A method for forming a lithium titanate battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a formation method of a lithium titanate battery, which at least comprises the following steps: under preset clamping pressure P0 and preset temperature T, a lithium titanate battery is charged to above 90% SOC at a first preset current I1; the lithium titanate battery is subjected to 2-4 times of constant voltage charging at preset voltages, the preset voltage of each time of constant voltage charging is higher than that of the previous time, the clamping pressure is increased to be greater than P0 during each time of constant voltage charging and is decreased to P0 after the constant voltage charging; after the last time of constant voltage charging, the lithium titanate battery is discharged to a first preset voltage U1 at a second preset current I2; the lithium titanate battery is charged to a second preset voltage U2 at the second preset current I2 and is subjected to constant voltage charging at the second preset voltage U2 until the current decreases to 0.02C. The formation method provided by the application can form a uniform, compact and stable SEI film in the formation of the lithium titanate battery, and solves the problem of swelling caused by the reaction between the lithium titanate material and the electrolyte.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion batteries, in particular to a formation method of a lithium titanate battery. BACKGROUND

[0002] Compared with traditional lead-acid batteries, lithium ion batteries have higher energy density and longer cycle life, and are widely used in new energy vehicle, wind power, photovoltaic power generation and other energy storage fields. The negative electrode material of the currently commercialized lithium ion battery is mainly graphite material, and the following problems exist in the charging and discharging process of the battery: the low migration rate of lithium ions in the carbon material leads to poor large-rate charging and discharging capacity and low-temperature charging and discharging capacity of the battery; the lithium ion insertion potential in the carbon material is close to the lithium precipitation potential, so that lithium is very easy to precipitate during the charging process, and if the deposited lithium metal pierces the separator film, internal short circuit of the positive and negative electrodes will occur, thereby causing safety problems; during the charging and discharging process, the insertion and extraction of lithium ions in the carbon material causes great volume change of the electrode, the structure of the electrode is damaged, the contact between the electrode and the electrolyte is poor, and the cycle performance of the battery is deteriorated.

[0003] The lithium titanate with a spinel structure is a new type of negative electrode material with excellent electrochemical performance. Compared with carbon materials, the diffusion coefficient of lithium ions in lithium titanate is one order of magnitude higher than that in carbon materials, so that the requirement of large-rate fast charging and discharging can be met. The lithium ion insertion potential in lithium titanate is much higher than the lithium precipitation potential, and there is no safety hazard of lithium precipitation. During the charging and discharging process, the insertion and extraction of lithium ions in lithium titanate almost have no volume change, which avoids the structural damage caused by the volume expansion of the electrode material and improves the cycle life of the battery.

[0004] However, the lithium titanate battery is prone to swelling during the charging and discharging cycle process. The swelling phenomenon not only causes the battery cell to bulge, but also greatly reduces the cycle performance of the battery, which seriously restricts the popularization and application of the lithium titanate battery. There are mainly two reasons for the swelling of the lithium titanate battery: firstly, the lithium titanate material itself is easy to absorb water, and the water reacts with the lithium titanate and the electrolyte to generate gas; secondly, the SEI film has the function of ion conduction and electron insulation, which can inhibit the continuous oxidative decomposition of the electrolyte on the negative electrode surface, and the lithium insertion potential of the lithium titanate negative electrode material is higher than the reduction potential of most electrolyte film-forming additives. In the conventional battery formation process, it is difficult for the lithium titanate battery to form a dense, stable and uniform SEI film, so the electrolyte is always in direct contact with the Ti 4+ of the lithium titanate with high catalytic activity, and gas is generated by reaction. SUMMARY

[0005] In view of this, the application provides a formation method of a lithium titanate battery, which can form a uniform, dense and stable SEI film in the formation of the lithium titanate battery, solves the swelling problem caused by the reaction of the lithium titanate material and the electrolyte, and overcomes the defects of the prior art.

[0006] To achieve the above-mentioned purposes, the application adopts the following technical solutions:

[0007] The application provides a formation method of a lithium titanate battery, which at least includes the following steps:

[0008] S1, under a preset clamping pressure P0 and a preset temperature T, the lithium titanate battery is charged to more than 90% SOC at a first preset current I1;

[0009] S2, the lithium titanate battery is charged at a preset voltage for 2-4 times, the preset voltage of each time is higher than that of the previous time, and the clamping pressure rises to more than P0 during each time of constant voltage charging and falls to P0 after the constant voltage charging;

[0010] S3, after the last time of constant voltage charging in S2, the lithium titanate battery is discharged to a first preset voltage U1 at a second preset current I2;

[0011] S4, the lithium titanate battery is charged to a second preset voltage U2 at the second preset current I2, and then charged to a third preset voltage U3 until the current decreases to 0.02C.

[0012] The scheme shown in the embodiment of the application can charge the lithium titanate battery at a preset pressure P0, so that the positive and negative electrodes and the separator are in good contact, and the existence of bubbles does not affect the movement of lithium ions, and charging at a preset temperature T is helpful to film formation; the lithium titanate battery is charged at a first preset current I1 to more than 90% SOC, so that the lithium intercalation state of the negative electrode is close to full charge, the potential of the negative electrode is reduced to the inflection point of the potential drop of the lithium titanate material or lower, and then the lithium titanate battery is charged at a constant voltage at a high SOC state, so that the lithium intercalation potential of the lithium titanate negative material is lower than the reduction potential of the electrolyte film forming additive, the film forming additive can be reduced on the surface of the negative electrode, and then the SEI film is formed; the charging is carried out at a gradually increasing voltage during the constant voltage charging, which can not only ensure that the charging is carried out at the smallest current, but also realize the step-up of the charging current from small to large, so that the negative electrode of the lithium titanate battery can form a uniform, dense and stable SEI film, and the problem of unstable film formation caused by the change of the current from large to small in the conventional constant current and constant voltage charging process is avoided; the battery clamping pressure is gradually increased during the constant voltage charging, which can improve the film formation effect on one hand, and force the gas generated in the formation process to be discharged from the battery body on the other hand; a cycle of charging and discharging after the formation charging can make the SEI film more stable, and overcome the defects of the prior art.

[0013] Preferably, the preset clamping pressure P0 is 0.1 MPa to 0.5 MPa, and the preset temperature T is 25 to 90 DEG C.

[0014] Since the crystal structure of the lithium titanate material hardly changes during the charging and discharging process, the thickness change of the electrode sheet of the lithium titanate battery during the charging and discharging process is generally smaller than that of the graphite system battery, in order to ensure that the lithium titanate battery has sufficient pressure during the charging and discharging process, the application gradually increases the battery clamping pressure before charging and during the constant voltage charging, which can maximize the simulation of the situation that the actual pressure is increased due to the rebound of the electrode sheet during the charging process of the graphite system battery, and is beneficial to improving the film formation effect.

[0015] Preferably, the first preset current I1 is 0.1C to 1.0C.

[0016] Preferably, the preset voltage of the last constant voltage charging in S2 is close to or equal to the cut-off voltage of the normal charging of the battery.

[0017] Preferably, the number of constant voltage charging is three.

[0018] Preferably, the duration of the first constant voltage charging is 10 to 60 min, the duration of the second constant voltage charging is 10 to 60 min, and the duration of the third constant voltage charging is 30 to 120 min.

[0019] Preferably, the second preset current I2 is 0.2C to 1.0C.

[0020] Preferably, the first preset voltage U1 is the cut-off voltage of the battery under normal discharge.

[0021] Preferably, the second preset voltage U2 is the cut-off voltage of the battery under normal charge.

[0022] The method for forming the lithium titanate battery provided by the present application charges the lithium titanate battery at a first preset current I1 to more than 90% SOC, and performs multiple constant voltage charging on the lithium titanate battery under a high SOC state, so that the lithium intercalation potential of the lithium titanate negative electrode material is lower than the reduction potential of the electrolyte film-forming additive, the film-forming additive can be reduced on the negative electrode surface, and then an SEI film is formed. During the constant voltage charging process, the charging is performed at a gradually increasing voltage, which can not only ensure charging at the smallest current, but also realize the stepwise increase of the charging current from small to large, so that the lithium titanate battery negative electrode can form a uniform, dense and stable SEI film. During the constant voltage charging process, the battery clamping pressure is gradually increased, which can not only improve the film-forming effect of the formation, but also force the gas generated during the formation process to be discharged from the battery main body. By using the method provided by the present application, a uniform, dense and stable SEI film can be formed in the lithium titanate battery formation, and the swelling problem caused by the reaction between the lithium titanate material and the electrolyte is solved. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0024] Example 1

[0025] The present embodiment provides a method for forming a lithium titanate battery, which uses lithium manganate material as the positive electrode, lithium titanate material as the negative electrode, and 12-micron-thick PE-based film as the separator film. After the shell assembly is baked at 85℃, the electrolyte formula is: LiPF6: 1.0M, EC / EMC / DEC = 2 / 4 / 4, 1.0% VC, 0.5% PS, 0.5% LiBOB.

[0026] (1) Put the lithium titanate battery after liquid injection and pre-sealing into a pressure formation cabinet, set the temperature to 55℃, and the clamping pressure to 0.2MPa;

[0027] (2) Charge at a constant current of 0.2C to a state of charge of 94% SOC;

[0028] (3) The lithium titanate battery is charged in a 2.6V constant voltage charging mode, the charging time is 20min, the clamping pressure is linearly increased from 0.2MPa to 0.3MPa, and the clamping pressure is restored to 0.2MPa after the charging is completed;

[0029] (4) The lithium titanate battery is charged in a 2.7V constant voltage charging mode, the charging time is 30min, the clamping pressure is linearly increased from 0.2MPa to 0.3MPa, and the clamping pressure is restored to 0.2MPa after the charging is completed;

[0030] (5) The lithium titanate battery is charged in a 2.8V constant voltage charging mode, the charging time is 60min, the clamping pressure is linearly increased from 0.2MPa to 0.3MPa, and the clamping pressure is restored to 0.2MPa after the charging is completed;

[0031] (6) The lithium titanate battery is discharged at 1.0C constant current to 1.5V;

[0032] (7) The lithium titanate battery is charged at 1.0C constant current to 2.8V, and then charged at 2.8V constant voltage until the current decreases to 0.02C.

[0033] Example 2

[0034] The present embodiment provides a formation method of a lithium titanate battery, which uses ternary material as a positive electrode, lithium titanate material as a negative electrode, 12-micron-thick PE-based film as a separator, and is baked at 85℃ after being assembled into a shell. The electrolyte formula is: LiPF6: 1.1M, EC / EMC / PC / DEC = 30 / 55 / 5 / 10, 0.5% VC, 0.5% PS, 1.0% LiBOB.

[0035] (1) The lithium titanate battery after liquid injection and pre-sealing is placed in a pressure formation cabinet, and the temperature is set to 55℃ and the clamping pressure is 0.2Mpa;

[0036] (2) Charged at 0.2C constant current to 94% SOC of state of charge.

[0037] (3) The lithium titanate battery is charged in a 2.5V constant voltage charging mode, the charging time is 30min, the clamping pressure is linearly increased from 0.2MPa to 0.3MPa, and the clamping pressure is restored to 0.2MPa after the charging is completed;

[0038] (4) The lithium titanate battery is charged in a 2.6V constant voltage charging mode, the charging time is 30min, the clamping pressure is linearly increased from 0.2MPa to 0.3MPa, and the clamping pressure is restored to 0.2MPa after the charging is completed;

[0039] (5) the lithium titanate battery is charged in a 2.7V constant voltage charging mode, the charging time is 90 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after the charging is completed;

[0040] (6) the lithium titanate battery is discharged at 1.0C constant current to 1.5V;

[0041] (7) the lithium titanate battery is charged at 1.0C constant current to 2.7V, and then charged at 2.7V constant voltage until the current decreases to 0.02C.

[0042] Example 3

[0043] The present example provides a formation method of a lithium titanate battery, which uses ternary material as a positive electrode, lithium titanate material as a negative electrode, 12 microns thick PE-based film as a separator, and is baked at 85℃ after being assembled into a shell. The electrolyte formula is: LiPF6: 1.1M, EC / EMC / PC / DEC = 30 / 55 / 5 / 10, 0.5% VC, 0.5% PS, 1.0% LiBOB.

[0044] (1) the lithium titanate battery after liquid injection and pre-sealing is placed in a pressure formation cabinet, and the temperature is set to 55℃ and the clamping pressure is 0.2Mpa;

[0045] (2) the lithium titanate battery is charged at 0.2C constant current to 97% SOC of the state of charge.

[0046] (3) the lithium titanate battery is charged in a 2.6V constant voltage charging mode, the charging time is 60 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after the charging is completed;

[0047] (4) the lithium titanate battery is charged in a 2.7V constant voltage charging mode, the charging time is 90 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after the charging is completed;

[0048] (5) the lithium titanate battery is discharged at 1.0C constant current to 1.5V;

[0049] (6) the lithium titanate battery is charged at 1.0C constant current to 2.7V, and then charged at 2.7V constant voltage until the current decreases to 0.02C.

[0050] Example 4

[0051] The embodiment provides a formation method of a lithium titanate battery. The lithium titanate battery takes lithium manganate material as a positive electrode, takes lithium titanate material as a negative electrode, adopts a 12-micron-thick PE-based film as a separator, is baked at 85 DEG C after being assembled into a shell, and the formula of an electrolyte is as follows: LiPF6: 1.0M, EC / EMC / DEC=2 / 4 / 4, 1.0% VC, 0.5% PS, and 0.5% LiBOB.

[0052] (1) the lithium titanate battery after liquid injection and pre-sealing is placed into a pressure formation cabinet, a temperature is set to 90 DEG C, and clamping pressure is 0.1 MPa;

[0053] (2) charging is performed at 0.9C constant current to 94% SOC of a state of charge;

[0054] (3) charging is performed on the lithium titanate battery in a 2.5V constant voltage charging mode, a charging time is 10 min, clamping pressure is linearly raised from 0.1 MPa to 0.2 MPa, and clamping pressure is restored to 0.1 MPa after charging is completed;

[0055] (4) charging is performed on the lithium titanate battery in a 2.6V constant voltage charging mode, a charging time is 30 min, clamping pressure is linearly raised from 0.1 MPa to 0.3 MPa, and clamping pressure is restored to 0.1 MPa after charging is completed;

[0056] (5) charging is performed on the lithium titanate battery in a 2.7V constant voltage charging mode, a charging time is 90 min, clamping pressure is linearly raised from 0.1 MPa to 0.4 MPa, and clamping pressure is restored to 0.1 MPa after charging is completed;

[0057] (6) charging is performed on the lithium titanate battery in a 2.8V constant voltage charging mode, a charging time is 110 min, clamping pressure is linearly raised from 0.1 MPa to 0.4 MPa, and clamping pressure is restored to 0.1 MPa after charging is completed;

[0058] (7) 1.0C constant current discharging is performed on the lithium titanate battery to 1.5V;

[0059] (8) 1.0C constant current charging is performed on the lithium titanate battery to 2.8V, and then 2.8V constant voltage charging is performed until the current drops to 0.02C.

[0060] Embodiment 5

[0061] The embodiment provides a formation method of a lithium titanate battery. The lithium titanate battery takes lithium manganate material as a positive electrode, takes lithium titanate material as a negative electrode, adopts a 12-micron-thick PE-based film as a separator, is baked at 85 DEG C after being assembled into a shell, and the formula of an electrolyte is as follows: LiPF6: 1.0M, EC / EMC / DEC=2 / 4 / 4, 1.0% VC, 0.5% PS, and 0.5% LiBOB.

[0062] (1) Put the lithium titanate battery after pre-sealing into the pressure formation cabinet, set the temperature to 25°C, and the clamping pressure to 0.2 MPa;

[0063] (2) Charge to 97% SOC at a constant current of 0.2C.

[0064] (3) Charge the lithium titanate battery in a constant voltage charging mode of 2.6V, the charging time is 60 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after charging is completed;

[0065] (4) Charge the lithium titanate battery in a constant voltage charging mode of 2.7V, the charging time is 90 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after charging is completed;

[0066] (5) Charge the lithium titanate battery in a constant voltage charging mode of 2.8V, the charging time is 110 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after charging is completed;

[0067] (6) Discharge the lithium titanate battery at a constant current of 1.0C to 1.5V;

[0068] (7) Charge the lithium titanate battery to 2.7V at a constant current of 1.0C, and then charge to a current drop of 0.02C at a constant voltage of 2.7V.

[0069] Comparative Example 1

[0070] This comparative example provides a formation method of a lithium titanate battery tested during the research process. The lithium titanate battery uses lithium manganate material as the positive electrode, lithium titanate material as the negative electrode, and a 12-micron-thick PE-based film as the separator film. After shell assembly, 85°C baking is performed, and the electrolyte formula is: LiPF6: 1.0M, EC / EMC / DEC = 2 / 4 / 4, 1.0% VC, 0.5% PS, 0.5% LiBOB;

[0071] (1) Put the lithium titanate battery after pre-sealing into the pressure formation cabinet, set the temperature to 55°C, and the clamping pressure to 0.2 MPa;

[0072] (2) Charge to 94% SOC at a constant current of 0.2C.

[0073] (3) Charge the lithium titanate battery at a constant current of 0.03C, the charging time is 20 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and the clamping pressure is restored to 0.2 MPa after charging is completed;

[0074] (4) the lithium titanate battery is charged at a constant current of 0.03C, the charging time is 30 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and after the charging is completed, the clamping pressure is restored to 0.2 MPa;

[0075] (5) the lithium titanate battery is charged at a constant current of 0.03C, the charging time is 60 min, the clamping pressure is linearly increased from 0.2 MPa to 0.3 MPa, and after the charging is completed, the clamping pressure is restored to 0.2 MPa;

[0076] (6) the lithium titanate battery is discharged at a constant current of 1.0C to 1.5V;

[0077] (7) the lithium titanate battery is charged at a constant current of 1.0C to 2.8V, and then charged at a constant voltage of 2.8V until the current decreases to 0.02C.

[0078] Comparative Example 2

[0079] This comparative example provides a lithium titanate battery tested in the research process, which uses ternary material as the positive electrode, lithium titanate material as the negative electrode, 12-micron-thick PE-based film as the separator film, is baked at 85°C after being assembled into a shell, and has an electrolyte formula of LiPF6: 1.1M, EC / EMC / PC / DEC = 30 / 55 / 5 / 10, 0.5% VC, 0.5% PS, and 1.0% LiBOB;

[0080] (1) the lithium titanate battery after liquid injection and pre-sealing is placed in a pressure formation cabinet, and the temperature is set to 55°C and the clamping pressure is 0.2 MPa;

[0081] (2) the lithium titanate battery is charged at a constant current of 0.2C to a state of charge of 94% SOC.

[0082] (3) the lithium titanate battery is charged in a constant voltage charging mode at 2.5V, and the charging time is 30 min;

[0083] (4) the lithium titanate battery is charged in a constant voltage charging mode at 2.6V, and the charging time is 30 min;

[0084] (5) the lithium titanate battery is charged in a constant voltage charging mode at 2.7V, and the charging time is 90 min;

[0085] (6) the lithium titanate battery is discharged at a constant current of 1.0C to 1.5V;

[0086] (7) the lithium titanate battery is charged at a constant current of 1.0C to 2.7V, and then charged at a constant voltage of 2.7V until the current decreases to 0.02C.

[0087] Effect Example

[0088] The formed batteries of the examples 1-5 and the comparative examples 1-2 of the present application were subjected to a 55℃ high-temperature storage test after the battery exhaust two-seal and the capacity test, and the test results are shown in Table 1:

[0089] Table 1

[0090]

[0091]

[0092] As can be seen from the data in Table 1, the formation method provided by the present application can form a uniform, dense and stable SEI film in the formation of lithium titanate batteries, effectively solving the swelling problem caused by the reaction of lithium titanate material and electrolyte.

[0093] The above description is merely preferred embodiments of the present application, but not to limit the present application, any modification, equivalent replacement or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of forming a lithium titanate battery, characterized by, At least comprising the following steps: S1, charging the lithium titanate battery to more than 90% SOC at a preset clamping pressure P0 and a preset temperature T with a first preset current I1; S2, performing 2-4 constant voltage charging on the lithium titanate battery at a preset voltage, the preset voltage of each constant voltage charging is higher than that of the previous one, and the clamping pressure rises to more than P0 during each constant voltage charging and falls to P0 after the constant voltage charging; S3, after completing the last constant voltage charging in S2, discharging the lithium titanate battery to a first preset voltage U1 with a second preset current I2; S4, charging the lithium titanate battery to a second preset voltage U2 with the second preset current I2, and then performing constant voltage charging at the second preset voltage U2 until the current drops to 0.02C.

2. The lithium titanate battery formation method of claim 1, wherein: The preset clamping pressure P0 is 0.1-0.5MPa, and the preset temperature T is 25-90℃.

3. The lithium titanate battery formation method of claim 1, wherein: The first preset current I1 is 0.1-1.0C.

4. The lithium titanate battery formation method of claim 1, wherein: The preset voltage of the last constant voltage charging in S2 is the cut-off voltage of normal charging of the battery.

5. The lithium titanate battery formation method of claim 1, wherein: The number of constant voltage charging is three.

6. The lithium titanate battery formation method of claim 5, wherein: The duration of the first constant voltage charging is 10-60min, the duration of the second constant voltage charging is 10-60min, and the duration of the third constant voltage charging is 30-120min.

7. The lithium titanate battery formation method of claim 1, wherein: The second preset current I2 is 0.2-1.0C.

8. The lithium titanate battery formation method of claim 1, wherein: The first preset voltage U1 is the cut-off voltage of normal discharging of the battery.

9. The lithium titanate battery formation method of claim 1, wherein: The second preset voltage U2 is the cut-off voltage of normal charging of the battery.

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