CN115566268A - Nitrile polymer solid electrolyte and preparation method and application thereof - Google Patents

Nitrile polymer solid electrolyte and preparation method and application thereof Download PDF

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CN115566268A
CN115566268A CN202211260559.9A CN202211260559A CN115566268A CN 115566268 A CN115566268 A CN 115566268A CN 202211260559 A CN202211260559 A CN 202211260559A CN 115566268 A CN115566268 A CN 115566268A
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王真
白岩
桂兴发
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Liaoning Dengsai New Energy Co ltd
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    • H—ELECTRICITY
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Abstract

The invention discloses a nitrile polymer solid electrolyte, a preparation method and application thereof, and particularly relates to the technical field of lithium batteries. The preparation method comprises the steps of firstly, synthesizing the PVA-CN based gel polymer electrolyte; dissolving PVA-CN resin inLiPF 6 EC: DMC: preparing a precursor solution from the electrolyte of DEC, and preparing the PVA-CN based gel polymer from the precursor solution by an in-situ synthesis method under the heating condition; step two, preparing a PVA-CN based polymer skeleton; smashing the PVA-CN based gel polymer, adding acetone for cleaning, and centrifuging to obtain black precipitate; mixing the black precipitate with acetone, centrifuging again, repeating for multiple times, and vacuum drying the black precipitate to remove the solvent to obtain precipitate; and (3) putting the precipitate into a dialysis bag, dialyzing and drying to obtain the PVA-CN based polymer skeleton, namely the PVA-CN polymer solid electrolyte. The PVA-CN based polymer skeleton prepared by the method is applied to a lithium battery, and the electrochemical performance of the lithium battery can be obviously improved.

Description

Nitrile polymer solid electrolyte and preparation method and application thereof
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a nitrile polymer solid electrolyte and a preparation method and application thereof.
Background
The lithium ion battery plays an important role in the fields of storage in large-scale stores of current portable energy storage devices, electric automobiles and power stations and the like due to the advantages of high working voltage, long cycle life, environmental friendliness, no memory effect and the like. However, the potential safety hazards of ignition, explosion, electrolyte leakage and the like caused by the use of the traditional organic electrolyte greatly restrict the development of high-capacity and high-power-density lithium ion batteries in the future. As an alternative to organic electrolytes, solid polymer electrolytes have attracted attention because of their good safety.
Nitrile materials are widely used in solid electrolytes of lithium ion batteries because of their advantages of good thermal stability and electrochemical oxidation resistance. The interaction between the nitrile group (-C ≡ N) and lithium ions is thought to be beneficial for improving the ionic conductivity of the electrolyte. Recently, nitrile ethyl substituted polyvinyl alcohol (PVA-CN) can be subjected to in-situ thermal polymerization in 1MLIPF6 organic electrolyte without an initiator and a cross-linking agent to prepare a gel polymer electrolyte, which has high ion transfer number (more than 0.84) and ion conductivity similar to that of the ion electrolyte, and has good application prospect when being applied to lithium ion batteries. However, the gel mechanism has not been studied systematically.
As a nitrile material, succinonitrile is widely used in all solid polymer batteries of lithium ion batteries. As a solid solvent, the high polarity of SN molecules enables a large amount of various lithium salts to be dissolved therein. More importantly, SN shows plastic crystal behaviors (ordered molecular position and disordered orientation) with high diffusivity in the temperature range of-40-60 ℃. Therefore, SN-based all-solid polymer electrolytes (mixtures of lithium salts such as LiTFSI and SN) exhibit high room-temperature ionic conductivities of greater than 10-3S/cm. However, in the case of an SN-based all-solid polymer electrolyte, the melting point thereof rapidly decreases with the increase in the amount of lithium salt added. Such electrolytes exhibit poor mechanical strength at room temperature and are difficult to prepare for use in film formation. Although a diaphragm is introduced or compounded with a high-strength mechanical structure, the mechanical strength of the SN-based all-solid-state polymer electrolyte can be effectively improved, and the low compatibility between SN and a reinforcing material causes the great reduction of the conductivity of lithium ions. In addition, the high-impedance interface between the SN-based all-solid polymer electrolyte and the electrode is yet to be further optimized.
Disclosure of Invention
Therefore, the invention provides a nitrile polymer solid electrolyte, and a preparation method and application thereof, which aim to solve the problems that the existing solid electrolyte has poor mechanical strength at room temperature and is difficult to prepare into a film for use.
In order to achieve the above purpose, the invention provides the following technical scheme:
the PVA-CN based gel polymer electrolyte and the nitrile group hierarchical structure all-solid-state electrolyte are prepared by adopting a convenient in-situ synthesis method, the performance characterization and the electrode/solid-state polymer electrolyte interface analysis are carried out systematically, and the practical application of the PVA-CN based gel polymer electrolyte and the nitrile group hierarchical structure all-solid-state electrolyte in the lithium ion battery is explored. The method mainly comprises the following points:
the invention analyzes the condition that PVA-CN resin contains LiPF 6 The in-situ gel mechanism in the electrolyte discovers that PVA-CN molecules can be prepared from LiPF 6 PF5 produced by the thermal decomposition and a trace amount of water in the electrolyte initiate a cationic polymerization reaction, resulting in a black gel polymer electrolyte.
The gelation process of the PVA-CN should be performed after the battery formation operation. The process optimization can construct a stable low-impedance electrode/gel polymer electrolyte interface, thereby improving the electrochemical performance of the PVA-CN based polymer battery.
The hierarchical structure and nitrile all-solid-state polymer electrolyte SEN is prepared by a multiphase composite means and an in-situ method. The plastic crystal property of SN provides high conductivity for SEN; the PAN-based electrospun fiber membrane provides mechanical support while greatly reducing the SEN membrane thickness. And the PVA-CN crosslinked network of cationic polymerization not only improves the mechanical strength of the electrolyte membrane, but also avoids the hidden trouble of liquid leakage at high temperature.
Based on the invention, the SEN film shows good mechanical property (tensile strength 15.31 MPA) and excellent safety, and has high ionic conductivity (0.3S), high electrochemical stability (more than 5.0V vs Li/Li +) and high lithium ion transport number (0.57). Meanwhile, the assembly process of the all-solid-state battery is greatly simplified by the in-situ synthesis technology, and the assembled LFP/SEN/Li all-solid-state battery shows excellent electrochemical performance (the reversible capacity of 100 cycles at 0.1C is kept at 149.6 mAh/g)
According to a first aspect of the present invention, there is provided a method for producing a nitrile polymer solid electrolyte, comprising:
step one, synthesis of PVA-CN based gel polymer electrolyte
Dissolving PVA-CN resin in LiPF 6 EC: DMC: preparing a precursor solution from the electrolyte of DEC, and preparing the PVA-CN based gel polymer from the precursor solution by an in-situ synthesis method under the heating condition;
step two, preparation of PVA-CN based polymer skeleton
Mashing the PVA-CN based gel polymer, adding acetone for cleaning, and centrifuging to obtain black precipitate; mixing the black precipitate with acetone, centrifuging again, repeating for multiple times, and vacuum drying the black precipitate to remove the solvent to obtain precipitate; and putting the precipitate into a dialysis bag, dialyzing and drying to obtain the PVA-CN based polymer skeleton, namely the PVA-CN polymer solid electrolyte.
Further, in the first step, the precursor solution is prepared by dissolving 2wt% of PVA-CN resin in 1MLiPF 6 EC: DMC: prepared in DEC.
Further, in the first step, the heating condition is 70 ℃.
According to a second aspect of the present invention, there is provided a nitrile polymer solid electrolyte prepared by the above method.
According to a third aspect of the present invention, there is provided a method for producing a PAN-CN electrospun fiber membrane using the nitrile polymer solid electrolyte as described aboveSaid method comprising placing 15% of the PVA-CN based polymer backbone in DMF and magnetically stirring the mixed solution; adding nano gamma-Al into the mixed solution 2 O 3 Heating and stirring, and ultrasonically dispersing uniformly at normal temperature to obtain AN-CN/Al 2 O 3 Solution, followed by adding PAN-CN/Al 2 O 3 Electrostatic spinning the solution on a rotary receiving target, and applying voltage on an electric spinning needle head to obtain an electric spinning fibrous membrane; and taking the electrospun fiber membrane off the receiving target, and drying to remove DMF to obtain the PAN-CN electrospun fiber membrane.
According to a fourth aspect of the present invention, there is provided a method for in-situ synthesis of a SEN membrane comprising in-situ polymerization of a precursor in the pores of a PAN-CN electrospun fiber membrane prepared by the method as described above.
Further, the method comprises the steps of putting the PVA-CN resin into the molten SN, stirring and dissolving to obtain PVA-CN/SN; sequentially adding LiTFSI and LiPF6 salt into PVA-CN/SN, and uniformly stirring to obtain PVA-CN precursor solution; and adding the precursor solution into the PAN-CN electrospun fiber membrane for uniform tape casting to obtain the SEN membrane.
According to a fifth aspect of the present invention, there is provided a lithium battery comprising a positive electrode, a negative electrode, a film and an electrolyte, the electrolyte being a PVA-CN polymer solid electrolyte; the membrane is a PAN-CN electro-spun fiber membrane or a SEN membrane.
The invention has the following advantages:
the PVA-CN based polymer framework prepared by the method is applied to the lithium battery, and the electrochemical performance of the lithium battery can be obviously improved.
The invention prepares the hierarchical structure and nitrile all-solid-state polymer electrolyte SEN by a multiphase composite means and an in-situ method. The plastic crystal property of SN provides high conductivity for SEN; the PAN-based electrospun fiber membrane provides mechanical support while greatly reducing the SEN membrane thickness. And the PVA-CN cross-linked network of cationic polymerization not only improves the mechanical strength of the electrolyte membrane, but also avoids the hidden trouble of liquid leakage at high temperature.
The SEN film prepared by the invention has good mechanical property (tensile strength 15.31 MPA) and excellent safety, and has high ionic conductance (0.3S), high electrochemical stability (more than 5.0V vs Li/Li +) and high lithium ion transfer number (0.57). Meanwhile, the assembly process of the all-solid-state battery is greatly simplified by the in-situ synthesis technology, and the assembled LFP/SEN/Li all-solid-state battery shows excellent electrochemical performance (the reversible capacity of 100 cycles at 0.1C is kept at 149.6 mAh/g)
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are merely exemplary, and that other embodiments can be derived from the drawings provided by those of ordinary skill in the art without inventive effort.
The structures, ratios, sizes, and the like shown in the present specification are only used for matching with the contents disclosed in the specification, so as to be understood and read by those skilled in the art, and are not used to limit the conditions that the present invention can be implemented, so that the present invention has no technical significance, and any structural modifications, changes in the ratio relationship, or adjustments of the sizes, without affecting the effects and the achievable by the present invention, should still fall within the range that the technical contents disclosed in the present invention can cover.
FIG. 1 is a diagram showing the state of products of various portions of a PVA-CN polymer solid electrolyte provided in example 1 of the present invention;
wherein, a-PVA-CN resin; b-PVA-CN polymer gel electrolyte; c-before formation; d-a real picture of the post-formation 034352 PVA-CN gel polymer battery;
FIG. 2 is a diagram illustrating a procedure of separating and purifying a polymer backbone from a PVA-CN based polymer electrolyte according to example 1 of the present invention;
FIG. 3 is a scheme of in situ synthesis of SEN according to example 3 of the present invention;
FIG. 4 is a representation of the polymer backbone in a PVA-CN based gel polymer electrolyte provided in Experimental example 1 of the present invention; wherein, a-a physical picture and an FE-SEM image of the gel skeleton; b-FTIR spectrum of PVA-CN resin and gel skeleton; c-N1sXPS spectra; d-C1sXPS spectra;
FIG. 5 is a schematic diagram of two different formation processes of a PVA-CN based polymer battery according to the experimental example 2 of the present invention;
FIG. 6 is a graph showing the first charge-discharge curve and cycle performance of a PVA-CN based polymer battery at 0.2C current density after treatment by different formation processes according to Experimental example 2 of the present invention;
wherein, a-first charge-discharge curve; b-cycle performance graph; c, cycling the PVA-CN based polymer battery under the current density of 02C for 1 time by using an EIS spectrogram after treatment by different processes; d-EIS spectrogram of the PVA-CN based polymer battery treated by different processes after circulating for 50 times under the current density of 02C;
FIG. 7 is a CV diagram at 0.1mVs scan rate for CR2032 LiCoO/gel polymer electrolyte/graphite button cells treated by different processes according to the invention in test example 2;
wherein, the method comprises the steps of a-process 1 and b-process 2;
FIG. 8 is a graph of the first charge-discharge curve and cycle performance at room temperature of 0.1C current density for LFP/SEN/Li and LFP/1MLiPF-EC/EMC/MC/Li batteries provided in test example 3 of the present invention;
wherein, a-first charge-discharge curve; b-cycle performance graph; C-EIS spectra after 1 and 100 cycles corresponding to 01C cells, the test was performed in a semi-discharged state; rate capability of d-LFP/SEN/Li cells;
Detailed Description
The present invention is described in terms of particular embodiments, other advantages and features of the invention will become apparent to those skilled in the art from the following disclosure, and it is to be understood that the described embodiments are merely exemplary of the invention and that it is not intended to limit the invention to the particular embodiments disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
This example provides a preparation of a PVA-CN polymer solid electrolyte:
PVA-CN based gel polymer electrolyte is synthesized in situ by heating a precursor solution in a sealed glass bottle.
Specifically, preparation of a precursor solution: 2wt% PVA-CN resin dissolved in 1M LiPF 6 EC: DMC: preparing DEC electrolyte;
heating the precursor solution at 70 ℃ to obtain the PVA-CN based gel polymer;
all the above operations were carried out in a glove box filled with high purity argon.
Separating and purifying a polymer skeleton in the PVA-CN gel polymer solid electrolyte:
mashing the PVA-CN based gel polymer, adding a large amount of acetone, cleaning, putting the mixture with the acetone into a centrifugal tube, and centrifuging for 15min at the rotating speed of 10000rpm to obtain black precipitate. And mixing the black precipitate with acetone, centrifuging again, repeating the process for three times, placing the black precipitate at 120 ℃ for vacuum drying, taking out all solvents, then placing the precipitate into a dialysis bag, placing the dialysis bag in distilled water for dialysis for three days to further remove residual ions, and finally completely drying at 120 ℃ to obtain the PVA-CN based polymer skeleton, namely the PVA-CN polymer solid electrolyte. I.e. indicated by b in figure 1.
Electrochemical characterization of PVA-CN: model 034352 LiCoO 3 Graphite soft pack cells (design capacity 2100 mAh) were used to evaluate the electrochemical performance of PVA-CN based gel polymer electrolytes.
The cell was charged with 95% LiCoO 2 :2wt% super P:3wt% of PVDF as positive electrode, 97.5 wt% of graphite 1.5wt% of SBR 1 wt% of CMC as negative electrode, precursor solution (2wt% of PVA-CN resin dissolved in 1MLiPF 6 EC: DMC: DEC) and PVA-CN polymer solid electrolyte are used as electrolyte, an SD216 type polyethylene diaphragm is used, positive and negative pole pieces and the diaphragm are wound and then are filled in an aluminum plastic film packaging bag to form an electric core, then precursor solution is injected and vacuum packaging is carried out, the battery is placed at room temperature for 12 hours, the precursor solution is ensured to fully soak the electrodes, and then the formation process is carried out in two modes respectively.
The process 1 comprises the following steps: the cell was first baked at 70 ℃ under 0.25Mpa for 24 hours to allow the precursor solution to polymerize sufficiently to form a gel polyelectrolyte, and then the cell was formed (0.5C constant current charge for 2h, followed by 0.1C constant current charge for 5h,1c = 2100ma). Finally obtaining the PVA-CN grade polymer battery.
And (2) a process: the battery is first subjected to a formation operation, then the battery is placed at 70 ℃ and 0.25MPa for baking for 24H, and finally the battery is degassed at 25 ℃ and 12H.
The constant current charge and discharge test of the PVA-CN based polymer battery is carried out at 0.2C and 25 ℃. In each cycle, the current was first constant current charged to 4.35V and then constant voltage charged to 4.35V until the current decayed to 21mA (0.01C). Subsequently, 0.2C was discharged to 3V.
The product of each step is shown in figure 1, wherein a is PVA-CN resin, and b is PVA-CN polymer gel electrolyte; c-before formation; d-picture of PVA-CN gel polymer battery model 034352 after formation.
Example 2
This example provides a preparation of PAN-CN electrospun fibrous membrane:
15% PVA-CN polymer solid electrolyte was placed in DMF and stirred magnetically at 70 ℃ for 5h to give a homogeneous solution. Proper amount of nano gamma-Al for enhancing the strength of the electrospun fiber 2 O 3 (Al 2 O 3 : PAN =1: 5) Adding into the solution, stirring at 70 deg.C for 5 hr, ultrasonic treating at room temperature for 2 hr to disperse uniformly, and adding PAN/Al 2 O 3 The solution was continuously electrospun onto a rotating receiving target at a rate of 1.0ml/h, with a voltage of 22kv applied to the electrospinning needle and a distance of 15cm between the needle and the receiving target. And taking the electrospun fiber membrane with a certain thickness from the receiving target, and drying at 60 ℃ for 12h before further use to remove DMF, thereby obtaining the PAN-CN electrospun fiber membrane.
Example 3
The embodiment provides an in-situ synthesis method of a SEN membrane, which comprises the following steps: the route pattern is shown in fig. 3.
The SEN film is formed by in-situ polymerization of precursors in PAN-based poly Kong Qianwei film pore channels. The precursor is composed of SN, PVA-CN monomer and LiPF 6 (initiator) and LiTFSI as per 83:5:2:10 mass ratio. Firstly, PVA-CN resin is placed in molten SN, and 2H is magnetically stirred at 50 ℃ until the PVA-CN resin is completely dissolved to obtain PVA-CN/SN; then LiTFSI and LiPF are added 6 Sequentially adding PVA-CN/SN into the salt, and continuously stirring for 2h at 50 ℃ to obtain uniformThe PVA-CN precursor solution. Adding the PVA-CN precursor solution into the PAN-CN electrospun fiber membrane for casting uniformly, and heating at 70 ℃ for 6 hours to ensure that the PVA-CN is fully polymerized in the melting process to obtain the SEN membrane.
LiPF during heating at 70 ℃ for 6 h. PFs are generated by thermal decomposition, and the PFs trigger the PVA-CN resin to generate polymerization reaction, and finally a cross-linked three-dimensional skeleton structure is formed in the SN-based solid electrolyte filled in the pores of the electrospun fiber membrane, so that the SEN preparation and the assembly of the all-solid-state lithium ion battery are synchronously completed. Compared with the traditional process, the in-situ synthesis technology obviously greatly simplifies the assembly process of the all-solid-state polymer lithium ion battery and has great application value.
The above operation is performed in a glove box.
Test example 1
The assembly and electrochemical properties of the PAN-CN electrospun fibrous membrane solid-state battery obtained in example 2 were characterized in this test example:
CR2032 button cells were used to evaluate the utility of PAN-CN electrospun fibrous membranes in lithium ion batteries. The cell assembly was performed in a glove box filled with argon.
The batteries were charged with LFP: super-P: PVDF (mass ratio 8. The above precursor (5 wt%, PVA-CN dissolved in lithium salt/SN mixture) was dissolved at 50 ℃, and then injected into a PVA-CN based electrospun fiber membrane to complete the battery assembly. The assembled battery is kept stand at 50 ℃ for 2h to ensure that the precursor fully soaks the electrode, and then kept stand at 70 ℃ for 6h to ensure that the monomer is fully polymerized. The current constant current discharge test is carried out in the interval of 2.4-4.2V, and the current density is 0.1-5C (1C = 170mA/g).
To determine the initiation system of the gel reaction, 2wt% of PVA-CN resin was dissolved in 1M LiPF 6 In EC DMC EMC electrolyte and EC, DMC, EMC pure solvent, and heating at 70 deg.C for 24h. Interestingly, the black gel polymer electrolyte was only on LiPF 6 Can be formed in the presence of conditions. In 1MLiClO 4 EC DMC EMC or pure EC: DMC: no gel reaction was observed in the EMC solvent, indicating PF 6 - Coagulation of anions in PVA-CNThe glue plays a key role.
To further determine the functional groups of the PVA-CN molecules participating in the gel reaction, the polymer backbone was isolated and purified from the PVA-CN based gel electrolyte. The resulting black polymer backbone exhibits a typical porous structure. As shown in a in FIG. 4, it can be seen that the spectrum of PVA-CN at 2250cm is comparable to that of PVA-CN -1 The peak intensity of the C ≡ N is obviously increased, and the peak intensity is 3432-3461cm -1 the-OH peak intensity is obviously reduced, and the-OH functional group on the surface is partially converted into-OCH in the process of the nitrile treatment of PVA 2 CH 2 And (C) CN. Further analysis of the FIRT spectrum of the polymer backbone revealed 2250cm -1 The absorption peak at C.ident.N almost disappeared at 1670cm -1 The absorption peak is greatly enhanced, and C = N double bonds exist in the surface polymer framework. In conclusion, FIRT indicates that C.ident.N triple bonds are generated with C = N double bonds when cleaved during the gelation of PVA-CN resin.
As can be seen, the mechanism of in situ polymerization of PVA-CN resins can be inferred from the strong Lewis acid PF 5 (LiPF 6 Pyrolysis) initiated nitrile-based cationic polymerization. The chemical reaction mechanism of the polymer is shown in the figure, and PF is used as a common cationic polymerization catalyst 5 Can react with trace amount of water in a precursor solution to generate H + (PF 5 OH) -which is used as an initiation system to initiate a gel process, and due to the fact that thermodynamics of C ≡ N triple bond are very stable, the invention uses PF 5 The mechanism of initiating the nitrile-containing polymer is of great significance for the future design and development of nitrile electrolyte materials.
The action mechanism is as follows:
Figure BDA0003891401480000091
test example 2
This test example provides a lithium cell prepared using the PVA-CN polymer solid electrolyte obtained in example 1:
at present, the influence of the battery formation process on the electrode/gel polymer electrolyte interface has not been studied for gel polymer electrolytes prepared by in-situ thermal polymerization methods. Here we assembled a soft-packed LiCoO/graphite cell designed to have a capacity of 2100mAh to explore the possibility of improving the electrode/gel polymer electrolyte interface by optimizing the formation process. Based on the difference in gelation order, we designed two formation processes: process 1, gelation of the precursor solution before the cell formation operation: process 2, the precursor solution gels after the cell formation operation (see fig. 5). In order to enhance the contrast and better study the influence of different formation processes on the battery performance, a film-forming additive capable of reducing gas generation is not added into the electrolyte.
FIG. 6 (a) shows LiCoO treated by different formation processes 2 First charge and discharge curve under 0.2C current density of gel polymer electrolyte/graphite battery. It can be seen that the formation process has a significant effect on the cell formation voltage. The voltage rapidly increased to the set cut-off voltage (4.35V) in the formation operation of the PVA-CN based polymer battery treated by the formation process 1, while the voltage slowly increased with the charging time, similar to the control battery using the electrolyte, of the PVA-CN based polymer battery treated by the formation process 2. This phenomenon can be explained as follows. It is known that an SEI film is generated on the surface of a graphite negative electrode during battery formation operation, and an electrolyte is decomposed to generate organic gas. When the PVA-CN is gelled before the formation operation of the battery (process 1), a layer of PVA-CN based gel is coated on the graphite surface in advance (fig. 5, upper row), which hinders the reduction reaction of the electrolyte in the formation operation and thus causes a high-impedance SEI film to be coated on the surface of the final graphite negative electrode, resulting in large polarization during the formation operation. In addition, the battery formation operation in process 1 is completed in a quasi-solid phase. Since the rate of diffusion of gas in the gel (from the electrode surface to the gas pouch strip) is much lower than in the electrolyte, a large number of small bubbles are generated and accumulated on the negative electrode surface (fig. 5, upper row), blocking the insertion of lithium ions and increasing concentration polarization, thus exacerbating the rapid increase in cell voltage during the formation operation. However, when PVA-CN gelled after the cell formation operation (process 2), the PVA-CN based gel covered the surface of the pre-formed low resistance SEI film while almost no air bubbles accumulated on the electrode surface (fig. 5, bottom row). This surface structure is expected to exhibit high electrochemical stability and low polarization. In thatAfter the formation operation and gelation, the PVA-CN based polymer battery is subjected to a degassing process. During the subsequent charging process, the charging voltage of the PVA-CN based polymer battery treated by the formation process 1 was significantly higher than that of the PVA-CN based polymer battery treated by the formation process 2 and the control battery using the electrolyte, indicating that the polarization of the former battery was significantly higher than that of the latter battery.
The PVA-CN based polymer battery treated by the formation process 2 released initial reversible capacity of 2086mAh and first coulombic efficiency of 85.5%, similar to the control battery using electrolyte (2111mah. The PVA-CN based polymer battery treated by the formation process 1 only has the reversible capacity of 1939mAh, and the initial coulombic efficiency is only 84.9%. It can be seen that the formation process has an important influence on the reversible capacity of the PVA-CN based polymer battery. The cycle performance of the PVA-CN based polymer battery is shown in FIG. 6 (b). The capacity retention rates of the PVA-CN based polymer battery treated by the process 2 and a reference battery using the electrolyte after 50 times of 0.2C circulation are 82.0% and 86.0% respectively. This small difference in cycling performance can be explained by the fact that a small amount of monomer remaining during the gelling of the gel polymer electrolyte undergoes a side reaction on the electrode surface during cycling, and an inert film is formed to increase the interfacial resistance. In contrast, the gel polymer battery 02C treated in process 1 exhibited only 68.2% capacity retention after 50 cycles, which is significantly lower than the battery treated in process 2. The above results are sufficient to demonstrate that placing the cell formation operation before the gelation process of PVA-CN helps to improve the electrochemical performance of the gel polymer cell.
EIS was used to study the electrode/electrolyte interface phenomena of PVA-CN based polymer batteries. EIS spectra of LiCoO/GPE/graphite batteries treated by different formation processes after 1 and 50 cycles are respectively shown in FIGS. 6 (c, d). As can be seen, these EIS spectra consist of two partially overlapping flat semicircles in the medium and high frequency regions and a diagonal line in the low frequency region. The EIS spectra were further fitted using Z-view software (the fitting circuit is shown in the inset of FIG. 6 (c), and the resulting impedance parameters are listed in Table 1. According to the equivalent circuit, the intersection of the EIS semi-circle with the solid axis represents the bulk resistance R (the overall resistance of the electrode and electrolyte/membrane system), the high frequency flat semi-circle represents the SEI membrane resistance R and constant phase element CPE1, and the medium frequency flat semi-circle represents the interfacial charge transfer resistance Rc and constant phase element CPE2. CPE1 and CPE2 are constant phase elements that correct the SEI membrane capacitance CSFI and the electric double layer capacitance Ca, respectively, taking into account the electrode particle surface roughness. The low frequency slash represents the Warburg impedance (Zw) associated with ion diffusion between the particles.
TABLE 1
Figure BDA0003891401480000111
Figure BDA0003891401480000121
As can be seen in table 1, for the cells injected with PVA-CN precursor solution without gelation, the R and Re were slightly larger than the control cell using the electrolyte, mainly due to the decrease in conductivity caused by the increase in viscosity of the electrolyte due to the introduction of PCV-CN resin. After the PVA-CN precursor solution is treated by the formation process 2 (firstly, the battery formation operation is carried out, and then, gelation is carried out), the batteries R and Rc are not obviously changed, but the RSEI is obviously increased, which shows that a PVA-CN polymer framework with high resistivity is generated on the surface of an SEI film. In contrast, when PVA-CN formed a gel prior to the cell formation operation (formation process 1), the R and RSEI of the cell were much higher than those of the cells treated by process 2. This phenomenon can be explained as follows: firstly, the PVA-CN gel skeleton is covered on the surface of the battery in advance before the battery formation operation, which causes the SEI film resistance to be increased obviously as mentioned before; secondly, bubbles generated in the formation operation are difficult to discharge out of the gel by degassing, greatly hindering lithium ion transport. The increase in R and Re resulted in the battery treated by formation process 1 exhibiting a lower initial capacity.
After 50 cycles, the increase in Rb, rct, and RSEI was much higher for cells treated by formation process 1 than for cells treated by formation process 2 (especially R and R), indicating that the electrochemical stability of the latter was much higher than the former. For the battery treated by the process 1, electrolyte decomposition, electrode/gel polymer electrolyte interface contact deterioration and other electrochemical side reactions are aggravated because a stable SEI film is not formed on the surface of the graphite cathode, and meanwhile, bubbles gathered on the surface of the electrode easily cause non-uniform charge distribution on the surface of the electrode, so that a lithium precipitation phenomenon is caused. Therefore, the capacity decayed rapidly during the cycling of the battery treated by the formation process 1, as shown in fig. 6 (b).
LiCoO 2 CV diagram of/gel polymer electrolyte/graphite button cell is shown in fig. 7. When the battery was subjected to CV test before PVA-CN gelation (process 2), the current at 2.5-3.6V in the first cycle of CV was significantly higher than that in the second cycle, which could be attributed to the SEI film 169 generated by reductive decomposition of the electrolyte on the surface of the graphite negative electrode (fig. 7 (a)). However, when the battery was subjected to CV test after PVA-CN gelation (process 1) the SEI film formation voltage was reduced to 2.5 to 3.4V (fig. 7 (b)), verifying that PVA-CN based gel previously coated on the electrode surface hindered the reduction reaction of the electrolyte and the construction of the SEI film in the formation operation. In addition, the CV curve of the first 2-volumes in fig. 7 (b) substantially coincides with the CV curve of the subsequent 3-5-volumes, indicating that the subsequent gelation process of PVA-CN does not substantially affect the kinetic characteristics of the electrode after the SEI film is formed on the surface of the negative electrode. In contrast, the process-treated cells exhibited lower oxidation peak currents (starting from 37V) and higher oxidation peak voltages, indicating that cell polarization was more severe. The oxidation peak current is gradually increased along with the increase of CV scanning times, and the oxidation peak voltage is gradually reduced along with the increase of CV scanning times, which indicates that the metastable SEI film is continuously subjected to a destruction-reconstruction process in subsequent cycles. This phenomenon indicates that the construction of a stable SEI film during a formation operation is hindered by a preformed SEI film. Further, the voltage difference (Δ E) between the oxidation peak and the reduction peak in the CV diagram measures the degree of polarization of the electrode. It can be seen from fig. 7 that the cell using process 2 exhibited a smaller E and a higher peak current than that using process 1, consistent with the electrochemical test results in fig. 7. In conclusion, the formation process plays an important role in the construction of an electrode/gel polymer electrolyte interface and the electrochemical performance of a polymer cell. The formation process should be completed in liquid phase to ensure that a stable and low-resistance SEI film is formed on the surface of the electrode.
Test example 3
This experimental example provides electrochemical performance of a SEN-based all-solid-state battery:
the LFP/SEN/Li cell was assembled in situ to evaluate the electrochemical performance of SEN in a lithium ion cell. The first charge-discharge curve at 0.1C for the LFP/SEN/Li battery is shown in fig. 8 (a). The curve shows a distinct voltage plateau, indicating that the first discharge specific capacity of the reversible cycling characteristic LFP/SEN/Li battery is 154.6mAhg, and the coulombic efficiency reaches 99.9%, which is very close to the level of a control battery using a 1M LiPF6-EC/EMC/DMC electrolyte (1608mAhg, 100.0%). As shown in FIG. 8 (b), after 100 cycles at 0.1C, the LFP/SEN/Li battery can maintain a capacity of 149.6mAhg (capacity retention rate 96.7%). In comparison, the capacity retention ratio of the comparative battery using the electrolyte was only 93.2%. It can be seen that SEN lithium ion batteries exhibit similar capacity and cycling performance to electrolytes at low currents, mainly due to the high ionic conductance of SEN and good interfacial contact between SEN and electrodes.
Although the invention has been described in detail above with reference to a general description and specific examples, it will be apparent to one skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (8)

1. A method for preparing a nitrile polymer solid electrolyte is characterized by comprising the following steps:
step one, synthesis of PVA-CN based gel polymer electrolyte
Dissolving PVA-CN resin in LiPF 6 EC: DMC: preparing a precursor solution from the electrolyte of DEC, and preparing the PVA-CN based gel polymer from the precursor solution by an in-situ synthesis method under the heating condition;
step two, preparation of PVA-CN based polymer skeleton
Mashing the PVA-CN based gel polymer, adding acetone for cleaning, and centrifuging to obtain black precipitate; mixing the black precipitate with acetone, centrifuging again, repeating for multiple times, and vacuum drying the black precipitate to remove the solvent to obtain precipitate; and (3) putting the precipitate into a dialysis bag, dialyzing and drying to obtain the PVA-CN based polymer skeleton, namely the PVA-CN polymer solid electrolyte.
2. The method for preparing nitrile polymer solid electrolyte according to claim 1, wherein in the first step, 2wt% of PVA-CN resin is dissolved in 1MLiPF 6 EC: DMC: prepared in DEC.
3. The method for preparing a nitrile polymer solid electrolyte according to claim 1, wherein in the first step, the heating is performed under a temperature of 70 ℃.
4. A nitrile polymer solid electrolyte characterized by being produced by the method according to any one of claims 1 to 3.
5. A method for producing PAN-CN electrospun fiber membrane using nitrile polymer solid electrolyte as claimed in claim 4, characterized in that the method comprises placing 15% of PVA-CN based polymer backbone in DMF, and magnetically stirring the mixed solution; adding nano gamma-Al into the mixed solution 2 O 3 Heating and stirring, and ultrasonically dispersing uniformly at normal temperature to obtain AN-CN/Al 2 O 3 Solution, followed by adding PAN-CN/Al 2 O 3 Electrostatic spinning the solution on a rotary receiving target, and applying voltage on an electric spinning needle head to obtain an electric spinning fibrous membrane; and taking the electrospun fiber membrane off the receiving target, and drying to remove DMF to obtain the PAN-CN electrospun fiber membrane.
6. A method for in-situ synthesis of SEN membrane, characterized in that the SEN membrane is prepared by in-situ polymerization of precursor in the PAN-CN electrospun fiber membrane pore canal prepared by the method of claim 5.
7. The SEN membrane in-situ synthesis method according to claim 6, wherein the method comprises the steps of putting PVA-CN resin into molten SN, stirring and dissolving to obtain PVA-CN/SN; then LiTFSI and LiPF are added 6 Sequentially adding salt into PVA-CN/SN, and uniformly stirring to obtain PVA-CN precursor solution; and adding the precursor solution into the PAN-CN electrospun fiber membrane for uniform tape casting to obtain the SEN membrane.
8. A lithium battery comprises a positive electrode, a negative electrode, a film and an electrolyte, and is characterized in that the electrolyte is a PVA-CN polymer solid electrolyte; the membrane is a PAN-CN electro-spun fiber membrane or a SEN membrane.
CN202211260559.9A 2022-10-14 2022-10-14 Nitrile polymer solid electrolyte and preparation method and application thereof Pending CN115566268A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116742278A (en) * 2023-08-14 2023-09-12 中材锂膜(宜宾)有限公司 Separator, preparation method thereof, electrochemical cell using separator and electricity utilization device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116742278A (en) * 2023-08-14 2023-09-12 中材锂膜(宜宾)有限公司 Separator, preparation method thereof, electrochemical cell using separator and electricity utilization device
CN116742278B (en) * 2023-08-14 2023-10-24 中材锂膜(宜宾)有限公司 Separator, preparation method thereof, electrochemical cell using separator and electricity utilization device

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