Lithium ion battery with silicon-graphite compounded negative electrode and formation method of lithium ion battery

Abstract

The invention discloses a lithium ion battery with a silicon-graphite compounded negative electrode and a formation method of the lithium ion battery. The formation method comprises the following steps: a first stage: carrying out constant-current charging to 10-20% SOC (State of Charge) by using a current of 0.05-0.1 C at the temperature of 30-60 DEG C; in the second stage, constant-current charging is carried out to 50%-70% SOC with the current of 0.1 C to 0.2 C, and the temperature is 30 DEG C to 60 DEG C; in the third stage, constant-voltage charging treatment is carried out by using a fixed potential of 3.8-4.2 V, the treatment time is 2-5 hours, and the temperature is 30-60 DEG C; and in the fourth stage, the current of 0.2-0.5 C is used for constant-current discharging to 70-80% SOC, and the temperature is 30-60 DEG C. The SEI film structure stability of the silicon-graphite compound negative electrode can be improved, so that the first effect and the cycle performance of a battery cell are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium-ion battery with a silicon-graphite composite negative electrode and its formation method. Background Technology

[0002] The biggest problem currently hindering the development of lithium-ion batteries is battery capacity, especially the capacity of the negative electrode material. Silicon, due to its high theoretical specific capacity (4200 mAh / g) and low lithium intercalation potential (0.37 mV Li / Li), is a suitable candidate for lithium-ion batteries. + Silicon, with its vast reserves on Earth and mature production processes, is increasingly attracting the attention of researchers in anode materials. However, the drastic volume changes during lithium insertion and extraction not only cause anode material collapse and electrode structure instability, but more importantly, they lead to the continuous rupture and regeneration of the SEI film on the anode surface, resulting in a sharp decline in its electrochemical performance. The main stage for SEI film formation in battery production is the formation stage. How to form a stable, structurally stable, uniform, and dense SEI film on the silicon surface during this stage, thereby reducing the rupture and regeneration of the SEI film during lithium insertion and extraction, is of great significance for improving battery performance.

[0003] Traditional graphite anode formation processes are relatively mature, but there are still many problems to be solved in the formation process of silicon anodes. First, the lithium intercalation process of silicon anodes is an "alloying" process, and its volume expands by about 400% after lithium intercalation. During the lithium intercalation and deintercalation process, the drastic volume change causes the SEI film to break and continuously regenerate, resulting in poor battery cycle performance and low coulombic efficiency. Studies have shown that compared to the high electronic conductivity and ion mobility of graphite anodes, the semiconductor properties of silicon result in its electronic conductivity and ion mobility being several orders of magnitude lower than those of graphite anodes. Therefore, in the early stages of formation, lithium ions preferentially intercalate into the graphite interlayer, forming an SEI film on the graphite surface, and only later in the formation process do they intercalate into silicon and form an SEI film on its surface. This results in insufficient and loose formation of the SEI film on the silicon surface.

[0004] In order to overcome the above-mentioned shortcomings of the existing technology, the present invention is thus developed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a lithium-ion battery with a silicon-graphite composite negative electrode and its formation method. This invention can improve the SEI film structure stability of the silicon-graphite composite negative electrode, thereby improving the cell's initial efficiency and cycle performance.

[0006] The technical solution of this invention is:

[0007] This application relates to a formation method for a lithium-ion battery, the lithium-ion battery having a silicon-graphite composite negative electrode, the formation method comprising the following steps:

[0008] (1) First stage: Use a constant current of 0.05-0.1C to charge to 10-20% SOC, temperature 30-60℃;

[0009] (2) Second stage: Charge to 50-70% SOC using a constant current of 0.1-0.2C at a temperature of 30-60℃;

[0010] (3) Third stage: constant voltage charging treatment with a fixed potential of 3.8-4.2V for 2-5 hours at a temperature of 30-60℃;

[0011] (4) Fourth stage: Discharge at a constant current of 0.2-0.5C to 70-80% SOC, at a temperature of 30-60℃.

[0012] In the first stage of formation, a small constant current charging of 0.05C-0.1C is used to ensure the integrity of the SEI film formation. The selection of the constant potential parameters in the third stage is based on the potential of the SEI film formation on the silicon anode surface. A suitable potential is conducive to the formation of a denser SEI film on the silicon anode surface. This constant potential maintenance step ensures the integrity and density of the SEI film formation on the silicon anode surface, which has a certain limiting effect on the volume change of the silicon anode during the lithium insertion / extraction process.

[0013] Preferably, the lithium-ion battery is a pouch-type lithium-ion battery.

[0014] Preferably, the electrolyte-filled cells need to be baked and allowed to stand before formation, under the following conditions: baked and allowed to stand at 40-50°C for 24-72 hours.

[0015] Preferably, the negative electrode active material of the silicon-graphite composite negative electrode is graphite and silicon material, wherein the silicon material is silicon oxide and / or silicon carbon.

[0016] Preferably, the mass of Si accounts for 10-30% of the total mass of the graphite and silicon materials.

[0017] Preferably, the positive electrode active material of the lithium-ion battery is a high-nickel ternary positive electrode material, with a nickel molar content of 80%-95%.

[0018] Preferably, the high-nickel ternary cathode material is an 8-series and / or 9-series high-nickel ternary cathode material.

[0019] Preferably, the temperature of the third stage is higher than the temperature of any of the first, second, and fourth stages.

[0020] Preferably, the temperature of the third stage is 5°C higher than the temperature of the first stage, the temperature of the third stage is 5°C higher than the temperature of the second stage, and the temperature of the third stage is 5°C higher than the temperature of the fourth stage.

[0021] The present invention also relates to a lithium-ion battery, which is prepared by the above-described formation method.

[0022] Preferably, after the formation process, the formed cells need to be resealed and capacity tested to complete the battery manufacturing.

[0023] The beneficial effects of this invention are:

[0024] (1) The third stage of the formation method of the present invention adopts a constant potential maintenance method to achieve full wetting of electrolyte, deep lithium intercalation of silicon and graphite in the formation stage, activate the electrode to reduce polarization in the subsequent charging and discharging process, and fully carry out the side reaction to form a strong SEI film, thereby improving the overall performance of the cell.

[0025] (2) The present invention uses a constant potential charging process to ensure that the SEI film on the surface of the silicon anode is fully formed in the later stage of formation. In order to make the formed SEI film more compact and eliminate the SEI film cracking caused by silicon volume change, the influence of different potentials on the properties of the SEI film was investigated and suitable formation parameters were obtained. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0027] In the following examples and comparative examples, NCM811 and NCM90505 used to prepare the positive electrode were purchased from Rongbai Technology, graphite used in the negative electrode was purchased from Shenzhen BTR BFC-Q4, silicon carbide used in the negative electrode was purchased from Shenzhen BTR BAS-1, and the carbonate-based electrolyte containing LiPF6 was purchased from Shenzhen Capchem LBC421B33.

[0028] Unless otherwise specified, all other materials are commercially available products.

[0029] Example 1

[0030] (1) Battery system: Soft-pack lithium-ion battery (capacity: 5Ah)

[0031] Among them, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811);

[0032] Negative electrode active material: artificial graphite + SiO2 (silicon mass percentage: 15%);

[0033] Electrolyte: Carbonate-based electrolyte containing LiPF6.

[0034] The battery manufacturing process is as follows:

[0035] Preparation of the positive electrode sheet: The positive electrode active material (NCM811), conductive carbon black (SP) and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1.5:1.5; N-methylpyrrolidone (NMP) solvent is added and stirred until a uniform slurry is formed; the slurry is coated on aluminum foil (12μm thick) with a coating density of 20mg / cm²; then dried at 85℃, cold-pressed (compacted density 3.4g / cm³), and cut to obtain the positive electrode sheet.

[0036] Fabrication of the negative electrode sheet: The negative electrode active material (artificial graphite BFC-Q4 + SiO2, of which silicon accounts for 15% by mass), styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener are mixed in a mass ratio of 96.5:2:1.5; deionized water is added and stirred until a uniform slurry is formed; the slurry is coated on copper foil (thickness 8μm) with a coating density of 12mg / cm²; after drying at 90℃, cold pressing (compacted density 1.6g / cm³), it is slit to obtain the negative electrode sheet.

[0037] The positive electrode, separator, and negative electrode are assembled to form a soft-pack lithium-ion battery cell. The cell is placed in an outer package, filled with electrolyte, sealed, and then baked at 45°C and left to stand for 48 hours.

[0038] (2) Chemical formation process

[0039] First stage: Constant current charging (CC), current 0.08C (0.4A), charging to 15% SOC, temperature 45℃;

[0040] Second stage: Constant current charging (CC), current 0.15C (0.75A), charging to 65% SOC, temperature 45℃;

[0041] Third stage: Constant voltage charging (CV), constant voltage 4.0V (vs. Li / Li) + ), constant pressure for 4 hours, temperature 50℃ (time ends);

[0042] Fourth stage: Constant current discharge (DCC), current 0.3C (1.5A), discharge to 75% SOC, temperature 45℃.

[0043] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0044] Results: 88% initial efficiency, >85% capacity retention after 1000 cycles, low DCR at room temperature 1C discharge, high capacity recovery after high temperature storage (60℃ / 7d), and <8% thickness expansion rate.

[0045] Example 2

[0046] (1) Battery system: pouch lithium-ion battery (capacity: 3Ah)

[0047] Among them, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811);

[0048] Negative electrode active material: artificial graphite + SiC (silicon-carbon, silicon mass percentage: 10%);

[0049] Electrolyte: Carbonate-based electrolyte containing LiPF6.

[0050] The positive and negative electrode sheets were prepared according to the battery manufacturing process in Example 1, with the only difference being that the silicon material in the negative electrode active material was silicon-carbon, and the silicon mass ratio was 10%. Then, the positive electrode sheet, separator, and negative electrode sheet were assembled to form a soft-pack lithium-ion battery cell. The cell was placed in an outer packaging, filled with electrolyte, sealed, and then baked at 40°C and left to stand for 72 hours.

[0051] (2) Chemical formation process

[0052] First stage: Constant current charging (CC), current 0.05C (0.15A), charging to 15% SOC, temperature 40℃;

[0053] Second stage: Constant current charging (CC), current 0.1C (0.3A), charging to 60% SOC, temperature 40℃;

[0054] Third stage: Constant voltage charging (CV), constant voltage 3.8V (vs. Li / Li) + The constant pressure time is 5 hours, and the temperature is 45℃ (time ends).

[0055] Fourth stage: Constant current discharge (DCC), current 0.2C (0.6A), discharge to 70% SOC, temperature 40℃.

[0056] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0057] Effects: 90% initial efficacy, excellent cycle stability, and good low-temperature performance.

[0058] Example 3

[0059] (1) Battery system: Soft-pack lithium-ion battery (capacity: 4.5Ah)

[0060] Among them, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811);

[0061] Negative electrode active material: artificial graphite + SiO2 (silicon mass percentage: 25%);

[0062] Electrolyte: Carbonate-based electrolyte containing LiPF6.

[0063] The positive and negative electrode sheets were prepared according to the battery manufacturing process in Example 1, with the only difference being that the silicon mass ratio in the negative electrode active material was 25%. The positive electrode sheet, separator, and negative electrode sheet were then assembled to form a soft-pack lithium-ion battery cell. The cell was placed in an outer packaging, filled with electrolyte, sealed, and then baked at 50°C for 24 hours.

[0064] (2) Chemical formation process

[0065] First stage: Constant current charging (CC), current 0.1C (0.45A), charging to 15% SOC, temperature 50℃;

[0066] Second stage: Constant current charging (CC), current 0.2C (0.9A), charging to 70% SOC, temperature 50℃;

[0067] Third stage: Constant voltage charging (CV), constant voltage 4.2V (vs. Li / Li) + ), constant pressure for 2 hours, temperature 55℃ (time ends);

[0068] Fourth stage: Constant current discharge (DCC), discharge to 80% SOC with a current of 0.5C (2.25A) at a temperature of 50℃.

[0069] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0070] Results: For systems with high silicon content, a higher voltage is used to promote deep lithium intercalation and film formation reactions, with a slightly shorter reaction time. First-time efficiency is 85%, cycle life is good, and high-rate performance (2C discharge retention >95%) is outstanding.

[0071] Example 4

[0072] (1) Battery system: pouch lithium-ion battery (capacity: 6Ah)

[0073] Among them, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811);

[0074] Negative electrode active material: artificial graphite + SiC (silicon mass percentage: 20%);

[0075] Electrolyte: Carbonate-based electrolyte containing LiPF6.

[0076] The positive and negative electrode sheets were prepared according to the battery manufacturing process in Example 1, with the only difference being that the silicon material in the negative electrode active material was silicon-carbon, and the silicon mass ratio was 20%. Then, the positive electrode sheet, separator, and negative electrode sheet were assembled to form a soft-pack lithium-ion battery cell. The cell was placed in an outer packaging, filled with electrolyte, sealed, and then baked at 45°C and left to stand for 36 hours.

[0077] (2) Chemical formation process

[0078] First stage: Constant current charging (CC), current 0.07C (0.42A), charging to 15% SOC, temperature 40℃;

[0079] Second stage: Constant current charging (CC), current 0.18C (1.08A), charging to 68% SOC, temperature 40℃;

[0080] Third stage: Constant voltage charging (CV), constant voltage 4.1V (vs. Li / Li) + ), constant pressure for 3 hours, temperature 45℃ (time ends);

[0081] Fourth stage: Constant current discharge (DCC), discharge to 78% SOC with a current of 0.4C (2.4A) at a temperature of 40℃.

[0082] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0083] Effects: 87% initial efficiency, excellent cycle life, slow resistance growth, and low gas production.

[0084] Example 5

[0085] (1) Battery system: Soft-pack lithium-ion battery (capacity: 5.5Ah)

[0086] Among them, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 (NCM811);

[0087] Negative electrode active material: artificial graphite + SiO2 (silicon mass percentage: 18%);

[0088] Electrolyte: Carbonate-based electrolyte containing LiPF6.

[0089] The positive and negative electrode sheets were prepared according to the battery manufacturing process in Example 1, with the only difference being that the silicon mass ratio in the negative electrode active material was 18%. The positive electrode sheet, separator, and negative electrode sheet were then assembled to form a soft-pack lithium-ion battery cell. The cell was placed in an outer packaging, filled with electrolyte, sealed, and then baked at 48°C for 60 hours.

[0090] (2) Chemical formation process

[0091] First stage: Constant current charging (CC), current 0.09C (0.495A), charging to 15% SOC, temperature 48℃;

[0092] Second stage: Constant current charging (CC), current 0.16C (0.88A), charging to 67% SOC, temperature 48℃;

[0093] Third stage: Constant voltage charging (CV), constant voltage 3.9V (vs. Li / Li) + The constant pressure time was 4.5 hours, and the temperature was 48℃ (time ended).

[0094] Fourth stage: Constant current discharge (DCC), current 0.35C (1.925A), discharge to 76% SOC, temperature 48℃.

[0095] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0096] Results: Using a slightly lower voltage but a longer constant voltage period, the SEI film achieves full growth and stability. First-time efficiency is 88.5%, cycle life is excellent, and the SEI film exhibits low and stable impedance.

[0097] Example 6

[0098] (1) Battery system: pouch lithium-ion battery (capacity: 4Ah)

[0099] Among them, the positive electrode active material is LiNi. 0.9 Co 0.05 Mn 0.05 O2 (NCM90505);

[0100] Negative electrode active material: artificial graphite + SiO2 (silicon mass percentage: 12%);

[0101] Electrolyte: Carbonate-based electrolyte containing LiPF6.

[0102] The positive and negative electrode sheets were prepared according to the battery manufacturing process in Example 1, with the only difference being that the positive active material used in this example is NCM90505, and the silicon content in the negative active material is 12% by mass. Then, the positive electrode sheet, separator, and negative electrode sheet were assembled to form a soft-pack lithium-ion battery cell. The cell was placed in an outer packaging, filled with electrolyte, sealed, and then baked at 42°C and left to stand for 54 hours.

[0103] (2) Chemical formation process

[0104] First stage: Constant current charging (CC), current 0.06C (0.24A), charging to 15% SOC, temperature 42℃;

[0105] Second stage: Constant current charging (CC), current 0.12C (0.48A), charging to 62% SOC, temperature 42℃;

[0106] Third stage: Constant voltage charging (CV), constant voltage 4.05V (vs. Li / Li) + Constant pressure for 3.5 hours, temperature 47℃ (time ends);

[0107] Note: The voltage is selected to be slightly lower than 4.2V to ensure the stability of the high-nickel cathode;

[0108] Fourth stage: Constant current discharge (DCC), current 0.25C (1.0A), discharge to 72% SOC, temperature 42℃.

[0109] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0110] Results: For higher nickel cathodes (more sensitive to high voltage), a slightly conservative voltage is used. Initial efficiency is 89%, cycle life is good, and high-temperature storage performance is excellent (capacity recovery >98% at 60℃ / 7d).

[0111] Example 7

[0112] (1) Battery system: Soft-pack lithium-ion battery (capacity: 5Ah) - Same as the system in Example 1

[0113] The raw materials and manufacturing process of this battery system are the same as those of the battery system in Example 1.

[0114] (2) Chemical formation process

[0115] First stage: Constant current charging (CC), current 0.08C (0.4A), charging to 15% SOC, temperature 45℃;

[0116] Second stage: Constant current charging (CC), current 0.15C (0.75A), charging to 65% SOC, temperature 45℃;

[0117] Third stage: Constant voltage charging (CV), constant voltage 3.8V, constant voltage time 4 hours, temperature 50℃ (time cut-off);

[0118] Fourth stage: Constant current discharge (DCC), current 0.3C (1.5A), discharge to 75% SOC, temperature 45℃.

[0119] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0120] Results: Compared to Example 1 (4.0V), the initial efficiency was slightly lower (86%), the cycle life was comparable or slightly better (due to a denser SEI), but the rate performance was slightly inferior (due to differences in lithium insertion depth or SEI ion conductivity). This demonstrates that 3.8V is effective within the range, but not optimal.

[0121] Example 8

[0122] (1) Battery system: pouch lithium-ion battery (capacity: 5Ah) - same as the system in Example 1.

[0123] The raw materials and manufacturing process of this battery system are the same as those of the battery system in Example 1.

[0124] (2) Chemical formation process

[0125] First stage: Constant current charging (CC), current 0.08C (0.4A), charging to 15% SOC, temperature 45℃;

[0126] Second stage: Constant current charging (CC), current 0.15C (0.75A), charging to 65% SOC, temperature 45℃;

[0127] Third stage: Constant voltage charging (CV), constant voltage 4.2V (vs. Li / Li) + ), constant pressure for 4 hours, temperature 50℃ (time ends);

[0128] Fourth stage: Constant current discharge (DCC), current 0.3C (1.5A), discharge to 75% SOC, temperature 45℃.

[0129] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0130] Results: Compared to Example 1 (4.0V), the initial efficiency was 88%, and the initial cycling performance was comparable, but long-term cycling stability (especially at high temperatures) and gas production need to be monitored (slightly higher than the 4.0V scheme). This demonstrates that 4.2V is effective within the range, but careful monitoring of the positive electrode side reactions is necessary.

[0131] Comparative Example 1 (Conventional Constant Current Formation)

[0132] (1) Battery system: pouch lithium-ion battery (capacity: 5Ah) - same as the system in Example 1.

[0133] The raw materials and manufacturing process of this battery system are the same as those of the battery system in Example 1.

[0134] (2) Chemical formation process:

[0135] Phase 1: Constant current charging (CC), 0.1C (0.45A) charging to 100% SOC, temperature 45℃;

[0136] Phase 2: Constant current discharge (DCC), current 0.3C (1.5A), discharge to 80% SOC, temperature 45℃.

[0137] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0138] Comparative Example 2 (without constant voltage charging stage)

[0139] (1) Battery system: pouch lithium-ion battery (capacity: 5Ah) - same as the system in Example 1.

[0140] The raw materials and manufacturing process of this battery system are the same as those of the battery system in Example 1.

[0141] (2) Chemical formation process:

[0142] Phase 1: Constant current charging (CC), current 0.08C (0.4A), charging to 15% SOC, temperature 45℃;

[0143] Phase 2: Constant current charging (CC), current 0.15C (0.75A), charging to 65% SOC, temperature 45℃;

[0144] Phase 3: Constant current discharge (DCC), current 0.3C (1.5A), discharge to 5% SOC, temperature 45℃.

[0145] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0146] Comparative Example 3 (Insufficient constant voltage time during the constant voltage charging stage)

[0147] (1) Battery system: pouch lithium-ion battery (capacity: 5Ah) - same as the system in Example 1.

[0148] The raw materials and manufacturing process of this battery system are the same as those of the battery system in Example 1.

[0149] (2) Process: Same as Example 1, but the constant pressure time in the third stage is only 0.5 hours.

[0150] First stage: Constant current charging (CC), current 0.08C (0.4A), charging to 15% SOC, temperature 45℃;

[0151] Second stage: Constant current charging (CC), current 0.15C (0.75A), charging to 65% SOC, temperature 45℃;

[0152] Third stage: Constant voltage charging (CV), constant voltage 4.0V (vs. Li / Li) + Constant pressure for 0.5 hours, temperature 50℃ (time ends);

[0153] Fourth stage: Constant current discharge (DCC), current 0.3C (1.5A), discharge to 75% SOC, temperature 45℃.

[0154] (3) Subsequent processes: After formation, the cells undergo secondary sealing, aging and capacity testing.

[0155] The key formation process parameters and performance comparisons of each embodiment and comparative example are shown in Table 1 below.

[0156] Table 1

[0157]

[0158] Comparative Example 1 uses a conventional constant current formation process, and the corresponding first efficiency is 78%.

[0159] The formation process of Comparative Example 2 lacked a critical constant potential stabilization period, resulting in poor SEI film quality (insufficiently dense and tough); insufficient / uniform side reactions; inadequate activation of the silicon anode; and significantly inferior cycle performance compared to the other examples, with a first-efficiency of 75%.

[0160] Although Comparative Example 3 has a constant voltage charging stage, the constant voltage time is too short to achieve the purpose of deep lithium intercalation and stable SEI film, and the effect is close to that of Comparative Example 2.

[0161] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method of forming a lithium ion battery, characterized by, The lithium ion battery has a silicon-graphite composite negative electrode, and the formation method comprises the following steps: (1) First stage: constant current charging to 10-20% SOC using a current of 0.05-0.1C, temperature 30-60℃; (2) Second stage: constant current charging to 50-70% SOC using a current of 0.1-0.2C, temperature 30-60℃; (3) Third stage: constant voltage charging treatment using a fixed potential of 3.8-4.2V, treatment time 2-5h, temperature 30-60℃; (4) Fourth stage: constant current discharging to 70-80% SOC using a current of 0.2-0.5C, temperature 30-60℃.

2. The formation method according to claim 1, characterized by, The lithium ion battery is a soft-pack lithium ion battery.

3. The formation method according to claim 2, characterized by, The liquid injection cell needs to be baked and left to stand before formation, with the conditions being: baking and leaving to stand at 40-50℃ for 24-72h.

4. The formation method of claim 1, wherein, The negative active material of the silicon-graphite composite negative electrode is graphite and silicon material, and the silicon material is silicon oxide and / or silicon carbon.

5. The formation method according to claim 4, characterized by, The mass of Si accounts for 10-30% of the total mass of the graphite and silicon material.

6. The formation method of claim 1, wherein, The positive active material of the lithium ion battery is a high-nickel ternary positive material, and the molar content of nickel is 80-95%.

7. The formation method according to claim 6, characterized by, The high-nickel ternary positive material is an 8-series and / or 9-series high-nickel ternary positive material.

8. The formation method of claim 1, wherein, The temperature of the third stage is higher than that of any of the first, second and fourth stages.

9. The formation method according to claim 8, characterized by, The temperature of the third stage is 5℃ higher than that of the first stage, the temperature of the third stage is 5℃ higher than that of the second stage, and the temperature of the third stage is 5℃ higher than that of the fourth stage.

10. A lithium-ion battery, characterized by, The formation method is prepared by any one of claims 1-9.

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