Formation method and application of battery

Abstract

The invention provides a formation method and application of a battery, and the formation method of the battery comprises the following steps: injecting a first electrolyte into a dry battery to be injected with the electrolyte to obtain a first battery; carrying out first standing on the first battery, and then cooling to obtain a second battery; carrying out second standing on the second battery, and then repeatedly carrying out first charging and first discharging at the first temperature to obtain a third battery; injecting the second electrolyte into the third battery, and then carrying out third standing to obtain a fourth battery; and carrying out second charging, third charging and fourth charging on the fourth battery at a second temperature to obtain a formed battery. According to the formation method of the battery disclosed by the invention, the problems of SEI deformation and fracture caused by volume expansion of the silicon-based negative electrode battery in the cycle process are effectively relieved by adopting a mode of mutual cooperation of low temperature and large current and the like, and the coulombic efficiency and the cycle stability of the battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a battery formation method and application. Background Art

[0002] With the vigorous development of the new energy industry, lithium-ion batteries are gradually developing towards higher energy density, longer cycle life and fast charging performance. The existing theoretical capacity of graphite anode is only 372mAh / g, which can no longer meet the future requirements for battery energy density. Silicon-based anode has the advantages of high theoretical specific capacity, abundant natural silicon reserves, low raw material cost, and slightly higher working voltage than graphite (0.2V). It is a very promising high-energy lithium-ion anode material in the future. However, the volume of silicon material will expand to varying degrees during the lithium insertion process, causing the silicon material particles to squeeze each other and deform; during the lithium removal process, the silicon material will shrink to varying degrees due to lithium removal, resulting in the breakage of silicon particles after multiple cycles. The repeated expansion and contraction of silicon material causes the silicon particles to separate from each other, the silicon particles from the conductive agent, and the silicon particles from the current collector, and the conductive network is destroyed and collapsed, resulting in electrode failure. The volume change of silicon materials will also cause the SEI film to deform and rupture. The newly exposed active substances will consume the electrolyte to generate a new SEI film. This will be repeated to form an uneven and thick SEI film, resulting in low coulombic efficiency and irreversible capacity loss, which seriously affects the practical application of silicon negative electrodes. Current research focuses on using the stability of carbon materials to coat silicon materials or embed silicon materials into carbon materials to prepare silicon-carbon composite negative electrode materials to help build a stable SEI film, but there are problems such as complex preparation process, difficulty in mass production and high production cost. There are also methods to increase the adhesion between active materials and between active materials and current collectors to inhibit expansion and improve conductivity by selecting suitable binders. However, the preparation process of functional binders is complicated and the cost is high. In addition, the addition of these functional binders will also cause difficulties in the homogenization process and increase resistance. Summary of the invention

[0003] In view of this, one purpose of the present application is to provide a battery formation method, which adopts the combination of low temperature and large current to effectively alleviate the SEI deformation and rupture problems caused by volume expansion of silicon-based negative electrode batteries during the cycle process, thereby improving the coulombic efficiency and cycle stability of the battery.

[0004] Another object of the present application is to provide a method for preparing a secondary battery.

[0005] Another object of the present application is to provide a secondary battery.

[0006] To achieve the above-mentioned object, the first aspect of the present application provides a battery formation method, wherein the battery comprises a negative electrode active material and an electrolyte, wherein the negative electrode active material comprises a silicon-based material, and the electrolyte comprises a first electrolyte and a second electrolyte, wherein the first electrolyte and the second electrolyte both comprise fluoroethylene carbonate and vinylene carbonate;

[0007] The method of forming comprises:

[0008] Injecting the first electrolyte into the dry cell to be injected with the electrolyte to obtain a first battery;

[0009] placing the first battery in a first resting state and then cooling the battery to obtain a second battery;

[0010] The second battery is subjected to a second resting state, and then the first charging and the first discharging are repeated at a first temperature to obtain a third battery; the first temperature is below 45° C., and the current of the first charging is above 0.01 C;

[0011] injecting the second electrolyte into the third battery, followed by a third standing, to obtain a fourth battery;

[0012] The fourth battery is subjected to a second charge, a third charge and a fourth charge at a second temperature to obtain a formed battery.

[0013] In some embodiments, the first static temperature is comparable to the third static temperature, and both are greater than the second static temperature, the first temperature, and the second temperature.

[0014] In some embodiments, the first temperature is comparable to the second static temperature, and both are lower than the second temperature.

[0015] In some embodiments, the first standing temperature and the third standing temperature are both 50-60°C.

[0016] In some embodiments, the second standing temperature and the first temperature are both 0-45°C, and can be optionally 0-15°C.

[0017] In some embodiments, the second temperature is 20-45°C, optionally 25-35°C.

[0018] In some embodiments, the first charging current is 0.01-0.3C, and can be optionally 0.2-0.3C.

[0019] In some embodiments, the discharge current is 0.1-0.3C, and can be optionally 0.2-0.3C.

[0020] In some embodiments, the first charge is to 1-10% SOC, optionally 1-5% SOC.

[0021] In some embodiments, the discharging is to 2.5-2.8V.

[0022] In some embodiments, the second charging current is 0.01-0.1C.

[0023] In some embodiments, the second charge is to 1-10% SOC.

[0024] In some embodiments, the third charging current is 0.1-0.3C.

[0025] In some embodiments, the third charge is to 10-30% SOC.

[0026] In some embodiments, the fourth charging current is 0.1-0.5C.

[0027] In some embodiments, the fourth charge is to 30-100% SOC.

[0028] In some implementations, the second charging current, the third charging current, and the fourth charging current increase sequentially.

[0029] In some implementations, the SOC proportion of the second charging, the SOC proportion of the third charging, and the SOC proportion of the fourth charging increase sequentially.

[0030] In some embodiments, the mass content of the first electrolyte in the electrolyte is a, the mass content of the second electrolyte in the electrolyte is b, and a is greater than b.

[0031] In some embodiments, the mass content of the fluoroethylene carbonate in the first electrolyte is c1, the mass content of the vinylene carbonate in the first electrolyte is d1, the mass content of the fluoroethylene carbonate in the second electrolyte is c2, and the mass content of the vinylene carbonate in the second electrolyte is d2, and c1, d1, c2, and d2 satisfy: c1>c2 and d1<d2.

[0032] Preferably, c1, d1, c2, and d2 satisfy: c1>d1, c2<d2, c1>c2, and d1<d2.

[0033] In some embodiments, the a is 60-70%.

[0034] In some embodiments, the c1 is 4-6%.

[0035] In some embodiments, the d1 is 1-3%.

[0036] In some embodiments, the c2 is 1-3%.

[0037] In some embodiments, the d2 is 4-6%.

[0038] In some embodiments, the silicon-based material includes at least one of nano-silicon, micro-silicon, porous silicon, amorphous silicon, silicon alloys, silicon-oxygen compounds, and silicon-carbon composite materials.

[0039] In some embodiments, the silicon-based material includes at least one of a silicon-oxygen compound and a silicon-carbon composite material.

[0040] In some embodiments, the negative electrode active material further includes graphite.

[0041] In some embodiments, when the negative electrode active material includes graphite and a silicon-based material, the mass ratio of the graphite to the silicon-based material is (0.7-0.5):(0.3-0.5).

[0042] In some embodiments, the first electrolyte further includes a first lithium salt and a first solvent.

[0043] In some embodiments, the second electrolyte further includes a second lithium salt and a second solvent.

[0044] In some embodiments, the first lithium salt and the second lithium salt each include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bistrifluoromethylsulfonyl imide, and lithium bis(oxalatoborate).

[0045] In some embodiments, the first solvent includes ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0046] In some embodiments, the second solvent includes ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0047] In some embodiments, the battery further includes a separator, wherein the separator includes a polyolefin wet-process separator.

[0048] A second aspect of the present application provides a method for preparing a secondary battery, including a formation step, wherein the formation method is the formation method of the battery described in the present application.

[0049] In some embodiments, the method for preparing a secondary battery further includes the steps of preparing a positive electrode sheet and preparing a negative electrode sheet.

[0050] In some embodiments, the step of preparing the positive electrode sheet includes:

[0051] Mixing the positive electrode binder with the positive electrode solvent to obtain a positive electrode glue solution;

[0052] Adding a positive electrode conductive agent to the positive electrode glue solution and dispersing the positive electrode conductive agent to obtain a positive electrode conductive glue;

[0053] Adding positive electrode active material to the positive electrode conductive glue and dispersing it to obtain positive electrode slurry; and / or,

[0054] In some embodiments, the step of preparing the negative electrode sheet includes:

[0055] A first negative electrode conductive agent is added to the negative electrode active material and mixed uniformly, and then a negative electrode binder, a negative electrode solvent and a second negative electrode conductive agent are added and dispersed to obtain a negative electrode slurry.

[0056] A third aspect of the present application provides a secondary battery, wherein the secondary battery is a secondary battery prepared by the method for preparing a secondary battery described in the present application.

[0057] The battery formation method described in this application can at least bring the following beneficial effects:

[0058] The first electrolyte and the second electrolyte are injected into the battery by means of secondary injection, wherein the first charging and the first discharging process after the first electrolyte is injected into the battery are pre-formation, and the low temperature and the large current are used in combination during the pre-formation, which not only avoids the loose SEI film formed when the current is too large, but also avoids the SEI film with low conductivity formed at low temperature, and increases the content of organic components in the SEI film close to the negative electrode side, thereby improving the flexibility of the protective film on the surface of the silicon negative electrode, and then discharges to further activate the electrode material and improve the stability of the electrode structure. This process should be completed in a relatively short time, and more FEC additives are consumed to form a tightly structured protective film on the surface of the silicon negative electrode, and the consumed FEC is replenished during the secondary injection. After the second injection, an open formation method with a relatively large current is used above room temperature. After pre-formation, an inorganic layer with high mechanical toughness is further obtained on the organic layer side. Finally, a large current is used for charging, and an organic layer with high flexibility is obtained on the electrolyte side. This organic layer-inorganic layer-organic layer SEI membrane not only hinders the further reaction of the electrolyte, but also has great toughness as a whole due to the coating of the double organic layers, which effectively alleviates the deformation, rupture and regeneration of the SEI membrane caused by the volume expansion of the silicon-based negative electrode battery during the cycle, reduces the consumption of active lithium, and improves the coulombic efficiency and cycle stability of the battery.

[0059] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings.

[0061] in:

[0062] Figure 1 The present invention is a flowchart of a battery formation method according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0063] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

[0064] In this application, the disclosure of numerical ranges includes all values ​​within the entire range and the disclosure of further subdivided ranges, including the endpoints and sub-ranges given in these ranges.

[0065] In this application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be made through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0066] The term "and / or", when used in a list of two or more items, means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression "A and / or B" is intended to mean A or B or A and B, that is, only A, only B, or a combination of A and B.

[0067] In the present application, normal temperature and room temperature are both 25-30°C.

[0068] <Battery Formation Method>

[0069] A battery formation method according to an embodiment of the present application is described below with reference to the accompanying drawings.

[0070] The battery formation method of the embodiment of the present application, wherein the battery includes a negative electrode active material and an electrolyte, the negative electrode active material includes a silicon-based material, the electrolyte includes a first electrolyte and a second electrolyte, and the first electrolyte and the second electrolyte both include fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0071] In some embodiments, the silicon-based material includes but is not limited to at least one of nano-silicon, micro-silicon, porous silicon, amorphous silicon, silicon alloys, silicon-oxygen compounds, and silicon-carbon composite materials.

[0072] As an optional example, the silicon-based material includes at least one of a silicon-oxygen compound and a silicon-carbon composite material.

[0073] Exemplarily, the chemical formula of the silicon oxide compound is SiO x , where 0<x≤2.

[0074] Exemplarily, the value of x includes but is not limited to 0.1, 0.5, 1, 1.5 or 2, and is preferably 1, in which case the silicon oxide compound is silicon monoxide.

[0075] Exemplarily, the chemical formula of the silicon-carbon composite material is SiC y , where 0<y≤2.

[0076] Exemplarily, the value of y includes but is not limited to 0.1, 0.5, 1, 1.5 or 2, etc.

[0077] Exemplarily, the silicon alloy includes silicon-tin alloy and the like.

[0078] In some embodiments, the negative electrode active material further includes graphite.

[0079] Exemplarily, when the negative electrode active material includes graphite and silicon-based material, the mass ratio of the graphite to the silicon-based material is (0.7-0.5): (0.3-0.5), including but not limited to 0.7:0.3, 0.6:0.4, 0.5:0.5 or 0.65:0.35, etc. At this time, the battery of the embodiment of the present application is a highly mixed silicon-based negative electrode battery.

[0080] As an optional example, the negative electrode active material is a mixture of graphite and silicon-based materials.

[0081] In the embodiment of the present application, the first electrolyte and the second electrolyte both include fluoroethylene carbonate and vinylene carbonate, which can form a tightly structured protective film on the surface of the silicon negative electrode. Adding VC to the first electrolyte can improve the temperature adaptability of the lithium-ion battery and reduce gas generation during the formation process. The combination of FEC and VC can improve the first charge specific capacity and first coulomb efficiency of the battery and improve the cycle stability of the battery.

[0082] In some embodiments, the mass content of the first electrolyte in the electrolyte is a, the mass content of the second electrolyte in the electrolyte is b, and a is greater than b.

[0083] In the embodiments of the present application, based on the mass of the entire electrolyte, the content of the first electrolyte is greater than that of the second electrolyte. The purpose of this arrangement is to ensure that the electrolyte fully infiltrates the dry battery cell, and that there is sufficient electrolyte to form a SEI film during pre-formation. The second electrolyte is added to replenish the FEC and VC consumed in the formation of the SEI film, and to replenish the electrolyte consumed in the pre-formation to ensure cycle stability.

[0084] Exemplarily, the mass content (a) of the first electrolyte in the electrolyte is 70-90%, including but not limited to 82.5%, 85% or 87.5%, etc.

[0085] As an optional example, the electrolyte consists of a first electrolyte and a second electrolyte that are independently set.

[0086] In some embodiments, the mass content of the fluoroethylene carbonate in the first electrolyte is c1, the mass content of the vinylene carbonate in the first electrolyte is d1, the mass content of the fluoroethylene carbonate in the second electrolyte is c2, and the mass content of the vinylene carbonate in the second electrolyte is d2, and c1, d1, c2, and d2 satisfy:

[0087] c1>c2 and d1<d2.

[0088] In the embodiment of the present application, the mass content of the fluoroethylene carbonate in the first electrolyte (c1), the mass content of the vinylene carbonate in the first electrolyte (d1), the mass content of the fluoroethylene carbonate in the second electrolyte (c2), and the mass content of the vinylene carbonate in the second electrolyte (d2) satisfy the above relationship, which can form a stable SEI film on the surface of the negative electrode of the battery, provide better thermal stability and oxidation resistance, and reduce the capacity loss of the battery during charging and discharging. If the above relationship is not satisfied, for example: c1 is less than or equal to c2, the stability of the SEI film formation during the pre-forming process is affected; d1 is greater than or equal to d2, a thicker SEI film will be generated during pre-forming, resulting in a lower initial coulombic efficiency of the battery.

[0089] As a preferred example, the c1, d1, c2, and d2 satisfy: c1>d1, c2<d2, c1>c2, and d1<d2. In the embodiment of the present application, under the premise of the above c1>c2 and d1<d2, c1>d1, c2<d2 are further satisfied, which can increase the shear storage modulus of the SEI film, enhance the stability of the SEI film, reduce the battery impedance, and improve the cycle stability of the battery.

[0090] In some embodiments, the mass content (c1) of the fluoroethylene carbonate in the first electrolyte is 4-6%, including but not limited to 4.25%, 4.5%, 4.75%, 5%, 5.25%, 5.5% or 5.75%, etc.

[0091] In some embodiments, the mass content (d1) of the vinylene carbonate in the first electrolyte is 1-3%, including but not limited to 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5% or 2.75%, etc.

[0092] In some embodiments, the mass content (c2) of the fluoroethylene carbonate in the second electrolyte is 1-3%, including but not limited to 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5% or 2.75%, etc.

[0093] In some embodiments, the mass content (d2) of the vinylene carbonate in the second electrolyte is 4-6%, including but not limited to 4.25%, 4.5%, 4.75%, 5%, 5.25%, 5.5% or 5.75%, etc.

[0094] In some embodiments, the first electrolyte further includes a first lithium salt and a first solvent.

[0095] In some embodiments, the second electrolyte further includes a second lithium salt and a second solvent.

[0096] It should be noted that in the embodiments of the present application, the first lithium salt and the second lithium salt may be any lithium salt known in the art that can be used in lithium-ion batteries, and the first solvent and the second solvent may also be any non-aqueous organic solvent known in the art that can be used in lithium-ion batteries.

[0097] Exemplarily, the first lithium salt and the second lithium salt both include but are not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and lithium bis(oxalatoborate) (LiBOB), and lithium hexafluorophosphate (LiPF6) may be selected.

[0098] It should be noted that, in the embodiments of the present application, the first lithium salt and the second lithium salt may be the same or different.

[0099] In some embodiments, the concentration of the first lithium salt in the first electrolyte is 0.8-1.2 mol / L, including but not limited to 0.85 mol / L, 0.9 mol / L, 1 mol / L or 1.15 mol / L, etc., and can be optionally 1 mol / L.

[0100] In some embodiments, the concentration of the second lithium salt in the second electrolyte is 0.8-1.2 mol / L, including but not limited to 0.85 mol / L, 0.9 mol / L, 1 mol / L or 1.15 mol / L, etc., and can be optionally 1 mol / L.

[0101] In an embodiment of the present application, the concentration of the first lithium salt in the first electrolyte and the concentration of the second lithium salt in the second electrolyte may be equal or different.

[0102] In some embodiments, the first solvent includes but is not limited to ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like.

[0103] As an optional example, the first solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), and may be a mixed solvent of EC, DMC and EMC in a volume ratio of 1:1:1.

[0104] In some embodiments, the second solvent includes, but is not limited to, ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like.

[0105] As an optional example, the second solvent is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and may be a mixed solvent of EC, DEC and EMC in a volume ratio of 1:1:1.

[0106] As an optional example, the first electrolyte includes a lithium salt, a first solvent and a first additive; the lithium salt is LiPF6, and the concentration of the lithium salt in the first electrolyte is 1 mol / L; the first solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1; the first additive is composed of fluoroethylene carbonate (FEC) and vinylene carbonate (VC), FEC accounts for approximately 5.0% by weight of the first electrolyte, and VC accounts for approximately 2.0% by weight of the first electrolyte.

[0107] As an optional example, the second electrolyte includes a lithium salt, a second solvent and a second additive; the lithium salt is LiPF6, and the concentration of the lithium salt in the first electrolyte is 1 mol / L; the second solvent is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1; the second additive is composed of fluoroethylene carbonate (FEC) and vinylene carbonate (VC), FEC accounts for approximately 2.0% by weight of the second electrolyte, and VC accounts for approximately 5.0% by weight of the second electrolyte.

[0108] In some embodiments, the battery further includes a positive electrode active material.

[0109] It should be noted that in the embodiments of the present application, the positive electrode active material can be any lithium salt known in the art that can be used in lithium-ion batteries.

[0110] Exemplarily, the positive electrode active material includes but is not limited to at least one of lithium iron phosphate, high-nickel ternary nickel cobalt manganese oxide (NCM), lithium cobalt oxide, lithium manganese oxide, etc., and lithium iron phosphate can be selected.

[0111] In some embodiments, the battery further includes a separator, wherein the separator includes a polyolefin wet-process separator, such as a polypropylene (PP) wet-process separator.

[0112] In some embodiments, the battery further comprises a housing.

[0113] In some embodiments, the battery includes a lithium ion battery or the like.

[0114] Figure 1 The present invention is a flowchart of a battery formation method according to an exemplary embodiment of the present invention.

[0115] like Figure 1 As shown, the formation method of the battery comprises the following steps:

[0116] S101, injecting the first electrolyte into a dry cell to be injected with electrolyte to obtain a first cell.

[0117] S102, placing the first battery in a first stationary state, and then cooling the first battery to obtain a second battery.

[0118] In the embodiment of the present application, the purpose of subjecting the first battery to the first static condition is to ensure that the first battery is at the target temperature condition of the first static condition and the electrolyte fully infiltrates the battery cell.

[0119] In some embodiments, the first standing temperature is 50-60°C, including but not limited to 52.5°C, 55°C or 57.5°C, etc., and can be 55°C.

[0120] In some embodiments, the first standing time is 20-28 hours, including but not limited to 22 hours, 24 hours or 26 hours, etc., and can be optionally 24 hours.

[0121] In some embodiments, cooling is performed in a room temperature environment to room temperature.

[0122] S103, subjecting the second battery to a second resting state, and then repeating the first charging and the first discharging at the first temperature to obtain a third battery; the first temperature is below 45° C., and the first charging current is above 0.01 C.

[0123] In the embodiment of the present application, step S103 adopts the method of cooperating low temperature and large current to avoid the loose SEI film formed when the current is too large, and the SEI film with low conductivity formed at low temperature. The content of organic components in the SEI film is increased near the negative electrode side, thereby improving the flexibility of the protective film on the surface of the silicon negative electrode. The discharge then further activates the electrode material and improves the stability of the electrode structure. This process should be completed in a relatively short time, and a large amount of FEC additive is consumed to form a tightly structured protective film on the surface of the silicon negative electrode. The consumed FEC is replenished during the subsequent secondary injection.

[0124] In some embodiments, the first temperature and the second static temperature are both lower than the first static temperature.

[0125] It should be noted that, in the embodiments of the present application, the second static temperature and the first temperature may be the same or different.

[0126] In some embodiments, the first temperature is comparable to the second resting temperature.

[0127] In some embodiments, the second standing temperature and the first temperature are both 0-45°C.

[0128] Exemplarily, the second standing temperature and the first temperature include but are not limited to 0°C, 2°C, 5°C, 7.5°C, 10°C, 12.5°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C, etc., and can be optionally below 30°C, and can further be optionally below 20°C.

[0129] As an optional example, the second static temperature and the first temperature are both 0-15°C.

[0130] In some embodiments, the second standing time is 2-4 hours, including but not limited to 2.5 hours, 3 hours or 3.5 hours, and can be optionally 3 hours.

[0131] In some embodiments, the first charging current is 0.01-0.3C, including but not limited to 0.01C, 0.05C, 0.1C, 0.15C, 0.2C, 0.25C or 0.3C.

[0132] As an optional example, the first charging current is 0.2-0.3C.

[0133] In some embodiments, the discharge current is 0.1-0.3C, including but not limited to 0.1C, 0.15C, 0.2C, 0.25C or 0.3C.

[0134] As an optional example, the discharge current is 0.2-0.3C.

[0135] In some embodiments, the first charge is to 1-10% SOC, including but not limited to 1% SOC, 2.5% SOC, 5% SOC, 7.5% SOC or 10% SOC, etc.

[0136] As an optional example, the first charging is to 1-5% SOC.

[0137] In some embodiments, the discharge to 2.5-2.8V, including but not limited to 2.6V, 2.65V, 2.7V or 2.75V, etc., can be 2.5V.

[0138] In some embodiments, the first charge and the first discharge are repeated at the first temperature 2-5 times, including but not limited to 2 times, 3 times, 4 times or 5 times, and can be 5 times.

[0139] S104, injecting the second electrolyte into the third battery, followed by a third standing step to obtain a fourth battery.

[0140] In the embodiment of the present application, the purpose of the third static state is to ensure that the third battery is at the target temperature condition of the third static state and the electrolyte fully infiltrates the battery cell.

[0141] In some embodiments, the third resting temperature is comparable to the first resting temperature and greater than the second resting temperature.

[0142] In some embodiments, the third standing temperature is 50-60°C, including but not limited to 52.5°C, 55°C or 57.5°C, etc., and can be 55°C.

[0143] In some embodiments, the third standing time is 8-16 hours, including but not limited to 10 hours, 12 hours or 14 hours, etc., and can be optionally 12 hours.

[0144] S105, performing a second charge, a third charge, and a fourth charge on the fourth battery at the second temperature to obtain a formed battery.

[0145] In the embodiment of the present application, after the secondary liquid injection, step S105 adopts a post-formation method with a relatively large current. After pre-formation, an inorganic layer with high mechanical toughness is further obtained on the organic layer side. Finally, a large current is used for charging, and an organic layer with high flexibility is obtained on the electrolyte side. This organic layer-inorganic layer-organic layer SEI film not only hinders the further reaction of the electrolyte, but also makes the SEI film as a whole have great toughness due to the coating of the double organic layers.

[0146] In some embodiments, the second temperature is less than the temperature of the first rest and the temperature of the third rest.

[0147] In some embodiments, the second temperature is greater than the first temperature and the second rest temperature.

[0148] In some embodiments, the second temperature is 20-45°C, including but not limited to 25°C, 30°C, 35°C, 40°C or 45°C, etc.

[0149] As an optional example, the second temperature is 25-35°C.

[0150] In some embodiments, the second charging current is 0.01-0.1C, including but not limited to 0.02C, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, 0.08C or 0.9C, etc.

[0151] In some embodiments, the second charging is to 1-10% SOC, including but not limited to 1% SOC, 2.5% SOC, 5% SOC, 7.5% SOC or 10% SOC, etc.

[0152] In some embodiments, the third charging current is 0.1-0.3C, including but not limited to 0.1C, 0.15C, 0.2C, 0.25C or 0.3C.

[0153] In some embodiments, the third charge is to 10-30% SOC, including but not limited to 12.5% ​​SOC, 15% SOC, 17.5% SOC, 20% SOC, 22.5% SOC, 25% SOC or 27.5% SOC, etc.

[0154] In some embodiments, the fourth charging current is 0.1-0.5C, including but not limited to 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, 0.35C, 0.4C or 0.45C, etc.

[0155] In some embodiments, the fourth charge is to 30-100% SOC, including but not limited to 35% SOC, 40% SOC, 45% SOC, 50% SOC, 55% SOC, 60% SOC, 65% SOC, 70% SOC, 75% SOC, 80% SOC, 85% SOC, 90% SOC, or 95% SOC, etc.

[0156] In some implementations, the second charging current, the third charging current, and the fourth charging current increase sequentially.

[0157] In some implementations, the SOC proportion of the second charging, the SOC proportion of the third charging, and the SOC proportion of the fourth charging increase sequentially.

[0158] The battery formation method of the embodiment of the present application can at least bring the following beneficial effects:

[0159] The first electrolyte and the second electrolyte are injected into the battery by means of secondary injection, wherein the first charging and the first discharging process after the first electrolyte is injected into the battery are pre-formation, and the low temperature and the large current are used in combination during the pre-formation, which not only avoids the loose SEI film formed when the current is too large, but also avoids the SEI film with low conductivity formed at low temperature, and increases the content of organic components in the SEI film close to the negative electrode side, thereby improving the flexibility of the protective film on the surface of the silicon negative electrode, and then discharges to further activate the electrode material and improve the stability of the electrode structure. This process should be completed in a relatively short time, and more FEC additives are consumed to form a tightly structured protective film on the surface of the silicon negative electrode, and the consumed FEC is replenished during the secondary injection. After the second injection, an open formation method with a relatively large current is used above room temperature. After pre-formation, an inorganic layer with high mechanical toughness is further obtained on the organic layer side. Finally, a large current is used for charging, and an organic layer with high flexibility is obtained on the electrolyte side. This organic layer-inorganic layer-organic layer SEI membrane not only hinders the further reaction of the electrolyte, but also has great toughness as a whole due to the coating of the double organic layers, which effectively alleviates the deformation, rupture and regeneration of the SEI membrane caused by the volume expansion of the silicon-based negative electrode battery during the cycle, reduces the consumption of active lithium, and improves the coulombic efficiency and cycle stability of the battery.

[0160] <Method for preparing secondary battery>

[0161] The method for preparing a secondary battery in the embodiment of the present application includes a formation step, and the formation method is the formation method of the battery in the embodiment of the present application.

[0162] In some embodiments, the method for preparing a secondary battery further includes steps such as preparing a positive electrode sheet, preparing a negative electrode sheet, and assembling a battery.

[0163] It should be noted that the present application does not limit the specific composition and operation methods of the steps of preparing the positive electrode sheet, preparing the negative electrode sheet, and assembling the battery. It can be any composition and preparation technology of the positive electrode sheet, negative electrode sheet, and battery assembly that are well known in the art and can be used for secondary batteries, especially lithium-ion batteries.

[0164] Exemplarily, the step of preparing the positive electrode sheet includes:

[0165] Mixing the positive electrode binder with the positive electrode solvent to obtain a positive electrode glue solution;

[0166] Adding a positive electrode conductive agent to the positive electrode glue solution and dispersing the positive electrode conductive agent to obtain a positive electrode conductive glue;

[0167] A positive electrode active material is added to the positive electrode conductive glue and dispersed to obtain a positive electrode slurry.

[0168] Exemplarily, the step of preparing the negative electrode sheet includes:

[0169] A first negative electrode conductive agent is added to the negative electrode active material and mixed uniformly, and then a negative electrode binder, a negative electrode solvent and a second negative electrode conductive agent are added and dispersed to obtain a negative electrode slurry.

[0170] In the embodiments of the present application, the material selection and dosage of the positive electrode binder, positive electrode conductive agent, positive electrode solvent, negative electrode binder, negative electrode solvent, first negative electrode conductive agent, second negative electrode conductive agent, etc. can adopt any material and dosage well-known in the art that can be used for secondary batteries, especially lithium-ion batteries, such as positive electrode binders, positive electrode conductive agents, positive electrode solvents, negative electrode binders, negative electrode solvents and negative electrode conductive agents.

[0171] Exemplarily, the positive electrode binder is polyvinylidene fluoride (PVDF), the positive electrode conductor is conductive carbon black (SP), the positive electrode solvent is N-methylpyrrolidone (NMP), the negative electrode binder is polyacrylic acid (PAA), the negative electrode solvent is deionized water, the first negative electrode conductor is conductive carbon black (SP), and the second conductive agent is single-walled carbon nanotubes (SWCNTs).

[0172] Exemplarily, the viscosity of the positive electrode slurry is about 6000 mPa·s to about 8000 mPa·s, including but not limited to 6000 mPa·s, 6500 mPa·s, 7000 mPa·s, 7500 mPa·s or 8000 mPa·s.

[0173] Illustratively, the viscosity of the negative electrode slurry is about 4000 mPa·s to about 6000 mPa·s, including but not limited to 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s or 6000 mPa·s, etc.

[0174] Exemplarily, in the process of obtaining the positive electrode conductive glue, the positive electrode slurry, and the negative electrode slurry, the dispersion is high-speed dispersion, and the dispersion speed is 2200-4500 r / min.

[0175] Exemplarily, the above dispersion speed includes but is not limited to 2500 r / min, 3000 r / min, 3500 r / min or 4000 r / min, etc.

[0176] <Secondary Battery>

[0177] The secondary battery of the embodiment of the present application is a secondary battery prepared by the method for preparing a secondary battery of the embodiment of the present application.

[0178] In some embodiments, the double-sided density of the negative electrode sheet is 60-120 g / m 2 , including but not limited to 70g / m 2 , 80g / m 2 , 90g / m 2 or 100g / m 2 wait.

[0179] The preparation method of the secondary battery and the secondary battery of the embodiment of the present application both have at least the beneficial effects of the formation method of the battery of the embodiment of the present application.

[0180] Certain features of the present technology are further illustrated in the following non-limiting examples.

[0181] 1. Examples and Comparative Examples

[0182] In the following examples and comparative examples, "about" means that the value fluctuates within ±1% compared to the base value. For example, for a carbon-coated aluminum foil with a thickness of about 13 μm, it means that the thickness fluctuates within ±1% based on 13 μm.

[0183] The normal temperature and room temperature involved in the following examples and comparative examples are both 25°C.

[0184] Example 1

[0185] The method for preparing the battery of the embodiment of the present application comprises the following steps:

[0186] (1) Preparation of positive electrode sheets: Polyvinylidene fluoride (PVDF) and solvent N-methylpyrrolidone (NMP) are mixed to prepare a positive electrode paste with a solid content of about 6 weight%. To the obtained positive electrode paste, add about 1 weight% of conductive carbon black (SP) based on the weight of the positive electrode paste and disperse it at a high speed of 3200r / min to obtain a positive electrode conductive glue. To the obtained positive electrode conductive glue, add about 97 weight% of lithium iron phosphate based on the weight of the positive electrode conductive glue and disperse it at a high speed of 3200r / min to obtain a positive electrode slurry with a viscosity of about 7000mPa·s. The above-mentioned positive electrode slurry is evenly coated on the two opposite surfaces of a carbon-coated aluminum foil with a thickness of 13μm, and after rolling, die-cutting and drying, a double-sided surface density of about 400g / m 2 The positive electrode.

[0187] (2) Preparation of negative electrode sheet: Mix a highly mixed silicon-based negative electrode material with a weight ratio of artificial graphite: silicon-based negative electrode material SiO=6:4, add about 0.9% conductive carbon black (SP) based on the weight of the negative electrode material to the obtained negative electrode material and mix it evenly, then add about 3% polyacrylic acid (PAA), deionized water and 0.05% single-walled carbon nanotubes (SWCNTs) based on the weight of the above mixed material, and disperse at a high speed of 3200r / min to obtain a negative electrode slurry with a viscosity of about 5000mPa·s. The above negative electrode slurry is evenly coated on the two opposite surfaces of a copper foil with a thickness of 6μm, and after rolling, die-cutting and drying, a double-sided surface density of about 90g / m 2 The negative electrode.

[0188] (3) Preparation of electrolyte:

[0189] The electrolyte consists of a first electrolyte and a second electrolyte which are independently arranged, and the mass content of the first electrolyte in the electrolyte is 80%, and the mass content of the second electrolyte in the electrolyte is 20%.

[0190] 1) Preparation of the first electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF6 is added to the mixed solvent and mixed, and then fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are added and stirred to obtain the first electrolyte.

[0191] Wherein, the concentration of LiPF6 in the first electrolyte is 1 mol / L, FEC accounts for about 5.0% by weight of the first electrolyte, and VC accounts for about 2.0% by weight of the second electrolyte.

[0192] 2) Preparation of the second electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF6 is added to the mixed solvent and mixed evenly, and then fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are added and stirred to obtain a second electrolyte.

[0193] Wherein, the concentration of LiPF6 in the first electrolyte is 1 mol / L, FEC accounts for about 2.0% by weight of the second electrolyte, and VC accounts for about 5.0% by weight of the second electrolyte.

[0194] (4) Diaphragm selection: The diaphragm is a 12 μm polypropylene (PP) wet-process diaphragm.

[0195] (5) Assembly: The positive electrode sheet, the negative electrode sheet and the separator are stacked, assembled and baked according to the order of separator-negative electrode sheet-separator-positive electrode sheet to obtain a dry cell to be injected with electrolyte. Subsequently, the process of primary liquid injection, pre-forming, secondary liquid injection, forming and capacity division is carried out to produce a highly mixed silicon-based negative electrode battery.

[0196] Among them, the specific steps of liquid injection and formation are as follows:

[0197] ① injecting a first electrolyte into a dry cell to be injected with an electrolyte to obtain a first cell;

[0198] ② Place the first battery in a 55°C environment for 24 hours, cool it to room temperature at room temperature, and obtain a second battery.

[0199] ③ The second battery was placed in a 10°C environment for 3 hours, and then the treated battery was charged to 1% SOC with a current of 0.2C in a 10°C environment, and then discharged to 2.5V with a current of 0.2C, and the charge and discharge were repeated 3 times to obtain a third battery.

[0200] ④ Inject the second electrolyte into the third battery, and then let it stand in a 55°C environment for 12 hours to obtain a fourth battery.

[0201] ⑤ The fourth battery was charged to 1% SOC with a current of 0.1C in a 25°C environment, then charged to 30% SOC with a current of 0.2C, and then charged to 70% SOC with a current of 0.5C to obtain a highly mixed silicon-based negative electrode battery.

[0202] Embodiment 2 (Compared with Embodiment 1, the first charging SOC ratio is the upper limit 10%)

[0203] This embodiment is basically the same as Embodiment 1, except that:

[0204] During the injection and formation process of step (5), in step ③: the treated battery is charged to 10% SOC with a current of 0.2C in an environment of 10°C, and then discharged to 2.5V with a current of 0.2C, and the charge and discharge are repeated 3 times.

[0205] Embodiment 3 (Compared with Embodiment 1, the first charging current is the upper limit 0.3C)

[0206] This embodiment is basically the same as Embodiment 1, except that:

[0207] During the injection and formation process of step (5), in step ③: the treated battery is charged to 1% SOC at 0.3C in a 10°C environment, and then discharged to 2.5V at 0.3C, and the charge and discharge are repeated 3 times.

[0208] Example 4 (Compared with Example 1, the second and third charging currents are both lower limits, and the fourth charging current is the middle 0.3C)

[0209] This embodiment is basically the same as Embodiment 1, except that:

[0210] During the injection and formation process of step (5), step ⑤ is: charging the fourth battery to 1% SOC with a current of 0.01C in a 25°C environment, then charging it to 30% SOC with a current of 0.1C, and then charging it to 70% SOC with a current of 0.3C to obtain a highly mixed silicon-based negative electrode battery.

[0211] Embodiment 5 (Compared with Embodiment 1, the second charging current is the upper limit, the third charging current is the middle, the fourth charging current is the upper limit 0.5C, and the second charging SOC ratio is the upper limit 10%)

[0212] This embodiment is basically the same as Embodiment 1, except that:

[0213] During the injection and formation process of step (5), step ⑤ is: charging the fourth battery to 10% SOC with a current of 0.1C in a 25°C environment, then charging it to 30% SOC with a current of 0.2C, and then charging it to 70% SOC with a current of 0.5C to obtain a highly mixed silicon-based negative electrode battery.

[0214] Embodiment 6 (Compared with Embodiment 1, the second charging current is the upper limit, the third charging current is the middle, the fourth charging current is the upper limit 0.5C, and the fourth charging SOC ratio is the upper limit 100%)

[0215] This embodiment is basically the same as Embodiment 1, except that:

[0216] During the injection and formation process of step (5), step ⑤ is: charging the fourth battery to 1% SOC with a current of 0.1C in a 25°C environment, then charging it to 30% SOC with a current of 0.2C, and then charging it to 100% SOC with a current of 0.5C to obtain a highly mixed silicon-based negative electrode battery.

[0217] Example 7 (Compared with Example 1, the first temperature is an upper limit of 45°C, and the first charging current is a lower limit of 0.01C)

[0218] This embodiment is basically the same as Embodiment 1, except that:

[0219] During the injection and formation process of step (5), in step ③: the treated battery is charged to 1% SOC at a current of 0.01C in a 45°C environment, and then discharged to 2.5V at a current of 0.2C, and the charge and discharge are repeated 3 times.

[0220] Example 8 (Compared with Example 1, the first temperature is an upper limit of 45°C)

[0221] This embodiment is basically the same as Embodiment 1, except that:

[0222] During the injection and formation process of step (5), in step ③: the treated battery is charged to 1% SOC at a current of 0.2C in a 45°C environment, and then discharged to 2.5V at a current of 0.2C, and the charge and discharge are repeated 3 times.

[0223] Example 9 (Compared with Example 1, the second temperature is an upper limit of 45°C, and the second charging current is a lower limit of 0.01C)

[0224] This embodiment is basically the same as Embodiment 1, except that:

[0225] During the injection and formation process of step (5), step ⑤ is: charging the fourth battery to 1% SOC with a current of 0.01C in a 45°C environment, then charging it to 30% SOC with a current of 0.2C, and then charging it to 70% SOC with a current of 0.5C to obtain a highly mixed silicon-based negative electrode battery.

[0226] Example 10 (the first charging temperature is the lower limit 0°C)

[0227] This embodiment is basically the same as Embodiment 1, except that:

[0228] During the process of injection and formation in step (5), step ③ is: the second battery is allowed to stand in a 0°C environment for 3 hours, and then the treated battery is charged to 1% SOC with a current of 0.2C in a 0°C environment, and then discharged to 2.5V with a current of 0.2C, and the charge and discharge are repeated 3 times to obtain a third battery.

[0229] Example 11 (the first charging temperature is 15°C below the middle temperature)

[0230] This embodiment is basically the same as Embodiment 1, except that:

[0231] During the injection and formation process of step (5), step ③ is: the second battery is allowed to stand in a 15°C environment for 3 hours, and then the treated battery is charged to 1% SOC with a current of 0.2C in a 15°C environment, and then discharged to 2.5V with a current of 0.2C, and the charge and discharge are repeated 3 times to obtain a third battery.

[0232] Example 12 (the first charging temperature is the middle 22.5°C)

[0233] This embodiment is basically the same as Embodiment 1, except that:

[0234] During the process of injection and formation in step (5), step ③ is: the second battery is allowed to stand in a 10°C environment for 3 hours, and then the treated battery is charged to 1% SOC with a current of 0.2C in a 22.5°C environment, and then discharged to 2.5V with a current of 0.2C, and the charge and discharge are repeated 3 times to obtain a third battery.

[0235] Example 13 (the dosage ratio of the first electrolyte to the second electrolyte is 7:3)

[0236] This embodiment is basically the same as Embodiment 1, except that:

[0237] In step (3), the mass content of the first electrolyte in the electrolyte is 70%, and the mass content of the second electrolyte in the electrolyte is 30%.

[0238] Example 14 (the dosage ratio of the first electrolyte to the second electrolyte is 9:1)

[0239] This embodiment is basically the same as Embodiment 1, except that:

[0240] In step (3), the mass content of the first electrolyte in the electrolyte is 90%, and the mass content of the second electrolyte in the electrolyte is 10%.

[0241] Example 15 (Only silicon-based material in the negative electrode active material)

[0242] This embodiment is basically the same as Embodiment 1, except that:

[0243] In step (2), "mix the highly mixed silicon-based negative electrode material in a weight ratio of artificial graphite: silicon-based negative electrode material SiO uniformly" is replaced by "take negative electrode material SiO".

[0244] Example 16 (the ratio of graphite to silicon-based material in the negative electrode active material is 5:5 as the lower limit)

[0245] This embodiment is basically the same as Embodiment 1, except that:

[0246] In step (2), the highly mixed silicon-based negative electrode material is evenly mixed at a weight ratio of artificial graphite: silicon-based negative electrode material SiO=5:5.

[0247] Example 17 (the ratio of graphite to silicon-based material in the negative electrode active material is an upper limit of 7:3)

[0248] This embodiment is basically the same as Embodiment 1, except that:

[0249] In step (2), the highly mixed silicon-based negative electrode material is evenly mixed at a weight ratio of artificial graphite: silicon-based negative electrode material SiO=7:3.

[0250] Example 18 (the lower limit of FEC content and the upper limit of VC content in the first electrolyte; the opposite in the second electrolyte - the situation where the amounts of the two additives are closest)

[0251] This embodiment is basically the same as Embodiment 1, except that:

[0252] In step 1) of step (2), FEC accounts for about 4.0% by weight of the first electrolyte, and VC accounts for about 3.0% by weight of the second electrolyte.

[0253] In step (2) of step (2), FEC accounts for about 3.0% by weight of the second electrolyte, and VC accounts for about 4.0% by weight of the second electrolyte.

[0254] Example 19 (the upper limit of FEC content and the lower limit of VC content in the first electrolyte; the opposite in the second electrolyte - the situation where the difference in the amount of the two additives is the largest)

[0255] This embodiment is basically the same as Embodiment 1, except that:

[0256] In step 1) of step (2), FEC accounts for about 6.0% by weight of the first electrolyte, and VC accounts for about 1.0% by weight of the second electrolyte.

[0257] In step (2) of step (2), FEC accounts for about 1.0% by weight of the first electrolyte, and VC accounts for about 6.0% by weight of the second electrolyte.

[0258] Example 20 (the total content of FEC and VC in the first electrolyte is the lower limit)

[0259] This embodiment is basically the same as Embodiment 1, except that:

[0260] In step 1) of step (2), FEC accounts for about 4.0% by weight of the first electrolyte, and VC accounts for about 1.0% by weight of the second electrolyte.

[0261] Example 21 (the total content of FEC and VC in the second electrolyte is the lower limit)

[0262] This embodiment is basically the same as Embodiment 1, except that:

[0263] In step (2) of step (2), FEC accounts for about 1.0% by weight of the first electrolyte, and VC accounts for about 3.0% by weight of the second electrolyte.

[0264] Example 22 (the positive electrode material is not lithium iron phosphate, and the silicon-based material is silicon carbide)

[0265] This embodiment is basically the same as Embodiment 1, except that:

[0266] In step (1), replace lithium iron phosphate with NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 02).

[0267] In step (2), the silicon-based negative electrode material SiO is replaced by SiC.

[0268] Comparative Example 1

[0269] This comparative example is basically the same as Example 1, except that:

[0270] In step (3), FEC and VC in the second electrolyte are replaced by tris(trimethylsilyl)phosphate, and the tris(trimethylsilyl)phosphate accounts for about 7.0% by weight of the second electrolyte.

[0271] During the injection and formation process, in step ③: the treated battery is charged at 35° C. with a current of 0.1 C for 40 min to obtain a third battery.

[0272] Comparative Example 2 (No FEC in the First Electrolyte)

[0273] This comparative example is basically the same as Example 1, except that:

[0274] In step (3), there is no FEC in the first electrolyte.

[0275] Comparative Example 3 (No VC in the First Electrolyte)

[0276] This comparative example is basically the same as Example 1, except that:

[0277] In step (3), there is no VC in the first electrolyte.

[0278] Comparative Example 4 (No FEC in the Second Electrolyte)

[0279] This comparative example is basically the same as Example 1, except that:

[0280] In step (3), there is no FEC in the second electrolyte.

[0281] Comparative Example 5 (No VC in the Second Electrolyte)

[0282] This comparative example is basically the same as Example 1, except that:

[0283] In step (3), there is no VC in the second electrolyte.

[0284] 2. Performance Test

[0285] The electrochemical performance of the battery prepared in each embodiment or comparative example was tested. The specific test method was as follows: charging at a constant current of 1C at 25°C±2°C until the battery voltage reached 3.65V and then switching to constant voltage charging. Charging was stopped when the current dropped to 0.05C current, and the battery was left standing for 1 hour after charging. Discharging at a current of 1C at 25°C±2°C until the battery voltage reached 2.5V, and the capacity retention rate and the full charge expansion rate of the negative electrode sheet were tested after 50 cycles. The test results are shown in Table 1.

[0286] Table 1 Performance test results

[0287]

[0288]

[0289] It can be seen from Table 1 that under the same conditions, the embodiments of the present application have higher coulombic efficiency and cycle capacity retention rate, and lower expansion rate than the comparative example.

[0290] The expansion rate of Example 1 is lower than that of Examples 2 and 3, and the capacity retention rate also shows excellent performance; the full-charge expansion rate of Example 1 after 50 cycles is much lower than that of Examples 7 and 8, and the capacity retention rate of 50 cycles is also much better than that of Example 7, and the first efficiency of Example 1 is higher than that of Examples 10-12; it shows that the pre-formation current should be moderate, the time should not be too long, and the appropriate formation temperature and current cooperate with each other, which can effectively alleviate the expansion and cycle stability of the silicon negative electrode; the coulomb efficiency and capacity retention rate of Example 1 are higher than those of Examples 4, 5, 6 and Example 9, and the full-charge expansion rate of Example 1 after 50 cycles is the lowest, indicating that the formation current and temperature cooperate with each other, and at the appropriate current and temperature, it is conducive to the formation of SEI on the surface of the silicon negative electrode. The electrolyte additives combined with FEC and VC are conducive to the formation of a dense and tough SEI film on the surface of the silicon negative electrode, which plays a key role in improving the first efficiency and cycle capacity retention rate of the battery.

[0291] This shows that the use of low-temperature, high-current pre-formation can generate a more flexible organic layer on the SEI film close to the negative electrode side, which greatly alleviates the deformation and rupture of the SEI caused by the expansion of the silicon negative electrode during the cycle, so that new active substances are not exposed to consume the electrolyte and cause capacity decay.

[0292] In summary, the present application provides a formation method suitable for silicon-based negative electrode batteries, which effectively alleviates the problems of SEI deformation, rupture and regeneration caused by volume expansion of silicon-based negative electrode batteries during the cycle process, reduces the consumption of active lithium, and improves the coulombic efficiency and cycle stability of the battery.

[0293] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0294] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0295] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A battery formation method, characterized in that: The battery comprises a negative electrode active material and an electrolyte, wherein the negative electrode active material comprises a silicon-based material, and the electrolyte comprises a first electrolyte and a second electrolyte, wherein the first electrolyte and the second electrolyte both comprise fluoroethylene carbonate and vinylene carbonate; The method of forming comprises: Injecting the first electrolyte into the dry cell to be injected with the electrolyte to obtain a first battery; placing the first battery in a first resting state and then cooling the battery to obtain a second battery; The second battery is subjected to a second resting state, and then the first charging and the first discharging are repeated at a first temperature to obtain a third battery; the first temperature is below 45° C., and the current of the first charging is above 0.01 C; injecting the second electrolyte into the third battery, followed by a third standing, to obtain a fourth battery; The fourth battery is subjected to a second charge, a third charge and a fourth charge at a second temperature to obtain a formed battery.

2. The chemical formation method according to claim 1, characterized in that: The first static temperature is equivalent to the third static temperature, and both are greater than the second static temperature, the first temperature, and the second temperature; and / or, The first temperature is equivalent to the second static temperature, and both are lower than the second temperature.

3. The chemical formation method according to claim 1, characterized in that: The first static temperature and the third static temperature are both 50-60° C.; and / or, The second standing temperature and the first temperature are both 0-45°C; and / or, The second temperature is 20-45°C.

4. The chemical formation method according to claim 3, characterized in that: The second standing temperature and the first temperature are both 0-15° C.; and / or, The second temperature is 25-35°C.

5. The chemical formation method according to claim 1, characterized in that: The first charging current is 0.01-0.3C; and / or, The discharge current is 0.1-0.3C; and / or, The first charging is to 1-10% SOC; and / or, The discharge to 2.5-2.8V; and / or, The second charging current is 0.01-0.1C; and / or, The second charging is to 1-10% SOC; and / or, The third charging current is 0.1-0.3C; and / or, The third charging to 10-30% SOC; and / or, The fourth charging current is 0.1-0.5C; and / or, The fourth is charged to 30-100% SOC.

6. The chemical formation method according to claim 5, characterized in that: The first charging current is 0.2-0.3C; and / or, The discharge current is 0.2-0.3C; and / or, The first charging is to 1-5% SOC; and / or, The second charging current, the third charging current and the fourth charging current increase in sequence; and / or, The SOC proportion of the second charging, the SOC proportion of the third charging, and the SOC proportion of the fourth charging increase in sequence.

7. The chemical formation method according to claim 1, characterized in that: The mass content of the first electrolyte in the electrolyte is a, the mass content of the second electrolyte in the electrolyte is b, and a is greater than b; and / or, The mass content of the fluoroethylene carbonate in the first electrolyte is c1, the mass content of the vinylene carbonate in the first electrolyte is d1, the mass content of the fluoroethylene carbonate in the second electrolyte is c2, and the mass content of the vinylene carbonate in the second electrolyte is d2, and c1, d1, c2, and d2 satisfy: c1>c2 and d1<d2; and / or, The silicon-based material includes at least one of nano-silicon, micro-silicon, porous silicon, amorphous silicon, silicon alloy, silicon-oxygen compound and silicon-carbon composite material; and / or, The negative electrode active material further comprises graphite; and / or, The first electrolyte further includes a first lithium salt and a first solvent; and / or, The second electrolyte further includes a second lithium salt and a second solvent; and / or, The battery further includes a separator including a polyolefin wet-process separator.

8. The chemical formation method according to claim 7, characterized in that: The a is 60-70%; and / or, The c1 is 4-6%; and / or, The d1 is 1-3%; and / or, The c2 is 1-3%; and / or, The d2 is 4-6%; and / or, The c1, d1, c2, and d2 satisfy: c1>d1, c2<d2, c1>c2 and d1<d2; and / or, The silicon-based material includes at least one of a silicon-oxygen compound and a silicon-carbon composite material; and / or, The first lithium salt and the second lithium salt both include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(oxalatoborate); and / or, When the negative electrode active material comprises graphite and a silicon-based material, the mass ratio of the graphite to the silicon-based material is (0.7-0.5): (0.3-0.5); and / or, The first solvent comprises ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; and / or, The second solvent includes ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

9. A method for preparing a secondary battery, characterized in that: The method comprises the step of chemical formation, wherein the chemical formation method is the chemical formation method according to any one of claims 1 to 8; Preferably, the method for preparing the secondary battery further comprises the steps of preparing a positive electrode sheet and a negative electrode sheet; The step of preparing the positive electrode sheet comprises: Mixing the positive electrode binder with the positive electrode solvent to obtain a positive electrode glue solution; Adding a positive electrode conductive agent to the positive electrode glue solution and dispersing the positive electrode conductive agent to obtain a positive electrode conductive glue; Adding positive electrode active material to the positive electrode conductive glue and dispersing it to obtain positive electrode slurry; and / or, The step of preparing the negative electrode sheet comprises: A first negative electrode conductive agent is added to the negative electrode active material and mixed uniformly, and then a negative electrode binder, a negative electrode solvent and a second negative electrode conductive agent are added and dispersed to obtain a negative electrode slurry.

10. A secondary battery, characterized in that: The secondary battery is a secondary battery prepared by the preparation method of claim 9.

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