Negative electrode sheet and lithium ion battery comprising same

Abstract

A negative electrode sheet and a lithium ion battery comprising same. A proper amount of hard carbon negative electrode material is blended in an existing common negative electrode system, so that the physical resilience rate and porosity of a negative electrode sheet are significantly improved, the contact area of the negative electrode sheet and an electrolyte is increased, and the cycle performance of the lithium ion battery is improved. The powder compaction density of a negative electrode active material is further matched with the compaction density of the negative electrode sheet, so that the advantages of the hard carbon material are fully exerted, and thus the physical resilience rate and porosity of the negative electrode sheet can be effectively improved, battery cell bulging, cycle deterioration, etc. caused by overvoltage of the negative electrode sheet can be avoided, and the cycle life and the quick charging capability of the lithium ion battery are significantly improved.

Description

A negative electrode sheet and a lithium ion battery comprising the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 15, 2023, with application number 202311194179.4 and application name “A negative electrode sheet and a lithium-ion battery comprising the negative electrode sheet”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the technical field of negative electrode sheets, and in particular relates to a negative electrode sheet and a lithium ion battery comprising the negative electrode sheet. Background Art

[0003] Graphite negative electrode material is the most widely used type of negative electrode material in lithium-ion secondary batteries. However, in the actual battery manufacturing process, the negative electrode sheet is prone to insufficient infiltration with the electrolyte during the rolling process, which affects the lithium ion diffusion process, resulting in lithium deposition and purple spots in the finished battery, affecting the battery cycle performance.

[0004] Research has found that a reasonable design of the negative electrode sheet's compaction density can avoid excessive copper foil expansion and insufficient strength under ultra-high pressure. Insufficient negative electrode sheet strength can lead to sheet breakage, battery inflation, and reduced cycle retention.

[0005] Summary of the Invention

[0006] To address the issues of purple spots and lithium deposition caused by conventional graphite negative electrode sheets used in lithium-ion batteries, low capacity retention, and excessively high negative electrode density leading to negative electrode sheet breakage, battery bulging, and poor battery cycle performance, the present invention provides a negative electrode sheet and a lithium-ion battery including the same. The negative electrode sheet comprises graphite and hard carbon negative electrode materials and can effectively improve the cycling performance of lithium-ion batteries.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, wherein the negative electrode active material comprises a first negative electrode active material and a second negative electrode active material; wherein the first negative electrode active material comprises a hard carbon negative electrode material; and wherein the second negative electrode active material comprises at least one of a graphite negative electrode material, a silicon negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, and a soft carbon negative electrode material;

[0009] The negative electrode sheet satisfies:

[0010] 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55;

[0011] Among them, II-PD 1+2 is the powder compaction density of the negative electrode active material, unit is g / cm 3 Ⅱ-α 1+2 is the compaction density of the negative electrode sheet, in g / cm 3 .

[0012] According to the present invention, the powder compaction density II-PD of the negative electrode active material 1+2 1.3-2.5g / cm 3 ; and / or, the compaction density of the negative electrode sheet II-α 1+2 0.9-1.8g / cm 3 .

[0013] According to the present invention, the compaction density A of the negative electrode sheet is less than the ultimate compaction density α of the negative electrode sheet.

[0014] According to the present invention, the ultimate compaction density α of the negative electrode sheet is 0.950-2.155 g / cm 3 .

[0015] According to the present invention, the ultimate compaction density α of the negative electrode sheet satisfies one of the following:

[0016] (1) When II-Dv50 / I-Dv50 ≥ 2.4, α1 = PD1-4T×wt1% + PD2-3T×wt2%;

[0017] (2) When 2≤II-Dv50 / I-Dv50<2.4, α2=PD1-3T×wt1%+PD2-3T×wt2%;

[0018] (3) When 1≤II-Dv50 / I-Dv50<2, α3=PD1-2T×wt1%+PD2-3T×wt2%;

[0019] Wherein, I-Dv50 is the median particle size of the first negative electrode active material, in μm; II-Dv50 is the median particle size of the second negative electrode active material, in μm;

[0020] wt1% is the mass percentage of the first negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material; wt2% is the mass percentage of the second negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material;

[0021] PD1-2T is the powder compaction density of the first negative electrode active material under a pressure of 20 kN, in g / cm 3PD1-3T is the powder compaction density of the first negative electrode active material under a pressure of 30 kN, in g / cm 3 PD1-4T is the powder compaction density of the first negative electrode active material under a pressure of 40 kN, in g / cm 3 PD2-3T is the powder compaction density of the second negative electrode active material under a pressure of 30 kN, in g / cm 3 .

[0022] According to the present invention, the median particle size I-Dv50 of the first negative electrode active material is 0.5-12 μm; and / or the median particle size II-Dv50 of the second negative electrode active material is 5-20 μm.

[0023] According to the present invention, the wt1% is 0.5%-50%; and / or, the wt2% is 50%-99.5%.

[0024] According to the present invention, the PD1-2T is 0.6-1.18 g / cm 3 ; and / or, the PD1-3T is 0.7-1.25g / cm 3 ; and / or, the PD1-4T is 0.8-1.3g / cm 3 ; and / or, the PD2-3T is 1.3-2.2 g / cm 3 .

[0025] According to the present invention, the ultimate compaction density α1 of the negative electrode sheet is 1.050-2.155 g / cm 3 and / or, the ultimate compaction density α2 of the negative electrode sheet is 1.000-2.153 g / cm 3 and / or, the ultimate compaction density α3 of the negative electrode sheet is 0.950-2.150 g / cm 3 .

[0026] According to the present invention, the physical rebound rate of the negative electrode sheet is 5%-15%.

[0027] According to the present invention, the porosity of the negative electrode sheet is 13-50%.

[0028] According to the present invention, the X-ray diffraction (XRD) spectrum of the hard carbon negative electrode material has a characteristic peak located between 15° and 35°, and the half-peak width of the characteristic peak is 4° to 12°;

[0029] And / or, the maximum pore diameter of the ultrafine pores of the hard carbon negative electrode material is 0.35-1.5 nm;

[0030] And / or, the true density of the hard carbon negative electrode material is 1.3-2.2 g / cm 3 ;

[0031] and / or, the powder conductivity of the hard carbon negative electrode material at 20 kN is 0.1-100 S / cm;

[0032] And / or, the d of the hard carbon negative electrode material 002 The lattice spacing is 0.35-0.42nm.

[0033] The present invention also provides a lithium-ion battery, which includes the above-mentioned negative electrode sheet.

[0034] According to the present invention, the lithium ion battery satisfies: 60.00%≤C 锂 / D 锂 ≤99.9%;

[0035] Among them, C 锂 D is the discharge capacity of the battery when it drops from 4.45V to 3V, in mAh; 锂 It is the discharge capacity of the battery when it drops from 4.45V to 2.5V, in mAh.

[0036] Beneficial effects of the present invention:

[0037] The present invention provides a negative electrode sheet and a lithium-ion battery including the negative electrode sheet. The present invention is to mix an appropriate amount of hard carbon negative electrode material into the existing common negative electrode system, significantly improve the physical rebound rate and porosity of the negative electrode sheet, increase the contact area between the negative electrode sheet and the electrolyte, and improve the cycle performance of the lithium-ion battery; and further, through the mutual cooperation of the powder compaction density of the negative electrode active material and the compaction density of the negative electrode sheet, give full play to the advantages of the hard carbon material, which can not only effectively improve the physical rebound rate and porosity of the negative electrode sheet, but also avoid the problems of battery cell bulging and cycle deterioration caused by overvoltage of the negative electrode sheet, thereby achieving a significant improvement in the cycle life and fast charging capability of the lithium-ion battery. According to the particle size distribution and powder compaction density of the negative electrode active material, the present invention can also reasonably design the compaction density of the electrode sheet to avoid the problems of battery cell bulging and cycle deterioration caused by overvoltage of the negative electrode sheet. DETAILED DESCRIPTION

[0038] <Negative electrode>

[0039] As mentioned above, the present invention provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a first negative electrode active material and a second negative electrode active material; the first negative electrode active material includes a hard carbon negative electrode material; the second negative electrode active material includes at least one of a graphite negative electrode material, a silicon negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, and a soft carbon negative electrode material; the negative electrode sheet satisfies:

[0040] 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55;

[0041] Among them, II-PD 1+2 is the powder compaction density of the negative electrode active material, unit is g / cm 3 Ⅱ-α 1+2 is the compaction density of the negative electrode sheet, in g / cm 3 .

[0042] According to an embodiment of the present invention, the negative electrode sheet satisfies: 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55, II-PD 1+2 / Ⅱ-α 1+2 For example, it is 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45 or 1.55. Studies have found that if the actual compaction density of the negative electrode sheet mixed with hard carbon negative electrode material is too large, it is easy to cause abnormal conditions such as crushing of negative electrode active material particles and too low physical rebound rate of the negative electrode sheet. When the negative electrode sheet meets 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 When it is ≤1.55, it can not only effectively improve the physical rebound rate and porosity of the negative electrode sheet, but also avoid the problems of cell bulging and cycle deterioration caused by overvoltage of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0043] According to an embodiment of the present invention, the powder compaction density II-PD of the negative electrode active material 1+2 It is the powder compaction density of the negative active material of the negative electrode sheet in the 0% SOC state measured under the "5T rapid test" program of the automatic powder compactor at a pressure of 30kN.

[0044] According to an embodiment of the present invention, the compaction density of the negative electrode sheet is II-α 1+2 It is the measured compaction density of the negative electrode sheet at 0% SOC. Specifically, it can be calculated by the "small disc method" commonly used in the industry to calculate the density of the negative electrode active material layer, and then inferred after measuring the thickness of the electrode sheet with a micrometer.

[0045] According to an embodiment of the present invention, the powder compaction density II-PD of the negative electrode active material 1+2 1.3-2.5g / cm 3 , for example 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 or 2.5g / cm 3 Crushing the negative electrode active material particles will reduce the overall particle size of the negative electrode active material, making the negative electrode active material powder compacted smaller. Within this limited range, the negative electrode active material can maintain a good morphology and achieve a good cycle life.

[0046] According to an embodiment of the present invention, the compaction density of the negative electrode sheet is II-α 1+2 0.9-1.8g / cm 3 , for example 0.9 g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 or 1.8g / cm 3 Because the over-pressured negative electrode exceeds the range of its elastic deformation, the physical rebound rate of the electrode will be significantly reduced, resulting in a larger value of the measured compaction density of the negative electrode.

[0047] According to an embodiment of the present invention, the ultimate compaction density α of the negative electrode sheet satisfies one of the following:

[0048] (1) When II-Dv50 / I-Dv50 ≥ 2.4, α1 = PD1-4T×wt1% + PD2-3T×wt2%;

[0049] (2) When 2≤II-Dv50 / I-Dv50<2.4, α2=PD1-3T×wt1%+PD2-3T×wt2%;

[0050] (3) When 1≤II-Dv50 / I-Dv50<2, α3=PD1-2T×wt1%+PD2-3T×wt2%;

[0051] Wherein, I-Dv50 is the median particle size of the first negative electrode active material, in μm; II-Dv50 is the median particle size of the second negative electrode active material, in μm;

[0052] wt1% is the mass percentage of the first negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material; wt2% is the mass percentage of the second negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material;

[0053] PD1-2T is the powder compaction density of the first negative electrode active material under a pressure of 20 kN, in g / cm 3 PD1-3T is the powder compaction density of the first negative electrode active material under a pressure of 30 kN, in g / cm 3 PD1-4T is the powder compaction density of the first negative electrode active material under a pressure of 40 kN, in g / cm 3 PD2-3T is the powder compaction density of the second negative electrode active material under a pressure of 30 kN, in g / cm 3 .

[0054] The study found that by coordinating the compaction density of the negative electrode active material powder and the compaction density of the negative electrode sheet, the advantages of the hard carbon material are fully utilized. This can effectively improve the physical rebound rate and porosity of the negative electrode sheet, while also avoiding problems such as cell bulging and cycle deterioration caused by overvoltage of the negative electrode sheet, thereby significantly improving the cycle life and fast charging capability of lithium-ion batteries. Further, by calculating the characteristic data of the negative electrode material and obtaining the processing parameters of the negative electrode sheet, the advantages of the hard carbon negative electrode material can be fully utilized. The synergistic effect of the two can significantly improve the cycle life and fast charging capability of lithium-ion batteries.

[0055] <Negative electrode>

[0056] As described above, the present invention provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a first negative electrode active material and a second negative electrode active material; the first negative electrode active material includes a hard carbon negative electrode material; the second negative electrode active material includes at least one of a graphite negative electrode material, a silicon negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material and a soft carbon negative electrode material; the physical rebound rate of the negative electrode sheet is ≥5%.

[0057] According to an embodiment of the present invention, the ultimate compaction density α of the negative electrode sheet satisfies one of the following:

[0058] (1) When II-Dv50 / I-Dv50 ≥ 2.4, α1 = PD1-4T×wt1% + PD2-3T×wt2%;

[0059] (2) When 2≤II-Dv50 / I-Dv50<2.4, α2=PD1-3T×wt1%+PD2-3T×wt2%;

[0060] (3) When 1≤II-Dv50 / I-Dv50<2, α3=PD1-2T×wt1%+PD2-3T×wt2%;

[0061] Wherein, I-Dv50 is the median particle size of the first negative electrode active material, in μm; II-Dv50 is the median particle size of the second negative electrode active material, in μm;

[0062] wt1% is the mass percentage of the first negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material; wt2% is the mass percentage of the second negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material;

[0063] PD1-2T is the powder compaction density of the first negative electrode active material under a pressure of 20 kN, in g / cm 3 PD1-3T is the powder compaction density of the first negative electrode active material under a pressure of 30 kN, in g / cm 3 PD1-4T is the powder compaction density of the first negative electrode active material under a pressure of 40 kN, in g / cm 3 PD2-3T is the powder compaction density of the second negative electrode active material under a pressure of 30 kN, in g / cm 3 .

[0064] According to an embodiment of the present invention, the negative electrode sheet satisfies:

[0065] 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55;

[0066] Among them, II-PD 1+2 is the powder compaction density of the negative electrode active material, unit is g / cm 3 Ⅱ-α 1+2 is the compaction density of the negative electrode sheet, in g / cm 3 .

[0067] <Negative electrode>

[0068] As described above, the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, wherein the negative electrode active material comprises a first negative electrode active material and a second negative electrode active material; the first negative electrode active material comprises a hard carbon negative electrode material; the second negative electrode active material comprises at least one of a graphite negative electrode material, a silicon negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, and a soft carbon negative electrode material; and the ultimate compaction density α of the negative electrode sheet satisfies one of the following:

[0069] (1) When II-Dv50 / I-Dv50 ≥ 2.4, α1 = PD1-4T×wt1% + PD2-3T×wt2%;

[0070] (2) When 2≤II-Dv50 / I-Dv50<2.4, α2=PD1-3T×wt1%+PD2-3T×wt2%;

[0071] (3) When 1≤II-Dv50 / I-Dv50<2, α3=PD1-2T×wt1%+PD2-3T×wt2%;

[0072] Wherein, I-Dv50 is the median particle size of the first negative electrode active material, in μm; II-Dv50 is the median particle size of the second negative electrode active material, in μm;

[0073] wt1% is the mass percentage of the first negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material; wt2% is the mass percentage of the second negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material;

[0074] PD1-2T is the powder compaction density of the first negative electrode active material under a pressure of 20 kN, in g / cm 3 PD1-3T is the powder compaction density of the first negative electrode active material under a pressure of 30 kN, in g / cm 3 PD1-4T is the powder compaction density of the first negative electrode active material under a pressure of 40 kN, in g / cm 3 PD2-3T is the powder compaction density of the second negative electrode active material under a pressure of 30 kN, in g / cm 3 .

[0075] According to an embodiment of the present invention, the physical rebound rate of the negative electrode sheet is ≥5%.

[0076] According to an embodiment of the present invention, the negative electrode sheet satisfies:

[0077] 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55;

[0078] Among them, II-PD 1+2 is the powder compaction density of the negative electrode active material, unit is g / cm 3 Ⅱ-α 1+2 is the compaction density of the negative electrode sheet, in g / cm 3 .

[0079] Among the three negative electrode sheets mentioned above

[0080] According to an embodiment of the present invention, the physical rebound rate of the negative electrode sheet is 5% to 15%, for example, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 10%, 11%, 12%, 13%, 14% or 15%. The physical rebound rate of the negative electrode sheet is within the above-mentioned appropriate range, which can avoid the zero rebound and low porosity anomalies caused by overvoltage, ensure the presence of pores on the surface of the negative electrode sheet, so as to achieve better contact and infiltration between the negative electrode sheet and the electrolyte, avoid the problems of electrolyte bridging and purple spot lithium precipitation, and achieve a significant improvement in the cycle life and fast charging capability of the lithium-ion battery.

[0081] According to an embodiment of the present invention, the physical rebound rate of the negative electrode sheet is the growth rate of the thickness of the electrode sheet after the negative electrode sheet is subjected to cold roller rolling (the temperature of the cold roller is room temperature) for 24 hours compared to the thickness of the electrode sheet when the rolling is just completed; specifically (D1-D2) / D1, wherein D1 is the thickness of the electrode sheet when the rolling is just completed, in μm, and D2 is the thickness of the electrode sheet after 24 hours of rolling, in μm.

[0082] According to an embodiment of the present invention, the ultimate compaction density α of the negative electrode sheet can be reasonably obtained based on the particle size distribution and powder compaction density of the negative electrode active material. Research has found that the compaction density of the negative electrode sheet is related to the powder compaction density of the first and second negative electrode active materials, the particle size and mass ratio of the different negative electrode active materials, etc.

[0083] When II-Dv50 / I-Dv50≥2.4, the small-particle first negative electrode active material can enter the gaps between the arranged and stacked large-particle second negative electrode active materials, thereby achieving a higher compaction density of the negative electrode sheet. At this time, the compaction density of the negative electrode sheet satisfies α=PD1-4T×wt1%+PD2-3T×wt2%.

[0084] When 2≤II-Dv50 / I-Dv50<2.4, only a portion of the small-particle first negative electrode active material enters the gaps between the large-particle second negative electrode active material arrangements and stacks, and the remaining small-particle first negative electrode active material and the large-particle second negative electrode active material are co-stacked. At this time, the compaction density of the negative electrode sheet satisfies α=PD1-3T×wt1%+PD2-3T×wt2%.

[0085] When 1≤II-Dv50 / I-Dv50<2, the first negative electrode active material and the second negative electrode active material are co-stacked, satisfying α=PD1-2T×wt1%+PD2-3T×wt2%.

[0086] In some embodiments, the median particle size I-Dv50 of the first negative electrode active material is 0.5-12 μm, preferably 2-9 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm. When the median particle size of the first negative electrode active material is within the above-mentioned suitable range, on the one hand, the first negative electrode active material can have good electrolyte infiltration performance, and on the other hand, the first negative electrode active material can have a suitable specific surface area, thereby reducing the active ions that are excessively consumed due to the formation of an excessive SEI film on the surface of the first negative electrode active material during the first charge. Therefore, the negative electrode active material of the present application is applied to a secondary battery, which can enable the secondary battery to have both good kinetic performance and high first coulombic efficiency.

[0087] In some embodiments, the median particle size II-Dv50 of the second negative electrode active material is 5-20 μm, preferably 8-17 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm. When the median particle size of the second negative electrode active material is within the above-mentioned suitable range, on the one hand, the second negative electrode active material can be prevented from having too small a particle size that reduces the usable capacity and the first coulombic efficiency, and on the other hand, the second negative electrode active material can be prevented from having too large a particle size that affects the processing performance and fast charge and discharge performance.

[0088] In some embodiments, the wt1% is 0.5%-50%, preferably 1%-35%, such as 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48% or 50%.

[0089] In some embodiments, the wt2% is 50%-99.5%, preferably 65%-98%, such as 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98% or 99%.

[0090] In some embodiments, when the mass ratio of the first negative electrode active material to the second negative electrode active material is within the above-mentioned appropriate range, it can not only increase the porosity of the electrode sheet and improve the cycle performance, but also reduce the volume expansion rate of the negative electrode sheet in a fully charged state, thereby increasing the energy density of the secondary battery.

[0091] In some embodiments, the PD1-2T is the powder compaction density of the first negative electrode active material measured at a pressure of 20 kN under the "5T rapid test" program of an automatic powder compactor.

[0092] In some embodiments, the PD1-3T is the powder compaction density of the first negative electrode active material measured at a pressure of 30 kN under the "5T rapid test" program of an automatic powder compactor.

[0093] In some embodiments, the PD1-4T is the powder compaction density of the first negative electrode active material measured at a pressure of 40 kN under the "5T rapid test" program of an automatic powder compactor.

[0094] In some embodiments, the PD2-3T is the powder compaction density of the second negative electrode active material measured at a pressure of 30 kN under the "5T rapid test" program of an automatic powder compactor.

[0095] In some embodiments, the inner diameter of the mold of the automatic powder compactor is 1.3 cm, and the powder loading amount for each test is 1±0.001 g.

[0096] In some embodiments, the "5T rapid test" procedure includes the following steps:

[0097] 1. Displacement control: 10 min / min, force control: 20 kN; 2. Force holding: 30 s; 3. Displacement control: 10 min / min, force control: 20 N; 4. Force holding: 30 s; 5. Displacement control: 10 min / min, force control: 30 kN; 6. Force holding: 30 s; 7. Displacement control: 10 min / min, force control: 20 N; 8. Force holding: 30 s; 9. Displacement control: 10 min / min, force control: 40 kN; 10. Force holding: 30 s; 11. Displacement control: 10 min / min, force control: 20 N; 12. Force holding: 30 s; 13. Displacement control: 10 min / min, force control: 50 kN; 14. Force holding: 30 s; 15. Displacement control: 10 min / min, force control: 20 N; 16. Force holding: 30 s.

[0098] In some embodiments, the PD1-2T is 0.6-1.18 g / cm 3 , preferably 0.8-1.1g / cm 3 , for example 0.6 g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 or 0.18g / cm 3 .

[0099] In some embodiments, the PD1-3T is 0.7-1.25 g / cm 3 , preferably 0.9-1.15g / cm 3 , for example 0.7 g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 or 1.25g / cm 3 .

[0100] In some embodiments, the PD1-4T is 0.8-1.3 g / cm 3 , preferably 0.9-1.2g / cm 3 , for example 0.8 g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm3 , 1.2g / cm 3 or 1.3 g / cm 3 .

[0101] In some embodiments, the PD2-3T is 1.3-2.2 g / cm 3 , preferably 1.4-2.1g / cm 3 , for example 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 or 2.2g / cm 3 .

[0102] The study found that by adding an appropriate amount of hard carbon negative electrode material to the existing common negative electrode system and calculating and obtaining the negative electrode sheet processing parameters through the characteristic data of the negative electrode material, the advantages of the hard carbon negative electrode material can be fully utilized, and a significant improvement in the cycle life and fast charging capability of the lithium-ion battery can be achieved. By mixing hard carbon negative electrode materials into the negative electrode sheet, the physical rebound rate and porosity of the negative electrode sheet can be significantly improved, the contact area between the negative electrode sheet and the electrolyte can be increased, and the cycle performance of the lithium-ion battery can be improved. Furthermore, based on the particle size distribution and powder compaction density of the negative electrode active material, the ultimate compaction density of the negative electrode sheet is obtained, and a reasonable electrode sheet compaction density is selected. The obtained negative electrode sheet can avoid problems such as cell bulging and cycle deterioration caused by overvoltage of the negative electrode sheet.

[0103] According to an embodiment of the present invention, the compaction density A of the negative electrode sheet is less than the ultimate compaction density α of the negative electrode sheet. Studies have found that when the compaction density of the negative electrode sheet blended with hard carbon negative electrode material is too high, abnormalities such as crushing of the negative electrode active material particles and too low a physical rebound rate of the negative electrode sheet are prone to occur. When the compaction density A of the negative electrode sheet is less than the ultimate compaction density α of the negative electrode sheet, it can effectively improve the physical rebound rate and porosity of the negative electrode sheet, while also avoiding problems such as cell bloating and cycle deterioration caused by overvoltage of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0104] According to an embodiment of the present invention, the ultimate compaction density α of the negative electrode sheet is 0.950-2.155 g / cm 3 , for example 0.950 g / cm 3 , 1.150g / cm 3 , 1.250g / cm 3, 1.450g / cm 3 , 1.650g / cm 3 、1.850g / cm 3 , 2.050g / cm 3 or 2.155g / cm 3 .

[0105] According to an embodiment of the present invention, when II-Dv50 / I-Dv50≥2.4, the ultimate compaction density α1 of the negative electrode sheet is 1.050-2.155 g / cm 3 .

[0106] According to an embodiment of the present invention, when 2≤II-Dv50 / I-Dv50<2.4, α2 is 1.000-2.153 g / cm 3 .

[0107] According to an embodiment of the present invention, when 1≤II-Dv50 / I-Dv50<2, α3 is 0.950-2.150 g / cm 3 .

[0108] According to an embodiment of the present invention, the porosity of the negative electrode sheet is 13-50%, for example, 13%, 14%, 15%, 16%, 18%, 20%, 23%, 25%, 28%, 31%, 33%, 35%, 38%, 40%, 44%, 47% or 50%. The porosity of the negative electrode sheet is within the above-mentioned appropriate range, so that the electrolyte can fully penetrate the negative electrode active material, thereby improving the dynamic performance; when the porosity is too large, the contact points between the negative electrode active material particles are reduced, the internal resistance of the battery is increased, and the energy density of the matrix is ​​also lost; when the porosity is too small, the electrolyte and the negative electrode sheet are not sufficiently infiltrated, the transmission of lithium ions between the negative electrode active materials is interrupted and hindered, and the improvement of the battery's cycle performance is affected.

[0109] According to an embodiment of the present invention, the negative electrode active material refers to a material in the negative electrode sheet that has the function of reversibly removing and inserting lithium during the charge and discharge process of the battery.

[0110] According to an embodiment of the present invention, the hard carbon anode material has a microstructure of graphite microlayers and ultrafine pores, resulting in lower true and tapped densities than graphite anode materials. The addition of the hard carbon anode material can increase the physical rebound rate and porosity of the anode sheet, increase the contact area between the electrolyte and the anode sheet, improve lithium plating, and enhance battery cycle performance.

[0111] In some embodiments, the X-ray diffraction (XRD) pattern of the hard carbon negative electrode material has a characteristic peak located between 15° and 35°, and the half-maximum width of the characteristic peak is 4° to 12°. When the XRD pattern of the negative electrode material has the above characteristic peak and the 002 interplanar spacing (d002 ) is between 0.35nm and 0.42nm, proving that it contains at least the hard carbon negative electrode material. The interplanar spacing of the hard carbon negative electrode material is much larger than the 002 interplanar spacing of pure graphite. The larger 002 interplanar spacing helps to quickly deintercalate lithium ions inside the hard carbon negative electrode material, improve the constant current time in the constant current and constant voltage charging system and reduce the constant voltage time, thereby achieving improvements in fast charging performance and cycle performance. Therefore, the negative electrode active material of the present application is applied to secondary batteries, which can improve the cycle and fast charging rate performance of secondary batteries.

[0112] In some embodiments, the ultrafine pores of the hard carbon negative electrode material have a maximum pore diameter of 0.35-1.5 nm. This suitable range facilitates the smooth deposition and release of lithium ions (with an ionic radius of approximately 76 μm) within the micropores, thereby improving the reversible capacity of the hard carbon negative electrode material. As a result, the negative electrode active material of the present application can have a high reversible capacity and, when applied to secondary batteries, can enable the battery to have a higher energy density.

[0113] In some embodiments, the true density of the hard carbon negative electrode material is 1.3-2.3 g / cm 3 In the negative electrode active material of the present application, the hard carbon negative electrode material has more micropores and a larger 002 interplanar spacing, thereby being able to have a lower true density while having a high capacity. Therefore, the negative electrode active material of the present application can be used in secondary batteries to improve the mass energy density of secondary batteries.

[0114] In some embodiments, the powder conductivity of the hard carbon negative electrode material at 20 kN is 0.1-100 S / cm. In the negative electrode active material of the present application, the hard carbon negative electrode material has a relatively large microporous structure and a relatively low true density, which makes the powder conductivity of the hard carbon negative electrode material much lower than that of the graphite negative electrode material.

[0115] In some embodiments, the "powder conductivity at 20 kN" test is performed using a four-probe conductivity tester. The test voltage is limited to 10 V, the probe spacing is 3.0 mm, the sample mold radius is 10 mm, the sample weight is 2.75 ± 0.25 g, and the electrode radius is 0.7 mm.

[0116] According to an embodiment of the present invention, the graphite negative electrode material, silicon negative electrode material, silicon-oxygen negative electrode material, silicon-carbon negative electrode material and soft carbon negative electrode material are negative electrode materials known in the art.

[0117] According to an embodiment of the present invention, the negative electrode sheet further includes a negative electrode current collector.

[0118] In some embodiments, the present application does not limit the negative electrode current collector of the negative electrode plate. Metal foil, porous metal plate or composite current collector can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). As an example, the negative electrode plate is a negative electrode plate of a lithium ion battery, and the negative electrode current collector can be copper foil. As another example, the negative electrode plate is a negative electrode plate of a sodium ion battery, and the negative electrode current collector can be copper foil or aluminum foil.

[0119] In some embodiments, the negative electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the negative electrode active material layer may be disposed on one surface of the negative electrode current collector, or may be disposed on both surfaces of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in its thickness direction, and the negative electrode active material layer may be disposed on either one surface or both surfaces of the two opposite surfaces of the negative electrode current collector.

[0120] According to an embodiment of the present invention, the negative electrode active material layer may further optionally include a binder. The binder may include at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0121] According to an embodiment of the present invention, the negative electrode active material layer may further optionally include a conductive agent. The conductive agent may include a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. For example, the carbon-based material may include at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metal-based material may include metal powder or metal fiber. The conductive polymer may include a polyphenylene derivative.

[0122] According to an embodiment of the present invention, the negative electrode active material layer may optionally further include other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0123] According to embodiments of the present invention, the negative electrode sheet in this application can be prepared according to conventional methods in the art. For example, the negative electrode active material, conductive agent, binder, and thickener are dispersed in a solvent, which can be deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, and the negative electrode sheet is obtained through drying, cold roller pressing, and other processes. During the rolling process, the rolling pressure and roller gap are controlled to control the compaction density A of the obtained negative electrode sheet, and ensure that the compaction density A of the negative electrode sheet is less than the ultimate compaction density α of the negative electrode sheet.

[0124] It should be noted that the parameters of each negative electrode active material layer given in this application refer to the parameter range of the negative electrode active material layer on one side. When the negative electrode active material layer is provided on both sides of the negative electrode current collector, the parameters of the negative electrode active material layer on either side that meet the requirements of this application are considered to fall within the scope of protection of this application.

[0125] In addition, the negative electrode sheet in this application does not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode active material layer.

[0126] <Lithium-ion battery>

[0127] The present invention also provides a lithium-ion battery, which includes the above-mentioned negative electrode sheet.

[0128] According to an embodiment of the present invention, the lithium ion battery satisfies: 60.00%≤C 锂 / D 锂 ≤99.9%;

[0129] Among them, C 锂 is the discharge capacity of the lithium-ion battery when it drops from 4.45V to 3V, in mAh; D 锂 The discharge capacity of the lithium-ion battery when it drops from 4.45V to 2.5V is recorded in mAh.

[0130] According to an embodiment of the present invention, the lithium ion battery satisfies: 60.00%≤C 锂 / D 锂 ≤99.9%; especially meeting 75.00%≤C 锂 / D 锂 ≤99.9%, indicating that the lithium-ion battery has good cycle performance.

[0131] According to an embodiment of the present invention, the lithium-ion battery includes a positive electrode sheet, a separator, and an electrolyte.

[0132] According to an embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a solid electrolyte, a conductive agent, and the above-mentioned binder.

[0133] According to an embodiment of the present invention, the positive electrode active material layer includes the following components in mass percentage: 60-80 wt% of positive electrode active material, 15-25 wt% of solid electrolyte, 0.05-10 wt% of conductive agent, and 0.05-10 wt% of binder.

[0134] According to an embodiment of the present invention, the positive electrode active material includes lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (Li z Ni x Co y Mn 1-x-y O2, where 0.95 ≤ z ≤ 1.05, x > 0, y > 0, 0 < x + y < 1), lithium manganese oxide (LiMnO2), lithium nickel cobalt aluminum oxide (Li z Ni x Co y Al 1-x- y O2, where 0.95 ≤ z ≤ 1.05, x > 0, y > 0, 0.8 ≤ x + y < 1), lithium nickel cobalt manganese aluminum oxide (Li z Ni x Co y Mn w Al 1-x-y-w O2, where 0.95 ≤ z ≤ 1.05, x > 0, y > 0, w > 0, 0.8 ≤ x + y + w < 1), nickel cobalt aluminum tungsten material, lithium-rich manganese-based solid solution positive electrode material (xLi2MnO3·(1 - x)LiMO2, where M = Ni / Co / Mn), lithium nickel cobalt oxide (LiNi x Co y O2, where x > 0, y > 0, x + y = 1), lithium nickel titanium magnesium oxide (LiNi x Ti y Mg z O2, where x > 0, y > 0, z > 0, x + y + z = 1), lithium nickel oxide (Li2NiO2), spinel lithium manganese oxide (LiMn2O4), nickel cobalt tungsten material, or a combination of one or more of them.

[0135] According to an embodiment of the present invention, the conductive agent includes one or more of conductive carbon black, Ketjen black, conductive fiber, conductive polymer, acetylene black, carbon nanotube, graphene, flake graphite, conductive oxide, and metal particles.

[0136] According to an embodiment of the present invention, the single surface density of the positive electrode sheet is 2 to 30 mg / cm 2 .

[0137] According to an embodiment of the present invention, the thickness of the positive electrode current collector is 3 μm to 15 μm, preferably 4 μm to 10 μm, such as 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm or 15 μm.

[0138] According to an embodiment of the present invention, the positive electrode current collector is a single-sided aluminum foil, a double-sided aluminum foil or a porous aluminum foil.

[0139] According to an embodiment of the present invention, the thickness of the positive electrode active material layer (the thickness of the single-sided positive electrode active material layer after rolling) is 10μm to 200μm, preferably 50μm to 100μm, such as 10μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 190μm or 200μm.

[0140] According to an embodiment of the present invention, the separator is polyethylene, polypropylene, polyvinylidene fluoride or a multilayer composite membrane thereof.

[0141] According to an embodiment of the present invention, the electrolyte includes an organic solvent. In some embodiments, the organic solvent includes one or more of a carbonate and a carboxylate. In some embodiments, the carbonate includes at least one of a cyclic carbonate and a chain carbonate. In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and its halogenated derivatives, butylene carbonate and its halogenated derivatives, γ-butyrolactone and its halogenated derivatives, and pentylene carbonate and its halogenated derivatives. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate and its halogenated derivatives, diethyl carbonate and its halogenated derivatives, dipropyl carbonate and its halogenated derivatives, and ethyl methyl carbonate and its halogenated derivatives. In some embodiments, the carboxylate includes at least one of ethyl butyrate, methyl butyrate, propyl propionate, ethyl propionate, methyl propionate, ethyl acetate, and methyl acetate.

[0142] According to an embodiment of the present invention, the electrolyte further comprises a lithium salt. In some embodiments, the lithium salt comprises one or more of an inorganic lithium salt and an organic lithium salt. In some embodiments, the lithium salt comprises lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiB(C2O4)2, abbreviated as LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4)).

[0143] According to an embodiment of the present invention, the lithium-ion battery is prepared by the following method:

[0144] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, ensuring that the separator is between the positive and negative electrode sheets to play an isolating role, and then a bare cell is obtained by winding or stacking the sheets layer by layer; the bare cell is placed in an aluminum-plastic film shell, and after packaging, electrolyte injection, aging, formation, and secondary sealing processes, the required lithium-ion battery is obtained.

[0145] <Battery>

[0146] The present invention also provides a battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a first negative electrode active material and a second negative electrode active material; the first negative electrode active material comprises a hard carbon negative electrode material; the second negative electrode active material comprises at least one of a graphite negative electrode material, a silicon negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, and a soft carbon negative electrode material;

[0147] The battery meets the following requirements:

[0148] 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55;

[0149] Among them, II-PD 1+2 is the powder compaction density of the negative electrode active material, unit is g / cm 3 Ⅱ-α 1+2 is the compaction density of the negative electrode sheet, in g / cm 3 .

[0150] According to an embodiment of the present invention, the battery satisfies: 1.15≤II-PD 1+2 / Ⅱ-α 1+2 ≤1.55, II-PD 1+2 / Ⅱ-α 1+2For example, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45 or 1.55; Studies have found that if the actual compaction density of the negative electrode sheet mixed with hard carbon negative electrode material is too large, it is easy to cause abnormal conditions such as crushing of negative electrode active material particles and too low physical rebound rate of the negative electrode sheet. When the battery meets 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 When it is ≤1.55, it can not only effectively improve the physical rebound rate and porosity of the negative electrode sheet, but also avoid the problems of cell bulging and cycle deterioration caused by overvoltage of the negative electrode sheet, thereby improving the cycle performance of the battery.

[0151] According to an embodiment of the present invention, the powder compaction density II-PD of the negative electrode active material 1+2 It is the powder compaction density of the negative active material of the negative electrode sheet in the 0% SOC state measured under the "5T rapid test" program of the automatic powder compactor at a pressure of 30kN.

[0152] According to an embodiment of the present invention, the compaction density of the negative electrode sheet is II-α 1+2 It is the measured compaction density of the negative electrode sheet at 0% SOC. Specifically, it can be calculated by the "small disc method" commonly used in the industry to calculate the density of the negative electrode active material layer, and then inferred after measuring the thickness of the electrode sheet with a micrometer.

[0153] According to an embodiment of the present invention, the powder compaction density II-PD of the negative electrode active material 1+2 1.3-2.5g / cm 3 , for example 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 or 2.5g / cm 3 Crushing the negative electrode active material particles will reduce the overall particle size of the negative electrode active material, making the negative electrode active material powder compacted smaller. Within this limited range, the negative electrode active material can maintain a good morphology and achieve a good cycle life.

[0154] According to an embodiment of the present invention, the compaction density of the negative electrode sheet is II-α 1+20.9-1.8g / cm 3 , for example 0.9 g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 or 1.8g / cm 3 Because the over-pressured negative electrode exceeds the range of its elastic deformation, the physical rebound rate of the electrode will be significantly reduced, resulting in a larger value of the measured compaction density of the negative electrode.

[0155] According to an embodiment of the present invention, the negative electrode sheet in the battery is obtained by the following method: disassembling a battery that is discharged (0% SOC, 3±0.1V) to obtain the negative electrode sheet.

[0156] According to an embodiment of the present invention, the negative electrode active material in the battery is obtained by the following method: disassembling a discharged battery (0% SOC, 3±0.1V) to obtain a negative electrode sheet; soaking the negative electrode sheet in deionized water until the negative electrode active material is completely peeled off, filtering out impurities and diaphragm white glue with a sieve, drying and calcining in an air atmosphere at 400°C for 3h to obtain a powdered negative electrode active material.

[0157] According to an embodiment of the present invention, the median particle size II-I-Dv50 of the first negative electrode active material in the battery is 0.5-12 μm, preferably 2-9 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm.

[0158] According to an embodiment of the present invention, the median particle size II-II-Dv50 of the second negative electrode active material in the battery is 5-20 μm, preferably 8-17 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0159] According to an embodiment of the present invention, the II-I-Dv50 and II-II-Dv50 can be obtained by observing the average particle size of the two negative electrode active materials in the field of view of the negative electrode active material under a high-resolution transmission electron microscope with a magnification factor of 1000 times. 002 The lattice fringe width can distinguish the two negative electrode active materials, among which the d002 The lattice spacing is 0.35-0.42nm.

[0160] According to an embodiment of the present invention, the battery satisfies: 60.00%≤C 锂 / D 锂 ≤99.9%;

[0161] Among them, C 锂 D is the discharge capacity of the battery when it drops from 4.45V to 3V, in mAh; 锂 The discharge capacity of the battery when it drops from 4.45V to 2.5V is recorded in mAh.

[0162] According to an embodiment of the present invention, the battery satisfies: 60.00%≤C 锂 / D 锂 ≤99.9%; especially meeting 75.00%≤C 锂 / D 锂 ≤99.9%, indicating that the battery has good cycle performance.

[0163] In the present invention, unless otherwise specified, the term "negative electrode sheet" refers to a "negative electrode sheet blended with a hard carbon negative electrode material".

[0164] The preparation method of the present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection intended by the present invention.

[0165] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0166] Example 1:

[0167] A battery is prepared by the following method:

[0168] (1) Preparation of negative electrode sheet

[0169] The hard carbon negative electrode material (the maximum micropore diameter is 0.79nm, d 002 =0.38nm, XRD characteristic peak position is 23.4°, characteristic peak half-maximum width is 7.5°, true density is 1.76g / cm 3 The powder conductivity at 20kN is 19.6S / cm. The tap density is 0.81g / cm 3 , I-Dv50 is 4.8μm, PD1-2T is 0.896g / cm 3, PD1-3T is 0.933 g / cm 3 PD1-4T is 0.959g / cm 3 ), graphite negative electrode material (II-Dv50 is 14.5μm, PD2-3T is 1.783g / cm 3 ), sodium carboxymethyl cellulose (binder), styrene-butadiene rubber (binder), and Super P (conductive agent) were mixed in a mass ratio of 30:65:2:2:1, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum mixer. The negative electrode slurry was evenly coated on the surface of a copper foil with a thickness of 6 μm (negative electrode current collector) with a coating surface density of 5.0 mg / cm 2 The copper foil coated with negative electrode slurry was transferred to a 90°C oven for drying for 24 hours, and then the negative electrode sheet was rolled and compacted to 1.51 g / cm 3 , and finally cut to obtain the negative electrode sheet.

[0170] (2) Preparation of positive electrode sheet

[0171] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), acetylene black, and carbon nanotubes (CNTs) were mixed in a mass ratio of 96:2:1.5:0.5, and N-methylpyrrolidone was added. The mixture was stirred in a vacuum mixer until a uniform positive electrode slurry was formed. The positive electrode slurry was evenly coated on a 9μm thick aluminum foil (positive electrode current collector) with a surface density of 9.3mg / cm 2 The coated aluminum foil was baked in an oven and then dried in a 120°C oven for 8 hours. The foil was then rolled and slit to produce the positive electrode sheet. The positive electrode sheet was smaller than the negative electrode sheet, and its reversible capacity per unit area was approximately 4% lower than that of the negative electrode sheet.

[0172] (3) The positive and negative electrode sheets are welded with their metal tabs.

[0173] (4) A polyethylene diaphragm with a thickness of 9 μm was selected.

[0174] (5) The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, ensuring that the separator is located between the positive and negative electrode sheets to provide isolation, and then wound to obtain a bare cell. The bare cell is placed in a casing with an aluminum-plastic film thickness of 0.090 mm, and after encapsulation, electrolyte injection, aging, formation, and secondary sealing, the desired lithium-ion battery is obtained.

[0175] Comparative Example 1:

[0176] The other operations are the same as those in Example 1, except that the negative electrode sheet compaction density A during roller pressing is 1.54 g / cm 3 .

[0177] Example 2:

[0178] Other operations are the same as in Example 1, except that:

[0179] Graphite anode material (II-Dv50 is 11.8μm, PD2-3T is 1.755g / cm 3 )different.

[0180] The negative electrode sheet compaction density A during roller pressing is 1.50 g / cm 3 .

[0181] Comparative Example 2:

[0182] The other operations are the same as those in Example 2, except that the negative electrode sheet compaction density A during roller pressing is 1.51 g / cm 3 .

[0183] Example 3:

[0184] Other operations are the same as in Example 1, except that:

[0185] Graphite anode material (II-Dv50 is 13.5μm, PD2-3T is 2.065g / cm 3 )different.

[0186] The compaction density A of the negative electrode sheet during roller pressing is 1.71 g / cm 3 .

[0187] Comparative Example 3:

[0188] The other operations are the same as those in Example 3, except that the negative electrode sheet compaction density A during roller pressing is 1.73 g / cm 3 .

[0189] Example 4:

[0190] Other operations are the same as in Example 1, except that:

[0191] Hard carbon anode material (the most likely micropore size is 0.53nm, d 002 =0.394nm, XRD characteristic peak position is 24.2°, characteristic peak half-maximum width is 7.1°, true density is 2.17g / cm 3 The powder conductivity at 20kN is 89.1S / cm and the tap density is 0.79g / cm 3 , I-Dv50 is 6.1μm, PD1-2T is 1.061g / cm 3 , PD1-3T is 1.107g / cm 3 PD1-4T is 1.136 g / cm 3 )different.

[0192] The compaction density A of the negative electrode sheet during roller pressing is 1.55 g / cm 3 .

[0193] Comparative Example 4:

[0194] The other operations are the same as those in Example 4, except that the compaction density A of the negative electrode sheet during roller pressing is 1.59 g / cm 3 .

[0195] Example 5:

[0196] Other operations are the same as in Example 1, except that:

[0197] Hard carbon anode material (the maximum micropore size is 0.75nm, d 002 =0.381nm, XRD characteristic peak position is 32.5°, characteristic peak half-maximum width is 4.6°, true density is 2.27g / cm 3 The powder conductivity at 20kN is 0.21S / cm and the tap density is 0.68g / cm 3 , I-Dv50 is 7.1μm, PD1-2T is 1.002g / cm 3 , PD1-3T is 1.037g / cm 3 PD1-4T is 1.059g / cm 3 ) is different. The negative electrode sheet compaction density A during roller pressing is 1.53g / cm 3 .

[0198] Comparative Example 5:

[0199] The other operations are the same as those in Example 5, except that the compaction density A of the negative electrode sheet during roller pressing is 1.56 g / cm 3 .

[0200] Example 6:

[0201] Other operations are the same as in Example 1, except that:

[0202] Hard carbon anode material (the most likely micropore size is 0.46nm, d 002 =0.397nm, XRD characteristic peak position is 18.8°, characteristic peak half-maximum width is 11.4°, true density is 1.39g / cm 3 The powder conductivity at 20kN is 10.53S / cm and the tap density is 0.66g / cm 3 , I-Dv50 is 7.4μm, PD1-2T is 1.032g / cm 3 , PD1-3T is 1.103 g / cm 3 PD1-4T is 1.150g / cm 3) is different. The negative electrode sheet compaction density A during roller pressing is 1.53g / cm 3 .

[0203] Comparative Example 6:

[0204] The other operations are the same as those in Example 6, except that the negative electrode sheet compaction density A during roller pressing is 1.57 g / cm 3 .

[0205] Example 7:

[0206] Other operations are the same as those in Example 6, except that:

[0207] Graphite anode material (II-Dv50 is 10.8μm, PD2-3T is 1.350g / cm 3 ) is different. The negative electrode sheet compaction density A during roller pressing is 1.24g / cm 3 .

[0208] Comparative Example 7:

[0209] The other operations are the same as those in Example 7, except that the negative electrode sheet compaction density A during roller pressing is 1.27 g / cm 3 .

[0210] Example 8:

[0211] Other operations are the same as those in Example 7, except that:

[0212] Hard carbon anode material (the most likely micropore size is 0.61nm, d 002 =0.382nm, XRD characteristic peak position is 26.7°, characteristic peak half-maximum width is 5.3°, true density is 2.13g / cm 3 The powder conductivity at 20kN is 4.30S / cm and the tap density is 0.76g / cm 3 , I-Dv50 is 9.9μm, PD1-2T is 0.885g / cm 3 , PD1-3T is 0.926g / cm 3 , PD1-4T is 0.953g / cm 3 ) is different. The negative electrode sheet compaction density A during roller pressing is 1.20g / cm 3 .

[0213] Comparative Example 8:

[0214] The other operations are the same as those in Example 8, except that the negative electrode sheet compaction density A during roller pressing is 1.22 g / cm 3 .

[0215] Example 9:

[0216] Other operations are the same as those in Example 3, except that:

[0217] Hard carbon negative electrode material, graphite negative electrode material, sodium carboxymethyl cellulose (binder), styrene-butadiene rubber (binder), and Super P (conductive agent) are mixed in a mass ratio of 1:94:2:2:1. The negative electrode sheet compaction density A during roller pressing is 1.98 g / cm 3 .

[0218] Comparative Example 9:

[0219] Other operations are the same as those in Example 9, except that no hard carbon negative electrode material is used, that is, the proportion of graphite negative electrode material in the negative electrode active material is 100 wt%.

[0220] Example 10:

[0221] Other operations are the same as in Example 1, except that:

[0222] Hard carbon anode material, graphite anode material (II-Dv50 is 10.8μm, PD2-3T is 1.350g / cm 3 ), sodium carboxymethyl cellulose (binder), styrene-butadiene rubber (binder), and Super P (conductive agent) were mixed in a mass ratio of 46:49:2:2:1. The compacted density A of the negative electrode during roller pressing was 1.14 g / cm 3 .

[0223] Comparative Example 10:

[0224] Other operations are the same as in Example 1, except that:

[0225] Hard carbon anode material, graphite anode material (II-Dv50 is 10.8μm, PD2-3T is 1.350g / cm 3 ), sodium carboxymethyl cellulose (binder), styrene-butadiene rubber (binder), and Super P (conductive agent) were mixed in a mass ratio of 50:45:2:2:1. The compacted density A of the negative electrode during roller pressing was 1.12 g / cm 3 .

[0226] Example 11:

[0227] Other operations are the same as in Example 1, except that:

[0228] The second negative electrode active material contains a silicon-carbon negative electrode material in addition to the graphite negative electrode material. The silicon-carbon negative electrode material accounts for 10 wt% of the second negative electrode active material. The II-Dv50 of the second negative electrode active material is 13.2 μm, and the PD2-3T is 1.713 g / cm 3The negative electrode sheet compaction density A during roller pressing is 1.46 g / cm 3 .

[0229] Comparative Example 11:

[0230] The other operations are the same as those in Example 11, except that the negative electrode sheet compaction density A during roller pressing is 1.48 g / cm 3 .

[0231] The negative electrode sheets obtained in the above examples and comparative examples were subjected to the following tests:

[0232] (1) Test of the physical rebound rate of the negative electrode sheet. This can be obtained by measuring and calculating the growth rate of the thickness of the negative electrode sheet after the cold roller rolling and standing for 24 hours compared to the thickness of the electrode sheet just after the rolling is completed. Specifically, the growth rate of the thickness of the prepared negative electrode sheet after the cold roller rolling for 24 hours compared to the thickness of the electrode sheet just after the rolling is completed is the physical rebound rate of the negative electrode sheet; specifically (D1-D2) / D1, where D1 is the thickness of the electrode sheet just after the rolling is completed, in μm, and D2 is the thickness of the electrode sheet after 24 hours of rolling, in μm.

[0233] The batteries obtained in the above examples and comparative examples were tested as follows:

[0234] (1) 6C cycle 50T negative electrode sheet status: The 6C cycle is based on the battery's theoretical design capacity C. In a 25°C constant temperature box, the battery is charged and discharged at 6C constant current and constant voltage for 50 cycles. The battery is then dissected. The surface state of the negative electrode sheet after dissection is the result of this test. It should be noted that the 6C constant current and constant voltage charge and discharge cycle refers to charging at a 6C rate to the upper limit voltage, then continuing to charge at a constant upper limit voltage until the current reaches 0.05C, standing for 10 minutes after charging is completed, discharging at a 6C rate to the lower limit voltage, and then continuing to discharge at a constant voltage until the current reaches 0.05C.

[0235] (2) Normal temperature cycle life: The normal temperature cycle life refers to the number of cycles when the battery capacity retention rate is ≥80% under the 6C constant current and constant voltage charge and discharge test system in a 25°C environment, where T is the number of cycles.

[0236] (3)Ⅱ-PD 1+2 / Ⅱ-α 1+2 Testing: This test involved disassembling a fresh battery with a 0% SOC and obtaining a "secondary composite negative electrode sheet." This "secondary composite negative electrode sheet" was soaked in deionized water until the negative electrode material and current collector were completely separated and detached. A sieve was then used to filter out impurities and the white diaphragm adhesive to obtain a black powdered negative electrode material. This powder was then dried and calcined in air at 400°C for 3 hours to obtain the "secondary negative electrode active material."

[0237] II-PD1+2 The powder compaction of the "secondary negative electrode active material" is measured using the "5T rapid test" program of the automatic powder compactor after maintaining a pressure of 30kN for 30s. 1+2 The measured compaction density of the negative electrode active material layer of the "secondary composite negative electrode sheet" at 0% SOC can be calculated by punching the small disc method to calculate the negative electrode active material layer density, and then inferring it after measuring the thickness of the negative electrode active material layer with a micrometer. Among them, the "punching small disc method" is to use a circular mold with a specific diameter R to punch out the disassembled double-sided negative electrode sheet and the empty foil respectively, to obtain a double-sided negative electrode disc and an empty foil disc, and weigh the mass w1 of the double-sided negative electrode disc and the mass w2 of the empty foil disc respectively, and use the formula 2(w1-w2) / πR 2 Calculate the areal density of the negative electrode sheet.

[0238] (4) Porosity test: The test is performed on a "secondary composite negative electrode sheet" obtained by disassembling a fresh battery with a 0% SOC. The secondary composite negative electrode sheet is laid flat on a glass tabletop and cut into a certain size. The thickness of the sheet is measured with a micrometer, and the volume of the sheet is calculated as V1. The sheet is then placed in a test device, the gas valve is opened, helium is introduced, and the true volume of the sheet, V2, is measured. The porosity of the negative electrode sheet is calculated using the formula (V1-V2) / V1*100%.

[0239] Table 1. Test parameters of negative electrode active materials and negative electrode sheets of Examples and Comparative Examples

[0240] Table 2. Test parameters of negative electrode sheets and negative electrode active materials after disassembly of the battery cells of the embodiment and comparative example

[0241] As can be seen from the data in Table 1, the data for Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, Example 3 and Comparative Example 3, Example 4 and Comparative Example 4, Example 5 and Comparative Example 5, Example 6 and Comparative Example 6, Example 7 and Comparative Example 7, and Example 8 and Comparative Example 8 demonstrate that the α value calculated based on the median particle size of the negative electrode active material can effectively obtain and control the compaction density of the negative electrode sheet. This demonstrates the universality of the relationship: when II-Dv50 / I-Dv50 ≥ 2.4, α = PD1-4T × wt1% + PD2-3T × wt2%; when 2 ≤ II-Dv50 / I-Dv50 < 2.4, α = PD1-3T × wt1% + PD2-3T × wt2%; when 1 ≤ II-Dv50 / I-Dv50 < 2, α = PD1-2T × wt1% + PD2-3T × wt2%. When the compaction density is less than the limiting compaction density α, the beneficial effect of hard carbon incorporation can be fully realized, achieving a higher rolling rebound rate. As shown in Table 1 for Example 11 and Comparative Example 11, when the second negative electrode active material containing silicon carbon and graphite is blended with hard carbon, the negative electrode sheet still satisfies the relationship and exhibits excellent cycling performance, demonstrating the reliability of the relationship.

[0242] As can be seen from the data in Table 2, the data of Example 1 and Comparative Example 1, Example 4 and Comparative Example 4, Example 6 and Comparative Example 6, and Example 10 and Comparative Example 10 show that a higher electrode porosity can improve the contact between the negative electrode and the electrolyte, while avoiding electrode breakage, cycle deterioration, and cell bloating caused by overvoltage, and achieve a cycle life advantage of 500T over the overvoltage comparative group. The batteries of all examples also meet C 锂 / D 锂 interval range.

[0243] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, wherein the negative electrode active material comprises a first negative electrode active material and a second negative electrode active material; wherein the first negative electrode active material comprises a hard carbon negative electrode material; and wherein the second negative electrode active material comprises at least one of a graphite negative electrode material, a silicon negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material and a soft carbon negative electrode material; The negative electrode sheet satisfies: 1.10≤Ⅱ-PD 1+2 / Ⅱ-α 1+2 ≤1.55; in, II-PD 1+2 is the compacted density of the negative electrode active material powder, in g / cm 3 ;Ⅱ-α 1+2 is the compaction density of the negative electrode, in g / cm 3 .

2. The negative electrode sheet according to claim 1, characterized in that: Powder compaction density of the negative electrode active material II-PD 1+2 1.3-2.5g / cm 3 ; And / or, the compaction density of the negative electrode sheet is II-α 1+2 0.9-1.8g / cm 3 .

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The compaction density A of the negative electrode sheet is less than the limit compaction density α of the negative electrode sheet; And / or; the ultimate compaction density α of the negative electrode sheet is 0.950-2.155g / cm 3 .

4. The negative electrode sheet according to claim 3, characterized in that: The limiting compaction density α of the negative electrode sheet satisfies one of the following: (1) When II-Dv50 / I-Dv50≥2.4, α1=PD1-4T×wt1%+PD2-3T×wt2%; (2) When 2≤II-Dv50 / I-Dv50<2.4, α2=PD1-3T×wt1%+PD2-3T×wt2%; (3) When 1≤II-Dv50 / I-Dv50<2, α3=PD1-2T×wt1%+PD2-3T×wt2%; Wherein, I-Dv50 is the median particle size of the first negative electrode active material, in μm; II-Dv50 is the median particle size of the second negative electrode active material, in μm; wt1% is the mass percentage of the first negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material; wt2% is the mass percentage of the second negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material; PD1-2T is the powder compaction density of the first negative electrode active material under a pressure of 20 kN, in g / cm 3 PD1-3T is the powder compaction density of the first negative electrode active material under a pressure of 30 kN, in g / cm 3 PD1-4T is the powder compaction density of the first negative electrode active material under a pressure of 40 kN, in units g / cm 3 PD2-3T is the powder compaction density of the second negative electrode active material under a pressure of 30 kN, in g / cm 3 .

5. The negative electrode sheet according to claim 4, characterized in that: The median particle size I-Dv50 of the first negative electrode active material is 0.5-12 μm; and / or, the median particle size II-Dv50 of the second negative electrode active material is 5-20 μm; And / or, the wt1% is 0.5%-50%; And / or, the wt2% is 50%-99.5%; And / or, the PD1-2T is 0.6-1.18 g / cm 3 ; And / or, the PD1-3T is 0.7-1.25 g / cm 3 ; And / or, the PD1-4T is 0.8-1.3 g / cm 3 ; And / or, the PD2-3T is 1.3-2.2 g / cm 3 . And / or, the ultimate compaction density α1 of the negative electrode sheet is 1.050-2.155 g / cm 3 ; And / or, the ultimate compaction density α2 of the negative electrode sheet is 1.000-2.153 g / cm 3 ; And / or, the ultimate compaction density α3 of the negative electrode sheet is 0.950-2.150 g / cm 3 .

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The physical rebound rate of the negative electrode sheet is 5%-15%.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The porosity of the negative electrode sheet is 13-50%.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The X-ray diffraction (XRD) spectrum of the hard carbon negative electrode material has a characteristic peak located between 15° and 35°, and the half-peak width of the characteristic peak is 4° to 12°; And / or, the maximum pore size of the ultrafine pores of the hard carbon negative electrode material is 0.35-1.5 nm; And / or, the true density of the hard carbon negative electrode material is 1.3-2.3 g / cm 3 ; And / or, the powder conductivity of the hard carbon negative electrode material at 20 kN is 0.1-100 S / cm; And / or, the hard carbon negative electrode material 002 The lattice spacing is 0.35-0.42nm.

9. A lithium ion battery, comprising the negative electrode sheet according to any one of claims 1 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery meets: 60.00% ≤ C 锂 / D 锂 ≤99.9%; Among them, C 锂 is the discharge capacity of the battery when it drops from 4.45V to 3V, in mAh; D 锂 yes The discharge capacity of the battery when it drops from 4.45V to 2.5V is recorded in mAh.

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