CATALYTIC PLATES, LITHIUM-ION BATTERIES, AND ELECTRICAL EQUIPMENT

Abstract

The invention relates to a cathode plate, lithium-ion battery, and electrical device. The compression density A, electrolyte absorption time B, and electrolyte retention ratio C of the cathode plate satisfy the following relationship expression: 2.65 ≤ 100A / (B × C) ≤ 7.74, where the unit of A is g / cm³, the unit of B is s, and the compression density A of the cathode plate is in the range of 1.30 to 1.75 g / cm³. By controlling the value of 100A / (B × C) within a specific range, it is possible to adjust and control the high cycle performance and capacity. The cathode plate not only has a relatively high specific capacity but also excellent cycle life and safety.

Description

Negative electrode sheets, lithium-ion batteries and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311233157.4 filed with the China Patent Office on September 22, 2023, entitled “A negative electrode plate, lithium-ion battery and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a negative electrode sheet, a lithium-ion battery, and an electrical device. Background Art

[0004] With the rapid development of new energy vehicles, addressing the issue of short electric vehicle range has become a pressing issue. There is an urgent need to develop high-energy-density lithium-ion batteries. Improving the compaction density of positive and negative electrodes is one method for increasing lithium-ion battery capacity. Positive and negative electrodes are key materials in lithium-ion batteries. During lithium battery manufacturing, compaction density is closely related to the electrode specific capacity, efficiency, internal resistance, and battery cycle performance.

[0005] When the compaction density is too low, the higher porosity causes some particles to fall off during cycling, forming an insulating state and being unable to participate in charge and discharge. This results in low discharge specific capacity, poor contact between the electrode coating and the current collector, and high contact internal resistance and exchange impedance. Generally speaking, within the material's allowable compaction range, the greater the electrode compaction density, the higher the battery capacity. Therefore, compaction density is also considered a reference indicator for the material's energy density.

[0006] However, when the compaction density is too large, the degree of extrusion between the material particles is large, the porosity of the electrode is small, the ability of the electrode to absorb electrolyte is poor, the electrolyte is difficult to infiltrate, the electronic conduction and ion conduction are not coordinated, and dead lithium or lithium precipitation areas are formed, resulting in a low specific capacity of the material and poor liquid retention capacity of the battery. The greater the polarization during the battery cycle, the greater the attenuation will be, the internal resistance will increase significantly, and the rate performance and cycle performance will be poor.

[0007] Therefore, finding the right compaction density is crucial for battery design.

[0008] Summary of the Invention

[0009] A negative electrode sheet, wherein the compaction density A of the negative electrode sheet, the liquid absorption time B of the negative electrode sheet, and the liquid retention rate C of the negative electrode sheet satisfy the following relationship: 2.65≤100A / (B×C)≤7.74; wherein the unit of A is g / cm 3, the unit of B is s; and the compaction density A of the negative electrode sheet is 1.30 to 1.75 g / cm 3 .

[0010] In some embodiments, the compaction density A of the negative electrode plate is 1.40 to 1.75 g / cm 3 .

[0011] In some embodiments, the liquid absorption time B of the negative electrode plate is 40 to 220 seconds.

[0012] In some embodiments, the liquid retention rate C of the negative electrode plate is 30% to 42%.

[0013] In some embodiments, the absorption time B is the time taken for the electrolyte to completely soak into the negative electrode plate.

[0014] In some embodiments, the liquid retention rate C = (m2-m1) / (m1-m0)×100%, wherein m0 is the mass of the current collector in the negative electrode plate, m1 is the total mass of the negative electrode plate before being soaked in the electrolyte, and m2 is the total mass of the negative electrode plate after being completely soaked in the electrolyte.

[0015] In some embodiments, the first discharge specific capacity of the negative electrode plate is ≥320 mAh / g.

[0016] In some embodiments, the capacity retention rate of the negative electrode plate after 200 cycles at 1C is ≥90%.

[0017] In some embodiments, the capacity retention rate of the negative electrode plate after 500 cycles at 1C is ≥89%.

[0018] In some embodiments, the capacity retention rate of the negative electrode plate after 800 cycles at 1C is ≥87%.

[0019] A lithium-ion battery comprises the negative electrode plate.

[0020] An electrical device comprises the lithium-ion battery. DETAILED DESCRIPTION

[0021] The advantages of the embodiments in the application content will be explained in the embodiment section of the specification below, and some of them are obvious from the specification, or can be obtained through some embodiments of the embodiments of the present disclosure.

[0022] The technical solution of the present disclosure is further illustrated below through some implementation methods.

[0023] In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the present disclosure is further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described herein are only used to explain the present disclosure and are not used to limit the present disclosure. In addition, the technical features involved in the various embodiments of the present disclosure described below can be combined with each other as long as they do not conflict with each other. Without departing from the principles of the embodiments of the present disclosure, several improvements and modifications can be made, and these improvements and modifications are also considered to be within the scope of protection of the embodiments of the present disclosure.

[0024] In a first aspect, the present disclosure provides a negative electrode sheet, wherein the compaction density A of the negative electrode sheet, the liquid absorption time B of the negative electrode sheet, and the liquid retention rate C of the negative electrode sheet satisfy the following relationship: 2.65≤100A / (B×C)≤7.74.

[0025] That is, the value of 100A / (B×C) is 2.65 to 7.74, including but not limited to any one of 2.65, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.4, 4.7, 5.0, 5.1, 5.4, 5.7, 6.0, 6.5, 6.8, 7.0, 7.3, 7.5, and 7.74, or a range between any two of the values.

[0026] The unit of compacted density A is g / cm 3 .

[0027] The unit of the liquid absorption time B is s (seconds).

[0028] It can be understood that the absorption time is the time taken for the electrolyte (such as propylene carbonate (PC)) to completely soak into the negative electrode plate, or the time taken for the electrolyte to be completely absorbed.

[0029] Furthermore, the compaction density A of the negative electrode sheet is 1.30 to 1.75 g / cm 3 , including but not limited to 1.30g / cm 3 , 1.305g / cm 3 , 1.40g / cm 3 , 1.405g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.75g / cm 3 Any point value in or any range of values ​​between them.

[0030] Appropriate electrode compaction density can increase the battery's discharge capacity, reduce internal resistance, minimize polarization loss, extend the battery's cycle life, and improve the utilization rate of lithium-ion batteries. Generally speaking, within the material's allowable compaction range, the greater the electrode compaction density, the higher the battery capacity. In other words, a higher compaction density can increase the battery's discharge capacity.

[0031] However, as the compaction density increases, the porosity of the electrode becomes smaller, the electrode's ability to absorb electrolyte is poor, the electrolyte is difficult to infiltrate, the electronic conduction and ion conduction are not coordinated, and dead lithium or lithium precipitation areas are formed, resulting in a lower specific capacity of the material and poor battery fluid retention. The greater the polarization during the battery cycle, the greater the attenuation will be, the internal resistance will increase significantly, and the rate performance and cycle performance will be poor.

[0032] Therefore, achieving a balance between high capacity and long cycle performance is a key and challenging aspect of negative electrode plate selection. This disclosure controls the compaction density, liquid absorption time, and liquid retention rate of different negative electrode plates to select negative electrode plates that satisfy the equation 2.65≤100A / (B×C)≤7.74. This effectively ensures the capacity, wettability, and liquid retention of the negative electrode plates, achieving a balanced balance between capacity and long cycle performance.

[0033] Therefore, the negative electrode provided by the present disclosure can achieve a high electrode compaction density while balancing the relationship between the electrode compaction density and the liquid absorption time and liquid retention rate, thereby ensuring good long-term cycle stability while ensuring the battery capacity.

[0034] In some specific embodiments, in order to further comprehensively consider the specific capacity and cycle performance, the compaction density A of the negative electrode sheet is 1.40 to 1.75 g / cm 3 , including but not limited to 1.40g / cm 3 , 1.405g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 , 1.75g / cm 3 Any point value in or any range of values ​​between them.

[0035] In some specific embodiments, in order to further comprehensively consider the specific capacity and cycle performance, the liquid absorption time B of the negative electrode plate is 40 to 220 s, including but not limited to any one of 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, 140s, 150s, 180s, 200s, and 220s, or a range between any two of the values.

[0036] In some specific embodiments, in order to further comprehensively consider the specific capacity and cycle performance, the liquid retention rate C of the negative electrode sheet is 30% to 42%, including but not limited to any one of 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, and 42%, or a range between any two of them.

[0037] In some specific embodiments, the absorption time B is the time taken for the electrolyte to completely soak into the negative electrode plate.

[0038] In some specific embodiments, the imbibition time is the time taken for 4 μl of electrolyte to completely soak the negative electrode sheet.

[0039] For example, if the time of dripping is t1 and the time for the electrolyte to completely penetrate the electrolyte after dripping is t2, then the absorption time B = t2 - t1, where both t2 and t1 are in seconds.

[0040] In some specific embodiments, the liquid retention rate C = (m2-m1) / (m1-m0)×100%, where m0 is the mass of the current collector in the negative electrode plate, m1 is the total mass of the negative electrode plate before being soaked in the electrolyte, and m2 is the total mass of the negative electrode plate after being completely soaked in the electrolyte.

[0041] In some specific embodiments, the current collector includes copper foil.

[0042] In some specific embodiments, a negative electrode sheet with a mass of m1 is immersed in an electrolyte, sealed and immersed for 24 hours, and then the mass m2 of the soaked negative electrode sheet is weighed and then substituted into the above formula C = (m2-m1) / (m1-m0)×100% for calculation.

[0043] In some specific embodiments, the compaction density A of the negative electrode sheet = negative electrode sheet area density / (negative electrode sheet thickness-current collector thickness).

[0044] In some specific embodiments, the thickness of the negative electrode sheet is adjusted by controlling the rolling pressure of the electrode sheet after coating, thereby adjusting the compaction density of the negative electrode sheet.

[0045] In some specific embodiments, the liquid absorption time and liquid retention rate can be adjusted by adjusting the compaction density.

[0046] In some specific embodiments, the first discharge specific capacity of the negative electrode plate is ≥320mAh / g, including but not limited to any one of 325mAh / g, 328mAh / g, 330mAh / g, 336mAh / g, 340mAh / g, 345mAh / g, 350mAh / g, 356mAh / g, 360mAh / g, 400mAh / g, 450mAh / g, and 500mAh / g, or a range between any two of them.

[0047] The negative electrode plate provided by the present disclosure has a higher initial discharge specific capacity.

[0048] In some specific embodiments, the capacity retention rate of the negative electrode plate after 200 cycles at 1C is ≥90%, including but not limited to any one of 90.5%, 91%, 91.5%, 92%, 93%, 93.5%, and 94%, or a range of values ​​between any two of them.

[0049] In some specific embodiments, the capacity retention rate of the negative electrode plate after 500 cycles at 1C is ≥89%, including but not limited to any point value of 89%, 90%, 91%, 92%, 93%, 94%, or a range of values ​​between any two of them.

[0050] In some specific embodiments, the capacity retention rate of the negative electrode plate after 800 cycles at 1C is ≥87%, including but not limited to any one of 87%, 88%, 89%, 90%, 91%, 92%, 93%, and 94%, or a range of values ​​between any two of them.

[0051] In some specific embodiments, the capacity retention rate of the negative electrode plate after 3000 cycles at 1C is ≥80%, including but not limited to any one of 80%, 81%, 82%, 83%, 84%, and 85%, or a range of values ​​between any two of them.

[0052] The negative electrode sheet provided by the present disclosure also has excellent cycle performance.

[0053] It is understandable that the above electrochemical performance results are all electrochemical performances measured after the negative electrode sheet is made into a lithium-ion battery.

[0054] The negative electrode sheet can be prepared by any conventional method, which is not limited in the present disclosure.

[0055] In some specific embodiments, the negative electrode plate includes a negative electrode active material. The negative electrode active material includes any commercially available negative electrode active material or any material prepared according to prior art. For example, the negative electrode active material may be one or more of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon (coal-based), soft carbon (coal-based), hard carbon (biomass-based), soft carbon (biomass-based), silicon-based materials, tin-based materials, lithium titanate, and metallic sodium, but is not limited thereto.

[0056] In some specific embodiments, the negative electrode plate includes a current collector and a negative electrode material coated on the current collector. The current collector includes, but is not limited to, copper foil. In addition to the negative electrode active material, the negative electrode material also includes at least one of a binder and a conductive agent. The binder can be a commonly used adhesive material in the art, such as at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, and a water-based adhesive. The conductive agent can be a commonly used conductive material in the art, such as at least one of conductive graphite, acetylene black, carbon nanotubes, nanopowder, and graphene.

[0057] In a second aspect, the present disclosure provides a lithium-ion battery comprising the negative electrode plate.

[0058] The lithium-ion battery provided by the present disclosure has both high specific capacity and excellent cycle performance, and has high safety performance.

[0059] In some specific embodiments, the lithium-ion battery further includes a positive electrode sheet, a separator, and an electrolyte.

[0060] Among them, the positive electrode plate, separator and electrolyte can be made of any commercially available or commonly used materials in the art, and this disclosure does not limit this.

[0061] In a third aspect, the present disclosure provides an electrical device comprising the lithium-ion battery.

[0062] Among them, electrical equipment includes any device, equipment or system that uses the above-mentioned lithium-ion batteries, such as electric vehicles, electric motorcycles, power tools, energy storage systems, electronic products, office equipment, etc., but is not limited to these.

[0063] Example 1-Example 14

[0064] The preparation method of the negative electrode sheets of Example 1 to Example 14 includes the following steps: weighing the negative electrode active material, conductive agent SP, CMC (carboxymethyl cellulose, as a binder) and SBR (styrene-butadiene rubber, as a binder) according to a mass ratio of 95:1.5:1.5:2.0, then mixing them evenly through a paddle mixer, and then preparing the negative electrode sheets through a coater and a roller press.

[0065] In Examples 1-14, the method for adjusting the different compaction densities is as follows: the coated negative electrode sheet is pressed to different thicknesses by adjusting the pressure. The compaction density A of the negative electrode sheet = negative electrode sheet area density / (negative electrode sheet thickness - current collector thickness).

[0066] In Examples 1-14, the absorption time B was measured by using a microsyringe to dropwise apply 4 μl of PC onto the surface of the negative electrode. The time of addition was recorded as t1. The time of complete PC immersion was recorded as t2. The absorption time B = t2 - t1. Both t2 and t1 are in seconds.

[0067] In Examples 1 to 14, the test method for the liquid retention rate C is as follows: a negative electrode sheet with a mass of m1 is immersed in PC. After sealing and immersing for 24 hours, the mass of the negative electrode sheet after immersion, m2, is weighed. The liquid retention rate C is then calculated according to the formula C = (m2-m1) / (m1-m0)×100%. Wherein, m0 is the mass of the current collector in the negative electrode sheet, m1 is the total mass of the negative electrode sheet before immersion, and m2 is the total mass of the negative electrode sheet after complete immersion.

[0068] The compaction density A, liquid absorption time B, liquid retention rate C, 100A / (B×C) value of the negative electrode sheets of Examples 1 to 14, and the types of negative electrode active materials used are shown in Table 1 below.

[0069] Comparative Example 1-Comparative Example 10

[0070] The preparation methods for the negative electrode sheets of Comparative Examples 1-10, and the testing methods for the compacted density A, liquid absorption time B, and liquid retention rate C of the negative electrode sheets, are the same as those of Examples 1-14. The compacted density A, liquid absorption time B, liquid retention rate C, and 100A / (B×C) values ​​of the negative electrode sheets prepared in Comparative Examples 1-10, as well as the types of negative electrode active materials used, are shown in Table 1 below.

[0071] Table 1 Types of negative electrode active materials, compaction density of negative electrode sheets, liquid absorption time, liquid retention rate and 100A / (B×C) value:

[0072] Experimental example

[0073] Coin-type half-cells were assembled using the negative electrode sheets of Examples 1-14 and the negative electrode sheets of Comparative Examples 1-10, respectively. A lithium sheet was used as the positive electrode, an electrolyte consisting of a lithium salt LiPF6 solution (concentration: 1 mol / L) and a solvent consisting of EC (ethylene carbonate) and DEC (diethyl carbonate) in a 1:1 volume ratio, and Celgard 2400 as the separator. The specific capacity of each cell was measured at an initial discharge of 0.1C. The results are shown in Table 2.

[0074] Soft-pack batteries were assembled using the negative electrode sheets of Examples 1 to 14 and the negative electrode sheets of Comparative Examples 1 to 10, respectively, with lithium iron phosphate as the positive electrode, a lithium salt LiPF6 solution (concentration 1 mol / L), EC (ethylene carbonate) + DEC (diethyl carbonate) in a 1:1 volume ratio as the electrolyte, and Enjie 9+1+1 as the separator. Cycling performance tests were then conducted on each battery. The cycling performance test parameters were as follows: 1C / 1C, 2.5-3.65V, and 25±3°C.

[0075] Table 2 Specific capacity and cycle performance test results:

[0076] By comparing Examples 1-14 and Comparative Examples 1-4, it can be seen that by controlling the compaction density A, liquid absorption time B, and liquid retention rate C of the negative electrode sheet to satisfy the relationship 2.65≤100A / (B×C)≤7.74, and controlling the compaction density A of the negative electrode sheet to be between 1.30 and 1.75 g / cm 3 Within this range, it not only has a higher specific capacity, but also has better cycle performance, achieving a balance between the capacity of the negative electrode and the cycle performance.

[0077] However, in Comparative Examples 1 and 2, the compaction density is too low, and the high porosity causes some particles to fall off during the cycle, forming an insulating state and being unable to participate in charge and discharge, resulting in low discharge specific capacity. In addition, the contact between the electrode coating and the current collector is poor, and the contact internal resistance and exchange impedance are large, resulting in poor cycle performance. In Comparative Examples 3 and 4, due to the excessive compaction density, the degree of compression between the material particles is large, the porosity of the electrode is small, the electrode's ability to absorb electrolyte is poor, the electrolyte is difficult to infiltrate, and electronic conduction and ion conduction are not coordinated, forming dead lithium or lithium precipitation areas, resulting in low specific capacity of the material, poor battery liquid retention, large polarization during battery cycling, greater attenuation, significantly increased internal resistance, and poor cycle performance.

[0078] By comparing Example 1 and Comparative Example 5, it can be seen that although Comparative Example 5 uses an appropriate compaction density, the liquid absorption time is low. This is essentially because the compaction is too low and the 100A / (B×C) value is too high. The active material is peeled off from the electrode during the cycle, resulting in poor cycle performance. By comparing Example 1 and Comparative Example 6, it can be seen that although Comparative Example 6 uses an appropriate compaction density, the liquid retention rate is low and the 100A / (B×C) value is too high, resulting in insufficient electrolyte during the cycle, resulting in poor cycle performance.

[0079] Comparing Example 10 with Comparative Example 7, it can be seen that in Comparative Example 7, due to the long liquid absorption time and the low 100A / (B×C) value, this is essentially due to the high compaction and poor electrode wettability, resulting in poor cycle performance. Comparing Example 10 with Comparative Example 8, it can be seen that in Comparative Example 8, due to the low liquid retention rate, the high 100A / (B×C) value and the high compaction, the electrode's poor liquid retention capacity, insufficient electrolyte during the cycle, and thus poor cycle performance.

[0080] Similarly, in Comparative Examples 9 and 10, due to the excessive compaction density, the degree of extrusion between the material particles is large, the porosity of the electrode is small, the ability of the electrode to absorb the electrolyte is poor, the electrolyte is difficult to infiltrate, the electronic conduction and the ion conduction are not coordinated, and dead lithium or lithium precipitation areas are formed, resulting in a low specific capacity of the material and poor liquid retention capacity of the battery. The greater the polarization during the battery cycle, the greater the attenuation will be, the internal resistance will increase significantly, and the cycle performance will be poor.

[0081] It can be seen that the present disclosure can comprehensively achieve the regulation of cycle performance and high capacity by controlling 100A / (B×C) within a specific range of values, thereby achieving a balance between capacity utilization and cycle performance.

[0082] Therefore, the negative electrode sheet of the lithium-ion battery obtained by the method disclosed in the present invention has a high specific capacity, while ensuring that the lithium-ion battery has a good cycle life and safety when used for a long time and quickly charged, with significant effects. Industrial Applicability

[0083] In summary, the present disclosure provides a negative electrode sheet, lithium-ion battery, and electrical device that, by controlling 100A / (B×C) within a specific range, can achieve comprehensive regulation of cycle performance and high capacity. This negative electrode sheet not only has a high specific capacity, but also has excellent cycle life and safety.

Claims

1. A negative electrode plate, characterized in that: The compaction density A of the negative electrode sheet, the liquid absorption time B of the negative electrode sheet, and the liquid retention rate C of the negative electrode sheet satisfy the following relationship: 2.65≤100A / (B×C)≤7.74; wherein the unit of A is g / cm 3 , the unit of B is s; The compaction density A of the negative electrode plate is 1.30 to 1.75 g / cm 3 .

2. The negative electrode sheet according to claim 1, characterized in that: The compaction density A of the negative electrode plate is 1.40-1.75 g / cm 3 .

3. The negative electrode sheet according to claim 1, characterized in that: The liquid absorption time B of the negative electrode plate is 40 to 220 seconds.

4. The negative electrode sheet according to claim 1, characterized in that: The liquid retention rate C of the negative electrode plate is 30% to 42%.

5. The negative electrode sheet according to claim 1, characterized in that: The absorption time B is the time taken for the electrolyte to completely soak the negative electrode plate.

6. The negative electrode sheet according to claim 1, characterized in that: The liquid retention rate C = (m2-m1) / (m1-m0)×100%, wherein m0 is the mass of the current collector in the negative electrode plate, m1 is the total mass of the negative electrode plate before being soaked in the electrolyte, and m2 is the total mass of the negative electrode plate after being completely soaked in the electrolyte.

7. The negative electrode sheet according to claim 1, characterized in that: The first discharge specific capacity of the negative electrode plate is ≥320 mAh / g.

8. The negative electrode sheet according to claim 1, characterized in that: Contains at least one of the following features (1) to (3): (1) The capacity retention rate of the negative electrode sheet after 200 cycles at 1C is ≥ 90%; (2) The capacity retention rate of the negative electrode plate after 500 cycles at 1C is ≥89%; (3) The capacity retention rate of the negative electrode plate after 800 cycles at 1C is ≥87%.

9. A lithium ion battery, characterized in that: It comprises the negative electrode sheet as described in any one of claims 1 to 8.

10. An electrical device, characterized in that: Comprising the lithium ion battery as claimed in claim 9.