In-situ polymer electrolyte, preparation method and battery

Abstract

An in-situ polymer electrolyte, preparation method and battery, including a separator and an electrolyte part, wherein the electrolyte part is obtained by an in-situ polymerization reaction, and the electrolyte part covers the surface of the separator and fills the pores of the separator; the electrolyte part includes a support structure, a lithium salt, and a solvent; the support structure has a crown ether-like structure, which can effectively attract the positive ions of the lithium salt and facilitate the dissociation of positive ions and negative ions; the crown ether-like structure is composed of one or two of C≡N, C=O, and C‑O; the separator can be made of a glass fiber diaphragm, a polypropylene diaphragm, or a polyethylene diaphragm. The present invention provides a polymer electrolyte with a high lithium ion migration number and ionic conductivity, and a battery containing the polymer electrolyte has excellent cycle stability and high rate performance at room temperature and high voltage.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and in particular relates to an in-situ polymer electrolyte, a preparation method and a battery. Background Art

[0002] Traditional lithium-ion batteries have low thermal stability, easy leakage and flammability, which can easily cause a large number of fire and explosion accidents, and pose great safety risks. Therefore, exploring solid-state batteries with high safety, high energy density and long cycle life is a hot topic in current research. Replacing liquid electrolytes with solid electrolytes can effectively solve the safety problem of lithium-ion batteries, but the resulting significant decrease in ionic conductivity, large interface impedance, and inability to meet the needs of high energy density batteries are problems that need to be solved urgently. Therefore, it is particularly important to develop solid electrolytes with high ionic conductivity.

[0003] Gel electrolyte is a semi-solid electrolyte with a three-dimensional network structure. Its rich internal pore structure can provide abundant lithium ion migration channels. This makes the gel electrolyte have both the high ion conductivity of traditional liquid electrolytes and the high safety of solid electrolytes.

[0004] The market needs a synthetic monomer that is easy to obtain, low in cost, with easily controllable synthesis conditions and a synthesis temperature that does not affect the stability and functionality of the electrolyte, positive and negative electrode materials and other related manufacturing materials.

[0005] For example, the insulating tape used in the post-process of battery manufacturing to insulate or fix the pole ears or pole groups will lose its adhesiveness and insulation properties at too high a temperature.

[0006] At the same time, the synthesized polymer membrane needs to have high conductivity and good ion permeability.

[0007] It would be best if it could be used directly in the battery manufacturing process, just like the liquid injection process, without changing the existing process and equipment. Summary of the invention

[0008] The present invention aims to provide an in-situ polymer electrolyte, a preparation method and a battery to solve the technical problems of battery safety and high ionic conductivity of the electrolyte.

[0009] In order to solve the above technical problems, the specific technical solutions of an in-situ polymer electrolyte, a preparation method and a battery of the present invention are as follows:

[0010] An in-situ polymer electrolyte comprises a separator and an electrolyte, wherein the electrolyte is obtained by in-situ polymerization, and the electrolyte covers the surface of the separator and fills the pores of the separator;

[0011] The electrolyte part includes a support structure, a lithium salt, and a solvent;

[0012] The support structure has a crown ether-like structure, which can effectively attract the positive ions of the lithium salt and facilitate the dissociation of the positive ions and negative ions;

[0013] The crown ether-like structure is composed of one or two of C≡N, C=O, and CO;

[0014] The isolation part may be made of a glass fiber diaphragm, a polypropylene diaphragm, or a polyethylene diaphragm.

[0015] Furthermore, the support structure is polymerized from organic monomers to form a cross-linked network structure. The cavities formed by the cross-linked network structure can accommodate negative ions and solvated positive ions of the lithium salt. The average pore diameter of the cross-linked structure is smaller than the diameter of the lithium salt negative ions and larger than the diameter of the solvated positive ions.

[0016] Furthermore, the solvent includes one or more of carbonates, accounting for 35-60% by mass of the polymer electrolyte;

[0017] The lithium salt may be one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalatoborate); the concentration of the electrolyte formed by the lithium salt being dissolved in the solvent is 1 mol / L;

[0018] The organic monomer is composed of one or more of diacrylate and its derivatives, acrylate and its derivatives and acrylonitrile, and the amount of the organic monomer is 5-20 times the mass of the lithium salt, preferably 10-15 times;

[0019] The diacrylate derivatives include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate;

[0020] The acrylate derivatives include ethylene glycol acrylate, ethylene glycol methacrylate, diethylene glycol methacrylate, diethylene glycol acrylate, polyethylene glycol methacrylate, and polyethylene glycol methyl ether methacrylate.

[0021] Furthermore, the electrolyte part may be added with an improving agent, and the improving agent may be one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and 1,3-propane sultone, and the amount used is 3-6% of the mass of the electrolyte.

[0022] Furthermore, the polymer monomer of the support structure uses an initiator to initiate a polymerization reaction, and the initiator includes one of azobisisobutyronitrile and dibenzoyl peroxide, and the amount used is 0.1-0.5% of the total amount of the polymer monomer;

[0023] The porosity of the separator is 50-68%.

[0024] The thickness of the in-situ polymer electrolyte is 50-250 μm.

[0025] The present invention also provides a method for preparing an in-situ polymer electrolyte, comprising the following steps:

[0026] Step 1, at room temperature, mixing one or more carbonate solvents in a preset ratio to obtain a mixed solvent;

[0027] Step 2: Add lithium salt to the mixed solvent, control the condition that the molar concentration is 1 mol / L, and mix evenly to obtain a colorless and transparent electrolyte solution.

[0028] Step 3: Add the polymer organic monomer to the electrolyte solution according to the preset ratio and continue stirring to fully dissolve.

[0029] Organic monomers include monomers containing C≡N bonds and acrylic ester monomers;

[0030] The control condition is the ratio of the total amount of organic monomers to the amount of lithium salt;

[0031] Step 4, adding an initiator and an electrolyte improver, and mixing them evenly to obtain an electrolyte precursor;

[0032] Step five, placing the isolating part between two thickness limiting parts, controlling the gap thickness between the thickness limiting parts, injecting the precursor solution into the gap between the thickness limiting parts, heating and curing, and obtaining an in-situ polymer electrolyte membrane.

[0033] Further, the temperature range of the heating and curing is 50-80°C;

[0034] The time range of the heating curing is 2-14 hours.

[0035] Furthermore, the isolation part may be made of a glass fiber diaphragm, a polypropylene diaphragm, or a polyethylene diaphragm;

[0036] The solvent includes one or more carbonates, accounting for 35-60% by mass of the polymer electrolyte;

[0037] The lithium salt is an organic lithium salt, and can be one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalatoborate); the concentration of the electrolyte formed by the lithium salt being dissolved in the solvent is 1 mol / L;

[0038] The organic monomer is composed of one or more of diacrylate and its derivatives, acrylate and its derivatives and acrylonitrile, and the amount of the organic monomer is 5-20 times the mass of the lithium salt, preferably 10-15 times;

[0039] The diacrylate derivatives include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate;

[0040] The acrylate derivatives include ethylene glycol acrylate, ethylene glycol methacrylate, diethylene glycol methacrylate, diethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol methyl ether methacrylate; the temperature range of the heating curing is preferably 65-75°C.

[0041] Furthermore, the improving agent may be one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and 1,3-propane sultone, and the amount used is 5% of the mass of the electrolyte;

[0042] The polymer monomer of the support structure uses an initiator to initiate a polymerization reaction, wherein the initiator includes one of azobisisobutyronitrile and dibenzoyl peroxide, and the amount used is 0.1-0.5% of the total amount of the polymer monomer;

[0043] The isolation portion has a porosity of 50-68% and a thickness of 10-300 μm;

[0044] The thickness of the in-situ polymer electrolyte is 50-250 μm;

[0045] The time range of the heating curing is preferably 4-8 hours.

[0046] The present invention also provides a battery, wherein the battery has the aforementioned in-situ polymer electrolyte or the in-situ polymer electrolyte obtained by the aforementioned method for preparing the in-situ polymer electrolyte.

[0047] The in-situ polymer electrolyte, preparation method and battery of the present invention have the following advantages:

[0048] 1. The present invention adds polyacrylonitrile structure and fluorine-containing substances during the polymerization process; compared with the current polymer system containing only ether oxygen, the functional groups in the supporting structure of the polymer electrolyte prepared in the present invention are similar to Li + The binding energy formed is small, and the introduced C≡N bond and fluorine-containing substances are bound to Li +The interaction formed between them is also weak, so the polymer electrolyte prepared in this way has a higher lithium ion migration number, and has a significant advantage in reducing the interface impedance between the polymer electrolyte and the electrode, thereby improving the cycle stability and high rate performance of the battery at room temperature and high voltage;

[0049] 2. The gel component unit in the present invention uses acrylonitrile, which is more + The strong interaction and high binding energy between the polymer chains containing C≡N and Li + The interaction between them is weak, which is conducive to the dissociation of positive and negative ions of lithium salt and the Li + Rapid migration;

[0050] 3. The present invention uses fluorine-containing substances to decompose in situ at the contact interface between the membrane and the electrode to form a stable interface film rich in inorganic Li3F compounds, thereby improving Li + Transport and interfacial stability between membranes and interfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of the interaction between negatively charged groups and lithium ions in the support structure of the present invention;

[0052] Figure 2a FTIR spectrum of the in-situ polymerized sample of the present invention;

[0053] Figure 2b It is a local enlarged view of the FTIR spectrum of the in-situ polymerized sample of the present invention in the wavelength range corresponding to C≡N;

[0054] Figure 3 It is a DSC analysis curve diagram of the in-situ polymerization sample of the present invention;

[0055] Figure 4 is a TGA curve diagram of the in-situ polymerization sample of the present invention;

[0056] Figure 5 This is a comparison diagram of the electrochemical windows of the in-situ polymerized samples of the present invention;

[0057] Figure 6 Capacity comparison charts of batteries made from electrolytes of multiple embodiments at different discharge rates are provided.

[0058] Figure 7 A graph of the cycling performance of a battery was produced for one embodiment. DETAILED DESCRIPTION

[0059] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of an in-situ polymer electrolyte, a preparation method and a battery of the present invention in conjunction with the accompanying drawings.

[0060] The purpose of the present invention is to produce a polymer electrolyte by an in-situ polymerization method, wherein the network cross-linked structure can effectively limit the migration of the negative ion groups of the electrolyte, and provide channels for the solvated positive ion groups to fully migrate. This design maximizes the solvated ion permeability effect, improves the conductivity and ion migration rate, and can effectively reduce the impact of concentration polarization. Based on this invention goal, we designed the following electrolyte and preparation method.

[0061] The present invention provides an in-situ polymer electrolyte and a preparation method thereof. The polymer electrolyte has high ionic conductivity, a wide electrochemical window, and good interface contact performance, and can effectively inhibit the formation of lithium dendrites and the occurrence of interface side reactions. At the same time, it has good compatibility with positive and negative electrode materials, which can not only effectively improve the solid-solid interface problem in contact with the positive and negative electrodes, but also effectively improve the comprehensive performance of the battery under high voltage.

[0062] An in-situ polymer electrolyte comprises a separator and an electrolyte, wherein the electrolyte is obtained by in-situ polymerization, and the electrolyte covers the surface of the separator and fills the pores of the separator;

[0063] The electrolyte part includes a support structure, a lithium salt, and a solvent;

[0064] The electrolyte part may also be added with an improving agent;

[0065] The isolation part may be made of a glass fiber diaphragm, a polypropylene diaphragm, or a polyethylene diaphragm;

[0066] The support structure has a crown ether-like structure, which can effectively attract the positive ions of the lithium salt and facilitate the dissociation of the positive ions and negative ions;

[0067] The crown ether-like structure is composed of one or two of C≡N, C=O, and CO;

[0068] The support structure is polymerized from organic monomers to form a cross-linked network structure. The cavities formed by the cross-linked network structure can accommodate negative ions and solvated positive ions of the lithium salt. The average pore diameter of the cross-linked structure is smaller than the diameter of the negative ions of the lithium salt and larger than the diameter of the solvated positive ions.

[0069] At the same time, in order to form a crown ether-like structure, it is necessary to select the polymerization monomer. Factors that need to be considered include the length of the carbon chain, the position and number of double bonds broken in the polymerization reaction, etc.

[0070] The solvent includes one or more carbonates, accounting for 35-60% by mass of the polymer electrolyte;

[0071] The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalatoborate); the concentration of the electrolyte formed by the lithium salt being dissolved in the solvent is 1 mol / L;

[0072] In order to form a crown ether-like structure,

[0073] The organic monomer is composed of one or more of diacrylate and its derivatives, acrylate and its derivatives and acrylonitrile, and the amount of the organic monomer is 5-20 times the mass of the lithium salt, preferably 10-15 times;

[0074] The diacrylate derivatives include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate;

[0075] The acrylate derivatives include ethylene glycol acrylate, ethylene glycol methacrylate, diethylene glycol methacrylate, diethylene glycol acrylate, polyethylene glycol methacrylate, and polyethylene glycol methyl ether methacrylate.

[0076] It should be noted that the monomers selected take into account that the C≡N due to the cyano group can be retained after polymerization, and the sp hybridized N, along with the increase in electronegativity, also improves the hardness of N as a basic site and enhances the ability to attract lithium ions. According to the theory of hard and soft acids and bases, oxygen is a hard base and lithium ions are hard acids with good binding ability; the hardness of the alkalinity of the N atom in the CN group is weaker than the combination of oxygen and lithium in the ether bond. Therefore, the interaction between this polyether-like structure and Li+ is weaker than that of crown ethers and polyethers; but it is conducive to the rapid migration of Li+, thereby forming a higher lithium ion migration number.

[0077] The improving agent may be one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and 1,3-propane sultone, and the amount used is 2-8% of the mass of the electrolyte;

[0078] The polymer monomer of the supporting structure uses an initiator to initiate a polymerization reaction. The initiator includes one of azobisisobutyronitrile and dibenzoyl peroxide, and the usage amount is 0.1-0.5% of the total amount of the polymer monomer.

[0079] The porosity of the isolation portion is 50-68%;

[0080] The thickness of the in-situ polymer electrolyte is 50-250 μm;

[0081] The temperature range of the heating and curing of the organic monomer is 40-80°C, preferably 65-75°C;

[0082] The time range of the heating curing is 2-14 hours, preferably 4-8 hours.

[0083] like Figure 1 As shown, the interaction mechanism between negatively charged groups in the support structure and lithium ions is shown.

[0084] like Figure 1 As shown in a and b, the crown ether center exhibits a higher electron density, which can electrostatically attract cations, and the space formed by the four oxygens in 12-crown-4 can accommodate lithium ions. At the same time, the fixation of lithium ions also attracts TFSI- to exist nearby. This attraction and the smaller space limit the migration of TFSI-. Therefore, in the solid electrolyte, the crown ether center can serve as a transfer channel for Li+, and with the assistance of the crown ether active site (ion transfer site), a higher ion conductivity is achieved, which is conducive to obtaining a higher lithium ion migration number.

[0085] like Figure 1 As shown in c, d, e, and f, a crown ether-like structure can also be formed in the polymer chain segment used in the present invention.

[0086] Formation of Li + The transmission channel is different from the crown ether formed by the ether bond of traditional polyethylene glycol in that the Li+ transmission channel formed in the present invention can be composed of three groups: ester group, cyano group and ether bond.

[0087] Compared with the polyethylene glycol dimethacrylate, which is currently more commonly used, the ethylene glycol dimethacrylate has a shorter ethylene glycol chain segment. The short chain supports the formation of small pores on the one hand, and is conducive to increasing the crown ether structure and attracting Li + The distance between the two polymer chains is small, and it is easy to interact with lithium ions. The effect of the ester group on lithium ions is weaker than that of the crown ether, which is beneficial to Li + Rapid migration of lithium ions, thereby increasing the number of lithium ion migration.

[0088] The cyano group in the chain segment can also form a crown ether-like structure, and then combine with Li+. On the one hand, due to the sp hybridization of N in the cyano group, along with the increase in electronegativity, the hardness of N as a basic site is also improved, and the ability to attract lithium ions is enhanced. According to the theory of hard and soft acids and bases, oxygen is a hard base and lithium ions are hard acids, and the two have good binding ability; the hardness of the alkalinity of the N atom in the CN group is weaker than the combination of oxygen and lithium in the ether bond. Therefore, the interaction between this polyether-like structure and Li+ is weaker than that of crown ethers and polyethers; but it is conducive to the rapid migration of Li+, thereby forming a higher lithium ion migration number.

[0089] like Figure 2a , 2b As shown in the FTIR spectrum of the in-situ polymerized sample, the -1and 2995cm -1 The typical peaks are attributed to -CH, which are at 3000-3100cm after thermal curing. -1 There is no characteristic peak in the range of 2248 cm-1, indicating that the =CH bond disappears and the monomer is completely converted into a polymer. -1 There is a C≡N stretching peak at 1780 cm-1. -1 The peak positions at 1357, 1190 and 1080 cm -1 The peaks are attributed to the bis(trifluoromethylsulfonyl)imide anion TFSI - The symmetric stretching vibration of O=S=O, the stretching vibration of -CF3, and the asymmetric stretching vibration of O=S=O. The results verify that the Li salt has good compatibility with the polymer.

[0090] like Figure 4 As shown, it can be seen from the thermogravimetric analysis (TGA) that the in-situ polymerized sample of the present invention has a 45% higher heat loss in the electrolyte when the temperature rises to 130°C. The TG curve shows a significant weight loss at around 340°C due to the decomposition of the polymer, which is consistent with the TG curve of Poly(AN-EDA), indicating that Poly(AN-EGDMA) is synthesized. However, thermogravimetric analysis (TGA) shows that there is almost no weight loss before 100°C, which is safer than flammable and volatile liquid electrolytes.

[0091] like Figure 3 As shown, differential scanning calorimetry (DSC) was applied to study the thermal transition of IPE heat flow measurement. The literature shows that the glass transition temperature (Tg) of PAN is about 90°C. Thanks to the addition of EMDGA, the Tg of all IPE-ANs decreased to -34.96°C, -36.76°C, -38.92°C, and -33.88°C, respectively. The reduction in crystallinity can greatly promote the movement of molecular segments, thereby enhancing the ionic conductivity of PAN segments.

[0092] like Figure 5 As shown in Figure 3, it can be observed that the electrochemical window of IPE-AN is wider than that of IPE-non-AN. It is noteworthy that the original oxidative stability of IPE-AN-10 is improved to 5.63 V by appropriate AN incorporation.

[0093] The analysis believes that due to the role of AN in improving the operating voltage window of the electrolyte, the electrochemical window of IPE has been significantly enhanced, which makes it promising for use with other lithium batteries or lithium-ion batteries with high voltage requirements, such as vanadium batteries.

[0094] The method for preparing the above-mentioned in-situ polymer electrolyte comprises the following steps:

[0095] Step 1, at room temperature, mixing one or more carbonate solvents in a preset ratio to obtain a mixed solvent;

[0096] Step 2: Add lithium salt to the mixed solvent, control the condition that the molar concentration is 1 mol / L, and mix evenly to obtain a colorless and transparent electrolyte solution.

[0097] Step 3: Add the polymer organic monomer to the electrolyte solution according to the preset ratio and continue stirring to fully dissolve.

[0098] Organic monomers include monomers containing C≡N bonds and acrylic ester monomers;

[0099] The control condition is the ratio of the total amount of organic monomers to the amount of lithium salt;

[0100] Step 4, adding an initiator and an electrolyte improver, and mixing them evenly to obtain an electrolyte precursor;

[0101] Step five, placing the isolating part between two thickness limiting parts, controlling the gap thickness between the thickness limiting parts, injecting the precursor solution into the gap between the thickness limiting parts, heating and curing, and obtaining an in-situ polymer electrolyte membrane.

[0102] The process of step five can also be implemented during the battery assembly process, wherein the thickness limiting components can be directly implemented using the positive and negative electrode sheets of the battery. The positive and negative electrode sheets and the isolation parts of the battery are manufactured into electrode groups according to a winding or lamination process, and then installed in the outer shell components of the battery. The precursor solution is injected into the battery according to the injection method of the traditional liquid electrolyte injection process. Through a vacuum or infiltration process, the precursor solution penetrates into the isolation parts between the electrode sheets and the gaps between the electrode sheets. The heating and curing steps can be completed through the battery baking process, and an in-situ polymer electrolyte can be directly formed in the electrode group of the battery.

[0103] By directly implementing the method in the battery assembly process, the step of making the electrolyte membrane separately is eliminated, and the existing production line of a large number of liquid lithium batteries can be used to produce solid-state batteries without changing the process. At the same time, this process can also fill the problems caused by the defects of the pole piece that cannot be filled by the ordinary solid electrolyte membrane, improve the chemical reaction interface stability of the battery, improve the reaction path of the solid electrolyte, reduce the possibility of polarization reaction and the appearance of lithium dendrites caused by the defects of the pole piece, and further improve the safety of the battery.

[0104] The pole piece defects include uneven coating, scratches, and edge powdering caused to the pole piece during the coating process or during the rolling, transfer, and cutting of the pole piece.

[0105] The isolation part may be made of a glass fiber diaphragm, a polypropylene diaphragm, or a polyethylene diaphragm;

[0106] The solvent includes one or more carbonates, accounting for 35-60% by mass of the polymer electrolyte;

[0107] The lithium salt may be one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalatoborate); the concentration of the electrolyte formed by the lithium salt being dissolved in the solvent is 1 mol / L;

[0108] The organic monomer is composed of one or more of diacrylate and its derivatives, acrylate and its derivatives and acrylonitrile, and the amount of the organic monomer is 5-20 times the mass of the lithium salt, preferably 10-15 times;

[0109] The diacrylate derivatives include ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate;

[0110] The acrylate derivatives include ethylene glycol acrylate, ethylene glycol methacrylate, diethylene glycol methacrylate, diethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol methyl ether methacrylate; the improver can be one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, and the usage amount is 2-8% of the mass of the electrolyte;

[0111] The polymer monomer of the supporting structure uses an initiator to initiate a polymerization reaction. The initiator includes one of azobisisobutyronitrile and dibenzoyl peroxide, and the usage amount is 0.1-0.5% of the total amount of the polymer monomer.

[0112] The isolation portion has a porosity of 50-68% and a thickness of 10-300 μm;

[0113] The thickness of the in-situ polymer electrolyte is 50-250 μm;

[0114] The temperature range of the heating curing is 50-80°C, preferably 65-75°C;

[0115] The time range of the heating curing is 2-14 hours, preferably 4-8 hours.

[0116] It should be noted here that when the isolation part uses a material with a higher initial thickness, for example, when a 300μm glass fiber diaphragm is used, the isolation part is placed between two thickness limiting parts. When the thickness between the thickness limiting parts is controlled, the glass fiber diaphragm can be compressed and controlled to 180μm, and then the precursor solution is injected. Due to the gap thickness control;

[0117] After the subsequent curing process is completed, the thickness of the polymer electrolyte can be controlled at 180 μm.

[0118] When the battery is manufactured by the winding process, the pole piece is used as a thickness limiting component during the winding process. The winding machine roller or tension controller also serves the purpose of limiting the thickness, thereby controlling the thickness of the isolation part in the final polymer electrolyte.

[0119] The method for making a battery containing the above-mentioned in-situ polymer electrolyte can be a method of assembling a battery with a pre-prepared polymer electrolyte and electrode sheets, or a method of assembling the battery by an in-situ polymerization method, assembling the positive and negative electrode sheets and the separator into an electrode group and then injecting a precursor solution.

[0120] The method of using a pre-prepared polymer electrolyte, taking a laminated battery as an example,

[0121] 1. Prefabricate the positive and negative electrode sheets and polymer electrolyte into the required sizes, with the negative electrode sheet being slightly larger than the positive electrode sheet, and the polymer electrolyte being slightly larger than the negative electrode sheet; connect the positive and negative electrode sheets to the pole ears or pole strips;

[0122] 2. Stack the positive electrode sheet, polymer electrolyte, negative electrode sheet, and polymer electrolyte in sequence to form an electrode group.

[0123] 3. Install the electrode group in the shell and connect the electrode ears or electrode band group to form a polymer battery.

[0124] The in-situ polymerization method is taken as an example of a wound battery, and of course, a laminated battery can also be used in this method.

[0125] The pre-prepared positive and negative electrode sheets and separators are wound into an electrode group according to the winding process, and then installed into the outer shell of the battery. The precursor solution is injected into the battery according to the injection method of the traditional liquid electrolyte injection process. The precursor solution penetrates into the separators between the electrode sheets and the gaps between the electrode sheets through a vacuum process or an infiltration process. The heating and curing steps can be completed through the battery baking process, and an in-situ polymer electrolyte can be directly formed in the battery electrode group; the assembly of the polymer battery is completed.

[0126] In order to more clearly describe the preparation and use of polymer electrolytes, typical organic monomers are selected for illustration in the specific embodiments. Since the number of monomers to be selected and compounded is too large, they are not described one by one.

[0127] Taking Example 1 as an example,

[0128] Step 1: Prepare gel electrolyte precursor solution:

[0129] At room temperature, the solvent was mixed evenly with 4.217 g of ethylene carbonate and 1.617 g of propylene carbonate in a volume ratio of 7:3 to obtain a mixed solvent; 1.308 g of lithium salt lithium bis(trifluoromethylsulfonyl)imide was added to the mixed solvent, the control condition was that the molar concentration of lithium bis(trifluoromethylsulfonyl)imide was 1 mol / L, and a colorless and transparent precursor solution was obtained by evenly mixing, and then 4.03 g of polymerized monomers acrylonitrile and 3.006 g of ethylene glycol dimethacrylate were added in a molar ratio of 5:1, and the control condition was that the mass ratio of the lithium salt was 20:1, and stirring was continued, and then 14 mg of azobisisobutyronitrile was added, and 0.356 g of fluoroethylene carbonate, an electrolyte additive, was added, and the mixture was evenly mixed to obtain a gel electrolyte precursor.

[0130] Step 2: Preparation of positive electrode sheet:

[0131] The positive electrode active material lithium iron phosphate (LiFeO4), the conductive agent acetylene black (Super P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 8:1:1, and evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a slurry. The slurry is coated on both sides of an aluminum foil, and then baked, rolled, and cut into pieces to obtain a positive electrode sheet.

[0132] The negative electrode active material artificial graphite (C), the conductive agent acetylene black (Super-P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 8:1:1, and evenly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a slurry. The slurry is coated on both sides of the copper foil, and then baked, rolled, and cut into pieces to obtain a negative electrode sheet.

[0133] The positive and negative electrode sheets are cut into sheets.

[0134] Step 3: Assemble into a solid full battery;

[0135] a. Place the negative electrode at the bottom of the negative electrode shell of the battery, and then stack the glass fiber diaphragm, the positive electrode sheet, and the glass fiber diaphragm in sequence, and weld the tabs to form a laminated electrode group;

[0136] b. Fill the precursor solution and seal the battery;

[0137] c. The assembled battery is left to stand at room temperature for 12 h to ensure that the electrolyte precursor is completely infiltrated into the positive and negative electrodes and the separator of the battery;

[0138] d. The static battery precursor is heated at 70° C. for 6 hours to completely polymerize and solidify the electrolyte precursor solution to prepare the in-situ solid-state battery.

[0139] Taking Example 3 as an example,

[0140] Step 1, same as in Example 1, the amount of chemical reagents input is as follows:

[0141] Ethylene carbonate (EC): 8.433 g; Propylene carbonate (PC): 3.246 g;

[0142] Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI): 2.617 g;

[0143] Acrylonitrile (AN): 4.03 g;

[0144] Ethylene glycol dimethacrylate (EGDMA): 3.01 g;

[0145] Azobisisobutyronitrile (AIBN): 14 mg;

[0146] Fluoroethylene carbonate (FEC): 0.712 g;

[0147] Step 2: The preparation of the positive and negative electrode sheets is the same as in Example 1. The electrode sheets and the glass fiber membrane are cut into strips.

[0148] Step 3: Assemble into a solid full battery

[0149] a. Superimpose the negative electrode sheet, glass fiber separator, positive electrode sheet, and glass fiber separator in sequence, wind them into a cylindrical electrode group, and weld the guide plate on the end surface to form an electrode group;

[0150] b. Fill the precursor solution and seal the battery;

[0151] c. The assembled battery is left to stand at room temperature for 8 h to ensure that the electrolyte precursor is completely infiltrated into the positive and negative electrodes and the separator of the battery;

[0152] d. The static battery precursor is heated at 70° C. for 5 hours to completely solidify the electrolyte precursor solution, thereby preparing the in-situ solid-state battery.

[0153] The operation method of each embodiment and reference group and the subsequent verification experiment is the same as the preparation method of positive and negative electrode sheets and soft-pack batteries. The difference between the experiments lies in the difference in the chemical reagents used. The material ratio of the solid electrolyte can be found in the experimental result comparison table.

[0154] Material abbreviations: ethylene carbonate (EC), propylene carbonate (PC), acrylonitrile (AN), azobisisobutyronitrile (AIBN), ethylene glycol dimethacrylate (EGDMA), fluoroethylene carbonate (FEC), lithium bistrifluoromethylsulfonyl imide (LiTFSI), polyethylene glycol dimethacrylate (Mn=550) (PEGDMA, Mn=550), polyethylene glycol dimethacrylate (Mn=1000) (PEGDMA, Mn=1000), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), vinylene carbonate (VC), 1,3-propane sultone (PS), dimethyl carbonate (DMC), diethyl carbonate (DEC).

[0155] Battery performance test plan:

[0156] Cycle performance test: At 25°C, the batteries obtained from each embodiment and comparative example were subjected to charge and discharge cycle tests at charge and discharge rates of 1C, 2C, and 2.5C in the range of 2.5-4.5V (1C = 170mAh / g)

[0157] Ionic conductivity test: At 25°C, the blocked batteries obtained in each implementation case and comparative example were subjected to AC impedance test using a Chenhua electrochemical workstation with a frequency range of 10 -1 Hz-10 6 Hz, substitute the impedance value obtained by the test into the following formula; and calculate the corresponding ionic conductivity of the electrolyte membrane.

[0158]

[0159] Wherein: L is the thickness of the film, R is the impedance value obtained by the test, and S is the apparent area of ​​the stainless steel sheet.

[0160] Lithium ion migration number test: The lithium ion migration number is determined by combining EIS with chronoamperometry (IT). IT test was performed at 25°C using a CHI660D electrochemical workstation, with a polarization voltage of 10mV and a test time of 3600s. EIS was performed on the symmetrical battery before and after the test to obtain the initial resistance and termination resistance.

[0161] The ion migration number of lithium ions in the prepared SPE is calculated by the following formula:

[0162]

[0163] in, is the lithium ion migration number; ΔV is the polarization voltage, the value is 0.01V; I0 is the initial current, I ss is the termination current, in A; R0 is the initial resistance, R ssis the termination resistance, measured in ohms (Ω).

[0164] The experimental results obtained from the experiment are listed in the experimental results comparison table.

[0165]

[0166] Example 1 and reference group 1 adopted a curing scheme of heating at 70°C for 6 hours;

[0167] Example 3 and reference group 2 adopted a curing scheme of heating at 65°C for 5h;

[0168] Example 2 adopts a curing scheme of heating at 55 degrees for 12 hours.

[0169] Example 4 adopts a curing scheme of heating at 75 degrees for 4 hours.

[0170] The above curing schemes can all achieve the effect of complete curing.

[0171] It should be noted here that, taking IPE-AN-5 as an example, AN means that the monomer contains AN, the number 5 represents the molar dosage multiple of the total monomer amount and the lithium salt, F means that an electrolyte improver containing F is added thereto, and non means that the AN monomer is not contained.

[0172] The electrolyte configuration and monomer dosage of the reference group were controlled according to the proportions of Example 3, wherein the purpose of designing reference group 1 was not to use acrylonitrile as a control, and the purpose of designing reference group 2 was not to use an improver as a control.

[0173] By comparing the experimental results of the examples with those of the reference group, it can be seen that the preferred contents of monomers, initiators and lithium salts in the gel electrolyte have a significant impact on the life of the battery. In the present invention, Example 1 has the best comprehensive performance.

[0174] By comparing the experimental results of Example 1 and Comparative Example 2, it can be seen that the design of a gel electrolyte containing FEC can effectively improve the rate performance of the battery. This is mainly because the addition of a small amount of FEC promotes the formation of a stable and effective SEI film on the electrode surface, improves the original solvation structure based on carbonate solvents, and reduces the binding energy with Li+.

[0175] By comparing the experimental results of the embodiment with those of the reference group 1, it can be seen that the gel electrolyte containing polyacrylonitrile segments has a higher potential for application in high energy density batteries. This is mainly because C≡N contains a lower lowest unoccupied molecular orbital and has the ability to bind to Li+. At the same time, compared with oxygen atoms, nitrogen atoms have a lower interaction with Li+, which is more conducive to the rapid movement of lithium ions, so that the corresponding battery has a higher lithium ion migration number, inhibits the growth of lithium dendrites, and obtains a longer cycle life and higher rate performance.

[0176] Figure 6 The capacity comparison of electrolytes with different proportions of AN added at different discharge rates is shown.

[0177] Figure 7 The cycling performance of the IPE-AN-10 fabricated battery is shown.

[0178] It can be seen that the in-situ polymer electrolyte with an appropriate proportion of AN has higher chemical stability, high rate performance and high cycle performance, achieving the goal of balanced improvement of multiple performances without sacrificing other performances due to the single improvement of one aspect.

[0179] Therefore, the in-situ polymer electrolyte of the present invention has the advantages of simple process and reasonable selection of chemical monomers; at the same time, it can be applied to the existing battery manufacturing process and has promising application prospects.

[0180] In addition, the following table also gives the data of various electrochemical properties of different solvents, different lithium salts, and different improvers when the amount of polymerized monomer is 10 times that of lithium salt. From the table, it can be seen that the performance of the pores formed by suitable monomers and advantageous lithium salts is better. If the negative ion radius of the lithium salt is smaller than or close to the formed pores, the electrolyte effect is relatively poor, such as the performance of verification tests 7 and 8. The scheme and test results of the verification test are listed in the table below.

[0181]

[0182]

[0183] In the above embodiment, the temperature was set at 50-80°C with an interval of 5 degrees, and the curing time was 2-12 hours. The cross-comparison experiment was carried out with an interval of 2 hours, and the effect of complete curing could be achieved.

[0184] It should be noted that PEGDMA (Mn=1000) means that the number of polymerized molecules of EGDMA is 1000. By comparing the polymerization of the polymerized PEGDMA with the polymerized monomer EGDMA and AN, it can be seen that the polymerization effect of the monomer is better.

[0185] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. An in-situ polymer electrolyte, characterized in that: It includes a separator and an electrolyte, wherein the electrolyte is obtained by in-situ polymerization, and the electrolyte covers the surface of the separator and fills the pores of the separator; The electrolyte part includes a support structure, a lithium salt, and a solvent; The support structure has a crown ether-like structure, which effectively attracts the positive ions of the lithium salt and facilitates the dissociation of the positive ions and the negative ions; The crown ether-like structure is composed of one or two of C≡N, C=O, and CO; The crown ether-like structure includes: One or more of; The support structure is formed by polymerizing organic monomers to form a cross-linked network structure; The organic monomer is composed of one or more of diacrylate and its derivatives, acrylate and its derivatives and acrylonitrile, and the amount of the organic monomer is 5-20 times the mass of the lithium salt; The diacrylate derivatives include one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and diethylene glycol dimethacrylate; The acrylate derivatives include one or more of ethylene glycol acrylate, ethylene glycol methacrylate, diethylene glycol methacrylate, and diethylene glycol acrylate; The isolation part adopts glass fiber diaphragm, polypropylene diaphragm or polyethylene diaphragm.

2. The in-situ polymer electrolyte according to claim 1, characterized in that The cavities formed by the cross-linked network structure can accommodate negative ions and solvated positive ions of the lithium salt, and the average diameter of the pores of the cross-linked structure is smaller than the diameter of the negative ions of the lithium salt and larger than the diameter of the solvated positive ions.

3. The in-situ polymer electrolyte according to claim 2, characterized in that The solvent includes one or more carbonates, accounting for 35-60% by mass of the polymer electrolyte; The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(oxalatoborate); the concentration of the electrolyte formed by the lithium salt being dissolved in a solvent is 1 mol / L; The amount of the organic monomer used is 10-15 times the amount of the lithium salt.

4. The in-situ polymer electrolyte according to claim 3, characterized in that The electrolyte part is further added with an improving agent, wherein the improving agent is one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and 1,3-propane sultone, and the amount used is 3-6% of the mass of the electrolyte.

5. The in-situ polymer electrolyte according to claim 4, characterized in that The polymer monomer of the supporting structure uses an initiator to initiate a polymerization reaction, wherein the initiator includes one of azobisisobutyronitrile and dibenzoyl peroxide, and the amount used is 0.1-0.5% of the total amount of the polymer monomer; The porosity of the separator is 50-68%. The thickness of the in-situ polymer electrolyte is 50-250 μm.

6. A method for preparing the in-situ polymer electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, at room temperature, mixing one or more carbonate solvents in a preset ratio to obtain a mixed solvent; Step 2: Add lithium salt to the mixed solvent, control the condition that the molar concentration is 1 mol / L, and mix evenly to obtain a colorless and transparent electrolyte solution. Step 3: Add the polymer organic monomer to the electrolyte solution according to the preset ratio and continue stirring to fully dissolve. The organic monomers include monomers containing CN bonds and acrylate monomers; The organic monomer comprises a crown ether-like structure after polymerization; The crown ether-like structure is composed of one or two of C≡N, C=O, and CO; The crown ether-like structure includes: One or more of; The organic monomer is composed of one or more of diacrylate and its derivatives, acrylate and its derivatives and acrylonitrile, and the amount of the organic monomer is 5-20 times the mass of the lithium salt; The diacrylate derivatives include one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and diethylene glycol dimethacrylate; The acrylate derivatives include one or more of ethylene glycol acrylate, ethylene glycol methacrylate, diethylene glycol methacrylate, and diethylene glycol acrylate; The control condition is the ratio of the total amount of the organic monomer to the amount of the lithium salt; Step 4, adding an initiator and an electrolyte improver, and mixing them evenly to obtain an electrolyte precursor; Step five, placing the isolation part between two thickness limiting parts, controlling the gap thickness between the thickness limiting parts, injecting the precursor solution into the gap between the thickness limiting parts, heating and curing, and obtaining an in-situ polymer electrolyte membrane.

7. The method for preparing an in-situ polymer electrolyte according to claim 6, characterized in that: The temperature range of the heating curing is 50-80°C; The time range of the heating curing is 2-14 hours.

8. The method for preparing an in-situ polymer electrolyte according to claim 7, characterized in that: The isolation part adopts a glass fiber diaphragm, a polypropylene diaphragm or a polyethylene diaphragm; The solvent includes one or more carbonates, accounting for 35-60% by mass of the polymer electrolyte; The lithium salt is an organic lithium salt, and is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, and lithium dioxalate borate; the concentration of the electrolyte formed by the lithium salt being dissolved in a solvent is 1 mol / L; The amount of the organic monomer is 10-15 times the amount of the lithium salt; the temperature range of the heating curing is 65-75°C.

9. The method for preparing an in-situ polymer electrolyte according to claim 8, characterized in that: The improving agent is one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and 1,3-propane sultone, and the amount used is 5% of the mass of the electrolyte; The polymer monomer of the supporting structure uses an initiator to initiate a polymerization reaction, wherein the initiator includes one of azobisisobutyronitrile and dibenzoyl peroxide, and the amount used is 0.1-0.5% of the total amount of the polymer monomer; The isolation portion has a porosity of 50-68% and a thickness of 10-300 μm; The thickness of the in-situ polymer electrolyte is 50-250 μm; The heating curing time ranges from 4 to 8 hours.

10. A battery, characterized in that: The battery comprises the in-situ polymer electrolyte according to any one of claims 1 to 5 or the in-situ polymer electrolyte obtained by the method according to any one of claims 6 to 9.

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