Lithium supplement battery formation method and lithium ion battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a lithium ion battery formation method and a lithium ion battery. The formation method comprises the following steps: S1, injecting an electrolyte into a positive electrode lithium supplementing battery to obtain a lithium supplementing battery core, and fully standing; s2, a multi-stage charging negative pressure formation process; comprising the following steps: S21) forming an SE I film; s22) a lithium supplement agent activation pre-stage; s23) a lithium supplement agent activation stage; and S24) adjusting the soc stage, and discharging to the cut-off capacity. According to the method, the standing time is prolonged after the lithium supplementing agent is activated and fully charged by changing the current and the standing time in different stages, the reaction time is provided for the residual side reaction of the lithium supplementing agent in the stage, complete exhaust of the lithium supplementing agent in the formation process is facilitated, and the formation efficiency is improved. Therefore, interface black spots caused by high-temperature standing gas production after formation of the positive electrode lithium supplement battery cell and secondary gas production after capacity grading are improved.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and particularly relates to a method for forming a lithium-compensated lithium battery and a lithium-ion battery. Background Art

[0002] During the first charging process of a lithium-ion battery, the organic electrolyte will be reductively decomposed on the surface of the negative electrode such as graphite to form a solid electrolyte interphase (SEI) film, permanently consuming a large amount of lithium from the positive electrode; moreover, side reactions occur during the first lithium intercalation process, which will also consume active lithium, resulting in irreversible capacity loss of the battery and affecting the first cycle efficiency and cycle life of the battery. The lithium compensation technology for lithium-ion batteries is an important means to improve the cycle life of the battery. By pre-lithiation, lithium is added to the battery interior before the lithium battery works to supplement lithium ions, so as to offset the irreversible lithium loss, thereby improving the total capacity and cycle life of the battery.

[0003] The method of lithium compensation can be through positive electrode lithium compensation or negative electrode lithium compensation. The negative electrode lithium compensation is restricted by the safety risks and process difficulties of metallic lithium itself and cannot be applied on a large scale. Positive electrode lithium compensation can directly add lithium-rich additives or use lithium-rich positive electrode materials during the homogenization process of the positive electrode slurry, without additional process improvement and with low cost. Therefore, the positive electrode lithium compensation technology is more suitable for the current lithium-ion battery manufacturing process. However, the reaction range of common lithium-rich compounds added to the positive electrode is mostly between 3.5 and 4.0 V, and gas will be generated in this voltage range. Therefore, the forming process of the lithium-compensated lithium battery is also different from that of the battery without adding a lithium compensation agent. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings in the prior art and provide a method for forming a lithium-compensated lithium battery and a lithium-ion battery.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for forming a lithium-compensated lithium battery includes the following steps: S1. First, inject electrolyte into the positive electrode lithium-compensated lithium battery to obtain a lithium-compensated battery core, and fully stand still;

[0007] S2. A multi-stage charging negative pressure forming process; including: S21) SEI film formation stage; S22) pre-activation stage of the lithium compensation agent; S23) activation stage of the lithium compensation agent; S24) adjust the soc stage, and discharge to the cut-off capacity.

[0008] Preferably, the standing still time between each of S21)-S23) is 2-5 min, preferably 5 min; the standing still time between S23)-S24) is 1-2 h, preferably 1 h. The extension of this standing still time can allow the residual side reactions of the lithium compensation agent to react further sufficiently, greatly improving the gas generation during the subsequent high-temperature aging process after forming.

[0009] S21) includes the following steps: First, charge the lithium-compensating battery cell at a first current I 1 at a constant current for a first duration t 1 , to obtain a battery cell in a first state, with a negative pressure of 20 - 40 kPa; then charge the battery cell in the first state at a second current I 2 at a constant current for a second duration t 2 , to obtain a battery cell in a second state, with a negative pressure of 60 - 90 kPa. Charging with a small current at this stage is beneficial to forming a dense SEI film, and stepwise adjusting the negative pressure is more conducive to gas evolution and discharge.

[0010] Preferably, I 2 > I 1 ; preferably, I 1 = 0.03 - 0.06C; I 2 = 0.1 - 0.2C; preferably, t 1 = 0.4 - 1 h; t 2 = 0.5 - 2 h.

[0011] S22) Charge with a current greater than I 2 until before the lithium-compensating agent reaction platform;

[0012] Specifically, it includes the following steps: Charge the battery cell in the second state at a third current I 3 at a constant current for a third duration t 3 , to obtain a battery cell in a third state, with a negative pressure of 20 - 60 kPa;

[0013] Charge the battery cell in the third state at a fourth current I 4 at a constant current until a preset voltage, to obtain a battery cell in a fourth state, with a negative pressure of 20 - 60 kPa;

[0014] Using a relatively large current at this stage can reduce the entire formation process time, and reducing the negative pressure value can effectively improve lithium plating of the battery.

[0015] Preferably, I 4 ≥ I 3 ≥ I 2 ; preferably, I 3 = 0.25 - 0.35C; I 4 = 0.4 - 0.6C; t 3 = 0.3 - 1 h; preferably, the cut-off voltage is 3.5 - 3.7V.

[0016] S23) Charge with a current less than I 1 within the lithium-compensating agent reaction platform range;

[0017] Specifically, it includes the following steps: Charge the battery cell in the fourth state at a fifth current I 5 at a constant current until a preset voltage, to obtain a battery cell in a fifth state, with a negative pressure of 20 - 60 kPa;

[0018] With the sixth current I 6 Constant current charge the battery cell in the fifth state to the full charge voltage to obtain a battery cell in the sixth state, with a negative pressure of 20 - 60 kPa;

[0019] With the seventh current I 7 Constant current charge the battery cell in the sixth state to the full charge voltage to obtain a battery cell in the seventh state, with a negative pressure of 20 - 60 kPa.

[0020] This stage is the lithium supplement agent reaction stage. Using a small current is beneficial for the full reaction of the lithium supplement agent and provides relatively sufficient time for negative pressure exhaust.

[0021] Preferably, I 7 <I 6 ≤I 5 ≤I 1 , preferably, I 5 =0.02 - 0.05C, I 6 =0.02 - 0.05C, I 7 =0.01 - 0.03C; preferably, the preset voltage is 3.7 - 3.9V; the full charge voltage is 3.9 - 4.2V.

[0022] S24) includes the following steps: With the eighth current I 8 Constant current discharge the battery cell in the seventh state to 20 - 80% soc of the capacity; preferably, I 8 =0.4 - 0.6C.

[0023] Preferably, the positive active material of the lithium - supplemented battery is lithium iron phosphate and a lithium supplement agent, and the lithium supplement agent is one or a combination of two of Li 5 FeO 4 , Li 2 N iO;

[0024] Preferably, the static temperature in step S1 is 25 - 50°C, and the static time is 12 - 48h;

[0025] Preferably, the formation temperature in step S2 is 25 - 50°C.

[0026] The present invention also includes a battery obtained by the lithium - supplemented battery formation method described above.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] The lithium - supplementing lithium - ion battery formation method of the present invention combines the characteristics of adding a lithium - supplementing agent to the positive electrode and performs a multi - stage charging and negative - pressure formation process, including: S21) SE I film formation stage; S22) pre - activation stage of the lithium - supplementing agent; S23) activation stage of the lithium - supplementing agent; S24) soc adjustment stage, discharging to the cut - off capacity. By changing the current and standing time in different stages, the standing time is extended after the lithium - supplementing agent is activated and fully charged. This stage provides reaction time for the residual side reactions of the lithium - supplementing agent, which is beneficial to the complete exhaust of the lithium - supplementing agent during the formation process, thus improving the interface black spots caused by gas generation during high - temperature standing and re - gas generation after grading of the positive - electrode lithium - supplementing lithium - ion battery after formation.

[0029] As a preferred form, the magnitude of the current is adjusted in combination with the gas - generation characteristics during the formation process of the lithium - supplementing lithium - ion battery. A relatively small current is used in the stages with more gas generation (SE I film formation stage and the stage where the lithium - supplementing agent functions), a relatively large current is used before activating the lithium - supplementing agent, and on the basis of good interface and the function of the lithium - supplementing agent, the formation time is shortened. Brief Description of the Drawings

[0030] Figure 1 It is the basic formation flow chart of the lithium - supplementing lithium - ion battery formation method of the present invention.

[0031] Figure 2 It is the interface disassembly diagram after high - temperature aging of Example 1 and Comparative Example 1. Detailed Description of the Embodiments

[0032] In order to enable those skilled in the art of the present technology to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the drawings and the best embodiments.

[0033] Embodiment

[0034] A lithium - iron phosphate battery using a positive electrode with lithium - iron phosphate + lithium - supplementing agent (where the lithium - supplementing agent is Li 5 FeO 4 、L i 2 Ni O, and the mass ratio of the lithium - supplementing agent is less than 5%) as the main active material and graphite as the main active material of the negative electrode is used as the example battery. The lithium - ion battery (lithium - iron phosphate battery) is formed at 45°C according to the following steps (the basic formation process Figure 1 is shown):

[0035] S1: First, the electrolyte is injected into the positive - electrode lithium - supplementing lithium - ion battery to obtain a lithium - supplementing lithium - ion battery cell, and it is fully left standing. The standing temperature is 25 - 50°C, which can be 25°C, 30°C, 45°C, 50°C; the standing time is 12 - 48h; it can be adjusted to 24h, 30h, 42h, 48h;

[0036] S2: Place the battery on the formation cabinet after standing still. The formation temperature is 25 - 50 °C, which can be 25 °C, 30 °C, 45 °C, 50 °C, and perform a multi-stage charging negative pressure formation process, including:

[0037] S21) SE I film formation stage; including the following steps: First, with a first current I 1 Constant current charge the lithium supplement battery cell for a first duration t 1 , to obtain a battery cell in the first state, with a negative pressure of 20 - 40 kPa; specifically, it can be 20 KPa, 30 KPa, 40 KPa; with a second current I 2 Constant current charge the battery cell in the first state for a second duration t 2 , to obtain a battery cell in the second state, with a negative pressure of 60 - 90 kPa, specifically, it can be 60 KPa, 70 KPa, 80 KPa, 90 KPa.

[0038] Charging with a small current in this stage is beneficial to form a dense SE I film, and stepwise adjusting the negative pressure is more conducive to gas production and discharge.

[0039] Preferably, I 2 > I 1 ; Preferably, I 1 = 0.03 - 0.06C, specifically, it can be 0.03C, 0.05C, 0.06C; I 2 = 0.1 - 0.2C, specifically, it can be 0.01C, 0.15C, 0.2C;

[0040] Preferably, t 1 = 0.4 - 1 h, specifically, it can be 0.4 h, 0.5 h, 1 h; t 2 = 0.5 - 2 h, specifically, it can be 0.5 h, 1 h, 2 h.

[0041] S22) Pre-activation stage of the lithium supplement agent; Charge with a current greater than I 2 until before the reaction platform of the lithium supplement agent;

[0042] Specifically, it includes the following steps: With a third current I 3 Constant current charge the battery cell in the second state for a third duration t 3 , to obtain a battery cell in the third state, with a negative pressure of 20 - 60 kPa, specifically, it can be 20 KPa, 40 KPa, 60 KPa;

[0043] With a fourth current I 4 Constant current charge the battery cell in the third state to a preset voltage, to obtain a battery cell in the fourth state, with a negative pressure of 20 - 60 kPa, specifically, it can be 20 KPa, 40 KPa, 60 KPa;

[0044] In this stage, using a relatively large current can reduce the entire formation process time, and reducing the negative pressure value can effectively improve the lithium plating of the battery.

[0045] Preferably, I 4 ≥I 3 ≥I 2 ; Preferably, I 3 = 0.25 - 0.35C; specifically, it can be 0.25C, 0.3C, 0.35C; I 4 = 0.4 - 0.6C, specifically, it can be 0.4C, 0.5C, 0.6C;

[0046] t 3 = 0.3 - 1h; specifically, it can be 0.3h, 0.5h, 1h;

[0047] Preferably, the cut-off voltage is 3.5 - 3.7V, specifically, it can be 3.5V, 3.65V, 3.7V.

[0048] S23) Lithium supplement agent activation stage; charging at a current less than I 1 within the lithium supplement agent reaction platform range;

[0049] Specifically, it includes the following steps: charging the battery cell in the fourth state at a constant current with the fifth current I 5 to a preset voltage to obtain a battery cell in the fifth state, with a negative pressure of 20 - 60 kPa, specifically, it can be 20 Kpa, 40 Kpa, 60 Kpa;

[0050] charging the battery cell in the fifth state at a constant current with the sixth current I 6 to a full charge voltage to obtain a battery cell in the sixth state, with a negative pressure of 20 - 60 kPa, specifically, it can be 20 Kpa, 40 Kpa, 60 Kpa;

[0051] charging the battery cell in the sixth state at a constant current with the seventh current I 7 to a full charge voltage to obtain a battery cell in the seventh state, with a negative pressure of 20 - 60 kPa, specifically, it can be 20 Kpa, 40 Kpa, 60 Kpa.

[0052] This stage is the lithium supplement agent reaction stage. Using a small current is beneficial for the full reaction of the lithium supplement agent and provides relatively sufficient time for negative pressure exhaust.

[0053] Preferably, I 7 <I 6 ≤I 5 ≤I 1 , Preferably, I 5 = 0.02 - 0.05C, specifically, it can be 0.02C, 0.045C, 0.05C; I 6= 0.02 - 0.05C, specifically it can be 0.02C, 0.045C, 0.05C; I 7 = 0.01 - 0.03C; specifically it can be 0.01C, 0.015C, 0.03C; preferably, the preset voltage is 3.7 - 3.9V, specifically it can be 3.7V, 3.8V or 3.9V; the full charge voltage is 3.9 - 4.2V, specifically it can be 3.9V, 4.1V or 4.2V.

[0054] S24) Adjust the soc stage and discharge to the cut-off capacity. At the eighth current I 8 Constant current discharge the battery cells in the seventh state to 20 - 80% soc of the capacity; specifically it can be 20%, 40%, 50%, 60%, 70%, 80%; preferably, I 8 = 0.4 - 0.6C, specifically it can be 0.4C, 0.5C, 0.6C.

[0055] The following will be described with specific preferred embodiments

[0056] Example 1

[0057] A method for forming a compensated lithium battery includes the following steps:

[0058] S1: First, inject electrolyte into the positive compensated lithium battery to obtain a compensated lithium battery cell, and let it stand fully; the standing temperature is 45°C and the standing time is 36h;

[0059] S2: Put the battery after standing on the formation cabinet, and the formation temperature is 45°C. Perform a multi-stage charging negative pressure formation process, including:

[0060] S21) SE I film formation stage; includes the following steps: First, constant current charge the compensated lithium battery cell at the first current I 1 = 0.05C for the first duration t 1 = 0.5h to obtain the battery cells in the first state, with a negative pressure of 30 kPa;

[0061] Let it stand for 5 minutes;

[0062] Constant current charge the battery cells in the first state at the second current I 2 = 0.15C for the second duration t 2 = 1h to obtain the battery cells in the second state, with a negative pressure of 80 kPa.

[0063] Let it stand for 5 minutes;

[0064] S22) Pre-stage of activator activation of the lithium supplement agent; charge with a current greater than I 2 = 0.15C until before the reaction platform of the lithium supplement agent;

[0065] Specifically includes the following steps: At the third current I3 = Constant current charge the battery cell in the second state for a third duration t 3 = 0.5 h to obtain a battery cell in the third state with a negative pressure of 40 kPa;

[0066] Let it stand for 5 min;

[0067] With a fourth current I 4 = 0.5 C to constantly charge the battery cell in the third state to a preset voltage of 3.65 V to obtain a battery cell in the fourth state with a negative pressure of 40 kPa;

[0068] Let it stand for 5 min;

[0069] S23) Lithium supplement agent activation stage; Charge with a current less than I 1 = 0.05 C within the lithium supplement agent reaction platform range;

[0070] Specifically, it includes the following steps: With a fifth current I 5 = 0.045 C to constantly charge the battery cell in the fourth state to a preset voltage of 3.9 V to obtain a battery cell in the fifth state with a negative pressure of 40 kPa;

[0071] Let it stand for 5 min;

[0072] With a sixth current I 6 = 0.045 C to constantly charge the battery cell in the fifth state to a full charge voltage of 4.1 V to obtain a battery cell in the sixth state with a negative pressure of 40 kPa;

[0073] Let it stand for 5 min;

[0074] With a seventh current I 7 = 0.015 C to constantly charge the battery cell in the sixth state to a full charge voltage of 4.1 V to obtain a battery cell in the seventh state with a negative pressure of 40 kPa.

[0075] Let it stand for 1 h;

[0076] S24) Adjust the SOC stage, discharge to the cut-off capacity. With an eighth current I 8 = 0.5 C to constantly discharge the battery cell in the seventh state to a capacity of 60% SOC;

[0077] Comparative Example 1

[0078] The same lithium iron phosphate battery as in Example 1 was formed at 45°C according to the following steps. The difference lies in step S23: After charging to the limiting voltage of 4.1 V with 0.015 C in the last step, the standing time is 5 min.

[0079] Such as Figure 2As shown, after the static time after the extended lithium supplementation and full charge in Example 1, there are basically no black spots at the interface of the battery after high-temperature aging (45°C, 48h) after formation, while there are many black spots at the interface of the battery in Comparative Example 1 after high-temperature aging.

[0080] Comparative Example 2

[0081] Taking the formation process of a conventional battery without a lithium supplementation agent as Comparative Example 2, the formation voltage of the conventional battery without a lithium supplementation agent is controlled not to exceed 3.65V, and only the first three steps of the process are carried out compared with the example.

[0082] The specific formation process is as follows: Constant current charge the lithium supplementation battery cell at the first current I1 = 0.05C for the first duration t1 = 0.5h to obtain the battery cell in the first state, with a negative pressure of 30 kPa; static for 5 min;

[0083] Constant current charge the battery cell in the first state at the second current I2 = 0.15C for the second duration t2 = 1h to obtain the battery cell in the second state, with a negative pressure of 80 kPa. Static for 5 min;

[0084] Constant current charge the battery cell in the second state at the third current I3 = 0.3C for the third duration t3 = 0.5h to obtain the battery cell in the third state, with a negative pressure of 40 kPa;

[0085] Charge the batteries after the formation of Example 1 and Comparative Example 2 to 3650 mV at the same time. The total capacity of Example 1 charged to 3650 mV is 115% SOC of the nominal capacity, and the total capacity of Comparative Example 2 charged to 3650 mV is 110% SOC of the nominal capacity. The capacity of Example 1 is higher than that of Comparative Example 2.

[0086] In summary, the formation method of the lithium supplementation battery of the present invention combines the characteristics of adding a lithium supplementation agent to the positive electrode, and the multi-stage charging negative pressure formation process includes: S21) SE I film formation stage; S22) pre-activation stage of the lithium supplementation agent; S23) activation stage of the lithium supplementation agent; S24) adjust the soc stage, discharge to the cut-off capacity; this method changes the current and static time in different stages, extends the static time after the lithium supplementation agent is activated and fully charged, and this stage provides reaction time for the residual side reactions of the lithium supplementation agent, which is beneficial to the complete exhaust of the lithium supplementation agent during the formation process, thereby improving the interface black spots caused by gas production during high-temperature static after the formation of the positive electrode lithium supplementation battery cell and gas production again after grading.

[0087] As a preferred form thereof, the current magnitude is adjusted in combination with the gas production characteristics during the formation of the lithium supplementation battery. A relatively small current is used in the stages with more gas production (SE I film formation stage and the stage where the lithium supplementation agent plays a role), and a relatively large current is used before activating the lithium supplementation agent, shortening the formation time on the basis of good interface and the role of the lithium supplementation agent.

[0088] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A lithium-supplemented battery formation method, characterized in that: The steps include: S1. First, inject electrolyte into the positive electrode lithium-replenishing battery to obtain a lithium-replenishing battery cell, and let it stand for a long time; S2, multi-stage charging negative pressure formation process; including: S21) SEI film formation stage; S22) pre-activation stage of lithium supplement; S23) lithium supplement activation stage; S24) Adjust the soc stage and discharge to the cut-off capacity.

2. The lithium-supplemented battery formation method according to claim 1, characterized in that: The standing time in each step S21)-S23) is 2-5 minutes, preferably 5 minutes; the standing time in each step S23)-S24) is 1-2 hours, preferably 1 hour.

3. The lithium-supplemented battery formation method according to claim 1, characterized in that: S21) includes the following steps: first, the lithium supplemented battery cell is charged with a first current I1 for a first time t1 to obtain a battery cell in a first state with a negative pressure of 20-40kPa; the battery cell in the first state is charged with a second current I2 for a second time t2 to obtain a battery cell in a second state with a negative pressure of 60-90kPa.

4. The lithium-supplemented battery formation method according to claim 3, characterized in that: I2>I1; Preferably, I1=0.03-0.06C; I2=0.1-0.2C; Preferably, t1=0.4-1h; t2=0.5-2h.

5. The lithium-supplemented battery formation method according to claim 1, characterized in that: S22) charging to the lithium supplementing agent reaction platform with a current greater than I2; Specifically, the steps include: charging the battery cell in the second state with a third current I3 for a third time t3 to obtain a battery cell in a third state with a negative pressure of 20-60 kPa; The battery cell in the third state is charged with a constant current to a preset voltage using a fourth current I4 to obtain a battery cell in a fourth state with a negative pressure of 20-60 kPa.

6. The lithium-supplemented battery formation method according to claim 5, characterized in that: I4≥I3≥I2; preferably, I3=0.25-0.35C; I4=0.4-0.6C; t3=0.3-1h; preferably, the cut-off voltage is 3.5-3.7V.

7. The lithium-supplemented battery formation method according to claim 1, characterized in that: S23) charging within the reaction platform range of the lithium supplement agent with a current less than I1; Specifically, the steps include: charging the battery cell in the fourth state with a fifth current I5 to a preset voltage to obtain a battery cell in the fifth state with a negative pressure of 20-60 kPa; The battery cell in the fifth state is charged with a sixth current I6 to a full-charge voltage to obtain a battery cell in a sixth state with a negative pressure of 20-60 kPa; The battery cell in the sixth state is charged with a constant current to a full-charge voltage using the seventh current I7 to obtain a battery cell in the seventh state with a negative pressure of 20-60 kPa.

8. The lithium-supplemented battery formation method according to claim 7, characterized in that: I7<I6≤I5≤I1, preferably, I5=0.02-0.05C, I6=0.02-0.05C, I7=0.01-0.03C; preferably, the preset voltage is 3.7-3.9V; and the full-charge voltage is 3.9-4.2V.

9. The lithium-supplemented battery formation method according to claim 1, characterized in that: S24) comprises the following steps: discharging the battery cell in the seventh state at a constant current with an eighth current I8 to a capacity of 20-80% soc; preferably, I8=0.4-0.6C. Preferably, the positive electrode active material of the lithium supplement battery is lithium iron phosphate and a lithium supplement agent, and the lithium supplement agent is one or a combination of Li5FeO4 and Li2NiO; Preferably, the standing temperature in step S1 is 25-50° C. and the standing time is 12-48 hours; Preferably, the formation temperature of step S2 is 25-50°C.

10. A lithium-ion battery obtained by the lithium-supplemented battery formation method according to any one of claims 1 to 9.

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