Lithium ion battery and electric device comprising same

Abstract

The invention provides a lithium ion battery and an electric device comprising the same, and relates to the technical field of lithium ion batteries. A negative electrode coating material of the lithium ion battery negative electrode comprises a graphite negative electrode active substance; according to the method, the three variables of the interlayer spacing d, the defect density ID / IG and the pole piece compaction density rho of the graphite negative electrode active material are optimized and adjusted through the parameter formula, and a reasonable parameter range is set, so that the rate capability and the cycling stability of the lithium ion battery are effectively improved. Meanwhile, the invention also provides a power utilization device comprising the lithium ion battery, and the power utilization device has more excellent lithium ion transmission capability and electrochemical stability in a fast charging mode according to the performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery and an electrical device containing the same. Background Art

[0002] With the rapid development of electric vehicles, smart grids and portable electronic devices, the market has put forward higher requirements for the energy density, power density, charging rate and cycle life of lithium-ion batteries. Especially in the high-rate fast charging scenario, how to balance fast charging performance and cycle stability has become the focus of industry attention. Graphite is currently the most widely used commercial negative electrode material. With its high theoretical specific capacity (372mAh g -1 ), low lithium insertion potential (about 0.1V vs.Li + / Li), excellent electrochemical stability and mature industrial preparation technology, it occupies a dominant position in the field of power batteries and energy storage batteries.

[0003] However, in high-rate charging mode, graphite negative electrodes still face many limitations. Their intrinsic characteristics affect the overall performance of lithium-ion batteries, which are mainly reflected in the following aspects: (1) The narrow graphite interlayer spacing (0.335nm) leads to a high lithium ion diffusion barrier. During high-rate charging, lithium ion embedding encounters greater resistance, which easily aggravates polarization. (2) The graphite basal surface pore (defect) density is insufficient. Lithium ions mainly diffuse along the interlayer channels and are difficult to transmit across layers, which further limits the diffusion rate of lithium ions and makes it easy for lithium dendrites to grow on the graphite surface, posing a short circuit risk. (3) High compaction density can increase the volume energy density of the battery, but it will cause the conductive network to be destroyed, increase the internal resistance of the battery, and further reduce the battery rate performance.

[0004] Therefore, when optimizing graphite negative electrode materials, it is necessary to find the best balance between interlayer spacing, defect density and compaction density to ensure that the battery can still maintain an efficient lithium ion diffusion rate in fast charging mode and maintain a long-term stable cycle life.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The first purpose of the present invention is to provide a lithium-ion battery, by regulating the interlayer spacing, defect density and pole piece compaction density of graphite in the negative electrode coating material of the lithium-ion battery, constructing a material performance parameter K, and setting a reasonable parameter range to achieve coordinated optimization of lithium-ion fast charging performance and cycle stability.

[0007] A second object of the present invention is to provide an electrical device comprising the above-mentioned lithium-ion battery.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] The present invention provides a lithium ion battery, wherein the negative electrode coating material of the negative electrode of the lithium ion battery contains a graphite-based negative electrode active material;

[0010] The graphite-based negative electrode active material meets the following material performance parameters:

[0011] The material performance parameter is K, 0.5≤K≤20;

[0012] in:

[0013] Where:

[0014] d is the interlayer distance of the negative electrode active material;

[0015] I D / I G is the intensity ratio of the D peak and the G peak in the Raman spectrum of the negative electrode active material;

[0016] ρ is the compaction density of the electrode.

[0017] Furthermore, the material performance parameter K of the graphite-based negative electrode active material is: 0.5≤K≤6.

[0018] Furthermore, the graphite-based negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon or hard carbon.

[0019] Furthermore, the interlayer spacing d of the negative electrode active material is 0.30 to 0.45 nm;

[0020] After the lithium ion battery is cycled 1000 times at 1C charge / 1C discharge, the d value change rate is ≤8%.

[0021] Furthermore, the negative electrode active material I D / I G It is 0.01~1.0.

[0022] Furthermore, the negative electrode active material has a ρ of 1.2 to 1.7 g / cm 3 .

[0023] Furthermore, the negative electrode of the lithium-ion battery is composed of a current collector and a negative electrode coating material coated on at least one surface thereof;

[0024] The negative electrode coating material is composed of a graphite-based negative electrode active material, a conductive agent and a binder, and the mass ratio is 92%-97%: 1%-3%: 1%-5%.

[0025] Furthermore, the conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black;

[0026] Furthermore, the binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

[0027] Furthermore, the negative electrode of the lithium-ion battery also includes a solid electrolyte interface film, and the solid electrolyte interface film is a solid electrolyte interface SEI film, and the thickness (h) of the SEI film is 10-200nm.

[0028] The present invention provides an electrical device, which includes the above-mentioned lithium-ion battery.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention provides a lithium ion battery, wherein the negative electrode coating material of the negative electrode of the lithium ion battery contains a graphite-based negative electrode active material; the present invention uses a parameter formula to calculate the interlayer spacing d, defect density I of the graphite-based negative electrode active material. D / I G The three variables of the electrode compaction density ρ are optimized and adjusted, thereby effectively improving the rate performance and cycle stability of lithium-ion batteries. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] According to one aspect of the present invention, a lithium-ion battery, wherein the negative electrode coating material of the negative electrode of the lithium-ion battery comprises a graphite-based negative electrode active material;

[0033] The graphite-based negative electrode active material meets the following material performance parameters:

[0034] The material performance parameter is K, 0.5≤K≤20;

[0035] in:

[0036] Where:

[0037] d is the interlayer distance of the negative electrode active material;

[0038] I D / I G is the intensity ratio of the D peak and the G peak in the Raman spectrum of the negative electrode active material;

[0039] ρ is the compaction density of the electrode.

[0040] The present invention provides a lithium ion battery, wherein the negative electrode coating material of the negative electrode of the lithium ion battery contains a graphite-based negative electrode active material; the present invention uses a parameter formula to calculate the interlayer spacing d, defect density I of the graphite-based negative electrode active material. D / I G The three variables of the electrode compaction density ρ are optimized and adjusted, thereby effectively improving the rate performance and cycle stability of lithium-ion batteries.

[0041] Specific:

[0042] d represents the interlayer spacing of the negative electrode active material, unit: nm, and the diffraction peak position corresponding to the crystal plane in the X-ray diffraction (XRD) spectrum is fitted by a Gaussian function according to the Bragg's Equation: It is calculated that n is the first-order diffraction and θ is the half-value of the diffraction angle;

[0043] I D / I G The D peak (~1350cm -1 ) and G peak (~1580cm -1 ) and intensity ratio;

[0044] ρ represents the compaction density of the pole piece, which is calculated according to the formula ρ = surface density / (total thickness of the pole piece - thickness of the current collector), unit: g / cm 3 .

[0045] In a preferred embodiment of the present invention, the material performance parameter K of the graphite-based negative electrode active material is: 0.5≤K≤6.

[0046] As a preferred embodiment, it has been experimentally verified that after 1000 cycles of an initial lithium battery with a K value ≤ 6, the d value change rate is <5%, showing better cycle stability.

[0047] In a preferred embodiment of the present invention, the graphite-based negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon or hard carbon.

[0048] In a preferred embodiment of the present invention, the interlayer spacing d of the negative electrode active material is 0.30 to 0.45 nm;

[0049] After the lithium ion battery is cycled 1000 times at 1C charge / 1C discharge, the d value change rate is ≤8%.

[0050] In a preferred embodiment of the present invention, the negative electrode active material I D / I G It is 0.01~1.0.

[0051] In a preferred embodiment of the present invention, the negative electrode active material has a p of 1.2 to 1.7 g / cm 3 .

[0052] In a preferred embodiment of the present invention, the negative electrode of the lithium ion battery is composed of a current collector and a negative electrode coating material coated on at least one surface thereof;

[0053] The negative electrode coating material is composed of a graphite-based negative electrode active material, a conductive agent and a binder, and the mass ratio is 92%-97%: 1%-3%: 1%-5%.

[0054] Wherein, the conductive agent comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black;

[0055] The binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

[0056] In a preferred embodiment of the present invention, the negative electrode of the lithium ion battery further includes a solid electrolyte interface SEI film, and the thickness of the SEI film is 10-200 nm.

[0057] It should be noted that the discharge characteristics of the lithium-ion battery of the present application are: after the lithium-ion battery charged to 100% SOC at 0.1C is left at rest for 6 hours at 25°C, it is discharged to 2.5V at 0.1C rate, and the corresponding discharge capacity is Q1; after charging under the same charging conditions, the discharge capacity of 2.5V at 5C is Q2; the retention rate of discharge capacity Q2 / Q1 ≥ 50%. After the lithium-ion battery is cycled at 1C charge / 1C discharge for 1000 times, the change rate of d value is ≤ 8%.

[0058] In a preferred embodiment of the present invention, the lithium ion battery comprises a positive electrode current collector and a positive electrode coating coated with at least one layer containing a positive electrode active material;

[0059] The positive electrode active material includes lithium nickel cobalt manganese oxide (Li 1 Ni x Co y Mn z M b O 2), wherein 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and the element M includes one or more of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B) and neodymium (Nd).

[0060] In a preferred embodiment of the present invention, the ratio N / P of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet is between 1.02 and 1.22.

[0061] In a preferred embodiment of the present invention, the electrolyte of the lithium ion battery comprises a lithium salt, a solvent and an additive.

[0062] In the above preferred embodiment, the lithium salt includes one or more combinations of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide;

[0063] In the above preferred embodiment, the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate;

[0064] In the above preferred embodiment, the additive includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, vinyl sulfate, vinyl sulfite, vinylene carbonate and vinyl carbonate.

[0065] According to one aspect of the present invention, an electrical device comprises the above-mentioned lithium-ion battery.

[0066] The electrical device provided by the present invention includes the above-mentioned lithium-ion battery. Determined by the performance of the lithium-ion battery, the electrical device has better lithium-ion transmission capacity and electrochemical stability in the fast charging mode.

[0067] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0068] Example 1

[0069] A lithium ion battery, a method for preparing the lithium ion battery, comprising the following steps:

[0070] (1) Positive electrode sheet production method: Take the positive electrode active material (Li 1 Ni 0.8 Co 0.1 Mn 0.1 O 2), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material, and then the positive electrode coating material is coated on a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained;

[0071] (2) Negative electrode manufacturing method: The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode coating material coated on both sides of the copper foil. Calculated by mass percentage, the negative electrode coating material includes 96.0% graphite, 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC) and 1.5% binder polyacrylic acid (PAA). The above substances are added to deionized water and stirred to form a negative electrode coating material with a solid content of 40%. The negative electrode coating material is then coated on both sides of the negative electrode current collector (copper foil), dried and cold pressed to form a negative electrode sheet with a compaction density of 1.5 g / cm 3 ;

[0072] The interlayer spacing d of the negative electrode active material is 0.33 nm, ID / IG is 0.06, and ρ is 1.5 g / cm 3 .

[0073] The material performance parameter K of the negative electrode active material is 1.3.

[0074] The surface of the negative electrode plate has a solid electrolyte interface SEI film, and the thickness of the SEI film is 51 nm.

[0075] (3) Preparation of electrolyte: Lithium hexafluorophosphate (LiPF 6 ), organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), a first type of additive fluoroethylene carbonate (FEC), a second type of additive vinyl sulfate (DTD) and a third type of additive vinylene carbonate (VC);

[0076] The electrolyte was obtained by mixing in a ratio of 10.0:20.0:55.0:2.0:8.0:5.0 by mass percentage.

[0077] (4) Diaphragm: A high-porosity diaphragm is selected, in which the thickness of the base film PE is 9 μm, the thickness of the ceramic coating on both sides of the base film is 1.0 μm, and the thickness of the PVDF coating is 1.0 μm.

[0078] (5) Assembly of lithium-ion battery: The positive electrode sheet and the negative electrode sheet are rolled and slit respectively, and then wound together with the separator to obtain a 21700 cylindrical battery core. The battery core is then welded to the connecting sheet and loaded into a battery shell. After completing the injection, sealing and formation processes, the lithium-ion battery of Example 1 is obtained. The shell of the lithium-ion battery is cylindrical, and its dimensional parameters are diameter: 21.0 mm, length 70.0 mm.

[0079] Example 2

[0080] The difference between this embodiment and embodiment 1 is that in step (2), the graphite is treated by low-temperature bromine intercalation method for 1 hour before use to increase the interlayer spacing, and the rest is the same as embodiment 1.

[0081] The operation steps of the low-temperature bromine intercalation method are as follows: first, seal graphite and excess Br in a glass tube and react at 60°C for 1 hour (Br diffuses and inserts into the interlayer to form CBr intercalation compounds), then quickly transfer to a 200°C tubular furnace, purge with nitrogen, and heat treat for 10 minutes. Br is vaporized by heat to generate pressure, and the distance between graphite layers increases.

[0082] Example 3

[0083] The difference between this embodiment and embodiment 1 is that in step (2), the graphite is treated by low-temperature bromine intercalation for 2 h before use to increase the interlayer spacing, and the rest is the same as embodiment 1.

[0084] The operation steps of the low-temperature bromine intercalation method are as follows: first, seal graphite and excess Br in a glass tube and react at 60°C for 2 hours (Br diffuses and inserts into the interlayer to form CBr intercalation compounds), then quickly transfer to a 200°C tubular furnace, purge with nitrogen, and heat treat for 10 minutes. Br is vaporized by heat to generate pressure, and the distance between graphite layers increases.

[0085] Example 4

[0086] The difference between this embodiment and embodiment 1 is that in step (2), the graphite is treated by low-temperature bromine intercalation method for 4 hours before use to increase the interlayer spacing, and the rest is the same as embodiment 1.

[0087] The operation steps of the low-temperature bromine intercalation method are as follows: first, seal graphite and excess Br in a glass tube and react at 60°C for 4 hours (Br diffuses and inserts into the interlayer to form CBr intercalation compounds), then quickly transfer to a 200°C tube furnace, purge with nitrogen, and heat treat for 10 minutes. Br is vaporized by heat to generate pressure, and the distance between graphite layers increases.

[0088] Example 5

[0089] The difference between this embodiment and embodiment 3 is that in step (2), the graphite is further treated with potassium hydroxide etching for 2 hours before use to increase the number of pores, and the rest is the same as embodiment 3.

[0090] The operation steps of potassium hydroxide etching method are as follows: First, graphite is mixed with 7M KOH solution and stirred at 400 rpm for 2 hours. After vacuum drying, it is transferred to a tube furnace and pyrolyzed under nitrogen protection by step-by-step temperature increase (200°C for water removal and 800°C for alkaline etching to form pores). Finally, by-products are removed by water washing to obtain graphite with small changes in interlayer spacing and specific surface area and a porous structure.

[0091] Potassium hydroxide etching method to control I D / I G The principle is: when heat treated at 800℃, KOH reacts with carbon (4KOH+C→K 2 CO 3 +K 2 O+2H 2 ↑), producing nanoscale pores and retaining the layered skeleton, and then the graphite was treated with potassium hydroxide etching to achieve:

[0092] (1) The introduction of the pore structure breaks the sp 2 The long-range order of the bonds increases the intensity of the D peak;

[0093] (2) The redox reaction during the etching process may introduce heteroatoms or functional groups (such as hydroxyl groups, carboxyl groups, etc.) on the surface of the carbon material, triggering the formation of defect structures and further increasing the intensity of the D peak.

[0094] Example 6

[0095] The difference between this embodiment and embodiment 3 is that in step (2), the graphite is treated with potassium hydroxide etching for 4 hours before use to increase the number of pores, and the rest is the same as embodiment 3.

[0096] The operation steps of potassium hydroxide etching method are as follows: First, graphite is mixed with 7M KOH solution and stirred at 400 rpm for 4 hours. After vacuum drying, it is transferred to a tube furnace and pyrolyzed by step-by-step temperature increase under nitrogen protection (200°C for water removal and 800°C for alkaline etching to form pores). Finally, by-products are removed by water washing to obtain graphite with small changes in interlayer spacing and specific surface area and a porous structure.

[0097] Example 7

[0098] The difference between this embodiment and embodiment 3 is that in step (2), the graphite is further treated with potassium hydroxide etching for 8 hours before use to increase the number of pores, and the rest is the same as embodiment 3.

[0099] The operation steps of potassium hydroxide etching method are as follows: First, graphite is mixed with 7M KOH solution and stirred at 400 rpm for 8 hours. After vacuum drying, it is transferred to a tube furnace and pyrolyzed by step-by-step temperature increase under nitrogen protection (200°C for water removal and 800°C for alkaline etching to form pores). Finally, the by-products are removed by water washing to obtain graphite with small changes in interlayer spacing and specific surface area and a porous structure.

[0100] Example 8

[0101] The difference between this embodiment and embodiment 3 is that in step (2), the graphite is further treated with potassium hydroxide etching for 12 hours before use to increase the number of pores, and the rest is the same as embodiment 3.

[0102] The operation steps of potassium hydroxide etching method are as follows: First, graphite is mixed with 7M KOH solution and stirred at 400 rpm for 12 hours. After vacuum drying, it is transferred to a tube furnace and pyrolyzed under nitrogen protection by step-by-step temperature increase (200°C for water removal and 800°C for alkaline etching to form pores). Finally, by-products are removed by water washing to obtain graphite with small changes in interlayer spacing and specific surface area and a porous structure.

[0103] Example 9

[0104] The difference between this embodiment and embodiment 7 is that the compaction density of the negative electrode sheet is 1.3 g / cm 3 , the rest are the same as Example 7.

[0105] Example 10

[0106] The difference between this embodiment and embodiment 7 is that the compaction density of the negative electrode sheet is 1.4 g / cm 3 , the rest are the same as Example 7.

[0107] Embodiment 11

[0108] The difference between this embodiment and embodiment 7 is that the compaction density of the negative electrode sheet is 1.6 g / cm 3 , the rest are the same as Example 7.

[0109] Comparative Example 1

[0110] The difference between this comparative example and Example 1 is that in step (2), the graphite is treated by low-temperature bromine intercalation for 48 hours before use, and the rest is the same as Example 1.

[0111] Comparative Example 2

[0112] The difference between this comparative example and Example 1 is that in step (2), the graphite is etched with concentrated sulfuric acid (98 wt %) and hydrogen peroxide (27% wt %) in a ratio of 10:1 (V / V) for 6 h before use, and the rest is the same as Example 1.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 1 is that the compaction density of the negative electrode sheet is 1.8 g / cm 3 , the rest are the same as in Example 1.

[0115] Test Example 1

[0116] In order to verify the technical effect of the lithium-ion battery of the present application, the lithium-ion batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 3 are tested and verified.

[0117] (I) The specific methods are as follows:

[0118] (1) Negative electrode active material d value and I D / I G Test method for value:

[0119] First, discharge the lithium-ion battery to 2.5V. In the glove box, carefully disassemble the battery and remove the negative electrode of the cylindrical cell. Next, soak the electrode in dimethyl carbonate for 30 minutes, wipe the surface after taking it out to remove the residual organic solvent, and repeat this process three times to ensure that all possible impurities and residues are removed. Subsequently, rinse the electrode with ethanol and wipe it again to remove the solvent, and finally let it stand in the glove box for 48 hours to ensure that the electrode is completely dry. After drying, scrape the material in the electrode feeding area and put it into a sealed bag, then take it out of the glove box and immediately perform XRD and Raman characterization.

[0120] 1. XRD specific determination method: using a copper target X-ray diffractometer (Cu-Kα radiation, λ=0.15nm, tube voltage 40kV, tube current 40mA), the sample is evenly dispersed on a silicon substrate, and the XRD spectrum is obtained at a scanning rate of 2° / min in the range of 2θ=10°-80°. According to the diffraction peak position (~25-27°) corresponding to the (002) crystal plane in the XRD diagram, according to the Bragg's equation: Calculated.

[0121] 2. Raman specific measurement method: Use 532nm laser as the excitation light source, evenly disperse the sample on the silicon substrate, and -1 The Raman spectrum is collected within the range. The peak position is determined by Lorentz fitting, and the intensity ratio of the D peak to the G peak is calculated. D / I G To evaluate the defect density (the larger the ratio, the more defects).

[0122] The d value and I of the initial lithium ion battery negative electrode active material are determined by the above method. D / I GValue, as well as the d value and I value of the negative electrode active material of the lithium-ion battery after 1000 cycles D / I G value.

[0123] (2) Test method for compaction density of negative electrode sheet:

[0124] First, the negative electrode sheet rinsed with dimethyl carbonate and vacuum dried was cut into 6 square samples of standard size (2.0 cm × 2.0 cm); then, the active materials on the front and back sides of 3 of the square samples were wiped off, rinsed with ethanol, dried, weighed and the average mass M1 was calculated, and the average thickness L1 of the sample was measured using a spiral micrometer; then, the mass of the other 3 square samples was weighed and the average mass M2 was calculated, and the average thickness L2 of the sample was measured, and the thickness of the electrode sheet was calculated: L2-L1, unit cm; the compaction density of the electrode sheet was calculated: Unit: g / cm3.

[0125] (3) Rate performance test method:

[0126] Place the battery in a 25°C constant temperature box for 4 hours and test it according to the following steps:

[0127] 1. Charge to 4.2V at constant current and constant voltage at 0.1C, with a cut-off current of 0.01C, and let stand for 10 minutes. The capacity charged to 4.2V at constant current is counted as Q1.

[0128] 2. Discharge at a constant current of 0.1C until the voltage is cut off at 2.5V, the cut-off current is 0.01C, and leave it for 10 minutes;

[0129] 3. Charge to 4.2V at constant current and constant voltage at 5C, with a cut-off current of 0.01C, and let stand for 10 minutes. The capacity charged to 4.2V at constant current is counted as Q2.

[0130] 4. Discharge at a constant current of 0.1C until the voltage is cut off at 2.5V, the cut-off current is 0.01C, and leave it for 10 minutes;

[0131] The calculation method of 5C capacity retention rate is: Q2 / Q1×100.

[0132] (4) Cyclic performance test method:

[0133] Place the battery in a 25°C constant temperature box for 4 hours and test it according to the following steps:

[0134] 1. First cycle constant current and constant voltage charging: Charge to 4.2V at a constant current of 0.1C, then switch to constant voltage charging until the current drops to 0.01C.

[0135] 2. After charging is complete, let it sit for 10 minutes.

[0136] 3. Perform constant current discharge and discharge to 2.5V at a rate of 0.1C.

[0137] 4. Repeat the above charging and discharging process: charge at a constant current rate of 1C to 4.2V. Let stand for 10 minutes again. Discharge at a constant current rate of 1C to 2.5V.

[0138] 5. Repeat the above charge and discharge process for a total of 1000 cycles. Count the capacity decay rate of the battery after 1 cycle and 1000 cycles.

[0139] (II) Specific test verification results are shown in Table 1 and Table 2:

[0140] Table 1:

[0141]

[0142]

[0143] As shown in Table 1, by comparing Examples 1 to 11 and Comparative Examples 1 to 3, it can be seen that when the K value approaches 6.0, the capacity retention rate of the lithium battery at 5C rate charging is higher; deviation from this value will lead to a decrease in the capacity retention rate;

[0144] The K value is less than 6.0, and the capacity decay rate of the lithium battery after 1000 cycles is low (<15%). This phenomenon is attributed to the interlayer spacing d of graphite, the defect structure I D / I G It is the result of coordinated optimization of (number of base surface channels) and pole piece compaction density ρ.

[0145] The increase in d value expands the graphite interlayer spacing, reduces the energy barrier for Li+ diffusion within the layer, and is beneficial to the improvement of rate performance.

[0146] I D / I G The increase in the value further increases the channels for Li+ diffusion, allowing Li+ to achieve cross-layer transmission and further improve the diffusion rate; however, too high I D / I G A large value will introduce more defects, resulting in reduced electron conductivity and increased internal resistance of the electrode. At the same time, more defects will also lead to more side reactions and affect structural stability.

[0147] A low pole compaction density ρ value will lead to increased contact resistance between active materials and between active materials and current collectors, and increased internal resistance; a high pole compaction density ρ value will lead to low pole porosity, increased pore impedance, and Li+ diffusion resistance; it will also cause the SEI film to break repeatedly during the cycle, seriously limiting the cycle stability.

[0148] Table 2:

[0149] K <![CDATA[d 1 (nm)]]> <![CDATA[d 1000 (nm)]]> d％ Example 1 1.3 0.33 0.34 3.0 Example 2 1.5 0.37 0.38 2.7 Example 3 1.6 0.41 0.42 2.4 Example 4 1.8 0.45 0.47 4.4 Example 5 3.0 0.41 0.42 2.4 Example 6 4.1 0.41 0.43 4.9 Example 7 5.7 0.41 0.42 2.4 Example 8 7.1 0.41 0.44 7.3 Example 9 6.6 0.41 0.44 7.3 Example 10 6.2 0.41 0.43 4.9 Embodiment 11 5.4 0.41 0.42 2.4 Comparative Example 1 7.3 0.52 0.54 3.8 Comparative Example 2 30.1 0.41 0.47 14.6 Comparative Example 3 8.6 0.41 0.45 9.8

[0150] Note: In Table 2, d1 and d1000 represent the initial interlayer spacing d value of the negative electrode active material of the lithium-ion battery and the interlayer spacing d value after 1000 cycles, respectively.

[0151] As shown in Table 2, after 1000 cycles, the d value change rate of the initial lithium battery with a K value less than 6.0 is less than 5%, showing better cycle stability. Therefore, appropriate interlayer expansion, reasonable defect density and compaction density can improve the rate performance and cycle performance of lithium batteries.

[0152] In summary, the present invention precisely controls the microstructural parameters of the graphite negative electrode to enable it to have better lithium ion transmission ability and electrochemical stability in fast charging mode, thereby providing a new technical solution for high-rate applications of lithium-ion batteries, and has broad application prospects in electric vehicles, energy storage systems and other high-power demand fields.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium ion battery, characterized in that: The negative electrode coating material of the negative electrode of the lithium ion battery contains a graphite-based negative electrode active material; The graphite-based negative electrode active material meets the following material performance parameters: The material performance parameter is K, 0.5≤K≤20; in: Where: d is the interlayer distance of the negative electrode active material; I D / I G is the intensity ratio of the D peak and the G peak in the Raman spectrum of the negative electrode active material; ρ is the compaction density of the electrode.

2. The lithium-ion battery according to claim 1, characterized in that The material performance parameter K of the graphite-based negative electrode active material is: 0.5≤K≤6.

3. The lithium-ion battery according to claim 1, characterized in that The graphite-based negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon or hard carbon.

4. The lithium-ion battery according to claim 1, characterized in that: The interlayer spacing d of the negative electrode active material is 0.30 to 0.45 nm; After the lithium ion battery is cycled 1000 times at 1C charge / 1C discharge, the d value change rate is ≤8%.

5. The lithium-ion battery according to claim 1, characterized in that: The negative electrode active material I D / I G It is 0.01~1.

0.

6. The lithium-ion battery according to claim 1, characterized in that The negative electrode active material has a ρ of 1.2 to 1.7 g / cm 3 .

7. The lithium-ion battery according to claim 1, characterized in that: The negative electrode of the lithium-ion battery is composed of a current collector and a negative electrode coating material coated on at least one surface thereof; The negative electrode coating material is composed of a graphite-based negative electrode active material, a conductive agent and a binder, and the mass ratio is 92%-97%: 1%-3%: 1%-5%.

8. The lithium-ion battery according to claim 7, characterized in that: The conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; The binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

9. The lithium-ion battery according to claim 7, characterized in that: The lithium ion battery negative electrode also includes a solid electrolyte interface SEI film, and the thickness of the SEI film is 10-200nm.

10. An electrical device, characterized in that: The electrical device comprises the lithium-ion battery according to any one of claims 1 to 9.

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