A method for improving the rate of electrochemical prelithiation

Abstract

The present invention discloses a method for improving the rate of electrochemical prelithiation. The characteristics of the method are as follows: the battery cell adopts a high N / P design and a low Overhang design. Specifically, N / P is 1.15 to 1.25, and Overhang is 0.5 to 1.5 mm; the negative electrode material includes secondary particles and / or hard carbon; the tap density of the negative electrode sheet is 1 to 1.6 g / cc; the secondary particles are graphite particles; the D50 of the secondary particles is 15 to 20 μm, and the D50 of the core particles is 8 to 10 μm; the D50 of the hard carbon particles is 8 to 15 μm. The method of the present invention can improve the rate of electrochemical prelithiation; promote the uniform distribution of lithium ions after prelithiation; and increase the amount of electrochemical prelithiation.

Description

Technical Field

[0001] The present invention relates to a method for improving the rate of electrochemical prelithiation, belonging to the field of prelithiation of battery cells. Background Art

[0002] In the past decade, with the deepening of the concept of environmental protection, the reduction of the use of fossil fuels has also received extensive attention. Since the advent of lithium-ion batteries, they have become the favorite of the new generation of automotive energy. Graphite has become the most commercially successful anode material today due to its wide raw material sources, low voltage platform, and relatively high theoretical capacity (372 mAh / g). However, the pursuit of high energy density has forced researchers to develop anode materials with higher capacities. Silicon, with wide raw material sources, high voltage platform, and high energy density (4200 mAh / g), has become the most promising lithium-ion anode material.

[0003] However, silicon-based anodes will experience a larger volume change during charge and discharge compared to tin-based anodes, resulting in problems such as silicon pulverization and electrode peeling. The consumption of lithium during the formation of the SEI film on the anode is the main reason for the reduction of active lithium. The volume expansion of silicon during the lithium insertion reaction can reach 420%, while the expansion of graphite is only about 10%. Therefore, after deformation, it means that a SEI film will be formed on a larger surface area, consuming more active lithium. This causes the irreversible capacity loss of silicon anode batteries during the first charge to reach about 20%, far exceeding the level of 5% - 10% of graphite, and the capacity decay is more obvious.

[0004] To overcome this most critical weakness, prelithiation technology has come into the view of researchers. The purpose is to replenish the lost lithium, and prelithiation is the goal while lithium supplementation is the means. Currently, the commonly used prelithiation technologies include: calendering prelithiation, evaporation coating prelithiation, powder prelithiation, electrochemical prelithiation, and material prelithiation, etc. Currently, the efficiency of electrochemical prelithiation is slow and the improvement in effect is not significant, which restricts further development. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the rate of electrochemical prelithiation to solve the problems of low rate of existing electrochemical prelithiation, uneven distribution of lithium ions after prelithiation, and low prelithiation amount.

[0006] The method for improving the rate of electrochemical prelithiation provided by the present invention is that the battery cell adopts a high N / P design and a low Overhang design.

[0007] In the above method, the N / P is 1.15 - 1.25;

[0008] The Overhang is 0.5 - 1.5 mm.

[0009] In the above method, the anode material includes secondary particles and / or hard carbon;

[0010] The compaction density of the negative electrode sheet is 1 to 1.6 g / cc.

[0011] In the above method, the secondary particles are graphite particles;

[0012] The D50 of the secondary particles is 15 to 20 μm, and the D50 of the bone particles is 8 to 10 μm;

[0013] The D50 of the hard carbon is 8 to 15 μm.

[0014] In the above method, when the negative electrode material includes the secondary particles or the hard carbon, its mass percentage is 50 to 100%;

[0015] When the negative electrode material includes the secondary particles and the hard carbon, the mass ratio of the two is 1:10 to 10:1.

[0016] In the above method, the lithium strip is subjected to surface treatment;

[0017] The surface treatment is a method for increasing the surface contact area of the lithium strip.

[0018] In the above method, the surface treatment is stripe treatment;

[0019] The stripe treatment includes indentations or scratches, wherein the trace width is 0.5 to 2 mm and the interval is 0.5 to 2 mm.

[0020] In the above method, after the battery cell is combined with the lithium strip, it is wrapped with a separator;

[0021] The separator is a base film or a strip-coated separator;

[0022] The coating and the gap width of the strip-coated separator are both 0.5 to 2 mm;

[0023] The number of wrapping layers is 1 to 7 layers.

[0024] In the above method, the lithium salt concentration of the electrolyte used in the battery cell is 1.2 to 2 mol / L;

[0025] The injection coefficient used in the battery cell is 4 g / Ah to 8 g / Ah.

[0026] The method of the present invention can improve the rate of electrochemical prelithiation; promote the uniform distribution of lithium ions after prelithiation; and increase the amount of electrochemical prelithiation. Specific Embodiments

[0027] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0028] Unless otherwise specified, the materials, reagents, etc. used in the following examples can all be obtained from commercial sources.

[0029] Example 1, Electrochemical Prelithiation

[0030] 1) The N / P ratio of the cell is designed to be 1.14, and the overhang is 1.5 mm;

[0031] 2) Prepare the negative electrode slurry, and the mass ratio of each component is main material / conductive agent / dispersant / binder = 95.5 / 1.5 / 1.2 / 1.8; among them, the main material is pure graphite primary particles with a D50 of 16 μm;

[0032] 3) The negative electrode uses 8-μm copper foil, and the double-sided coating surface density is 342 g / m 2 , and the electrode sheet is compacted to 1.6 g / cc in the rolling process;

[0033] 4) The cell adopts the stacking process, with 13 positive electrodes and 14 negative electrodes. The positive electrode is LFP, and the coating surface density is 342 g / m 2 , and the electrode sheet is compacted to 2.0 g / cc;

[0034] 5) Use an electrolyte with a LiPF6 concentration of 1.0 mol / L, and the injection coefficient is 3.5 g / Ah;

[0035] 6) Perform formation and aging at 45 °C, perform grading at 25 °C, and the cycling current at 25 °C is 1C / 1C.

[0036] Example 2, Electrochemical Prelithiation

[0037] Among them,

[0038] 1) The N / P ratio of the cell is designed to be 1.14, and the overhang is 1.5 mm;

[0039] 2) Prepare the negative electrode slurry, and the mass ratio of each component is main material / conductive agent / dispersant / binder = 95.5 / 1.5 / 1.2 / 1.8; among them, the main material is pure graphite primary particles with a D50 of 16 μm;

[0040] 3) The negative electrode uses 8-μm copper foil, and the double-sided coating surface density is 342 g / m 2 , and the electrode sheet is compacted to 1.6 g / cc in the rolling process;

[0041] 4) The cell adopts the stacking process, with 13 positive electrodes and 14 negative electrodes. The positive electrode is LFP, and the coating surface density is 342 g / m 2 , and the electrode sheet is compacted to 2.0 g / cc;

[0042] 5) Cut the lithium-copper composite tape into the shape and size of the cell, and composite it with the cell. The lithium tape copper foil is welded to the copper-plated nickel tab of the negative electrode of the cell;

[0043] 6) The electrolyte with a LiPF6 concentration of 1.0 mol / L is used, and the injection coefficient is 3.5 g / Ah;

[0044] 7) Formation and aging are carried out at 45 °C, and grading is carried out at 25 °C. The cycling current at 25 °C is 1C / 1C.

[0045] Example 3, Electrochemical prelithiation

[0046] The specific process parameters are the same as those in Example 2, except that:

[0047] In step 1), the N / P design of the battery cell is 1.2.

[0048] Example 4, Electrochemical prelithiation

[0049] The specific process parameters are the same as those in Example 2, except that:

[0050] In step 1), the overhang of the battery cell electrode is 1 mm.

[0051] Example 5, Electrochemical prelithiation

[0052] The specific process parameters are the same as those in Example 2, except that:

[0053] In the process of preparing the negative electrode slurry in step 2), the main material is pure graphite secondary particles with a D50 of 16 μm, and the core particles are 8 μm.

[0054] Example 6, Electrochemical prelithiation

[0055] The specific process parameters are the same as those in Example 2, except that:

[0056] In the process of preparing the negative electrode slurry in step 2), the main material is pure hard carbon particles with a D50 of 15 μm.

[0057] Example 7, Electrochemical prelithiation

[0058] The specific process parameters are the same as those in Example 2, except that:

[0059] In the process of preparing the negative electrode slurry in step 2), the main material is 80% secondary particles and 20% hard carbon; among them, the graphite secondary particles have a D50 of 16 μm, the core particles have a D50 of 8 μm; and the hard carbon has a D50 of 16 μm.

[0060] Example 8, Electrochemical prelithiation

[0061] The specific process parameters are the same as those in Example 2, except that:

[0062] In step 3), the compaction of the negative electrode sheet is 1.2 g / cc.

[0063] Example 9, Electrochemical prelithiation

[0064] The specific process parameters are the same as those in Example 2, except that:

[0065] In step 3) the rolling process, the negative electrode sheet is compacted to 1.4 g / cc.

[0066] Example 10, Electrochemical prelithiation

[0067] The specific process parameters are the same as those in Example 2, except that:

[0068] After the lithium copper composite tape is cut in step 5), scratches with a width of 1 mm are made on its surface at intervals of 1 mm.

[0069] Example 11, Electrochemical prelithiation

[0070] The specific process parameters are the same as those in Example 2, except that:

[0071] After the lithium copper composite tape is cut in step 5), indentations with a width of 1 mm are made on its surface at intervals of 1 mm.

[0072] Example 12, Electrochemical prelithiation

[0073] The specific process parameters are the same as those in Example 2, except that:

[0074] After the lithium strip and the battery cell are welded in step 5), the battery cell is wrapped with a 14-μm PE-based film in 3 layers.

[0075] Example 13, Electrochemical prelithiation

[0076] The specific process parameters are the same as those in Example 2, except that:

[0077] After the lithium strip and the battery cell are welded in step 5), the battery cell is wrapped with a coating separator with a coating and a spacing of 1 mm each in 3 layers.

[0078] Example 14, Electrochemical prelithiation

[0079] The specific process parameters are the same as those in Example 2, except that:

[0080] After the lithium strip and the battery cell are welded in step 5), the battery cell is wrapped with a 14-μm PE-based film in 1 layer.

[0081] Example 15, Electrochemical prelithiation

[0082] The specific process parameters are the same as those in Example 2, except that:

[0083] After the lithium strip and the battery cell are welded in step 5), the battery cell is wrapped with a 14-μm PE-based film in 3 layers.

[0084] Example 16, Electrochemical prelithiation

[0085] The specific process parameters are the same as those in Example 2, except that:

[0086] After the lithium strip and the battery cell are welded in step 5), the battery cell is wrapped with a 14-μm PE-based film for 7 layers.

[0087] Example 17, Electrochemical prelithiation

[0088] The specific process parameters are the same as those in Example 2, except that:

[0089] When injecting electrolyte in step 6), the concentration of the electrolyte LiPF6 is 1.2 mol / L.

[0090] Example 18, Electrochemical prelithiation

[0091] The specific process parameters are the same as those in Example 2, except that:

[0092] When injecting electrolyte in step 6), the concentration of the electrolyte LiPF6 is 1.5 mol / L.

[0093] Example 19, Electrochemical prelithiation

[0094] The specific process parameters are the same as those in Example 2, except that:

[0095] When injecting electrolyte in step 6), the injection coefficient is 5 g / Ah.

[0096] Example 20, Electrochemical prelithiation

[0097] The specific process parameters are the same as those in Example 2, except that:

[0098] When injecting electrolyte in step 6), the injection coefficient is 7 g / Ah.

[0099] Test analysis:

[0100] The above examples were subjected to formation and grading, and the parameters were recorded under the same conditions and organized into a table, as shown in Table 1.

[0101] Table 1 Performance of battery cells prepared in each example

[0102]

[0103] Example 1 was used as the control group without electrochemical prelithiation; Example 2 was subjected to electrochemical prelithiation without changing other parameters. It can be seen that both the formation capacity and the cycle performance of the battery cell after prelithiation have been significantly improved.

[0104] Examples 3-20 were based on Example 2 with some parameters changed. Using the method of controlling variables, it can be seen from the results that most examples can effectively improve the formation capacity and cycle performance of the battery cell.

[0105] Example 6: The hard carbon has a short-range ordered structure, with low capacity and low first efficiency. However, this structure is conducive to the movement of lithium ions and the infiltration of the electrolyte, so the time taken to reach 2.5 V is shorter.

[0106] Example 18: The high concentration of lithium salt leads to an increase in the viscosity of the electrolyte, making it difficult to infiltrate, and the capacity cannot be fully exerted. However, the high-concentration lithium salt is beneficial for the rapid insertion of lithium ions from the periphery of the electrode plate, shortening the time taken to reach 2.5 V.

[0107] Comparing Comparative Examples 8 and 9, it can be found that under the low-compaction state, the porosity of the active material on the electrode plate increases, and the electrolyte and ion transport rates increase, which is beneficial for shortening the infiltration time; comparing Comparative Examples 10 and 11, it can be found that increasing the specific surface area of the lithium strip is beneficial for the corrosion and ablation of lithium metal, shortening the infiltration time; comparing Comparative Examples 12 and 13, it can be found that different diaphragm types have no obvious difference in improving the prelithiation rate; comparing Comparative Examples 14, 15 and 16, it can be found that the number of wrapping layers has no obvious difference in improving the infiltration rate; comparing Comparative Examples 19 and 20, it can be found that a high liquid injection coefficient can appropriately improve the infiltration rate. Because the sufficient electrolyte provides sufficient lithium ions at the negative electrode of the negative electrode plate, but the limited electrode plate does not absorb more lithium ions with the gradually increasing electrolyte.

[0108] Examples 2-9, 17, 19 and 20 can improve the prelithiation amount and prelithiation rate from the material level, and Examples 10-16 can improve the prelithiation rate from the process.

[0109] In summary, through multi-faceted regulation, the present invention has achieved a very obvious improvement effect on the electrochemical prelithiation rate. And through the control variable method, the cell grading capacity and cycle stability under each obtained parameter have been greatly improved. While ensuring the improvement of comprehensive performance, the infiltration time is saved, the electrochemical prelithiation time is shortened, and the process efficiency is improved.

Claims

1. A method for improving the rate of electrochemical prelithiation, characterized in that: Stack the positive electrode sheet and the negative electrode sheet to form an electric core, and connect the lithium-copper composite tape to the negative electrode of the electric core; The electric core adopts a high N / P design and a low Overhang design; The N / P is 1.15 to 1.25; The Overhang is 0.5 to 1.5 mm; The compaction density of the negative electrode sheet is 1 to 1.6 g / cc; The negative electrode sheet includes a negative electrode material, the negative electrode material includes secondary particles, and the mass percentage content thereof is 50 to 100%; the secondary particles are graphite particles; the particle D50 of the secondary particles is 15 to 20 μm, and the bone particle D50 is 8 to 10 μm; The lithium tape is subjected to surface treatment; The surface treatment is a method for increasing the surface contact area of the lithium tape; The surface treatment is stripe treatment; The stripe treatment includes indentation or scratching, wherein the trace width is 0.5 to 2 mm and the interval is 0.5 to 2 mm; After the electric core and the lithium tape are combined, they are wrapped with a separator; The separator is a base film or a strip-coated separator; The coating and the gap width of the strip-coated separator are both 0.5 to 2 mm; The number of wrapping layers is 1 to 7 layers; The lithium salt concentration of the electrolyte used in the electric core is 1 mol / L or 1.2 mol / L; The injection coefficient adopted by the electric core is 4 g / Ah to 8 g / Ah.

2. The method according to claim 1, wherein: The negative electrode material includes the secondary particles and hard carbon, and the mass ratio of the two is 1:10 - 10:1; The particle D50 of the hard carbon is 8 to 15 μm.

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