Formation method of SiO-containing lithium supplementing battery

Abstract

The application discloses a formation method of a SiO-containing lithium supplement battery, which comprises charging a pre-lithiated battery under constant voltage to a cut-off current, and then charging the battery to a fixed voltage under step constant current. The application provides a formation method of a battery, which can realize uniform embedding of pre-lithiated metal lithium into a negative electrode sheet, thereby improving the electrochemical performance of the battery while reducing lithium precipitation. The formation method of the application is particularly suitable for the formation of a battery with a high mass ratio of SiO, and can improve the mass ratio of SiO in the negative electrode of the battery, thereby facilitating the improvement of the energy density of the battery. The formation method of the application is simple and easy to implement. The formation method of the application can also realize the supplement and repair of the SEI film, and improve the film forming property and film forming effect of the SEI.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a formation method of a SiO-containing lithium supplementing battery. BACKGROUND

[0002] The birth of lithium ion battery is a revolution in the field of energy storage. The wide application of lithium ion battery has completely changed people's way of life. Lightweight mobile phones, notebook computers, long-lasting electric vehicles and other products have become an integral part of people's life. With the continuous development of lithium ion battery technology, people have put forward higher requirements for the performance of lithium ion battery, hoping that lithium ion has higher energy density. The emergence of SiO negative electrode material has greatly improved the energy density of the battery. However, SiO needs to react with Li to generate elemental silicon, which will consume part of Li, leading to rapid decay of SiO negative electrode material battery in the early stage of cycle, thereby limiting the larger-scale application of the material. Currently, SiO negative electrode material is mainly applied to cylindrical or aluminum shell batteries.

[0003] The commonly used method at present is to improve the capacity and cycle performance of the battery by pre-lithiation and external lithium supplement. However, after lithium supplement, the lithium metal mainly deposits on the surface of the negative electrode sheet, and the lithium metal is not uniformly distributed in the negative electrode. Moreover, with the increase of the addition amount of SiO negative electrode material, the amount of lithium supplement required will also increase, resulting in poorer uniformity of lithium metal in the negative electrode. Due to the poor uniformity of metal lithium in the negative electrode, the metal lithium on the negative electrode sheet cannot be uniformly embedded in the negative electrode sheet during the formation process, so that the SEI film formed by the battery and the state of the battery electrode sheet cannot meet the expected requirements, and even the risk of surface lithium precipitation may occur, which greatly affects the performance of the battery, especially the battery with SiO mass fraction of more than 20%. SUMMARY

[0004] The present application discloses a formation method of a SiO-containing lithium supplementing battery, which can improve the mass fraction of SiO (20%-30%) in the negative electrode and realize the uniform distribution of metal lithium on the negative electrode sheet after pre-lithiation, thereby realizing uniform lithium embedding, improving the cycle performance of the battery and reducing the occurrence of lithium precipitation of the battery.

[0005] The present application is realized by the following technical solutions:

[0006] The formation method of the SiO-containing lithium supplementing battery provided by the present application includes charging the pre-lithiated battery to the cut-off current under constant voltage, and then performing stepwise constant current charging to a fixed voltage.

[0007] The above design of the present application, the pre-lithium battery, the metal lithium is deposited on the negative electrode surface unevenly, resulting in the formation of SEI film and the embedded lithium in the formation process are not ideal. By the battery formation process, the metal lithium deposited on the negative electrode plate can be quickly migrated by constant voltage charging, forming a uniform distribution, thereby facilitating the uniform embedding of metal lithium in the negative electrode plate during constant current charging, and the stepwise constant current charging process is conducive to the formation of stable SEI film. The formation method of the present application improves the embedding of lithium and the film forming property. In addition, the stepwise constant current charging process can also reduce the impedance increase of the SEI film caused by long-time small current charging. Most importantly, the formation method of the present application can improve the electrochemical performance of the battery while reducing the occurrence of lithium precipitation during the battery cycle.

[0008] As a further scheme, the constant voltage is 2.6V-3.0V, and the mass fraction of SiO in the negative electrode of the battery is not more than 15%. Under the formation method of the present application, uniform lithium insertion and SEI film formation in the negative electrode of the battery can be realized.

[0009] As a further scheme, the constant voltage is 2.6V-3.0V, and the mass fraction of SiO in the negative electrode of the battery is not more than 15%. Under the formation method of the present application, uniform lithium insertion and SEI film formation in the negative electrode of the battery can be realized.

[0010] As a further scheme, the cut-off current is 0.01C±0.005C.

[0011] As a further scheme, the formation method is under the condition that the temperature is 80degC±5degC, and the pressure is 0.8Mpa±0.2Mpa.

[0012] As a further scheme, the stepwise constant current charging to a fixed voltage includes:

[0013] S1: 0.2C±0.02C constant current charging to 3.95V±0.05V;

[0014] S2: 0.5C±0.02C constant current charging to 4.4V±0.05V. Using two charging voltages with a large difference can significantly reduce the time of small current charging and the impedance of SEI film.

[0015] As a further scheme, the formation method further includes staticizing the battery after constant current charging, and then performing constant current discharging to a cut-off voltage.

[0016] As a further scheme, the staticizing time is 10min±2min, the constant current discharging current is 0.5C±0.05C, and the cut-off voltage is 3.95V±0.05V.

[0017] The application also provides application of the formation method in a battery formation process.

[0018] The application has the following characteristics and advantages:

[0019] (1) The application provides a formation method of a battery, which can realize uniform embedding of pre-lithium metal lithium into a negative electrode sheet, thereby improving the electrochemical performance of the battery while reducing lithium precipitation.

[0020] (2) The formation method is particularly suitable for formation of a battery with a high mass ratio of SiO, and can realize improvement of the mass ratio of SiO in the negative electrode of the battery, thereby facilitating improvement of the energy density of the battery.

[0021] (3) The formation method is simple and easy to implement.

[0022] (4) The formation method can also realize supplementary repair of the SEI film, and improve the film-forming property and film-forming effect of the SEI. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0024] Figure 1 The battery cycle performance comparison schematic diagram is provided for the examples and comparative examples of the application. DETAILED DESCRIPTION

[0025] In order to facilitate understanding of the formation method of a SiO-containing lithium supplementing battery, the following will more comprehensively describe the formation method of a SiO-containing lithium supplementing battery, and embodiments of the application are given, but the scope of the application is not limited thereto.

[0026] The battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, a separator and a shell.

[0027] The positive electrode sheet comprises a positive electrode current collector aluminum foil, and the positive electrode current collector aluminum foil is uniformly coated with a positive electrode slurry, and the positive electrode slurry comprises a positive electrode active material, a positive electrode binder, a positive electrode dispersant and a positive electrode conductive agent.

[0028] The positive electrode active material comprises LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiMnPO4, LiFePO4, LiNi 0.5 Co 0.2 Mn 0.3O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, lithium iron phosphate, and lithium-rich manganese.

[0029] The positive electrode binder includes one or more of the following: polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and polyacrylic acid (PAA).

[0030] The positive electrode dispersant includes one or more of N-methylpyrrolidone, polyvinylpyrrolidone, polyethylene glycol, polyacrylic acid, and polyacrylate.

[0031] The positive electrode conductive agent includes one or more of the following: powdered nickel, powdered aluminum, carbon black, Ketjen black, natural graphite, artificial graphite, acetylene black, carbon fiber, metal fiber, fluorocarbon compound, nanotube, graphene, polyaniline, polythiophene, polyacetylene, polypyrrole, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

[0032] The negative electrode sheet includes a negative electrode current collector copper foil, and a negative electrode slurry is uniformly coated on the negative electrode current collector aluminum foil. The negative electrode slurry includes a negative electrode active material, a negative electrode binder, and a negative electrode dispersant.

[0033] The negative electrode active material includes SiO, and also includes one or more of the following: natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, nanotubes, carbon black, graphene, soft carbon, silicon (oxygen), silicon (oxygen)-carbon composites, alloy compounds, Sn, SnO, and SnO2.

[0034] The negative electrode binder includes one or more of polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), and nitrile rubber (NBR).

[0035] The negative electrode dispersant comprises one or more of N-methyl pyrrolidone, polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, and polyacrylate.

[0036] The ratio of the design capacity of the negative electrode to the design capacity of the positive electrode is N / P, and N / P is not less than 1.05.

[0037] The electrolyte comprises a solvent, an additive, and a salt.

[0038] The solvent comprises one or more of vinyl carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl propionate, propyl propionate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, fluorine ether, fluorobenzene, 1,3 dioxolane, and ethylene glycol dimethyl ether.

[0039] The additive comprises one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3 propane sulfite, 1,3 propylene sulfite, lithium difluorophosphate, lithium difluoro oxalate borate, lithium bisoxalate borate, lithium tetrafluoroborate, 1,3 dioxane, 1,4 dioxane, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium nitrate, adiponitrile, butanedinitrile, hexanetricarbonitrile, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tris(trimethylsilyl) borate.

[0040] The salt comprises a lithium salt.

[0041] The separator comprises one of a PP separator and a PE separator.

[0042] The shell comprises one of an aluminum foil plastic film and an aluminum shell.

[0043] The positive electrode sheet and the negative electrode sheet are isolated by the separator, and then the electrode is formed by winding, and the electrolyte is injected into the electrode to form the to-be-converted electrode (the electrode model is 425868, and the capacity is 2500 mAh).

[0044] The electrode is further sealed by air extraction to form a battery, and the battery is converted under the condition that the temperature is 80 degC and the pressure is 0.8 Mpa.

[0045] We compare the converted battery of the method of the present application with the battery converted by the conventional method, as follows.

[0046] Experimental group 1:

[0047] (1) The to-be-converted battery is charged at a constant voltage of 2.5 V to a cutoff current of 0.01 C;

[0048] (2) Constant current charging at 0.2 C to 3.95 V;

[0049] (3) Constant current charge to 4.4V at 0.5C;

[0050] (4) Stand for 10min;

[0051] (5) Constant current discharge to cut-off voltage 3.95V at 0.5C.

[0052] Experiment group 2:

[0053] (1) Constant voltage charge to cut-off current 0.01C at 2.6V;

[0054] (2) Constant current charge to 3.95V at 0.2C;

[0055] (3) Constant current charge to 4.4V at 0.5C;

[0056] (4) Stand for 10min;

[0057] (5) Constant current discharge to cut-off voltage 3.95V at 0.5C.

[0058] Experiment group 3:

[0059] (1) Constant voltage charge to cut-off current 0.01C at 2.7V;

[0060] (2) Constant current charge to 3.95V at 0.2C;

[0061] (3) Constant current charge to 4.4V at 0.5C;

[0062] (4) Stand for 10min;

[0063] (5) Constant current discharge to cut-off voltage 3.95V at 0.5C.

[0064] Experiment group 4:

[0065] (1) Constant voltage charge to cut-off current 0.01C at 2.8V;

[0066] (2) Constant current charge to 3.95V at 0.2C;

[0067] (3) Constant current charge to 4.4V at 0.5C;

[0068] (4) Stand for 10min;

[0069] (5) Constant current discharge to cut-off voltage 3.95V at 0.5C.

[0070] Experiment group 5:

[0071] (1) Constant voltage charge to cut-off current 0.01C at 2.9V;

[0072] (2) 0.2C constant current charging to 3.95V;

[0073] (3) 0.5C constant current charging to 4.4V;

[0074] (4) Rest for 10 min;

[0075] (5) 0.5C constant current discharging to cut-off voltage 3.95V.

[0076] Experiment group 6:

[0077] (1) The battery to be formed is charged at 3.0V constant voltage to cut-off current 0.01C;

[0078] (2) 0.2C constant current charging to 3.95V;

[0079] (3) 0.5C constant current charging to 4.4V;

[0080] (4) Rest for 10 min;

[0081] (5) 0.5C constant current discharging to cut-off voltage 3.95V.

[0082] Control group:

[0083] (1) The battery to be formed is charged at 0.2C constant current to 3.95V;

[0084] (2) 0.5C constant current charging to 4.4V;

[0085] (3) Rest for 10 min;

[0086] (4) 0.5C constant current discharging to cut-off voltage 3.95V.

[0087] We further tested the direct current resistance (DCR) of the battery, the process being as follows: the battery is fully charged, discharged for 10s using a current I1 of 0.1C rate, the voltage U1 at the end of discharging is recorded, discharged for 3s using a current I2 of 1.1C rate, the voltage U2 at the beginning of discharging is recorded; DCR = (U1-U2) / (I2-I1).

[0088] Results and analysis

[0089] Table 1 Lithium precipitation of batteries with different mass proportions of SiO in examples and comparative examples

[0090]

[0091]

[0092] Table 2 Influence of mass proportion of SiO in examples on battery expansion rate

[0093]

[0094] Table 3. DC resistance of the batteries in the examples and comparative examples.

[0095]

[0096]

[0097] The formation method of this invention can improve the energy density of the battery. Adding a high-mass proportion of SiO to the negative electrode leads to lithium consumption. To improve the battery's cycle performance, pre-lithiation is necessary before battery formation to compensate for the lithium consumption. During the constant-voltage charging process, the formation method of this invention allows for rapid migration of lithium metal deposited on the surface of the negative electrode, resulting in a more uniform distribution of lithium metal on the negative electrode. This promotes the formation of a stable SEI film on the surface of the negative electrode during the stepped constant-current charging process, while reducing lithium plating. This improves the battery's safety and cycle performance. Furthermore, the stepped constant-current charging process reduces the increase in SEI film resistance, further improving the battery's electrochemical performance. Therefore, we compared the electrochemical performance and lithium plating of batteries with different mass proportions of SiO using comparative examples and embodiments. As shown in Table 1, comparing Comparative Examples 1-7 and Embodiments 1-9 reveals that no lithium plating occurred in Embodiments 1-9. Comparative Examples 1 and 2 showed no lithium plating when the SiO mass percentage was no more than 5%. However, when the SiO mass percentage was no less than 20%, severe lithium plating occurred in the battery using conventional formation methods. In Examples 1-9, the SiO mass percentage increased from 0% to 40%. Using the formation method of this invention, rapid lithium ion migration was successfully promoted, resulting in uniform lithium metal intercalation. Even when the SiO mass percentage was as high as 40% (four times the SiO mass percentage when lithium plating occurs using conventional methods), no lithium plating occurred in the battery.

[0098] We further compared the formation methods of the embodiments and comparative examples to obtain the cycle performance of the batteries, such as... Figure 1 As shown, we start from Figure 1 As can be seen, after 300 cycles, the capacity retention of the battery in Example 2 is approximately 95%, while that of Comparative Example 2 is no higher than 86%. This demonstrates that the formation method of the present invention, through constant voltage charging, promotes rapid lithium metal migration, facilitates uniform lithium metal embedding during the stepped constant current charging process, and achieves the formation of a stable SEI film. Therefore, the method of the present invention not only reduces lithium plating compared to traditional methods but also significantly improves the cycle performance of the battery. Figure 1The mass ratio of SiO in the negative electrode in Example 1 and Comparative Example 1 is 0%, and the curves of Example 1 and Comparative Example 1 are highly coincident, which shows that the method of the application is particularly suitable for the formation of the battery containing SiO.

[0099] When the SiO in the negative electrode is reduced to elemental silicon, volume expansion occurs during the battery cycle, which will affect the safety performance to some extent, and the expansion rate of the battery is preferably not higher than 10%. Therefore, we further limit the maximum mass ratio of SiO in the negative electrode by the volume expansion rate of the battery after charge-discharge cycle, as shown in Table 2, we further limit the mass ratio of SiO in the negative electrode of the battery to not higher than 30%. In addition, when the design capacity of the negative electrode in the battery is lower than the actual pre-lithium amount, the excess metal lithium in the negative electrode will remain on the surface of the negative electrode, and lithium precipitation will occur during the battery cycle, as shown in Examples 35-41, we further limit the ratio of N / P to not less than 1.06.

[0100] On this basis, we further study the different formation voltages. When the formation voltage is too small, too much metal lithium is deposited, which may affect the migration speed of lithium, so that the metal lithium is not fully dispersed and uniform, thereby causing the battery to still have the situation of lithium precipitation during the charge-discharge cycle, as shown in Examples 10-14. When the formation voltage is only 2.5V, it cannot promote the uniform dispersion of metal lithium. We found from Examples 15-16 that when the charging voltage is increased to 2.6V, the mass ratio of SiO in the negative electrode is not higher than 15%, and lithium precipitation will not occur during the charge-discharge cycle of the battery, but further increasing the mass ratio of SiO will still cause lithium precipitation (as shown in Examples 17-19). Therefore, when the charging voltage is 2.6V-3.0V, the mass ratio of SiO in the negative electrode is not higher than 15%, so as not to produce lithium precipitation. During the formation of the battery, there is a great mutual influence between the formation voltage and the mass ratio of SiO in the negative electrode. We further verify from the examples that when the mass ratio of SiO in the negative electrode is certain (20%), as shown by the comparison of Examples 17, 22, 27, 32 and 5, the lithium precipitation during the cycle of the battery is different when the charging voltage during the formation process is different. It can be seen that when the mass ratio of SiO is certain, the migration speed can be increased by increasing the formation voltage, thereby reducing the occurrence of lithium precipitation; when the formation voltage is certain, as shown by the comparison of Examples 15-19 and Examples 20-34, the mass ratio of SiO in the negative electrode can be further adjusted according to the actual voltage. We further select the voltage of constant voltage charging to be 2.7V-3.0V, and we can further increase the mass ratio of SiO in the negative electrode. At this time, the mass ratio of SiO in the negative electrode of the battery is not higher than 30% and not less than 15%.

[0101] We further study the direct current resistance (DCR) of the battery after the chemical formation of the application, when the battery is reduced during the cycle process, the direct current resistance will be reduced, thereby improving the electrochemical performance of the battery, we take comparative example 5, example 5, example 12, example 17, example 22, example 27 as an example for comparison, as shown in table 3, when the mass ratio of SiO in the negative electrode is 20%, the direct current resistance of comparative example 5, example 12 and example 17 is very large, and the difference between comparative example 5 and example 12, example 17 is large, it can be seen that, although example 12 and example 17 have too small charging voltage, which leads to the uneven dispersion of SiO, but the method of the application also promotes the dispersion of part of the metal lithium to some extent, so the direct current resistance of example 12 and example 17 is smaller than that of comparative example 5. The direct current resistance of example 5, example 22 and example 27 which do not occur lithium precipitation is small and has little difference, it can be seen that the method of the application realizes the uniform dispersion of metal lithium on the negative electrode sheet, thereby realizing the process of uniform lithium intercalation, reducing the lithium precipitation during the cycle process of the battery and improving the electrochemical performance of the battery.

[0102] In summary, the chemical formation method of the application is particularly suitable for the rapid migration of metal lithium on the negative electrode sheet after pre-lithium of the battery with high mass ratio of SiO, and realizes the process of uniform lithium intercalation through the stepwise constant current charging process, which not only helps to improve the cycle performance of the battery and reduce the occurrence of lithium precipitation during the charging and discharging process of the battery, but also helps to generate stable SEI film.

[0103] It should be noted that the above only describes the preferred embodiments of the application and is not intended to limit the application, any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method for forming a SiO-containing lithium supplementing battery, characterized by, The formation method comprises charging the pre-lithiated battery under constant voltage to a cut-off current, and then charging the battery under constant current to a fixed voltage in steps; The constant voltage is 2.6V-3.0V, and the mass percentage of SiO in the negative electrode of the battery is not higher than 15%; The charging under constant current to a fixed voltage in steps comprises: S1: charging under constant current of 0.2C±0.02C to 3.95V±0.05V; S2: charging under constant current of 0.5C±0.02C to 4.4V±0.05V.

2. The formation method of a lithium supplement battery containing SiO according to claim 1, characterized in that, The constant voltage is 2.7V-3.0V, and the mass percentage of SiO in the negative electrode of the battery is not higher than 30% and not lower than 15%.

3. The formation method of a lithium supplement battery containing SiO according to claim 1, characterized in that, The cut-off current is 0.01C±0.005C.

4. The formation method of a lithium supplement battery containing SiO according to claim 1, characterized in that, The formation method is under the condition that the temperature is 80degC±5degC and the pressure is 0.8Mpa±0.2Mpa.

5. The formation method of a lithium supplement battery containing SiO according to claim 1, characterized in that, The formation method further comprises standing the battery after constant current charging, and then discharging the battery under constant current to a cut-off voltage.

6. The formation method of a lithium supplement battery containing SiO according to claim 5, characterized in that, The standing time is 10min±2min, the current for discharging under constant current is 0.5C±0.05C, and the cut-off voltage is 3.95V±0.05V.

7. Application of the formation method according to any one of claims 1-6 in the process of battery formation.

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