Formation method of battery and application thereof

Abstract

The application provides a battery formation method and application. The battery formation method comprises the following steps: injecting a first electrolyte into a dry battery to be injected with an electrolyte to obtain a first battery; performing first standing on the first battery, and then cooling to obtain a second battery; performing second standing on the second battery, and then repeatedly performing first charging and first discharging at a first temperature to obtain a third battery; injecting a second electrolyte into the third battery, and then performing third standing to obtain a fourth battery; performing second charging, third charging and fourth charging on the fourth battery at a second temperature to obtain a formed battery. The battery formation method of the application effectively alleviates the problems of SEI deformation and rupture caused by volume expansion of a silicon-based negative electrode battery in a cycle process by means of cooperation of low temperature and large current, and improves the coulomb efficiency and cycle stability of the battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a battery formation method and its application. Background Technology

[0002] With the booming development of the new energy industry, lithium-ion batteries are gradually moving towards higher energy density, longer cycle life, and faster charging performance. The existing graphite anode has a theoretical specific capacity of only 372 mAh / g, which is insufficient to meet future energy density requirements. Silicon-based anodes have advantages such as high theoretical specific capacity, abundant natural silicon reserves, low raw material costs, and a slightly higher operating voltage than graphite (0.2V), making them a very promising high-energy-density lithium-ion anode material. However, during lithium intercalation, the volume of silicon expands to varying degrees, causing deformation due to the mutual compression between silicon particles. During delithiation, the silicon shrinks to varying degrees, leading to particle breakage after multiple cycles. This repeated expansion and contraction causes separation between silicon particles, between silicon particles and the conductive agent, and between silicon particles and the current collector, resulting in damage and collapse of the conductive network and electrode failure. Volume changes in silicon can cause deformation and rupture of the SEI film. The newly exposed active material then consumes the electrolyte to form a new SEI film, and this process repeats, resulting in a thick, uneven SEI film. This leads to low coulombic efficiency and irreversible capacity loss, severely impacting the practical application of silicon anodes. Current research focuses on utilizing the stability of carbon materials to coat silicon or embedding silicon into carbon materials to prepare silicon-carbon composite anode materials to help construct a stable SEI film. However, this approach suffers from complex fabrication processes, difficulty in mass production, and high production costs. Other methods involve selecting suitable binders to increase the adhesion between active materials and between the active material and the current collector, suppressing expansion and improving conductivity. However, the preparation process of functional binders is complex and costly, and the addition of these functional binders can also cause difficulties in the homogenization process and increase resistance, among other problems. Summary of the Invention

[0003] In view of this, one objective of this application is to provide a battery formation method that uses a combination of low temperature and high current to effectively alleviate the problem of SEI deformation and rupture caused by volume expansion during cycling of silicon-based anode batteries, thereby improving the coulombic efficiency and cycle stability of the battery.

[0004] Another objective of this application is to provide a method for preparing a secondary battery.

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

[0006] To achieve the above objectives, the first aspect of this application proposes a battery formation method, the battery comprising a negative electrode active material and an electrolyte, the negative electrode active material comprising a silicon-based material, and the electrolyte comprising a first electrolyte and a second electrolyte, both the first electrolyte and the second electrolyte comprising fluoroethylene carbonate and vinylene carbonate.

[0007] The formation method includes:

[0008] The first electrolyte is injected into a dry cell containing the electrolyte to obtain a first cell;

[0009] The first battery is left to stand for a first time and then cooled to obtain the second battery;

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

[0011] The second electrolyte is injected into the third battery, followed by a third settling period to obtain the 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 the formed battery.

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

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

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

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

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

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

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

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

[0021] In some implementations, the discharge is carried out to 2.5-2.8V.

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

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

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

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

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

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

[0028] In some embodiments, the current of the second charge, the current of the third charge, and the current of the fourth charge increase sequentially.

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

[0030] In some embodiments, the mass content of the first electrolyte in the electrolyte is a, and the mass content of the second electrolyte in the electrolyte is b, wherein 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, wherein c1, d1, c2, and d2 satisfy: c1 > c2 and d1 < d2.

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

[0033] In some implementations, 'a' is 60-70%.

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

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

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

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

[0038] In some embodiments, the silicon-based material includes at least one of nano-silicon, micron-silicon, porous silicon, amorphous silicon, silicon alloy, silicon oxide, and silicon-carbon composite materials.

[0039] In some embodiments, the silicon-based material includes at least one of silicon oxide compounds and silicon-carbon composite materials.

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

[0041] In some embodiments, when the negative electrode active material comprises 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).

[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, both the first lithium salt and the second lithium salt comprise at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium dioxalate borate.

[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 methyl ethyl carbonate (EMC).

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

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

[0049] In some embodiments, the method for preparing the 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] The positive electrode binder is mixed with the positive electrode solvent to obtain the positive electrode adhesive solution;

[0052] A positive electrode conductive agent is added to the positive electrode adhesive and dispersed to obtain a positive electrode conductive adhesive;

[0053] Positive electrode active material is added to and dispersed in the positive electrode conductive adhesive to obtain a 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 well. 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 this application provides a secondary battery, which is a secondary battery prepared using the preparation method of the secondary battery described in this application.

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

[0058] The first electrolyte and the second electrolyte are injected into the battery in a two-stage injection process. The first charging and first discharging processes after the first electrolyte is injected into the battery constitute pre-formation. During pre-formation, a combination of low temperature and high current is used to avoid the formation of a loose SEI film when the current is too high, as well as the formation of a low conductivity SEI film when the temperature is low. The organic component content 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 subsequent discharge further activates the electrode material and improves the stability of the electrode structure. This process should be completed in a short time, consuming a large amount of FEC additive to form a tightly structured protective film on the surface of the silicon negative electrode. The consumed FEC is replenished during the second electrolyte injection. After secondary electrolyte injection, an open-cell formation method with a large current is used at room temperature or above. After pre-formation, an inorganic layer with high mechanical toughness is further obtained on the organic layer side. Finally, a high-current charging is used to obtain an organic layer with high flexibility on the side close to the electrolyte. This organic-inorganic-organic SEI film not only hinders further reaction of the electrolyte, but also, due to the double organic layer coating, the SEI film as a whole has great toughness. This effectively alleviates the problem of SEI film deformation, rupture and regeneration caused by volume expansion during the cycle of silicon-based anode batteries, reduces the consumption of active lithium, and improves the coulombic efficiency and cycle stability of the battery.

[0059] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

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

[0061] in:

[0062] Figure 1 This is a flowchart illustrating a battery formation method as an exemplary embodiment of this application. Detailed Implementation

[0063] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0064] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0065] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0066] When the term “and / or” is used in a list containing two or more items, it 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, A only, B only, or a combination of A and B.

[0067] In this application, the ambient temperature and room temperature are both 25-30℃.

[0068] <Battery Formation Method>

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

[0070] The battery formation method of this application embodiment includes a negative electrode active material and an electrolyte. The negative electrode active material includes a silicon-based material, and the electrolyte includes a first electrolyte and a second electrolyte. Both the first electrolyte and the second electrolyte 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, micron-silicon, porous silicon, amorphous silicon, silicon alloy, silicon oxide, and silicon-carbon composite materials.

[0072] As an optional example, the silicon-based material includes at least one of silicon oxide compounds and silicon-carbon composite materials.

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

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

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

[0076] For example, the values ​​of y include, but are not limited to, 0.1, 0.5, 1, 1.5, or 2.

[0077] For example, the silicon alloy includes silicon-tin alloys, etc.

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

[0079] For example, when the negative electrode active material comprises 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. In this case, the battery in this embodiment is a highly doped silicon-based negative electrode battery.

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

[0081] In the embodiments of this application, both the first electrolyte and the second electrolyte include fluoroethylene carbonate and vinylene carbonate, which can form a tightly structured protective film on the surface of the silicon anode. Adding VC to the first electrolyte can improve the temperature adaptability of the lithium-ion battery and reduce gas generation during formation. The combination of FEC and VC can improve the battery's initial charge specific capacity and initial coulombic efficiency, and enhance the battery's cycle stability.

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

[0083] In the embodiments of this application, the content of the first electrolyte is greater than the content of the second electrolyte by the total mass of the electrolyte. The purpose of this setting is to ensure that the electrolyte fully wets the dry cell, and that there is enough electrolyte to generate the SEI film during pre-formation. The second electrolyte is added to replenish the FEC and VC consumed in generating the SEI film, and to replenish the electrolyte consumed in pre-formation, so as to ensure cycle stability.

[0084] For example, 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%.

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

[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, wherein c1, d1, c2, and d2 satisfy the following:

[0087] c1>c2 and d1<d2.

[0088] In the embodiments of this application, the mass content (c1) of the fluoroethylene carbonate in the first electrolyte, the mass content (d1) of the vinylene carbonate in the first electrolyte, the mass content (c2) of the fluoroethylene carbonate in the second electrolyte, and the mass content (d2) of the vinylene carbonate in the second electrolyte satisfy the above-mentioned relationship. This allows for the formation of a stable SEI film on the surface of the battery negative electrode, providing better thermal stability and oxidation resistance, and reducing capacity loss during charge and discharge. If the above relationship is not satisfied, for example, if c1 is less than or equal to c2, the stability of SEI film formation during pre-formation will be affected; if d1 is greater than or equal to d2, a thicker SEI film will be generated during pre-formation, resulting in a lower initial coulombic efficiency of the battery.

[0089] As a preferred example, c1, d1, c2, and d2 satisfy: c1>d1, c2<d2, and c1>c2 and d1<d2. In the embodiments of this application, under the premise that c1>c2 and d1<d2, further satisfying c1>d1 and c2<d2 can improve the shear storage modulus of the SEI film, enhance the stability of the SEI film, reduce 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%.

[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%.

[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%.

[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%.

[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 this application, the first lithium salt and the second lithium salt can be any lithium salt known in the art that can be used in lithium-ion batteries, and the first solvent and the second solvent can also be any non-aqueous organic solvent known in the art that can be used in lithium-ion batteries.

[0097] For example, the first lithium salt and the second lithium salt are both including, but not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium dioxalate borate (LiBOB), and lithium hexafluorophosphate (LiPF6) is selected as the first lithium salt.

[0098] It should be noted that in the embodiments of this 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, and may be selected as 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, and may be selected as 1 mol / L.

[0101] In the embodiments of this 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 unequal.

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

[0103] As an optional example, the first solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), which 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), and methyl ethyl carbonate (EMC).

[0105] As an optional example, the second solvent is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate (EMC), which 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 comprises 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), with FEC accounting for approximately 5.0% of the weight of the first electrolyte and VC accounting for approximately 2.0% of the weight of the first electrolyte.

[0107] As an optional example, the second electrolyte comprises 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 consists of fluoroethylene carbonate (FEC) and vinylene carbonate (VC), with FEC accounting for approximately 2.0% of the weight of the second electrolyte and VC accounting for approximately 5.0% of the 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 this application, the positive electrode active material can be any lithium salt known in the art that can be used in lithium-ion batteries.

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

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

[0112] In some embodiments, the battery also includes a casing.

[0113] In some embodiments, the battery includes lithium-ion batteries, etc.

[0114] Figure 1 This is a flowchart illustrating a battery formation method as an exemplary embodiment of this application.

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

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

[0117] S102. The first battery is left to stand for a first time and then cooled to obtain the second battery.

[0118] In the embodiments of this application, the purpose of subjecting the first battery to a first static condition is to ensure that the electrolyte fully wets the battery cell under the target temperature conditions of the first static condition.

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

[0120] In some implementations, the first settling time is 20-28 hours, including but not limited to 22 hours, 24 hours or 26 hours, and can be selected as 24 hours.

[0121] In some implementations, cooling is carried out at ambient temperature, cooling to room temperature.

[0122] S103. The second battery is subjected to a second resting period, and then the first charging and first discharging are repeated at a first temperature to obtain a third battery; the first temperature is below 45°C, and the first charging current is above 0.01C.

[0123] In the embodiments of this application, step S103 employs a combination of low temperature and high current, which avoids both the formation of a loose SEI film when the current is too high and the formation of a low-conductivity SEI film at low temperatures. The organic component content 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. Subsequently, the discharge further activates the electrode material and improves the stability of the electrode structure. This process should be completed in a short time, consuming a large amount of FEC additive to form a tightly structured protective film on the surface of the silicon negative electrode. The consumed FEC is replenished during subsequent secondary liquid injection.

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

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

[0126] In some implementations, the first temperature is equivalent to the second settling temperature.

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

[0128] For example, the second settling 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 selected to be below 30°C, and further selected to be below 20°C.

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

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

[0131] In some embodiments, the current of the first charging 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 current of the first charge 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 implementations, the first charge is made to 1-10% SOC, including but not limited to 1% SOC, 2.5% SOC, 5% SOC, 7.5% SOC, or 10% SOC.

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

[0137] In some embodiments, the discharge to 2.5-2.8V includes, but is not limited to, 2.6V, 2.65V, 2.7V or 2.75V, and may be selected as 2.5V.

[0138] In some embodiments, the first charging and first discharging are repeated at the first temperature 2 to 5 times, including but not limited to 2, 3, 4 or 5 times, with 5 times being optional.

[0139] S104. The second electrolyte is injected into the third battery, followed by a third settling period to obtain the fourth battery.

[0140] In the embodiments of this application, the purpose of the third settling is to ensure that the electrolyte fully wets the cell under the target temperature conditions of the third settling.

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

[0142] In some embodiments, the temperature of the third settling period is 50-60°C, including but not limited to 52.5°C, 55°C or 57.5°C, and may be selected as 55°C.

[0143] In some implementations, the third settling time is 8-16 hours, including but not limited to 10 hours, 12 hours or 14 hours, and can be selected as 12 hours.

[0144] S105. The fourth battery is charged at a second temperature for a second charge, a third charge, and a fourth charge to obtain the formed battery.

[0145] In the embodiments of this application, after the second liquid injection, step S105 adopts a post-formation method with a 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 to obtain an organic layer with high flexibility on the side close to the electrolyte. This organic-inorganic-organic SEI film not only hinders the further reaction of the electrolyte, but also has great toughness as a whole due to the double organic layer coating.

[0146] In some implementations, the second temperature is lower than the first settling temperature and the third settling temperature.

[0147] In some implementations, the second temperature is greater than the first temperature and the second settling 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.

[0149] As an alternative 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.

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

[0152] In some embodiments, the current of the third charge 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 to 10-30% SOC includes, but is not limited to, 12.5% ​​SOC, 15% SOC, 17.5% SOC, 20% SOC, 22.5% SOC, 25% SOC, or 27.5% SOC.

[0154] In some embodiments, the current of the fourth charge 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.

[0155] In some embodiments, the fourth charge to 30-100% SOC includes, but is 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.

[0156] In some embodiments, the current of the second charge, the current of the third charge, and the current of the fourth charge increase sequentially.

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

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

[0159] The first electrolyte and the second electrolyte are injected into the battery in a two-stage injection process. The first charging and first discharging processes after the first electrolyte is injected into the battery constitute pre-formation. During pre-formation, a combination of low temperature and high current is used to avoid the formation of a loose SEI film when the current is too high, as well as the formation of a low conductivity SEI film when the temperature is low. The organic component content 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 subsequent discharge further activates the electrode material and improves the stability of the electrode structure. This process should be completed in a short time, consuming a large amount of FEC additive to form a tightly structured protective film on the surface of the silicon negative electrode. The consumed FEC is replenished during the second electrolyte injection. After secondary electrolyte injection, an open-cell formation method with a large current is used at room temperature or above. After pre-formation, an inorganic layer with high mechanical toughness is further obtained on the organic layer side. Finally, a high-current charging is used to obtain an organic layer with high flexibility on the side close to the electrolyte. This organic-inorganic-organic SEI film not only hinders further reaction of the electrolyte, but also, due to the double organic layer coating, the SEI film as a whole has great toughness. This effectively alleviates the problem of SEI film deformation, rupture and regeneration caused by volume expansion during the cycle of silicon-based anode batteries, reduces the consumption of active lithium, and improves the coulombic efficiency and cycle stability of the battery.

[0160] <Preparation Methods of Secondary Batteries>

[0161] The method for preparing a secondary battery according to the embodiments of this application includes a formation step, wherein the formation method is the formation method of the battery according to the embodiments of this application.

[0162] In some embodiments, the preparation method of a secondary battery also includes steps such as the preparation of a positive electrode, the preparation of a negative electrode, and battery assembly.

[0163] It should be noted that this application does not limit the specific composition and operation methods of the preparation of positive electrode sheets, negative electrode sheets, battery assembly, etc., and can be any well-known composition and preparation technology of positive electrode sheets, negative electrode sheets, and battery assembly that can be used in secondary batteries, especially lithium-ion batteries.

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

[0165] The positive electrode binder is mixed with the positive electrode solvent to obtain the positive electrode adhesive solution;

[0166] A positive electrode conductive agent is added to the positive electrode adhesive and dispersed to obtain a positive electrode conductive adhesive;

[0167] Positive electrode active material is added to the positive electrode conductive adhesive and dispersed to obtain positive electrode slurry.

[0168] For example, 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 well. 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 this application, the 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 all adopt any substances and dosages well known in the art that can be used in secondary batteries, especially lithium-ion batteries, as positive electrode binders, positive electrode conductive agents, positive electrode solvents, negative electrode binders, negative electrode solvents, and negative electrode conductive agents.

[0171] For example, the positive electrode binder is polyvinylidene fluoride (PVDF), the positive electrode conductive agent 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 conductive agent is conductive carbon black (SP), and the second conductive agent is single-walled carbon nanotubes (SWCNTs).

[0172] For example, the viscosity of the positive electrode slurry is from 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] For example, the viscosity of the negative electrode slurry is from 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.

[0174] For example, in the processes of obtaining the positive conductive adhesive, the positive slurry, and the negative slurry, the dispersion is carried out at high speed, with a dispersion speed of 2200-4500 r / min.

[0175] For example, the dispersion speeds mentioned above include, but are not limited to, 2500 r / min, 3000 r / min, 3500 r / min or 4000 r / min.

[0176] Secondary batteries

[0177] The secondary battery in this application embodiment is a secondary battery prepared using the preparation method of the secondary battery in this application embodiment.

[0178] In some embodiments, the bifacial areal density of the negative electrode sheet is 60-120 g / m². 2 including but not limited to 70g / m 2 80g / m 2 90g / m 2 Or 100g / m 2 wait.

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

[0180] The following non-limiting embodiments further illustrate certain features of the present technology.

[0181] I. Examples and Comparative Examples

[0182] In the following comparative examples, "about" means within ±1% of the baseline value. Taking a carbon-coated aluminum foil with a thickness of about 13 μm as an example, it means that the thickness is within ±1% of 13 μm.

[0183] The following examples and comparative examples all use a room temperature of 25°C.

[0184] Example 1

[0185] The battery preparation method of this application embodiment includes the following steps:

[0186] (1) Preparation of the positive electrode sheet: Polyvinylidene fluoride (PVDF) and solvent N-methylpyrrolidone (NMP) were mixed to prepare a positive electrode solution with a solid content of about 6% by weight. Conductive carbon black (SP) of about 1% by weight based on the weight of the positive electrode solution was added to the obtained positive electrode solution and dispersed at a high speed of 3200 r / min to obtain a positive electrode conductive adhesive. Lithium iron phosphate of about 97% by weight based on the weight of the positive electrode conductive adhesive was added to the obtained positive electrode conductive adhesive and dispersed at a high speed of 3200 r / min to obtain a positive electrode slurry with a viscosity of about 7000 mPa·s. The above positive electrode slurry was uniformly coated on two opposite surfaces of a carbon-coated aluminum foil with a thickness of 13 μm, and after rolling, die-cutting, and drying, a double-sided surface density of about 400 g / m² was obtained. 2 The positive electrode sheet.

[0187] (2) Preparation of the negative electrode sheet: A highly mixed silicon-based negative electrode material with a weight ratio of approximately 6:4 (artificial graphite:silicon-based negative electrode material SiO) was mixed uniformly. Then, approximately 0.9% conductive carbon black (SP) based on the weight of the obtained negative electrode material was added and mixed uniformly. Next, approximately 3% polyacrylic acid (PAA), deionized water, and 0.05% single-walled carbon nanotubes (SWCNTs) based on the weight of the above mixed material were added, and the mixture was dispersed at a high speed of 3200 r / min to obtain a negative electrode slurry with a viscosity of approximately 5000 mPa·s. The above negative electrode slurry was uniformly coated on two opposite surfaces of a 6 μm thick copper foil, and after rolling, die-cutting, and drying, a double-sided surface density of approximately 90 g / m² was obtained. 2 The negative electrode sheet.

[0188] (3) Electrolyte preparation:

[0189] The electrolyte consists of a first electrolyte and a second electrolyte, which are set separately. The first electrolyte has a mass content of 80% and the second electrolyte has a mass content of 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. LiPF6 is then added to the mixed solvent and mixed well. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are then added and stirred well to obtain the first electrolyte.

[0191] The concentration of LiPF6 in the first electrolyte is 1 mol / L, FEC accounts for approximately 5.0% of the weight of the first electrolyte, and VC accounts for approximately 2.0% of the 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. LiPF6 is then added to the mixed solvent and mixed well. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are then added and stirred well to obtain the second electrolyte.

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

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

[0195] (5) Assembly: The positive electrode, negative electrode and separator are stacked, assembled and baked in the order of separator-negative electrode-separator-positive electrode to obtain a dry cell to be injected with electrolyte. Then, a high-mixed silicon-based negative electrode cell is made by processes such as primary electrolyte injection, pre-formation, secondary electrolyte injection, formation and capacity testing.

[0196] The specific steps for liquid injection and formation are as follows:

[0197] ① The first electrolyte is injected into the dry cell containing the electrolyte to obtain the first cell;

[0198] ② The first battery was left to stand at 55°C for 24 hours, and then cooled to room temperature to obtain the second battery.

[0199] ③ The second battery was left to stand in a 10°C environment for 3 hours. Then the battery was charged to 1% SOC at a current of 0.2C in a 10°C environment, and then discharged to 2.5V at a current of 0.2C. This charging and discharging process was repeated 3 times to obtain the third battery.

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

[0201] ⑤ The fourth cell was charged to 1% SOC at 0.1C in an environment of 25°C, then charged to 30% SOC at 0.2C, and then charged to 70% SOC at 0.5C to obtain a highly doped silicon-based anode cell.

[0202] Example 2 (Compared to Example 1, the first charging SOC ratio is the upper limit of 10%)

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

[0204] In step (5) during the liquid injection and formation process, in step ③: the battery obtained by the treatment is charged to 10% SOC with a current of 0.2C in an environment of 10℃, and then discharged to 2.5V with a current of 0.2C. The charge and discharge are repeated 3 times.

[0205] Example 3 (compared to Example 1, the first charging current is the upper limit of 0.3C)

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

[0207] In step (5) during the liquid injection and formation process, in step ③: the battery obtained by the treatment is charged to 1% SOC with a current of 0.3C in an environment of 10℃, and then discharged to 2.5V with a current of 0.3C, and the charge and discharge are repeated 3 times.

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

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

[0210] In step (5) during the liquid injection and formation process, step ⑤ is: the fourth battery is charged to 1% SOC at 0.01C in an environment of 25°C, then charged to 30% SOC at 0.1C, and then charged to 70% SOC at 0.3C to obtain a highly doped silicon-based anode battery.

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

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

[0213] In step (5) during the liquid injection and formation process, step ⑤ is: the fourth cell is charged to 10% SOC at 0.1C in an environment of 25°C, then charged to 30% SOC at 0.2C, and then charged to 70% SOC at 0.5C to obtain a highly doped silicon-based anode cell.

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

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

[0216] In step (5) during the liquid injection and formation process, step ⑤ is: the fourth battery is charged to 1% SOC with a current of 0.1C in an environment of 25°C, then charged to 30% SOC with a current of 0.2C, and then charged to 100% SOC with a current of 0.5C to obtain a highly doped silicon-based anode battery.

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

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

[0219] In step (5) during the liquid injection and formation process, in step ③: the battery obtained by the treatment is charged to 1% SOC with a current of 0.01C in an environment of 45°C, and then discharged to 2.5V with a current of 0.2C. The charge and discharge are repeated 3 times.

[0220] Example 8 (compared to Example 1, the first temperature is the upper limit of 45°C)

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

[0222] In step (5) during the liquid injection and formation process, in step ③: the battery obtained by the treatment is charged to 1% SOC with a current of 0.2C in an environment of 45°C, and then discharged to 2.5V with a current of 0.2C. The charge and discharge are repeated 3 times.

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

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

[0225] In step (5) during the liquid injection and formation process, step ⑤ is: the fourth battery is charged to 1% SOC at 0.01C in an environment of 45°C, then charged to 30% SOC at 0.2C, and then charged to 70% SOC at 0.5C to obtain a highly doped silicon-based anode battery.

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

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

[0228] In step (5) during the liquid injection and formation process, step ③ is as follows: the second battery is left to stand in a 0°C environment for 3 hours, and then the battery obtained after treatment 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. This charging and discharging is repeated 3 times to obtain the third battery.

[0229] Example 11 (First charging temperature is 15°C lower than the middle)

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

[0231] In step (5) during the liquid injection and formation process, step ③ is as follows: the second battery is left to stand in an environment of 15°C for 3 hours, and then the battery obtained by the treatment is charged to 1% SOC with a current of 0.2C in an environment of 15°C, and then discharged to 2.5V with a current of 0.2C. The charging and discharging is repeated 3 times to obtain the third battery.

[0232] Example 12 (First charging temperature is the middle 22.5℃)

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

[0234] In step (5) during the liquid injection and formation process, step ③ is as follows: the second battery is placed in a 10°C environment for 3 hours, and then the battery obtained 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. This charging and discharging is repeated 3 times to obtain the third battery.

[0235] Example 13 (The 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 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 (The negative electrode active material consists only of silicon-based materials)

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

[0243] In step (2), replace “mix the highly mixed silicon-based anode material with an approximate weight ratio of artificial graphite to silicon-based anode material SiO = 6:4” with “take the anode material SiO”.

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

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

[0246] In step (2), the highly mixed silicon-based anode material with an approximate weight ratio of artificial graphite to silicon-based anode material SiO = 5:5 is mixed evenly.

[0247] Example 17 (The ratio of graphite to silicon-based material in the negative electrode active material is at 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 anode material with a weight ratio of approximately 7:3 of artificial graphite to silicon-based anode material SiO is mixed evenly.

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

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

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

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

[0254] Example 19 (Upper limit of FEC content and lower limit of VC content in the first electrolyte; the opposite in the second electrolyte—the case with the greatest difference in the amount of the two additives)

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

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

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

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

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

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

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

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

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

[0264] Example 22 (Cathode material is not lithium iron phosphate, silicon-based material is silicon carbide)

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

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

[0267] In step (2), the silicon-based anode material SiO is replaced with 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 with tris(trimethylsilyl)phosphate, which accounts for about 7.0% of the weight of the second electrolyte.

[0271] During the liquid injection and formation process, in step ③: the processed battery is charged at 35°C with a current of 0.1C for 40 minutes to obtain the 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 Vitamin C in the first electrolyte)

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

[0277] In step (3), there is no vitamin C 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 Vitamin C 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] II. Performance Testing

[0285] The electrochemical performance of the batteries prepared in each embodiment or comparative example was tested. The specific testing method was as follows: The batteries were charged at a constant current of 1C at 25℃±2℃ until the battery voltage reached 3.65V, then switched to constant voltage charging until the current dropped to 0.05C, at which point charging was stopped. The batteries were then allowed to stand for 1 hour after charging. The batteries were then discharged at a 1C current at 25℃±2℃ until the battery voltage reached 2.5V, at which point discharging was stopped. The capacity retention rate and the full-charge expansion rate of the negative electrode were tested after 50 cycles. The test results are shown in Table 1.

[0286] Table 1 Performance Test Results

[0287]

[0288]

[0289] As can be seen from Table 1, under the same conditions, the embodiments of this application have higher coulombic efficiency and cycle capacity retention rate compared to the comparative examples, and lower expansion rate. Specifically:

[0290] Example 1 exhibits a lower expansion rate and superior capacity retention compared to Examples 2 and 3. The fully charged expansion rate of Example 1 after 50 cycles is significantly lower than that of Examples 7 and 8, and the 50-cycle capacity retention rate is also much better than that of Example 7. The initial efficiency of Example 1 is higher than that of Examples 10-12. This indicates that the pre-formation current should be moderate, the time should not be too long, and a suitable formation temperature and current can effectively alleviate the expansion and cycle stability of the silicon anode. Example 1 has higher coulombic efficiency and capacity retention compared to Examples 4, 5, 6, and 9. Example 1 has the lowest fully charged expansion rate after 50 cycles, indicating that a suitable formation current and temperature are conducive to the formation of SEI on the silicon anode surface. The electrolyte additive combining FEC and VC is beneficial for the formation of a dense and tough SEI film on the silicon anode surface, playing a key role in improving the battery's initial efficiency and cycle capacity retention.

[0291] This indicates that the use of low-temperature, high-current pre-formation can generate a highly flexible organic layer in the SEI film near the negative electrode side, which greatly alleviates the deformation and cracking of the SEI caused by the expansion of the silicon negative electrode during cycling, and prevents new active materials from being exposed and consuming the electrolyte, thus avoiding capacity decay.

[0292] In summary, this application provides a formation method suitable for silicon-based anode batteries. This formation method effectively alleviates the problems of SEI deformation, cracking and regeneration caused by volume expansion during cycling of silicon-based anode batteries, reduces the consumption of active lithium, and improves the coulombic efficiency and cycle stability of the battery.

[0293] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0294] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0295] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for forming a battery, characterized in that, The battery includes a negative electrode active material and an electrolyte. The negative electrode active material includes a silicon-based material, and the electrolyte includes a first electrolyte and a second electrolyte. Both the first electrolyte and the second electrolyte include fluoroethylene carbonate and vinylene carbonate. The formation method includes: The first electrolyte is injected into a dry cell containing the electrolyte to obtain a first cell; The first battery is left to stand for a first time and then cooled to obtain the second battery; The second battery is subjected to a second settling period, and then the first charging and first discharging are repeated at a first temperature to obtain a third battery; the second settling temperature and the first temperature are both 0-15℃; the first charging current is 0.01-0.3C; the discharging current is 0.1-0.3C. The second electrolyte is injected into the third battery, followed by a third settling period to obtain the 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. The second temperature is 20-45℃; the second charging current is 0.01-0.1C, the third charging current is 0.1-0.3C, and the fourth charging current is 0.1-0.5C, with the second charging current, the third charging current, and the fourth charging current increasing sequentially.

2. The formation method according to claim 1, characterized in that, The temperature of the first settling period is comparable to that of the third settling period, and both are greater than the temperature of the second settling period, the first temperature, and the second temperature.

3. The formation method according to claim 1, characterized in that, The temperature for the first settling period and the temperature for the third settling period are both 50-60℃.

4. The formation method according to claim 1, characterized in that, The second temperature is 25-35℃.

5. The formation method according to claim 1, characterized in that, The first charge is brought to 1-10% SOC; and / or, The discharge is carried out to 2.5-2.8V; and / or, The second charge is brought to 1-10% SOC; and / or, The third charge is brought to 10-30% SOC; and / or, The fourth charge is brought to 30-100% SOC.

6. The 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 charge is brought to 1-5% SOC; And / or, The SOC percentage of the second charge, the SOC percentage of the third charge, and the SOC percentage of the fourth charge increase sequentially.

7. The formation method according to claim 1, characterized in that, The first electrolyte has a mass content of 'a' in the electrolyte, and the second electrolyte has a mass content of 'b' in the electrolyte, wherein '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. c1, d1, c2, and d2 satisfy the following: c1>c2 and d1<d2; and / or, The silicon-based material includes at least one of nano-silicon, micron-silicon, porous silicon, amorphous silicon, silicon alloy, silicon oxide, and silicon-carbon composite materials; and / or, The negative electrode active material further includes 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 also includes a separator, which comprises a polyolefin wet-process separator.

8. The formation method according to claim 7, characterized in that, The value of 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 conditions 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 silicon oxide compounds and silicon-carbon composite materials; and / or, Both the first lithium salt and the second lithium salt comprise at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium dioxalate borate; and / or, When the negative electrode active material comprises 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); and / or, The first solvent includes ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate; and / or, The second solvent includes ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate.

9. A method for preparing a secondary battery, characterized in that, The step includes a formation process, wherein the formation method is the formation method as described in any one of claims 1 to 8; Preferably, the method for preparing the secondary battery further includes the steps of preparing a positive electrode sheet and preparing a negative electrode sheet; The steps for preparing the positive electrode sheet include: The positive electrode binder is mixed with the positive electrode solvent to obtain the positive electrode adhesive solution; A positive electrode conductive agent is added to the positive electrode adhesive and dispersed to obtain a positive electrode conductive adhesive; Add positive electrode active material to the positive electrode conductive adhesive and disperse it to obtain a positive electrode slurry; and / or, The steps for preparing the negative electrode sheet include: A first negative electrode conductive agent is added to the negative electrode active material and mixed well. 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 prepared by the method of claim 9.

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