch