A semi-solid battery with high energy density and high safety and a preparation method thereof

Abstract

The application discloses a kind of high energy density and high safety's semi-solid battery and preparation method thereof. Using low temperature method uniform infiltration wetting, control temperature keeps at 15~20 ℃ to make electrolyte mixed solution before polymerization uniform infiltration into the positive electrode, negative electrode and separator of electric core, then gradually increase temperature by progressive way to make second mixed solution polymerization reaction, so that uniform polymerization in situ polymerization process, battery interface impedance is low, battery consistent stability is good, first cycle efficiency is high. By using fast ion conductor solid electrolyte for the coating of positive electrode particles and the coating modification of separator, the internal resistance of low-temperature polymerized solid-state battery is further reduced, and the overall cycle life of the battery is improved. The method of adding small molecule plasticizer can be used with low temperature infiltration, slow heating polymerization method, which improves the ion transport capacity of the battery, reduces the internal resistance, and further improves the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary batteries, and particularly relates to a semi-solid battery with high energy density and high safety and a preparation method thereof. BACKGROUND

[0002] Electrolytes are an important component of lithium ion batteries as they transport the required lithium ions from the cathode to the anode. They also protect the cathode and anode from degradation by forming a solid electrolyte interface that can shield the electrodes from adverse electrode-electrode or electrode-electrolyte reactions. The current industry primarily uses liquid electrolytes because of their high ionic conductivity and ease of customization through additives. However, despite the development of liquid electrolytes, their use in batteries is limited due to factors such as capacity, safety, and thermal efficiency of lithium ion batteries. Liquid electrolytes inherently require the use of binders and separators, which overall reduce the energy density of liquid electrolyte batteries. Additionally, liquid electrolytes, which are typically made of organic molecules, are flammable. At low temperatures, liquid electrolytes gradually freeze, reducing ionic conductivity, which leads to anode plating. However, at higher temperatures, liquid electrolytes can evaporate and create high impedance bubbles. Due to these limitations of liquid electrolytes, solid electrolytes are increasingly gaining attention from researchers as a potential alternative.

[0003] Compared to liquid electrolytes, solid electrolytes improve battery capacity by reducing battery mass, are non-flammable, are more stable throughout temperature, and do not leak at extreme temperatures or pressures. Unfortunately, existing solid-state battery technology is not mature enough to be industrialized. Existing preparation methods either are not optimized to produce solid-state batteries with high interfacial impedance between the produced electrodes and electrolytes (thus having poor rate and cycle performance), or use materials that are not commonly found in existing lithium ion battery production lines.

[0004] As a compromise, semi-solid batteries utilize both liquid and solid electrolytes to form in a gel form. This allows the resulting battery to have both high ionic conductivity and thermal stability over a wide range, as well as good safety characteristics. Additionally, semi-solid batteries can be produced using existing lithium ion battery production line machines and equipment, thus having good economic feasibility in existing large-scale lithium ion battery companies. Gel electrolytes are primarily prepared through in-situ polymerization, where the electrolyte is mixed with a monomer, lithium salt, cross-linking agent, and initiator compounds and injected into the battery, where, upon the application of heat, the electrolyte solidifies into a gel. Existing technologies that utilize such methods either result in bubble generation (which increases impedance and reduces first cycle efficiency) or incomplete formation of the solid electrolyte interface (which reduces cycle life performance). This is because the heat required for the uniform dispersion of the electrolyte also initiates the in-situ polymerization.

[0005] In addition to injection and heating, there are other technologies that utilize in-situ polymerization. Some technologies can initialize in-situ polymerization before assembling the battery. This can be done by coating electrolyte material on the membrane to form an electrolyte membrane. The membrane can have different compounds on both sides of the membrane. However, these multi-layer composite membranes not only have a complex procedure, but in order to manufacture them, the membrane must be coated outside the battery to form the membrane, and then stuck to the electrode. This results in poor electrode-electrolyte interface contact and high impedance, ultimately reducing battery capacity. In an attempt to solve this problem, the reaction monomer is mixed into the cathode and anode, and then the cross-linking agent and initiator are injected for in-situ polymerization. However, this solution still cannot solve the problem of uneven polymerization and high impedance.

[0006] In view of the current lithium battery industry, such as existing production lines, equipment and supply chain, the liquid injection version of in-situ polymerization is the simplest and most convenient battery preparation method, while also minimizing additional costs, stimulating the development of semi-solid batteries. However, current research on in-situ polymerization focuses more on the theoretical structure of the material and the polymerization reaction, and how to solve the problems of uneven polymerization, low first cycle efficiency and low energy density is needed to solve the industrial production of semi-solid batteries. SUMMARY

[0007] The present application is directed to the problem of low first cycle efficiency and low energy density of semi-solid batteries in the prior art, and provides a semi-solid battery with high energy density and high safety and a preparation method thereof.

[0008] A preparation method of a semi-solid battery with high energy density and high safety, the semi-solid battery comprising a dry battery cell, the dry battery cell comprising a positive electrode sheet, a negative electrode sheet and a separator, the preparation method comprising the following steps:

[0009] (1) preparing the positive electrode sheet, the negative electrode sheet and the separator respectively, the particle surface of the positive electrode sheet being uniformly coated with nanoscale solid-state electrolyte, and the surface of the separator being uniformly coated with micrometer-scale solid-state electrolyte on one side or both sides;

[0010] (2) assembling the positive electrode sheet, the negative electrode sheet and the separator into a dry battery cell;

[0011] (3) mixing reaction monomers, cross-linking agents, lithium salts, small molecule plasticizers and initiators to obtain a mixed solution;

[0012] (4) injecting the mixed solution into the dry battery cell to infiltrate the dry battery cell;

[0013] (5) heating to a polymerization temperature to cause the mixed solution to undergo a polymerization reaction, obtaining a semi-solid battery of semi-solid electrolyte.

[0014] Preferably, the nanoscale solid-state electrolyte coated on the particle surface of the positive electrode sheet is at least one of: Li1.4 Al 0.4 Ti 1.6 (PO4)3, Li 0.5 La 0.5 TiO3, Li3InCl6, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 , Li7La3Zr2O 12 , Li3ErCl6;

[0015] The micrometer scale solid state electrolyte coated on the surface of the separator is at least one of the following: Li7La3Zr2O 12 , Li 0.5 La 0.5 TiO3, Li3InCl6, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 , Li3ErCl6, Li 1.4 Al 0.4 Ti 1.6 (PO4)3.

[0016] The thickness of the nanometer scale solid state electrolyte coated on the surface of the particles of the positive electrode sheet is 10 nm to 100 nm.

[0017] The thickness of the micrometer scale solid state electrolyte coated on the surface of the separator is 2 μm to 4 μm.

[0018] Preferably, the reaction monomer is at least one of the following: polyethylene glycol methyl ether methacrylate, polyethylene glycol dimethyl methacrylate, methacryloyloxypropyl-terminated polydimethylsiloxane, monomethacryloyloxypropyl-terminated polydimethylsiloxane, poly(triethoxyvinylsilane). The reaction monomer is specially selected to produce a polymer that has both ionic conductivity and mechanical stability, and is also very common in the liquid lithium ion battery industry.

[0019] More preferably, the reaction monomer is composed of at least two different monomers, at least one of which is an amorphous, low glass transition temperature (Tg) reaction monomer, such as polyethylene glycol methyl ether methacrylate (POEM) and polyethylene glycol dimethyl methacrylate (PEGDMA). Preferably, the mass of such amorphous, low Tg reaction monomer can account for 20% to 50% of the total mass of the reaction monomer. By adding such amorphous, low Tg reaction monomer, the ion transport efficiency of the battery can be improved to some extent, and the macroscopic surface is improved to improve the electrical properties of the battery such as capacity and internal resistance.

[0020] Preferably, the crosslinking agent primarily functions to connect the long chains in the polymerization reaction, forming a crosslinked network. The crosslinking agent is at least one of the following: trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, or polyether polyacrylate.

[0021] The primary function of the lithium salt is to provide an ion transport carrier for the system. The lithium salt is at least one of the following: LiBF4, LiBF6, LiAsF6, LiPF6, LiClO4, LiB(C6H5)4, LiAlCl4, LiBr, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SOSO2)3, LiN(SO2C2F5)2, or Li[B(O4C2)]2.

[0022] An initiator is used to initiate the polymerization reaction of the monomers. The initiator is azobisisobutyronitrile (AIBN).

[0023] Preferably, in step (3), the small molecule plasticizer is at least one of the following: ethylene carbonate, diethylene carbonate, dimethyl carbonate, dipropyl carbonate, dimethyl sulfoxide dimethoxyethane, N-methyl-2-pyrrolidone, γ-butyrolactone, and polyethylene glycol dimethyl ether.

[0024] Preferably, by mass, for every 100 parts of reactant monomer, 10-40 parts of crosslinking agent, 12-24 parts of lithium salt, 1-2 parts of initiator, and 20-80 parts of small molecule plasticizer are added.

[0025] Preferably, in step (4), after injecting the mixture into the dry cell, the mixture is kept at 15°C to 20°C to allow it to soak the dry cell. After injection, the mixture needs to fully soak the dry cell for at least 48 hours. A longer soaking time is more beneficial for soaking, but it should be considered that the second mixture has already added both the reactive monomer and the initiator. Although the lower temperature can slow down the polymerization reaction, the polymerization reaction may still occur. Therefore, more preferably, the soaking time is 48 to 60 hours.

[0026] The low-temperature method is used to uniformly infiltrate and wet, and the temperature is controlled to be maintained at 15-20°C to make the electrolyte mixture before polymerization uniformly infiltrate into the positive electrode, negative electrode and separator of the battery cell, and then the temperature is gradually increased to make the second mixture gradually polymerize, so that the polymerization is uniform in the in-situ polymerization process, the battery interface impedance is low, the battery consistency stability is good, and the first cycle efficiency is high. By using the coating and modification of the separator and the positive electrode particles by the fast ion conductor solid electrolyte, the internal resistance of the low-temperature polymerized solid-state battery is further reduced, and the overall cycle life of the battery cell is improved. The method of adding a small molecule plasticizer can be used in cooperation with the low-temperature infiltration and slow heating polymerization method to improve the ion transport capacity of the battery cell and reduce the internal resistance, so that the cycle life of the battery cell is further improved.

[0027] In the present application, when the battery after liquid injection is heated from low temperature to a higher polymerization temperature to promote the polymerization reaction, the temperature field in the system will not be uniform if the heating rate is too fast, and the polymerization reaction may not uniformly polymerize at the same time. The corresponding battery performance capacity is low, and the cycle life is shortened. However, a longer heating time has an impact on production efficiency, and production energy consumption and cost are also increased. Therefore, preferably, after the infiltration is completed, the temperature of the mixture is gradually increased by a gradual method to make the mixture polymerize, the temperature is gradually increased at a heating rate of not more than 1°C / h, and the temperature is maintained at the polymerization temperature for not less than 24 h. More preferably, the temperature is gradually increased at a heating rate of 0.5-1°C / h during the polymerization reaction, and the temperature is gradually increased to 60-80°C. Most preferably, the temperature is gradually increased at a heating rate of 1°C / h during the polymerization reaction, and the temperature is gradually increased to 60-80°C.

[0028] The polymerization of the electrolyte is not easy to control when the polymerization electrolyte is injected at one time, and the polymerization reaction often starts gradually before the injection is completed. Therefore, the one-time injection method cannot be industrialized. By using the low-temperature uniform infiltration and wetting, the temperature is maintained at 15-20°C to make the electrolyte mixture before polymerization uniformly infiltrate into the positive electrode, negative electrode and separator of the battery cell, and then the temperature is gradually increased to make the second mixture gradually polymerize. By this heating method, the polymerization reaction is uniformly carried out, the polymerization is uniform in the in-situ polymerization process, the battery interface impedance is low, the battery consistency stability is good, and the first cycle efficiency is high.

[0029] In step (4), when the mixture is injected into the dry battery cell, the environmental dew point is controlled to be between -45°C and -65°C, and the vacuum degree is controlled to be between -98 kPa and -2 kPa.

[0030] Preferably, after the polymerization reaction in step (5), primary formation and primary degassing are carried out, and then the semi-solid electrolyte is aged, and after the aging is completed, secondary formation and secondary degassing are carried out.

[0031] The first formation step aims to complete the reaction between the electrolyte and the electrode and form a stable solid electrolyte interface. Preferably, the conditions for the first formation are: a charging current of 0.01C-0.5C, and a charging time of 30 minutes-360 minutes.

[0032] The first degassing step aims to collect and discharge the gas generated during the first formation. Preferably, the conditions for the first degassing are: -98kPa--2kPa pressure for 1-20 times, each time for 1-20s.

[0033] The second formation step aims to further improve the formation of the electrode and electrolyte interface. Preferably, the conditions for the second formation are: a charging current of 0.01C-0.5C, and a charging time until the voltage reaches the rated voltage of 4.2V.

[0034] The second degassing step aims to collect and discharge the gas generated during the second formation reaction. Preferably, the conditions for the second degassing are: -98kPa--2kPa pressure for 1-20 times, each time for 1-20s.

[0035] The purpose of aging is to make the initial side reactions of the battery complete, form a stable and firm SEI film on the surface of the positive and negative electrode particles, and enable subsequent stable battery cycling. The conditions for aging are: a temperature of 45-80℃, and a time of 12-120h.

[0036] The present application also provides a high-energy-density and high-safety semi-solid-state battery prepared by the preparation method. The full solid-state battery prepared by the present application has the advantages of no interface, high energy density, and high safety.

[0037] We made a full solid-state battery with a unique three-dimensional network structure without interface, thereby improving the first cycle efficiency and improving the overall electrochemical performance of the battery.

[0038] By coating the particle surface of the positive electrode and the separator surface with a solid-state electrolyte fast ion conductor, the resistance of the positive electrode particle and electrolyte interface and the separator surface and electrolyte interface is improved to some extent. The solid-state electrolyte fast ion conductor provides an additional fast channel for ion transmission, promotes the ion transmission rate between different phases, and macroscopically reduces the internal resistance of the battery, improves the initial efficiency and cycle life. Due to the small molecular characteristics of the small molecule plasticizer, it plays a role in lubrication and promoting chain segment movement in the semi-solid electrolyte, which improves the ionic conductivity of the semi-solid electrolyte; at the same time, the small molecule plasticizer improves the ion conduction at the interface between the electrode and the electrolyte and the separator and the electrolyte, and reduces the interface resistance. The small molecule plasticizer can also complex with lithium ions and move quickly under the action of an electric field, which plays a role in transporting lithium ions. The above effects macroscopically increase the initial efficiency and capacity of the battery, reduce the internal resistance, and improve the cycle life. In addition, the positive electrode particle surface coating and the separator surface coating of the solid-state electrolyte fast ion conductor and the addition of the small molecule plasticizer synergistically promote the ion transmission rate, reduce the internal resistance, and improve the cycle life. DETAILED DESCRIPTION

[0039] The positive electrode sheet, negative electrode sheet and separator in the semi-solid battery with high energy density and high safety prepared in the following examples are as follows:

[0040] The NCM811 electrode sheet was prepared as a positive electrode by using the conventional lithium ion battery preparation process, and the silicon / oxygen / graphite (capacity development of 450 mAh / g) electrode sheet was prepared as a negative electrode by using the conventional lithium ion battery preparation process.

[0041] 1. Preparation of the positive electrode:

[0042] The positive electrode slurry was coated on the positive electrode current collector aluminum foil, and dried in a vacuum drying box at 70-110°C for 10h, then the electrode was compacted by a roller press, and then cut and punched to obtain a composite positive electrode sheet.

[0043] The active component in the positive electrode slurry is NCM811, and the structural formula is: LiNi 0.8 Co 0.1 Mn 0.1 O2, and the material is a compound with a complex structure, which is uniformly coated with a nanoscale solid-state electrolyte material coating layer on the surface by using a physical blending and sintering method.

[0044] The composition of the solid-state electrolyte material is a nanoscale particle Li 1.4 Al 0.4 Ti 1.6 (PO4)3 (abbreviated as LATP), Li 0.5 La 0.5 TiO3 (abbreviated as LLTO), Li3InCl6, Li6.4 La3Zr 1.4 Ta 0.6 O 12 (abbreviated as LLZTO), Li7La3Zr2O 12 (abbreviated as LLZO), or Li3ErCl6, etc.

[0045] The mass percentage of each component in the positive electrode slurry is: NCM811: conductive agent: binder = 96.5: 1.5: 2, where the conductive agent is SP-acetylene black and the binder is PVDF5130.

[0046] 2. Preparation of the negative electrode:

[0047] The negative electrode slurry is coated onto the negative electrode current collector copper foil and dried in a vacuum drying oven at 70℃~110℃ for 10h. Then, the electrode is compacted by a roller press, and then the negative electrode sheet is obtained by slitting and stamping.

[0048] The active component in the negative electrode slurry, SiO / graphite, has a capacity of up to 450mAh / g (0.5C / 0.5C charge / discharge). The component's mass percentage in the negative electrode slurry is: SiO / graphite: conductive agent: CMC: SBR = 95.3: 1.0: 1.5: 2.2. The conductive agent is SP-acetylene black, and the binders are CMC and SBR.

[0049] 3. Preparation of the diaphragm:

[0050] A micron-scale solid electrolyte slurry is coated onto one or both sides of a porous polyethylene membrane and dried in a vacuum drying oven at 60℃~110℃ for 10 hours. Then, a multilayer composite membrane is obtained through processes such as winding, slitting, and static elimination.

[0051] The main component of the solid electrolyte is micron-sized Li particles. 0.5 La 0.5 TiO3, Li3InCl6, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li3ErCl6, Li 1.4 Al 0.4 Ti 1.6 (PO4)3 or Li7La3Zr2O 12 wait.

[0052] The solid electrolyte component accounts for 10% of the slurry mass. Other components in the slurry are solvent and a small amount of binder. The solvent evaporates after coating. The mass ratio of solid electrolyte to binder (PVDF5130) is 98.5:1.5.

[0053] Example 1

[0054] A method for preparing a high-energy-density and high-safety semi-solid cylindrical battery is as follows:

[0055] 1. Prepare a positive electrode sheet, a negative electrode sheet, and a separator, respectively. The surface of the positive electrode sheet is coated with a uniform solid-state electrolyte Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP) material, which is a compound with a complex phase structure, and the thickness of the coating layer is 10 nm. The coating layer raw material is purchased from Adrich Chemical Company. The surface of the separator is coated with a solid-state electrolyte, and the composition of the solid-state electrolyte is Li7La3Zr2O 12 , and the thickness of the coating on both sides of the separator is 2 μm. The coating layer raw material is purchased from Adrich Chemical Company.

[0056] 2. Wind, assemble, and dry the positive and negative electrode sheets and the separator prepared in step 1 to prepare a dry battery without liquid injection.

[0057] 3. Mix 5 g of polyethylene glycol methyl ether methacrylate (POEM) monomer, 5 g of methacryloxypropyl-terminated polydimethylsiloxane (PDMD) monomer, 1 g of polyether polyacrylate crosslinking agent, 2 g of ethylene carbonate small molecule plasticizer, 2 g of diethylene carbonate small molecule plasticizer, and 2.4 g of LiPF6, and 0.1 g of initiator azobisisobutyronitrile to prepare a primary electrolyte. Stir the mixture for 6 hours.

[0058] 4. Inject the electrolyte prepared in step 3 into the dry battery prepared in step 2. The dew point of the injection environment is controlled at -60°C, and the vacuum degree is -2 kPa. The battery is soaked at a temperature of 15°C for 60 h, then slowly heated to 60°C at a rate of 1°C / h, and kept at 60°C for 24 h to make the reaction proceed uniformly, and the obtained polymerization in situ is uniform.

[0059] 5. Perform formation and primary degassing on the polymerized battery prepared in step 4. The formation charging current is 0.01C, and the charging time is 360 minutes. The primary degassing vacuum degree is -98 kPa, and the exhaust is performed once with an exhaust time of 20 s.

[0060] 6. Perform aging, secondary formation, secondary degassing, and capacity grading on the battery prepared in step 5 to complete the preparation of the semi-solid battery. The aging temperature is 45°C, and the time is 120 h. The secondary formation charging current is 0.01C, and the charging is performed to a voltage of 4.2V. The secondary degassing vacuum degree is -2 kPa, and the exhaust is performed 20 times with an exhaust time of 20 s each time.

[0061] 7. The prepared semi-solid batteries were tested for electrochemical performance to measure capacity, internal resistance, cycle life, rate capability, and high-temperature storage performance. The batteries were also tested for safety performance, such as tests involving needle puncture and overcharging. No explosion or combustion was observed.

[0062] Example 2

[0063] A method for preparing a semi-solid prismatic battery with high energy density and high safety is as follows:

[0064] 1. Prepare a positive electrode sheet, a negative electrode sheet, and a separator, respectively. The surface of the positive electrode sheet is coated with a uniform solid-state electrolyte Li7La3Zr2O12, the surface of the negative electrode sheet is coated with a uniform solid-state electrolyte Li7La3Zr2O12, and one side of the separator is coated with a solid-state electrolyte. 1.4 Al 0.4 Ti 1.6 The coating layer has a thickness of 100 nm and is made of a compound with a complex phase structure, which is purchased from Adrich Chemicals. The surface of the separator is coated with a solid-state electrolyte, and the composition of the solid-state electrolyte is Li7La3Zr2O12. 12 One side of the separator is coated with a solid-state electrolyte with a thickness of 2 μm (the coating layer faces the positive electrode during winding), and the raw material of the coating layer is purchased from Adrich Chemicals.

[0065] 2. Wind, hot-press, assemble, and dry the positive and negative electrode sheets and the separator prepared in step 1 to prepare a dry battery without liquid injection.

[0066] 3. Mix 5 g of polyethylene glycol methyl ether methacrylate (POEM) monomer, 5 g of monomethyl methacryloxypropyl bis-terminated polydimethylsiloxane (PDMD) monomer, 4 g of polyether polyacrylate crosslinking agent, 1 g of vinyl carbonate small molecule plasticizer, 1 g of diethylene carbonate small molecule plasticizer, and 2.4 g of LiPF6 to prepare a primary electrolyte, add 0.2 g of initiator azobisisobutyronitrile, and stir the mixture for 6 hours.

[0067] 4. Inject the electrolyte prepared in step 3 into the dry battery prepared in step 2. The dew point of the injection environment is controlled at -45°C, and the vacuum degree is -98 kPa. The battery is soaked for 48 h at a temperature of 20°C, then slowly heated to 60°C at a rate of 1°C / h, and kept at 60°C for 24 h to allow the polymerization reaction to proceed uniformly.

[0068] 5. Perform formation and primary degassing on the battery after in-situ polymerization in step 4. The formation charging current is 0.5C, and the charging time is 30 minutes. The primary degassing vacuum degree is -2 kPa, and the 20 times of exhaust, each exhaust time is 20 s.

[0069] 6. The cell prepared in step 5 was aged, reformed, re-dissolved, and capacity graded to complete the preparation of the semi-solid battery. The aging condition was: temperature 80℃, time 12h. The reformation condition was: charging current 0.5C, and the voltage was charged to 4.2V. The re-dissolution vacuum degree was -98kPa, and the exhaust time was 1s.

[0070] 7. The semi-solid battery prepared was tested for electrochemical performance to measure capacity, internal resistance, life cycle, rate capability, and high-temperature storage performance. The battery also underwent safety performance tests, such as tests involving needle pricking and overcharging. No explosion or combustion was observed.

[0071] Example 3

[0072] The overall method was the same as in Example 1, except that in step 1, the double-sided coating thickness of the solid-state electrolyte coated on the surface of the separator was 4μm.

[0073] Comparative Example 1

[0074] The overall method was the same as in Example 1, except that in step 1, the surface of the separator was not coated with a solid-state electrolyte, and the surface of the positive electrode was not coated with a solid-state electrolyte.

[0075] Comparative Example 2

[0076] The overall method was the same as in Example 1, except that in step 3, no small molecule plasticizer was added.

[0077] Example 4

[0078] The overall method was the same as in Example 1, except that in step 3, the reaction monomers were polyethylene glycol dimethyl methacrylate and poly(triethoxyvinylsilane), and each was added in a mass of 5g; the lithium salt was LiCF3O3, and was added in a mass of 1.5g; a crosslinking agent was also added, the crosslinking agent was pentaerythritol tetraacrylate, and was added in a mass of 2.5g; the small molecule plasticizer was ethylene carbonate and propylene carbonate, and each was added in a mass of 2g; and the initiator azobisisobutyronitrile was added in a mass of 0.125g. In step 4, the battery was soaked at a temperature of 15℃ for 48h, then slowly heated to 80℃ at a rate of 1℃ / h, and kept at 80℃ for 24h to make the polymerization reaction proceed uniformly.

[0079] Example 5

[0080] The overall method is the same as in Example 1, except that in step 3, the monomer is poly(triethoxyvinylsilane), with an added mass of 10g; the lithium salt is LiBF4, with an added mass of 1.2g; a crosslinking agent is also added, which is polyethylene glycol diacrylate, with an added mass of 1g; small molecule plasticizers are γ-butyrolactone and polyethylene glycol dimethyl ether, with an added mass of 4g each; and the initiator is azobisisobutyronitrile, with an added mass of 0.125g. In step 4, the battery is kept immersed at a temperature of 20°C for 48 hours, and then the temperature is slowly increased to 70°C at a rate of 1°C / h, and held at this temperature for 24 hours to ensure uniform polymerization.

[0081] Comparative Example 3

[0082] The overall method is the same as in Example 1, except that in step 4, after liquid injection, the battery is kept immersed at 10°C for 60 hours, and then the temperature is slowly increased to 60°C at a rate of 1°C / h, and held at that temperature for 24 hours.

[0083] If the immersion temperature is too low, the fluidity of the electrolyte will decrease, which may lead to incomplete immersion and a correspondingly lower battery performance capacity.

[0084] Comparative Example 4

[0085] The overall method is the same as in Example 1, except that in step 4, after liquid injection, the battery is kept immersed at 25°C for 60 hours, and then the temperature is slowly increased to 60°C at a rate of 1°C / h, and held at that temperature for 24 hours.

[0086] Excessive temperature wetting may cause some polymerization reactions to occur prematurely, preventing uniform polymerization during in-situ polymerization. Consequently, the battery's electrical performance and capacity will be lower, and its cycle life will be shortened.

[0087] Comparative Example 5

[0088] The overall method is the same as in Example 1, except that in step 4, after liquid injection, the battery is kept immersed at 15°C for 60 hours, and then the temperature is slowly increased to 60°C at a rate of 2°C / h, and held at that temperature for 24 hours.

[0089] If the heating rate is too fast, the temperature field within the system will be inconsistent, and the polymerization reaction may not be uniform at the same time. Consequently, the battery's electrical performance capacity will be lower and the cycle life will be shortened.

[0090] Comparative Example 6

[0091] The overall method is the same as in Example 1, except that in step 4, after liquid injection, the battery is kept immersed at 15°C for 60 hours, and then the temperature is slowly increased to 60°C at a rate of 0.5°C / h and held for 24 hours to ensure uniform reaction and homogeneous polymerization during in-situ polymerization. However, the longer heating time affects production efficiency and increases energy consumption and costs.

[0092] Comparative Example 7

[0093] The overall method was the same as Example 1, except that in Step 4, after injection, the battery was controlled to soak at a temperature of 15°C for 60 h, and then directly warmed to 60°C for 24 h. The fast rate of temperature increase caused the temperature field in the system to be inconsistent, and the polymerization reaction might not have polymerized uniformly at the same time. The corresponding battery had a low capacity and a shortened cycle life.

[0094] Test Example 1

[0095] The semi-solid batteries prepared in each example and comparative example were subjected to electrochemical performance tests to measure the capacity, internal resistance, cycle life, rate capability, and high-temperature storage performance. The batteries were also subjected to safety performance tests, such as tests involving needle pricking and overcharging. No explosion or combustion was observed. The experimental results are shown in Table 1.

[0096] Table 1

[0097]

[0098] Result Analysis and Conclusion:

[0099] As can be seen from the comparison of Comparative Example 1 and Example 1, the surface coating of the positive electrode particles and the surface coating of the separator with the solid electrolyte fast ion conductor improved the resistance at the interface between the positive electrode particles and the electrolyte and the interface between the surface of the separator and the electrolyte. The solid electrolyte fast ion conductor provided an additional fast channel for ion transport, which promoted the ion transport rate at the interface between different phases, macroscopically resulting in a reduced internal resistance of the battery, an improved initial efficiency, and an improved cycle life.

[0100] As can be seen from the comparison of Comparative Example 2 and Example 1, the small-molecule plasticizer, due to its small molecular size, played a role in lubrication and promotion of chain segment movement in the semi-solid electrolyte, resulting in an improved ionic conductivity of the semi-solid electrolyte. At the same time, the small-molecule plasticizer improved the ion conduction at the interface between the electrode and the electrolyte and the interface between the separator and the electrolyte, and reduced the internal resistance. The small-molecule plasticizer could also complex with lithium ions and move quickly under the action of an electric field, thereby playing a role in transport of lithium ions. The above effects macroscopically resulted in an increased initial efficiency, an increased capacity, a reduced internal resistance, and an improved cycle life.

[0101] As can be seen from the comparison of Comparative Example 3 and Example 1, the low soaking temperature resulted in a reduced flowability of the electrolyte, which might have led to incomplete soaking, and a low capacity of the battery.

[0102] As can be seen from the comparison of Comparative Example 4 and Example 1, the high soaking temperature might have led to premature polymerization of some of the polymerization reactions, which could not have been uniformly polymerized in situ, and a low capacity and a shortened cycle life of the battery.

[0103] Comparing Comparative Examples 5 and 7 with Example 1, it can be seen that too fast a temperature increase rate leads to inconsistent temperature fields in the system, and the polymerization reaction can not be uniformly polymerized at the same time, resulting in relatively low battery capacity and shortened cycle life. Comparing Example 8 with Example 1, it can be seen that although the temperature increase time is longer, it has an impact on production efficiency, and the production energy consumption and cost are also increased.

[0104] As can be seen from the results of the examples, using the low-temperature method to uniformly penetrate and wet, and controlling the temperature to be maintained at 15-20°C to make the electrolyte mixture before polymerization uniformly penetrate into the positive electrode, negative electrode and separator of the battery cell, and then gradually increasing the temperature to make the second mixture undergo polymerization reaction, makes the polymerization uniform during in-situ polymerization, the battery interface impedance is low, the battery is consistent and stable, and the first cycle efficiency is high. By using the coating of the fast ion conductor solid electrolyte on the positive electrode particles and the coating modification of the separator, the internal resistance of the low-temperature polymerized solid-state battery is further reduced, and the overall cycle life of the battery cell is improved. The method of adding a small molecule plasticizer can be used in cooperation with the low-temperature infiltration and slow temperature increase polymerization method, which improves the ion transport capacity of the battery cell, reduces the internal resistance, and further improves the cycle life of the battery cell.

Claims

1. A method for preparing a high-energy-density and high-safety semi-solid-state battery, the semi-solid-state battery comprising a dry cell, the dry cell comprising a positive electrode, a negative electrode, and a separator, characterized in that, The preparation method includes the following steps: (1) Prepare a positive electrode, a negative electrode and a separator respectively, wherein the surface of the positive electrode particles is uniformly coated with nanoscale solid electrolyte, and the surface of the separator is uniformly coated with micron-scale solid electrolyte on one or both sides. (2) Assemble the positive electrode, negative electrode and separator into a dry cell; (3) Mix the reactant monomer, crosslinking agent, lithium salt, small molecule plasticizer and initiator to obtain a mixture; The reactant monomer is at least one of the following: polyethylene glycol methyl ether methacrylate, polyethylene glycol dimethacrylate, methacryloyloxypropyl-terminated polydimethylsiloxane, monomethacryloyloxypropyl-terminated polydimethylsiloxane, and poly(triethoxyvinylsilane). The crosslinking agent is at least one of the following: trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, or polyether polyacrylate. The initiator is azobisisobutyronitrile; The small molecule plasticizer is at least one of the following: ethylene carbonate, diethylene carbonate, dimethyl carbonate, dipropyl carbonate, dimethyl sulfoxide, dimethoxyethane, N-methyl-2-pyrrolidone, and γ-butyrolactone; (4) After injecting the mixture into the dry cell, maintain the temperature at 15℃~20℃ to allow the mixture to soak the dry cell for a period of not less than 48 hours. (5) After impregnation, gradually increase the temperature at a rate not exceeding 1℃ / h until the polymerization temperature is reached. The polymerization temperature is 60℃~80℃ and is maintained at the polymerization temperature for no less than 24 hours to obtain a semi-solid battery with a semi-solid electrolyte.

2. The preparation method according to claim 1, characterized in that, The nanoscale solid electrolyte coated on the surface of the positive electrode particles is at least one of the following: Li 1.4 Al 0.4 Ti 1.6 (PO4)3, Li 0.5 La 0.5 TiO3, Li3InCl6, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li7La3Zr2O 12 Li3ErCl6; The micron-scale solid electrolyte coated on the membrane surface is at least one of the following: Li7La3Zr2O 12 Li 0.5 La 0.5 TiO3, Li3InCl6, Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li3ErCl 6、 Li 1.4 Al 0.4 Ti 1.6 (PO4)3.

3. The preparation method according to claim 1, characterized in that, The thickness of the solid electrolyte coating on the surface of the positive electrode particles at the nanoscale is 10 nm to 100 nm. The thickness of the solid electrolyte coating on the membrane surface at the micrometer scale is 2μm~4μm per side.

4. The preparation method according to claim 1, characterized in that, The lithium salt is at least one of the following: LiBF4, LiBF6, LiAsF6, LiPF6, LiClO4, LiB(C6H5)4, LiAlCl4, LiBr, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SOSO2)3, LiN(SO2C2F5)2.

5. The preparation method according to claim 1, characterized in that, By mass, for every 100 parts of reactant monomer, add 10-40 parts of crosslinking agent, 12-24 parts of lithium salt, 1-2 parts of initiator, and 20-80 parts of small molecule plasticizer.

6. The preparation method according to claim 1, characterized in that, In step (4), when the mixture is injected into the dry cell, the ambient dew point is controlled between -45°C and -65°C, and the vacuum degree is controlled between -98kPa and -2kPa. After the polymerization reaction in step (5), a primary formation and initial degassing are performed, followed by aging of the semi-solid electrolyte. After aging, a secondary formation and secondary degassing are performed. The conditions for one-time formation are: charging current 0.01C-0.5C, charging time 30 minutes to 360 minutes; The conditions for secondary formation are: charging current of 0.01C~0.5C, charging until the voltage reaches the rated voltage; The conditions for primary and secondary degassing are: 1 to 20 cycles at a pressure of -98 kPa to -2 kPa, each cycle lasting 1 to 20 seconds; The aging conditions are: temperature 45~80℃, time 12~120h.

7. A semi-solid-state battery with high energy density and high safety prepared by any of the preparation methods described in claims 1 to 6.

Images