Negative electrode sheet and lithium-ion battery

Abstract

The present application provides a negative electrode sheet and a lithium-ion battery. The negative electrode sheet comprises a current collector and a first electrode material layer and a second electrode material layer which are sequentially stacked on the current collector in a direction moving away from the current collector, wherein both the first electrode material layer and the second electrode material layer comprise an active material, the active material comprises first active material particles and second active material particles, and the particle size of the first active material particles is greater than the particle size of the second active material particles; and in the first electrode material layer, the total mass of the first active material particles is less than the total mass of the second active material particles, and in the second electrode material layer, the total mass of the first active material particles is greater than the total mass of the second active material particles.

Description

Negative electrode sheet and lithium ion battery

[0001] The present application claims priority to the Chinese patent application No. 202411277212.4 filed on September 11, 2024 with the China National Intellectual Property Office, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a negative electrode sheet and a lithium ion battery. BACKGROUND

[0003] With the continuous popularization of new energy electric vehicles, the endurance mileage and charging time are increasingly concerned by consumers. To achieve high energy density of lithium ion batteries, higher specific capacity of positive and negative electrodes (such as high-nickel positive electrodes and silicon-carbon negative electrodes) and thick electrode design are needed. The development and use of thick electrodes can effectively increase the proportion of active materials in the battery, thereby improving the energy density of the battery and reducing the cost. SUMMARY

[0004] However, the use of thick electrodes also faces a series of problems. The increase in electrode thickness will prolong the transmission path of electrons and ions, increase the polarization of the battery, and deteriorate the electrode kinetics, thereby exhibiting poor cycle life and other defects in the battery.

[0005] The present application provides a negative electrode sheet, comprising a current collector and a first electrode material layer and a second electrode material layer stacked in turn on the current collector in a direction away from the current collector, the first electrode material layer and the second electrode material layer each comprising an active material, the active material comprising first active material particles and second active material particles, the particle size of the first active material particles being greater than the particle size of the second active material particles, the total mass of the first active material particles in the first electrode material layer being less than the total mass of the second active material particles, and the total mass of the first active material particles in the second electrode material layer being greater than the total mass of the second active material particles.

[0006] The present application also provides a lithium ion battery comprising the above negative electrode sheet. ADVANTAGEOUS EFFECTS

[0007] The negative pole piece provided by the application can effectively play the function of the first electrode material layer, is beneficial to the transmission of lithium ions and electrons in the electrode pores, improves the electrode reaction kinetics, and improves the cycle performance and electrical performance of the battery cell; meanwhile, the electrolyte can be better infiltrated into the electrode, which is beneficial to the charge exchange at the electrode and electrolyte interface, so that excellent cycle performance and fast charging performance can be exhibited in the high-energy-density lithium ion battery. Embodiments of the application

[0008] In the description of the application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or detachably connected, or integrated; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0009] In the application, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes that the first feature is directly above and obliquely above the second feature, and the horizontal height of the first feature is higher than that of the second feature. The first feature "under", "below" and "below" the second feature includes that the first feature is directly below and obliquely below the second feature, and the horizontal height of the first feature is less than that of the second feature.

[0010] In a first aspect, the embodiments of the application provide a negative pole piece, comprising a current collector and a first electrode material layer and a second electrode material layer which are sequentially stacked on the current collector in a direction away from the current collector, the first electrode material layer and the second electrode material layer both comprise active material, the active material comprises first active material particles and second active material particles, the particle size of the first active material particles is greater than that of the second active material particles, the total mass of the first active material particles in the first electrode material layer is less than that of the second active material particles, and the total mass of the first active material particles in the second electrode material layer is greater than that of the second active material particles.

[0011] ​In the present application, by regulating the ratio of the first active material particles and the second active material particles of different particle sizes in the first electrode material layer and the second electrode material layer, more large particles are allowed in the second electrode material layer to increase the porosity of the second electrode material layer, improve the infiltration effect of the electrolyte, so that the function of the first electrode material layer can be effectively exerted, which is beneficial to the transmission of lithium ions and electrons in the electrode pores, can improve the electrode reaction kinetics, and improve the cycle performance and electrical performance of the battery cell; at the same time, the electrolyte can be strengthened to the electrode, which is beneficial to the charge exchange at the electrode and electrolyte interface, so that excellent cycle performance and fast charging performance can be exhibited in high energy density lithium ion batteries.

[0012] In the present application, the active materials in the first electrode material layer and the second electrode material layer can be the same material, and the first active material particles and the second active material particles can be the same material.

[0013] In some embodiments, based on the total mass of the active material in the second electrode material layer, the mass percentage of the first active material particles is 55%-95%, for example, it can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc., and the mass percentage of the second active material particles is 5%-45%, for example, it can be 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc. Within this range, the porosity of the upper electrode material layer can be effectively increased, so that the function of the lower electrode material layer can be effectively exerted.

[0014] In some embodiments, based on the total mass of the active material particles in the first electrode material layer, the mass percentage of the first active material particles is 5%-45%, for example, it can be 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc., and the mass percentage of the second active material particles is 55%-95%, for example, it can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. Within this range, the function of the lower electrode material layer can be effectively exerted, which is beneficial to the transmission of lithium ions and electrons in the electrode pores, can strengthen the electrolyte to the electrode, and is beneficial to the charge exchange at the electrode and electrolyte interface.

[0015] In some embodiments, the D50 of the first active material particles is 12-20 μm, for example, it can be 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc. Within this range, the porosity of the upper and lower electrode materials can be controlled, so that the functions of the upper and lower electrode material layers can be effectively exerted.

[0016] In some embodiments, the D50 of the second active material particles is 5 μm-12 μm, for example, can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc. Within this range, the porosity of the upper and lower electrode material layers can be controlled, so as to effectively exert the functions of the upper and lower electrode material layers.

[0017] In an embodiment, the mass ratio of the active material in the first electrode material layer to the active material in the second electrode material layer is (3-8):(2-9), for example, can be 3:2, 3:5, 3:7, 3:9, 5:2, 5:5, 5:7, 5:9, 8:2, 8:5, 8:7, 8:9, etc. Within this range, the porosity of the upper and lower electrode material layers can be controlled, so as to effectively exert the functions of the upper and lower electrode material layers, facilitate the transport of lithium ions and electrons in the electrode pores, and strengthen the infiltration of the electrolyte into the electrode, which is conducive to the charge exchange at the electrode and electrolyte interface.

[0018] In some embodiments, the mass ratio of the active material in the first electrode material layer to the active material in the second electrode material layer is 1:1.

[0019] In some embodiments, the mass ratio of the second active material particles to the first active material particles in the first electrode material layer is the same as the mass ratio of the first active material particles to the second active material particles in the second electrode material layer.

[0020] In some embodiments, the first electrode material layer and the second electrode material layer each further comprise a conductive agent, and the mass ratio of the conductive agent in the first electrode material layer to the conductive agent in the second electrode material layer is (2-9):(1-8), for example, can be 2:8, 3:4, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, etc.

[0021] In the present application, by controlling the mass ratio of the conductive agent in the first electrode material layer and the second electrode material layer, the conductive network in the first electrode material layer and the second electrode material layer can be improved, thereby improving the electrode reaction kinetics.

[0022] In the present application, the conductive agent in the first electrode material layer and the second electrode material layer can be the same material or different materials.

[0023] In some embodiments, the first electrode material layer and the second electrode material layer each further comprise a binder, and the mass percentage of the binder in the first electrode material layer is 55% to 95%, for example, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc., and the mass percentage of the binder in the second electrode material layer is 5% to 45%, for example, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.

[0024] The binder in the first electrode material layer and the second electrode material layer in the present application can be the same material or different materials.

[0025] In the present application, by controlling the mass ratio of the binder in the first electrode material layer and the second electrode material layer, the amount of the binder in the upper layer is reduced, the liquid phase resistance is reduced, the porosity of the upper layer is increased, which is beneficial to the transmission of lithium ions and electrons in the electrode pores, at the same time, the infiltration of the electrolyte into the electrode is strengthened, which is beneficial to the charge exchange at the electrode-electrolyte interface, thereby excellent cycle performance and fast charging performance can be exhibited in high-energy-density lithium-ion batteries; in addition, the binder will float during the baking process of the electrode sheet, and the more binder in the lower layer can improve the adhesion between the electrode material and the current collector.

[0026] In some embodiments, the ratio of the mass sum of the active material, the mass sum of the conductive agent, and the mass sum of the binder in the first electrode material layer and the second electrode material layer is (71-115):(1-10):(1.5-30), for example, 71:1:1.5, 75:2:6, 80:3:9, 85:4:12, 90:5:15, 95:6:18, 100:7:21, 105:8:24, 110:9:27, 115:10:30.

[0027] In some embodiments, the active material comprises one or more of graphite, silicon material, and lithium alloy material.

[0028] In some embodiments, the gram capacity of the active material is 400 mAh / g to 2000 mAh / g, for example, 400 mAh / g, 600 mAh / g, 800 mAh / g, 1000 mAh / g, 1200 mAh / g, 1400 mAh / g, 1600 mAh / g, 1800 mAh / g, 2000 mAh / g, etc.

[0029] In the present application, the active material can be a mixture of several materials, and the gram capacity of the active material is the average gram capacity of the several materials.

[0030] In some embodiments, the carbon material includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, and activated carbon.

[0031] In some embodiments, the silicon material includes one or more of silicon, silicon carbon, and silicon oxygen.

[0032] In some embodiments, the lithium alloy material includes one or more of lithium alloy, lithium aluminum alloy, and lithium titanium alloy.

[0033] In some embodiments, the conductive agent includes one or more of acetylene black, conductive carbon black, graphene, and carbon nanotube.

[0034] In some embodiments, the carbon nanotube includes multi-walled carbon nanotube and / or single-walled carbon nanotube.

[0035] In some embodiments, the binder includes one or more of polyacrylic acid (PAA), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), sodium alginate, carboxymethyl chitosan, and polyacrylonitrile.

[0036] In some embodiments, the active material includes graphite, silicon, the binder includes polyacrylic acid, styrene butadiene rubber, and sodium carboxymethyl cellulose, and the mass ratio of the graphite, silicon, polyacrylic acid, styrene butadiene rubber, and sodium carboxymethyl cellulose is (70-95):(1-20):(0.5-10):(0.5-10):(0.5-10), for example, can be 70:4:0.5:0.5:0.5, 75:7:2:2:2, 80:10:4:4:4, 85:13:5.5:5.5:5.5, 90:17:7.5:7.5:7.5, 95:20:10:10:10, and the like.

[0037] In a second aspect, the embodiments of the present application provide a lithium ion battery, including the negative electrode sheet described above.

[0038] The following is described in conjunction with specific embodiments.

[0039] Embodiment 1

[0040] The sodium carboxymethyl cellulose (CMC) powder is mixed with deionized water at a mass ratio of 0.57:23.40, and stirred uniformly to obtain a CMC glue solution;

[0041] Take graphite (D50 is 20 μm, specific capacity 350 mAh / g) 45.72 kg and gas phase silicon material SiC (D50 is 10 μm, specific capacity 1800 mAh / g) 4.46 kg, dry mixing, then add 23.97 kg of CMC glue solution stirred, pre-mixing, then 8.84 kg of polyacrylic acid (PAA) binder, 0.28 kg of conductive carbon black, 4.19 kg of carbon nanotube are mixed and stirred, and water is added to adjust the viscosity, finally 0.62 kg of butadiene-styrene rubber (SBR) binder is added to obtain the upper layer slurry, and the discharge viscosity is controlled to keep at 5000 mPa.s;

[0042] Take graphite (D50 is 10 μm, specific capacity 350 mAh / g) 45.72 kg and gas phase silicon material SiC (D50 is 20 μm, specific capacity 1800 mAh / g) 4.46 kg, dry mixing, then add 23.97 kg of CMC glue solution stirred, pre-mixing, then 8.84 kg of polyacrylic acid (PAA) binder, 0.28 kg of conductive carbon black, 4.19 kg of carbon nanotube are mixed and stirred, and water is added to adjust the viscosity, finally 0.62 kg of butadiene-styrene rubber (SBR) binder is added to obtain the lower layer slurry, and the discharge viscosity is controlled to keep at 5000 mPa.s;

[0043] The prepared lower layer slurry and upper layer slurry are coated on the current collector in turn using a double-layer coating die at a coating speed of 15 m / min, and then baked at 100 ℃ to obtain the negative electrode sheet.

[0044] Example 2

[0045] The example is basically the same as example 1, the difference is that in the upper layer slurry of the example, the amount of graphite (D50 is 20 μm, specific capacity 350 mAh / g) is 37.64 kg, and the amount of graphite (D50 is 10 μm, specific capacity 350 mAh / g) is 8.09 kg, and in the lower layer slurry, the amount of graphite (D50 is 10 μm, specific capacity 350 mAh / g) is 37.64 kg, and the amount of graphite (D50 is 20 μm, specific capacity 350 mAh / g) is 8.09 kg.

[0046] Example 3

[0047] The example is basically the same as example 1, the difference is that in the upper layer slurry of the example, the amount of graphite (D50 is 20 μm, specific capacity 350 mAh / g) is 27.60 kg, and the amount of graphite (D50 is 10 μm, specific capacity 350 mAh / g) is 18.12 kg, and in the lower layer slurry, the amount of graphite (D50 is 10 μm, specific capacity 350 mAh / g) is 27.60 kg, and the amount of graphite (D50 is 20 μm, specific capacity 350 mAh / g) is 18.12 kg.

[0048] Example 4

[0049] This example is basically the same as Example 1, except that the D50 of the fumed silica material SiC in the upper layer slurry in this example is 5 μm.

[0050] Example 5

[0051] This example is basically the same as Example 1, except that the D50 of the fumed silica material SiC in the upper layer slurry in this example is 12 μm.

[0052] Example 6

[0053] This example is basically the same as Example 1, except that the D50 of the graphite in the upper layer slurry in this example is 12 μm.

[0054] Example 7

[0055] This example is basically the same as Example 1, except that the D50 of the graphite in the upper layer slurry in this example is 16 μm.

[0056] Example 8

[0057] This example is basically the same as Example 1, except that the amount of CMC glue solution in the lower layer slurry in this example is 33.56 kg, the amount of polyacrylic acid (PAA) binder is 12.38 kg, the amount of styrene-butadiene rubber (SBR) binder is 0.87 kg, the amount of CMC glue solution in the upper layer slurry is 14.38 kg, the amount of polyacrylic acid (PAA) binder is 5.3 kg, and the amount of styrene-butadiene rubber (SBR) binder is 0.37 kg.

[0058] Example 9

[0059] This example is basically the same as Example 1, except that the amount of CMC glue solution in the lower layer slurry in this example is 41.55 kg, the amount of polyacrylic acid (PAA) binder is 14.14 kg, the amount of styrene-butadiene rubber (SBR) binder is 0.99 kg, the amount of CMC glue solution in the upper layer slurry is 10.39 kg, the amount of polyacrylic acid (PAA) binder is 3.54 kg, and the amount of styrene-butadiene rubber (SBR) binder is 0.25 kg.

[0060] Example 10

[0061] This example is basically the same as Example 1, except that the amount of conductive carbon black in the lower layer slurry in this example is 0.39 kg, and the amount of carbon nanotubes is 5.87 kg, the amount of conductive carbon black in the upper layer slurry is 0.17 kg, and the amount of carbon nanotubes is 2.51 kg.

[0062] Example 11

[0063] This example is basically the same as Example 1, except that the amount of conductive carbon black in the lower layer slurry is 0.45 kg, and the amount of carbon nanotubes is 6.70 kg, and the amount of conductive carbon black in the upper layer slurry is 0.11 kg, and the amount of carbon nanotubes is 1.68 kg.

[0064] Comparative Example 1

[0065] This comparative example is basically the same as Example 1, except that the amount of graphite (D50 of 10 μm, gravimetric capacity of 350 mAh / g) and the amount of SiC (D50 of 20 μm, gravimetric capacity of 1800 mAh / g) in the upper layer slurry and the lower layer slurry are both 22.865 kg.

[0066] Comparative Example 2

[0067] This comparative example is basically the same as Example 1, except that the amount of graphite (D50 of 10 μm, gravimetric capacity of 350 mAh / g) is 45.72 kg, and the amount of SiC (D50 of 20 μm, gravimetric capacity of 1800 mAh / g) is 4.46 kg in the upper layer slurry, and the amount of graphite (D50 of 20 μm, gravimetric capacity of 350 mAh / g) is 45.72 kg, and the amount of SiC (D50 of 10 μm, gravimetric capacity of 1800 mAh / g) is 4.46 kg in the lower layer slurry.

[0068] Test Example:

[0069] The obtained negative electrode sheet was matched with a ternary positive electrode (LiNi 0.9 Co 0.05 Mn 0.05 O2) to assemble a full battery, and the cycle life and fast charging performance were tested, and the test results are shown in Table 1.

[0070] Cycle life test: 1C constant current and constant voltage charging to 4.2V at 25℃, 0.05C current cutoff; 1C constant current discharging to 2.5V, cycle test.

[0071] Fast charging test: using 12min fast charging simulation working condition, 10% SOC charging to 80% SOC, then using 0.5C constant current and constant voltage charging to 4.2V, 1C constant current discharging to 2.5V, cycle test.

[0072] Table 1

[0073] Capacity (Ah) cycle life test (300 cycles) capacity retention rate (%) fast charging performance test (300 cycles) capacity retention rate (%) Example 1 1.30 95.83 94.45 Example 2 1.28 95.86 94.46 Example 3 1.29 95.99 94.88 Example 4 1.31 96.02 95.90 Example 5 1.29 95.96 95.42 Example 6 1.32 96.02 95.50 Example 7 1.30 96.03 95.31 Example 8 1.28 96.10 95.32 Example 9 1.29 96.04 95.26 Example 10 1.27 96.03 95.30 Example 11 1.29 96.00 95.25 Comparative Example 1 1.28 94.56 93.12 Comparative Example 2 1.29 94.20 92.30

[0074] From Table 1, it can be seen that:

[0075] Compared with Example 1, Example 2 and Example 3, the capacity retention rate of the battery in Example 3 is higher, which shows that the ratio of large particles and small particles of the active material in the second electrode material layer and the first electrode material layer can affect the capacity retention rate of the battery.

[0076] Compared with Example 1, Example 6 and Example 7, the capacity retention rate of the battery in Example 7 is higher, which shows that the size of the large particles of the active material in the second electrode material layer can affect the capacity retention rate of the battery.

[0077] Compared with Example 1, Example 8 and Example 9, the capacity retention rate of the battery in Example 8 and Example 9 is higher, which shows that by making the binder of the first electrode material layer more than the binder of the second electrode material layer, the capacity retention rate of the battery can be improved.

[0078] Compared with Example 1, Example 10 and Example 11, the capacity retention rate of the battery in Example 10 and Example 11 is higher, which shows that by controlling the mass ratio of the conductive agent of the first electrode material layer to the conductive agent of the second electrode material layer, the capacity retention rate of the battery can be improved.

[0079] Compared with Comparative Example 1 and Comparative Example 2, the capacity retention rate of the battery in the example is higher, which shows that by making the mass of the large particles of the active material in the second electrode material layer greater than the mass of the small particles of the active material, the capacity retention rate of the battery can be improved.

[0080] The mass of the large particles of the active material in the first electrode material is less than the mass of the small particles of the active material, which can improve the capacity retention rate of the battery.

Claims

1. A negative electrode sheet, comprising a current collector, and a first electrode material layer and a second electrode material layer sequentially stacked on the current collector in a direction away from the current collector, wherein each of the first electrode material layer and the second electrode material layer comprises an active material, the active material comprises first active material particles and second active material particles, the first active material particles have a particle size larger than that of the second active material particles, the total mass of the first active material particles in the first electrode material layer is less than that of the second active material particles, and the total mass of the first active material particles in the second electrode material layer is greater than that of the second active material particles.

2. The negative electrode sheet according to claim 1, wherein The mass percentage of the first active material particles is 55%-95% and the mass percentage of the second active material particles is 5%-45% based on the total mass of the active material in the second electrode material layer; and / or, The mass percentage of the first active material particles is 5%-45% and the mass percentage of the second active material particles is 55%-95% based on the total mass of the active material particles in the first electrode material layer; and / or, The D50 of the first active material particles is 12-20 μm; and / or, The D50 of the second active material particles is 5-12 μm; and / or, The gravimetric capacity of the active material is 400-2000 mAh / g.

3. The negative electrode sheet according to claim 1, wherein The active material comprises one or more of a carbon material, a silicon material and a lithium alloy material.

4. The negative electrode sheet according to claim 3, wherein The carbon material comprises one or more of natural graphite, artificial graphite, soft carbon, hard carbon and activated carbon; and / or, The silicon material comprises one or more of silicon, silicon-carbon and silicon-oxygen; and / or, The lithium alloy material comprises one or more of lithium alloy, lithium-aluminum alloy and lithium-titanium alloy.

5. The negative electrode sheet according to claim 1, wherein The mass ratio of the active material in the first electrode material layer to the active material in the second electrode material layer is (3-8):(2-9).

6. The negative electrode sheet according to claim 1, wherein The mass ratio of the active material in the first electrode material layer to the active material in the second electrode material layer is 1:1; and / or, The mass ratio of the second active material particles to the first active material particles in the first electrode material layer is the same as that of the first active material particles to the second active material particles in the second electrode material layer. 7.The negative electrode sheet of claim 1, wherein each of the first electrode material layer and the second electrode material layer further comprises a conductive agent, and the mass ratio of the conductive agent in the first electrode material layer to the conductive agent in the second electrode material layer is (2-9):(1-8). 8.The negative electrode sheet of claim 7, wherein each of the first electrode material layer and the second electrode material layer further comprises a binder, and the mass percentage of the binder in the first electrode material layer is 55%-95% and the mass percentage of the binder in the second electrode material layer is 5%-45% based on the total mass of the binder in the first electrode material layer and the second electrode material layer.

9. The negative electrode sheet according to claim 8, wherein The ratio of the mass sum of the active material, the mass sum of the conductive agent and the mass sum of the binder in the first electrode material layer and the second electrode material layer is (71-115):(1-10):(1.5-30).

10. The negative electrode sheet according to claim 8, wherein The conductive agent comprises one or more of acetylene black, conductive carbon black, graphene and carbon nanotube; and / or, The binder comprises one or more of polyacrylic acid, butadiene-styrene rubber, sodium carboxymethyl cellulose, sodium alginate, carboxymethyl chitosan and polyacrylonitrile.

11. The negative electrode sheet according to claim 8, wherein The active material comprises graphite and silicon, the binder comprises polyacrylic acid, butadiene-styrene rubber and sodium carboxymethyl cellulose, and the mass ratio of the graphite, the silicon, the polyacrylic acid, the butadiene-styrene rubber and the sodium carboxymethyl cellulose is (70-95):(1-20):(0.5-10):(0.5-10):(0.5-10). 12.A lithium ion battery comprising the negative electrode sheet according to any one of claims 1-11.