Radical in-situ polymerization semi-solid battery

Abstract

The application discloses a kind of free radical in-situ polymerization semi-solid batteries;Including positive electrode, negative electrode and semi-solid electrolyte, the semi-solid electrolyte is the semi-solid electrolyte formed by adding polymerization monomer, plasticizer and initiator in-situ polymerization in liquid electrolyte;The polymerization monomer is the combination of vinylene carbonate VC and trimethylene carbonate TMC with mass ratio 20-35:0.1-1.5.The application improves gel electrolyte component, reduces battery impedance, improves battery performance, improves the hardness of gel electrolyte, is conducive to solid-solid interface in battery, improves the safety of battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, relates to the technical field of semi-solid batteries, and in particular to a free radical in-situ polymerization semi-solid battery. BACKGROUND

[0002] With the increasingly urgent requirement of improving the energy density of lithium ion batteries, the traditional lithium ion battery has been difficult to meet the demand of super high specific energy. The current commercialized negative electrode material of lithium battery is mainly modified natural graphite and artificial graphite, although the preparation technology is quite mature, but the theoretical specific capacity of graphite is only 372 mAh g -1 , which is difficult to meet the market demand for high energy density lithium ion batteries. Therefore, based on the demand for high energy density batteries, the negative electrode material with the advantage of super high specific energy has become a research hotspot. For example: silicon negative electrode, metal alloy negative electrode and metal lithium negative electrode. Taking the silicon negative electrode material as an example, at present, a certain amount of silicon material is mainly used to achieve the purpose of improving the specific capacity. Taking the metal lithium negative electrode as an example, the specific capacity is 3860 mAh g -1 , and the electrochemical potential is-3.04 V (vs. standard hydrogen electrode). The battery made of these negative electrode materials can effectively improve the energy density, and even can reach 400 Wh kg -1 or even higher. And the middle and high nickel ternary lithium battery has high activity, and after being matched with high specific capacity negative electrode material, the specific energy density is improved, and the safety of the battery is also a top priority.

[0003] However, based on the traditional lithium ion battery system, the high energy density battery material currently still has many safety hazards. The material itself has large volume expansion, structure change, and cycle life and safety hazard when matched with liquid electrolyte. The liquid electrolyte cannot effectively inhibit the huge expansion of the silicon negative electrode, or the structure change of the lithium metal negative electrode and the growth of metal dendrites, and the dendrites may pierce the separator and cause internal short circuit of the battery, causing greater safety problems.

[0004] At present, there are many gel semi-solid battery technologies. The semi-solid battery can effectively reduce the use amount of liquid electrolyte in the battery, and at the same time of improving the energy density of the battery, the safety hazard caused by the liquid electrolyte is also reduced. In addition, the semi-solid gel electrolyte can effectively inhibit the structure change of the negative electrode and the growth of metal dendrites to a certain extent, and at the same time of improving the specific energy, the safety of the battery can be greatly improved. However, the existing semi-solid gel electrolyte often has the problems of high battery impedance after polymerization and large performance loss.

[0005] The existing patent literature search found that the patent CN 112018438 A applied vinylene carbonate as a gel polymer monomer, azobis isobutyronitrile as an initiator, and a flexible agent and a crosslinking agent of an acrylic ester to initiate in-situ polymerization. However, the composition and content of the components also cause the battery impedance to be high after polymerization, and the performance loss is large. SUMMARY

[0006] Based on the above problems, the purpose of the present application is to provide a free radical in-situ polymerization semi-solid battery; the present application uses an in-situ polymerization method to make and produce a semi-solid battery, specifically using polymer monomers, plasticizers, initiators and other components to form a semi-solid gel electrolyte under certain conditions.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] The present application relates to a free radical in-situ polymerization semi-solid battery, comprising a positive electrode, a negative electrode and a semi-solid electrolyte, wherein the semi-solid electrolyte is a semi-solid electrolyte formed by adding polymer monomers, plasticizers and initiators to a liquid electrolyte and in-situ polymerization; the polymer monomers are a combination of vinylene carbonate VC and trimethylene carbonate TMC in a mass ratio of 20-35:0.1-1.5.

[0009] As an embodiment, the liquid electrolyte contains a lithium salt; the lithium salt is one or more of lithium hexafluorophosphate LiPF6, lithium bisfluorosulfonylimide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium trifluoromethylsulfonate LiCF3SO3, lithium tetrafluoroborate LiBF4, lithium bisoxalate borate LiBOB, lithium difluoro oxalate borate LiODFB, and lithium difluoro bisoxalate phosphate LiDFBP.

[0010] As a preferred embodiment, the polymer monomers are a combination of vinylene carbonate VC and trimethylene carbonate TMC in a mass ratio of 20-35:0.1-1.5. Preferably, the content of polymer monomer VC in the semi-solid electrolyte is 20-35 wt.%, and the content of TMC is 0.1-1.5 wt.%. In the system of the present application, VC is the main polymer monomer, and TMC is the auxiliary polymer monomer, and both are indispensable. The main role of TMC after polymerization is to increase the viscosity of the VC-based semi-solid electrolyte after polymerization. If TMC is the main polymer monomer and VC is the auxiliary, the semi-solid electrolyte properties are unstable and cannot effectively form a semi-solid electrolyte.

[0011] As an embodiment, the plasticizer adopts one or more of polyvinyl alcohol PEG, polyethylene glycol dimethyl ether PEGDME, dibutyl phthalate DBP, dimethyl phthalate DMP, dioctyl phthalate DOP, acetonitrile ACN, butanedinitrile SN, and thermoplastic polyurethane TPU. Butanedinitrile SN is preferred. Butanedinitrile SN has a relatively stable structure, good ionic conductivity, good thermal stability, and high oxidation stability. When used in a semi-solid electrolyte, it helps to increase the stability of the semi-solid electrolyte at high temperature and high voltage, and has less negative impact on impedance and performance.

[0012] As an embodiment, the initiator adopts one or more of 2,2-azobis isobutyronitrile AIBN, azobis isononanitrile ABVN, dimethyl 2,2-azobis isobutyrate AIBME, and benzoyl peroxide BPO.

[0013] As a preferred embodiment, the initiator is a combination of 2,2-azobis isobutyronitrile AIBN and benzoyl peroxide BPO in a mass ratio of 0.01-4:0.01-4. Preferably, the content of initiator AIBN in the semi-solid electrolyte is 0.1-0.5 wt.%, and the content of BPO is 0.03-0.1 wt.%. Most preferably, 0.18% AIBN + 0.05% BPO. The polymerization reaction initiated by AIBN has a high reaction rate and is relatively violent, while the polymerization reaction initiated by BPO is relatively mild; the combination of the two can effectively control the polymerization reaction rate, on the one hand to ensure the effective infiltration of the electrolyte before polymerization, and on the other hand to ensure that the polymerization reaction will not be too violent to damage the microstructure and morphology of the electrode sheet. If a high content of BPO and a small amount of AIBN are used, the reaction rate is too slow, and the high temperature time required is too long. The electrode sheet, material, and electrolyte will have undesirable decomposition side reactions under continuous high temperature.

[0014] As an embodiment, the content of the polymerized monomer in the semi-solid electrolyte is 20-40 wt.%, the content of the plasticizer is 0.1-5 wt.%, and the content of the initiator is 0.02-8 wt.%.

[0015] As an embodiment, the negative electrode is a silicon-doped graphite negative electrode, a lithium metal negative electrode, or a metal alloy negative electrode.

[0016] As an embodiment, the main material of the positive electrode is a nickel material, a nickel-manganese-aluminum material NCA, a lithium manganese iron phosphate LMFP, or a lithium iron phosphate LiFePO4.

[0017] As an embodiment, the amount of silicon doping in the silicon-doped graphite negative electrode is 3%-80%. Preferably, it is 5-60%, and further preferably, it is 8-30%.

[0018] As an embodiment, the metal alloy negative electrode comprises a Ga-Sn, Ge-Se or Sn-Al negative electrode.

[0019] As an embodiment, the nickel material comprises one or more of NCM811, Ni90, NCM111, NCM532, NCM622 and NCM712.

[0020] As an embodiment, a conductive agent is added to the positive and negative electrodes; the conductive agent comprises one or more of carbon black superP, acetylene black, multi-walled carbon nanotubes MWCNT and single-walled carbon nanotubes SWCNT.

[0021] As an embodiment, a binder is added to the positive and negative electrodes; the binder is one or more of polyethylene oxide PEO, polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose CMC, polyurethane PU, styrene butadiene rubber SBR, polyvinyl alcohol PVA, polyacrylic acid PAA and polyacrylonitrile PAN.

[0022] As an embodiment, the in-situ polymerization temperature is 58-65°C, and the in-situ polymerization time is 1.25-3h. Some additives in the electrolyte are unstable under continuous high temperature for a long time, and are prone to cause undesirable decomposition side reactions with the electrode materials. Therefore, the temperature needs to be controlled not to be too high, and the time needs to be controlled not to be too long.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] 1) The present application improves the components of the gel electrolyte, reduces the battery impedance and improves the battery performance; when the polymerization monomer is preferably a combination of vinylene carbonate and trimethylene carbonate, the hardness of the gel electrolyte can be adjusted and improved, which is beneficial to the solid-solid interface in the battery.

[0025] 2) The present application improves the safety of the battery through optimization of the components; for example, the use of plasticizer succinonitrile is beneficial to improve the flexibility of the gel electrolyte and helps to improve the safety of the battery.

[0026] 3) In the present application, the initiator is preferably a combination of 2,2-azobisisobutyronitrile and a small amount of benzoyl peroxide; the reaction speed of 2,2-azobisisobutyronitrile is too fast, while the polymerization reaction of benzoyl peroxide is more moderate, so the specific combination of the two is more conducive to the formation of in-situ gel electrolyte in the production process of the battery.

[0027] 4) The present application improves the battery production process. The in-situ polymerization of the present application has lower temperature and faster polymerization, which can effectively improve the efficiency and reduce the production cost. Moreover, it is produced in the actual battery, in-situ polymerization and gelation, which is more suitable for the actual battery production line, can better improve the efficiency and reduce the cost. BRIEF DESCRIPTION OF DRAWINGS

[0028] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, when read in conjunction with the accompanying drawings:

[0029] Figure 1 Schematic diagram of semi-solid battery production process;

[0030] Figure 2 Semi-solid gel electrolyte synthesis, inverted diagram shows that it is a viscous solid rather than a liquid state;

[0031] Figure 3 Impedance diagram of semi-solid gel electrolyte conductivity test of Example 7;

[0032] Figure 4 Lithium ion transference number test of semi-solid gel electrolyte of Example 7, (a) lithium symmetric impedance spectrum diagram of initial state and stable state, (b) polarization current diagram under chronopotentiometry;

[0033] Figure 5 Normal temperature impedance diagram of semi-solid battery of Example 7. DETAILED DESCRIPTION

[0034] The present application will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present application. These are within the scope of protection of the present application.

[0035] The present application provides a free radical in-situ polymerization semi-solid battery:

[0036] The negative electrode layer main material uses silicon-doped graphite negative electrode, and the silicon doping amount is 3%-80%, preferably 5-60%, and further preferably 8-30%. (It can also be a lithium metal negative electrode, or a metal alloy negative electrode, such as Ga-Sn, Ge-Se, Sn-Al, etc.)

[0037] The positive electrode layer main material uses high-nickel material (NCM811 and Ni90 material, i.e. LiNixCoyMnzO2, where x≥0.8), which can also be NCM111, NCM532, NCM622, NCM712, nickel-manganese-aluminum material NCA, lithium manganese iron phosphate LMFP or lithium iron phosphate LiFePO4.

[0038] The positive and negative electrode sheets need to mix conductive agents, specifically one or several of carbon black super P, acetylene black, multi-walled carbon nanotubes MWCNT, single-walled carbon nanotubes SWCNT. And binders, specifically one or several of PEO (polyethylene oxide), PVDF (polyvinylidene fluoride), CMC (sodium carboxymethyl cellulose), PU (polyurethane), SBR (styrene butadiene rubber), PVA (polyvinyl alcohol), PAA (polyacrylic acid), PAN (polyacrylonitrile).

[0039] The semi-solid gel electrolyte is made by adding polymer monomers, plasticizers and initiators to the liquid electrolyte. The electrolyte is a conventional lithium battery liquid electrolyte, containing lithium salt (one or several of lithium hexafluorophosphate LiPF6, lithium bisfluorosulfonylimide LiFSI, lithium bis-trifluoromethanesulfonylimide LiTFSI, lithium trifluoromethanesulfonate LiCF3SO3, lithium tetrafluoroborate LiBF4, lithium bisoxalate borate LiBOB, lithium difluoro oxalate borate LiODFB, lithium difluoro bisoxalate phosphate LiDFBP). The polymer monomer uses a monomer with an unsaturated double bond or triple bond, specifically a combination of VC (vinylene carbonate) and TMC (trimethylene carbonate). The plasticizer uses one or several of PEG (polyvinyl alcohol), PEGDME (polyethylene glycol dimethyl ether), DBP (dibutyl phthalate), DMP (dimethyl phthalate), DOP (dioctyl phthalate), ACN (acetonitrile), SN (butanedinitrile), TPU (thermoplastic polyurethane). The initiator uses one or several of AIBN (2,2-azobisisobutyronitrile), azobisisoheptyl nitrile (ABVN), dimethyl azobisbutyrate (AIBME), BPO (benzoyl peroxide).

[0040] As a preferred implementation example, the polymer monomer is selected as a combination of vinylene carbonate VC and trimethylene carbonate TMC with a mass ratio of 20-35:0.1-1.5; the initiator is selected as a combination of 2,2-azobisisobutyronitrile AIBN and benzoyl peroxide BPO. The content of polymer monomer VC in the semi-solid electrolyte is 20-35 wt.%, and the content of TMC is 0.1-1.5 wt.%; the content of plasticizer is 0.1-5 wt.%, preferably 1.2-3 wt.%; the content of initiator AIBN is 0.01-4 wt.%, and the content of BPO is 0.01-4 wt.%, preferably the content of AIBN is 0.1-0.5 wt.%, and the content of BPO is 0.03-0.1 wt.%.

[0041] When preparing, the assembled battery is injected with electrolyte, and then aged at a temperature of 20-50°C, preferably 45-48°C, for 24h. Then the battery is placed in a high-temperature environment for gelation reaction at a temperature of 50-70°C, preferably 58-65°C, for 0.5-24h, preferably 1.25-3h. Then the battery is subjected to formation, aging and capacity test to obtain the finished battery cell.

[0042] Examples 1-7

[0043] Examples 1-7 provide a series of radical in-situ polymerization semi-solid batteries, including a positive electrode, a negative electrode and a semi-solid electrolyte.

[0044] The process of preparing the battery is as follows:

[0045] First, the slurry is mixed, wherein the positive electrode slurry is mixed in a ratio of 9 series ternary material (NCM-Ni90): conductive carbon black (Super P): carbon nanotube (CNT800): binder (PVDF_1100) = 97:1.1:0.8:1.1, all in mass percentage (wt.%).

[0046] The negative electrode slurry is mixed in a ratio of graphite (BF): silicon-oxygen material (Si-O): conductive carbon black (Super P): carbon nanotube (CNT800): binder (sodium carboxymethyl cellulose CMC_500): binder (styrene-butadiene rubber SBR) = 88.1:6.5:0.2:1.2:2.2, all in mass percentage (wt.%).

[0047] 1.8:0.2:1.2:2.2, all in mass percentage (wt.%).

[0048] Then coating is performed, the positive electrode slurry is coated on the aluminum foil, and the negative electrode slurry is coated on the copper foil, and then drying and winding are performed. Then rolling is performed, and then slitting is performed. Then the core winding is performed using the prepared positive and negative electrode sheets and the separator, and the separator is PE separator (3μm PVDF adhesive layer+9μm base film+3μm Al2O3 ceramic layer+3μm PVDF adhesive layer). After the winding of the core, the top cover is welded, and then the dry battery cell is assembled into the shell.

[0049] After the dry battery cell is baked, it is injected with electrolyte.

[0050] The electrolyte in the semi-solid electrolyte is EC: EMC: DEC: LiPF6: LiFSI: LiPO2F2: FEC: DTD = 22:28.2:20:12:12:0.5:4.5:0.8, all in mass percentage (wt.%), and other components and amounts are shown in Table 1.

[0051] After the battery is infiltrated, it is subjected to formation, gelation and capacity test to obtain the finished battery cell.

[0052] The preparation process is shown in Figure 1 The battery assembly was performed according to the normal battery production process. The assembled battery was subjected to liquid injection (adding the polymerization monomer, plasticizer and initiator shown in Table 1 to the liquid electrolyte), and then was aged after the liquid injection, with the aging temperature being 45°C and the aging time being 24h. Then the battery was placed in a high-temperature environment for gel reaction, with the reaction temperature being 60°C and the reaction time being 2h, so as to initiate the gel polymerization of the electrolyte to form a semi-solid gel electrolyte. Then the battery was subjected to formation under high-temperature and high-pressure conditions (the temperature was 40±5°C, and the pressure was controlled by a clamp to be 2000N), was aged at 45°C, and was subjected to capacity distribution under room temperature conditions, to obtain a finished battery cell.

[0053] Comparative Examples 1-5

[0054] Comparative Examples 1-5 provide a series of radical in-situ polymerization semi-solid batteries, which are basically the same as Example 1, except that the composition of the semi-solid electrolyte is different. See Table 1 for details; wherein ETPTA is trimethylolpropane triacrylate.

[0055] Table 1 Composition and amount of each example and comparative example of semi-solid gel electrolyte except electrolyte

[0056]

[0057] Note: The amount is the content wt. % relative to the total weight of the semi-solid gel electrolyte.

[0058] Figure 2 For the synthesized semi-solid gel electrolyte, the inverted graph shows that it is a viscous solid rather than a liquid. The impedance spectrum of the semi-solid gel electrolyte prepared in Example 3 was tested at room temperature, as shown in Figure 3 , and the calculated ion conductivity at room temperature was about 2-3mS / cm. The lithium symmetric impedance graph and the polarization current graph under chronopotentiometry of the lithium ion transference number test are shown in Figure 4 , and the calculated lithium ion transference number of the semi-solid gel electrolyte was about 0.512. The room temperature impedance graph of the semi-solid battery of Examples 1-7 is shown in Figure 5 , and it can be seen from Figure 5 that the impedance of Examples 1-3 is low, and the impedance of Example 3 is the lowest.

[0059] Table 2 Performance comparison of semi-solid gel electrolyte in full battery of each example and comparative example

[0060]

[0061] It needs to be particularly pointed out that: the present application is not limited to lithium ion battery, also applicable to the manufacture of sodium ion semi-solid battery, potassium ion semi-solid battery, magnesium ion semi-solid battery, other kinds of electrochemical system battery of aluminum ion semi-solid battery, only the positive and negative electrode material and lithium salt are replaced by corresponding sodium material and sodium salt, or potassium material and potassium salt, or magnesium material and magnesium salt, or aluminum material and aluminum salt.

[0062] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the above specific embodiments, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A radical in-situ polymerization semi-solid battery comprising a positive electrode, a negative electrode, and a semi-solid electrolyte, characterized by, The semi-solid electrolyte is a semi-solid electrolyte formed by in-situ polymerization of a liquid electrolyte added with a polymerization monomer, a plasticizer and an initiator; the polymerization monomer is a combination of 20-35 wt.% of vinylene carbonate and 0.1-1.5 wt.% of trimethylene carbonate; the semi-solid electrolyte contains 20-35 wt.% of vinylene carbonate, 0.1-1.5 wt.% of trimethylene carbonate, 0.1-0.5 wt.% of initiator 2,2-azobisisobutyronitrile, 0.03-0.1 wt.% of initiator benzoyl peroxide and 0.1-5 wt.% of plasticizer. The liquid electrolyte contains a lithium salt; the lithium salt is one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethylsulfonate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium difluoro oxalate borate and lithium difluoro bisoxalate phosphate.

2. The free radical in-situ polymerization semi-solid battery of claim 1, wherein, The plasticizer is one or more of polyvinyl alcohol, polyethylene glycol dimethyl ether, dibutyl phthalate, dimethyl phthalate, dioctyl phthalate, acetonitrile, butanedinitrile and thermoplastic polyurethane.

3. The free radical in situ polymerization semi-solid battery of claim 1, wherein, The negative electrode is a silicon-doped graphite negative electrode, a lithium metal negative electrode or a metal alloy negative electrode, and the main material of the positive electrode is a nickel material, a nickel-manganese-aluminum material, manganese iron lithium phosphate or ferrous lithium phosphate; the nickel material includes one or more of NCM811, Ni90, NCM111, NCM532, NCM622 and NCM712.

4. The free radical in situ polymerization semi-solid battery of claim 1, wherein, The positive and negative electrodes are both added with a conductive agent and a binder; the conductive agent includes one or more of carbon black, acetylene black, multi-walled carbon nanotubes and single-walled carbon nanotubes; and the binder is one or more of polyethylene oxide, polyvinylidene fluoride, sodium carboxymethyl cellulose, polyurethane, butadiene-styrene rubber, polyvinyl alcohol, polyacrylic acid and polyacrylonitrile.

5. The free radical in situ polymerization semi-solid battery of claim 1, wherein, The in-situ polymerization temperature is 58-65℃, and the in-situ polymerization time is 1.25-3h.

6. The free radical in situ polymerization semi-solid battery of claim 1, wherein, ​

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