WO2023093568A1

WO2023093568A1 - Negative electrode active material, negative electrode sheet, and battery

Info

Publication number: WO2023093568A1
Application number: PCT/CN2022/131902
Authority: WO
Inventors: 薛佳宸; 李素丽; 刘春洋
Original assignee: 珠海冠宇电池股份有限公司
Priority date: 2021-11-29
Filing date: 2022-11-15
Publication date: 2023-06-01
Also published as: CN116190580A

Abstract

The present disclosure belongs to the technical field of batteries, and specifically relates to a negative electrode active material, a negative electrode sheet comprising the negative electrode active material, and a battery. The negative electrode active material in the negative electrode sheet in the battery of the present disclosure comprises a homogeneous SiC material and graphite. Compared with a conventional SiC material, the homogeneous SiC material of the present disclosure has a better cycle performance and a high gram capacity, such that the electrolyte consumption, secondary reactions and cyclic expansion are reduced, and the problems of a relatively low first effect, high cyclic attenuation, large cyclic expansion, etc. of a high-proportion mixed negative electrode can be effectively solved, thereby significantly improving the energy density and the cycle service life of the battery, such that the battery is suitable for large-scale commercial production.

Description

A kind of negative electrode active material, negative electrode sheet and battery

technical field

The disclosure belongs to the technical field of batteries, and in particular relates to a negative electrode active material, a negative electrode sheet and a battery including the negative electrode active material.

Background of the invention

Traditional lithium cobalt oxide (LCO), lithium iron phosphate (LFP), nickel-cobalt-manganese (NCM), nickel-cobalt-aluminum (NCA) cathode materials combined with graphite anode materials are far from meeting the growing demand for energy density in the market, so the new The development of high energy density positive and negative electrode systems is very necessary.

Silicon-based anode materials have excellent properties such as high specific capacity, low cost, and easy processing. Among them, although the silicon oxide (SiO _x , 1.2>x>0.8) material has a low gram capacity (<1800mAh/g), the material has a long cycle life, which is more in line with the requirements of the soft pack battery for the negative electrode material, and is increasingly being used as a soft pack battery. Although more and more manufacturers have shifted their research focus to SiO _x materials, the continuous increase in volume expansion during the cycle is still the main obstacle restricting its large-scale application.

Since the lithium intercalation mechanism of silicon-based negative electrode materials is different from that of anisotropic graphite-based negative electrode materials, the alloying process is accompanied by a very large isotropic expansion. In actual use, the expanded SiO _x material will produce a large The expansion in the plane of the pole piece causes the internal stress of the negative pole piece to increase, causing the negative pole piece to be distorted and deformed or even to tear the copper foil of the base material, which may seriously cause the failure of the battery cell and cause safety problems.

Si and SiC negative electrode materials have the advantages of high specific capacity (~3400mAh/g), long cycle life, and high initial Coulombic efficiency. Si composite materials mixed with graphite negative electrodes have been widely used in the field of high energy density cylindrical and steel shell power batteries . However, due to the large volume expansion during the cycle, the particles are easy to fall off, resulting in the effective active material detaching from the conductive network, the particle breakage leads to repeated generation and destruction of the SEI film, accelerated electrolyte consumption, and internal resistance increase, making Si and SiC negative electrode materials in the market. There are many difficulties in the practical application of pouch batteries. However, considering factors such as its higher gram capacity, long cycle life, and high initial Coulombic efficiency, the possibility and prospect of using SiC-based anode materials is even broader.

Therefore, it is urgent to develop a battery with good cycle stability, low expansion rate and long service life.

Contents of the invention

The inventors of the present disclosure have found through research that conventional SiC materials are secondary large particles composed of individual silicon nanoparticles composited with carbon, and there is an obvious phase separation of silicon and carbon in this material, that is, the two components are still in the microstructure. There are obvious boundaries, and this structure is not conducive to the cycle stability of SiC materials, and is prone to problems such as SEI film thickening and decay acceleration.

In order to improve the deficiencies of the prior art, the present disclosure provides a negative electrode active material and a negative electrode sheet and a battery including the negative electrode active material, the negative electrode active material includes a homogeneous SiC material and graphite, and the homogeneous SiC material has more Good cycle performance and high gram capacity, the negative electrode sheet including the negative electrode active material has good cycle performance and low expansion performance, which can solve the problem of tearing of the negative electrode current collector, and the battery including the negative electrode sheet has relatively high Good rate performance and low distortion.

The purpose of this disclosure is achieved through the following technical solutions:

A negative electrode active material, the negative electrode active material includes homogeneous SiC material and graphite; wherein, the homogeneous SiC material is a silicon carbon material composed of Si element and C element and has a double continuous phase structure.

In the present disclosure, the bicontinuous phase means that the phase formed by the Si element and the phase formed by the C element in the homogeneous SiC material are both continuous, and the two phases have no obvious boundary in the microstructure. The homogeneous SiC material described in the present disclosure is different from the existing conventional SiC-type negative electrode materials. It is a silicon-carbon material with a dual continuous phase structure formed by Si and C elements, and there is no phase separation structure of silicon and carbon. , that is, there is no obvious boundary between the two components in the microstructure. On the contrary, the Si element and the C element can respectively form a continuous phase structure, and this structure is conducive to the improvement of the cycle stability of the battery.

In one example, the graphite is artificial graphite or natural graphite.

In one example, the median diameter D _v50 of the graphite is 5 μm to 20 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19μm or 20μm.

In one example, the graphite accounts for 45-99wt% of the total mass of the negative electrode active material, such as 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt% or 99wt%.

In an example, the homogeneous SiC material can be purchased through commercial channels; alternatively, it can also be prepared by the following method:

In vacuum and at a temperature of 350°C to 450°C (such as 350°C, 380°C, 400°C, 420°C, 450°C), continuously feed silane gas into the porous carbon material for a certain period of time; ℃, 600°C, 650°C, 700°C, 750°C), and then pass carbon source gas for a certain period of time, and cool to room temperature under the protection of an inert atmosphere to obtain the homogeneous SiC material.

Wherein, the silane gas is, for example, SiH ₄ .

Wherein, the time for introducing the silane gas is 12h-24h, for example, 12h, 15h, 20h, 24h.

Wherein, the carbon source gas is at least one of ethylene and acetylene.

Wherein, the time for feeding the carbon source gas is 20 min to 60 min, for example, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min.

Wherein, the inert atmosphere is, for example, argon.

In an example, the median diameter D _v50 of the homogeneous SiC material is 5 μm˜15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

In an example, the specific surface area of the homogeneous SiC material is 3-10m ² /g, such as 3m ² /g, 4m ² /g, 5m ² /g, 6m ² /g, 7m ² /g, 8m ² /g, 9m ² /g, 10m ² /g.

In one example, the homogeneous SiC material accounts for 1wt% to 55wt% of the total mass of the negative electrode active material, such as 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% , 40wt%, 45wt%, 50wt% or 55wt%.

In an example, the homogeneous SiC material in the X-ray diffraction pattern has a maximum intensity of I ₁ of a broad peak at 2θ attributable to a range of 20°-40°, and a maximum intensity of a broad peak attributable to a range of 40°-60° Maximum intensity I ₂ , I ₁ >I ₂ . See, for example, that shown in FIG. 1 .

In one example, the mass percentage of C in the homogeneous SiC material is 30wt%-70wt%, such as 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt% % or 70wt%. Preferably, the content of C element is 40-60wt%.

In an example, within the homogeneous SiC material, in a region 100 nm away from the surface of the homogeneous SiC material, the mass proportions C _A and C B of the C element at any two points A and _B satisfy: |C _A -C _B |≤15%. When the mass ratio of the C element at any two points A and B positions C _A and C _B satisfies: |C _A -C _B |≤15%, it indicates that the SiC material of the present application is homogeneous, preferably, |C _A -C _B |≤10%.

In an example, the specific surface area of the phase formed by C element in the homogeneous SiC material is 900m ² /g-1500m ² /g, such as 900m ² /g, 1000m ² /g, 1100m ² /g, 1200m ² /g, 1300m ² /g, 1400m ² /g, 1500m ² /g, preferably, the specific surface area is 1000-1400m ² /g.

In an example, the porosity of the phase formed by C element in the homogeneous SiC material is 0.4cc/g-1.1cc/g, for example, 0.4cc/g, 0.5cc/g, 0.6cc/g, 0.7cc /g, 0.8cc/g, 0.9cc/g, 1cc/g, 1.1cc/g, preferably, the porosity is 0.6-0.9cc/g.

In one example, the phase formed by the C element in the homogeneous SiC material is a porous structure.

In one example, the porous structure is a mixed structure of mesopores and micropores; exemplary, the mesopore diameters are concentrated in the range of 4nm to 14nm; for another example, the mesopore diameters are concentrated in the range of 6nm to 12nm; Exemplarily, the pore size of the micropores is distributed within a range of less than or equal to 1 nm.

In one example, the micropore porosity of the phase formed by C element in the homogeneous SiC material is 0.3cc/g-0.9cc/g, such as 0.3cc/g, 0.4cc/g, 0.5cc/g, 0.6cc/g, 0.7cc/g, 0.8cc/g, 0.9cc/g, preferably, the microporosity is 0.4-0.6cc/g.

In one example, the mesoporosity of the phase formed by C element in the homogeneous SiC material is 0.1cc/g-0.4cc/g, such as 0.1cc/g, 0.15cc/g, 0.2cc/g, 0.25 cc/g, 0.3cc/g, 0.35cc/g, 0.4cc/g, preferably, the mesoporosity is 0.15-0.35cc/g.

The present disclosure also provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, and the negative electrode active material layer includes the above-mentioned negative electrode active material.

In one example, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent.

In one example, based on the total mass of the negative electrode active material layer, the mass percentages of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent in the negative electrode active material layer are:

80wt%-99.8wt% negative electrode active material (such as 80wt%, 85wt%, 90wt%, 95wt%, 99.8wt%), 0.1wt%-10wt% negative electrode conductive agent (such as 0.1wt%, 0.5wt% , 1wt%, 3wt%, 5wt%, 8wt%, 10wt%), 0.1wt%-10wt% negative electrode binder (such as 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt% , 10wt%).

90wt%-98wt% of negative electrode active material, 1wt%-5wt% of negative electrode conductive agent, 1wt%-5wt% of negative electrode binder.

In one example, the negative electrode conductive agent is selected from one or more combinations of conductive carbon black, carbon fiber, activated carbon, acetylene black, graphene, super P, and carbon nanotubes.

In one example, the negative electrode binder is selected from styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyurethane, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, sodium alginate, CMC- A combination of one or more of Na, CMC-Li, and PVP.

In one example, the negative electrode current collector is copper foil or porous copper foil.

The present disclosure also provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

Step 1: Add the negative electrode active material, the negative electrode binder and the negative electrode conductive agent into a stirred tank, and stir at 20°C to 45°C (such as 20°C, 25°C, 30°C, 40°C, 45°C) 6h～18h (such as 6h, 8h, 10h, 12h, 15h, 14h, 16h, 18h), the prepared solid content is 30wt%-50wt% (such as 30wt%, 35wt%, 40wt%, 45wt%, 50wt%) Negative electrode slurry;

Step 2: coating the prepared negative electrode slurry on at least one surface of the negative electrode current collector, drying and rolling to obtain a negative electrode sheet.

In one example, in step 2, the thickness of the negative electrode slurry applied on at least one side surface of the negative electrode current collector is 20 μm-100 μm, for example, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm .

The present disclosure also provides a battery, which includes the above-mentioned negative electrode sheet.

In one example, the battery further includes a positive pole piece, a separator and an electrolyte.

In one example, the battery is a lithium ion battery.

In one example, the positive electrode sheet contains a positive electrode active material, and the positive electrode active material is selected from lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobaltate, and nickel-cobalt-manganese ternary materials. , nickel-manganese/cobalt-manganese/nickel-cobalt secondary raw materials, lithium manganese oxide, and a combination of one or more of lithium-rich manganese-based materials.

In one example, the separator is polyethylene polymer, polypropylene polymer or non-woven fabric.

In one example, the electrolytic solution is a non-aqueous electrolytic solution, the non-aqueous electrolytic solution includes a carbonate solvent and a lithium salt, and the carbonate solvent is selected from ethylene carbonate (EC), propylene carbonate (PC) , diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), the lithium salt is selected from LiPF _6. A combination of one or more of LiBF ₄ , LiSbF ₆ , LiClO ₄ , LiCF ₃ SO3 , LiAlO ₄ , LiAlCl ₄ , Li(CF ₃ SO ₂ ) ₂ N, LiBOB and LiDFOB.

In the present disclosure, the homogeneous SiC material refers to silicon carbon material.

The beneficial effects of the present disclosure relative to the prior art:

The negative electrode active material in the negative electrode sheet in the battery of the present disclosure includes homogeneous SiC material and graphite. Compared with conventional SiC materials, the homogeneous SiC material of the present disclosure has better cycle performance and high gram capacity, and can reduce electrolysis liquid consumption, reduce side reactions, and reduce cycle expansion. At the same time, it can effectively solve the problems of low first effect, fast cycle attenuation, and large cycle expansion of high-proportion mixed negative electrodes, thereby significantly improving the energy density and cycle life of the battery. It is suitable for large-scale commercial production.

To sum up, the energy density of the battery of the present disclosure is significantly improved, and the problems of cycle attenuation and large expansion can be effectively improved, and the service life is longer.

Brief description of the drawings

FIG. 1 is an XRD spectrum of a homogeneous SiC material in Example 1 of the present disclosure.

FIG. 2 is a SEM cross-sectional view of the homogeneous SiC material in Example 1 of the present disclosure, and the interior of the particle is a homogeneous structure at a magnification of 50K.

3 is a SEM cross-sectional view of a conventional SiC material in Comparative Example 1 of the present disclosure, with Si/C phase separation inside the particle at a magnification of 50K (the light color is the Si phase component, and the dark color is the carbon phase component).

Detailed ways

The present disclosure will be further described in detail in conjunction with specific embodiments below. It should be understood that the following examples are only for illustrating and explaining the present disclosure, and should not be construed as limiting the protection scope of the present disclosure. All technologies implemented based on the above contents of the present disclosure are covered within the intended protection scope of the present disclosure.

The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents and materials used in the following examples can be obtained from commercial sources unless otherwise specified.

The relevant performance test process in following embodiment and comparative example:

1. Carbon content test in SiC materials

The carbon content in SiC materials was measured using a sulfur carbon meter.

2. Test of carbon content difference in SiC material particles

The section of the negative electrode sheet was polished with Ar particles, and SEM and EDS were selected to test the section of the negative electrode sheet in the examples and comparative examples. Calculate the mass proportion of C elements at any 4 points A, B, C, and D in any 5 SiC material particles within a region 100nm away from the SiC material particle surface by SEM and EDS C _A , C _B , C _C , C _D , After calculating |C _n -C _m | in pairs (n and m are any two points of A, B, C, and D), take the average value of Max|C _n -C _m | inside five particles.

3. Capacity retention after 500/600/800 cycles

Test steps: At room temperature, charge the battery to 4.45V with 0.5C or 3C constant current and constant voltage, cut off at 0.05C, then discharge the battery to 3.0V at 0.5C, cycle for 500/600/800 cycles, and calculate 500/ The capacity retention rate after 600/800 cycles is calculated by the following formula:

Capacity retention rate = terminal capacity / initial capacity * 100%.

4. Expansion rate after cycle

Test steps: At room temperature, charge the battery to 4.45V with 0.5C or 3C constant current and constant voltage, cut off at 0.05C, then discharge the battery to 3.0V at 0.5C, and cycle to the specified number of weeks (500/600/800 weeks, as shown in Table 1), calculated by the following formula:

Expansion rate = (THK1-THK0)/THK0×100%;

Among them, THK0 is the thickness of the initial 3.85V battery measured by 600g PPG, and THK1 is the thickness of the fully charged battery after cycling.

The conventional SiC material used in the following comparative examples is a secondary large particle composed of single silicon nanoparticle composite carbon, which has a structure shaped like a dragon fruit, and its median particle diameter D _v50 is 10 μm.

Fig. 3 is the SEM cross-sectional view of the conventional SiC material in comparative example 1 of the present disclosure, as can be seen from Fig. 3, under the 50K magnification, the Si/C phase separation inside the particle (the light color is the Si phase component, and the dark color is the Si phase component). Carbon phase component), indicating that it is a secondary large particle composed of a single silicon nanoparticle composite carbon, and there is an obvious phase separation of silicon and carbon in the material, that is, the two components still have a clear boundary under the microstructure.

Example 1

A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is prepared by coating the negative electrode slurry on the negative electrode current collector, and the negative electrode slurry includes a negative electrode active material (for the first time The charge and discharge efficiency is 88%, the reversible gram capacity is 500mAh/g), negative electrode binder and negative electrode conductive agent, the negative electrode active material is a mixture of homogeneous SiC material and artificial graphite, the homogeneous SiC and artificial graphite The mass ratio is 12:88.

Wherein, the homogeneous SiC is obtained by the following method:

Using the purchased mesoporous carbon material FDU-15, the silane gas (SiH ₄ ) was continuously passed through at 450°C for 20h under 100Pa vacuum condition, then the temperature was raised to 650°C and ethylene gas was passed through for 30min, and then obtained after cooling under the protection of argon.

The homogeneous SiC material is a silicon-carbon material with a bicontinuous phase structure formed by Si and C elements, with a median particle diameter D _v50 of 8 μm and a specific surface area of 5.4 m ² /g. In the homogeneous SiC material The mass percentage content of C element is 50.2wt%.

FIG. 1 is an XRD spectrum of a homogeneous SiC material in Example 1 of the present disclosure. It can be seen from Figure 1 that the homogeneous SiC material in the X-ray diffraction pattern has a maximum intensity of the broad peak at 2θ belonging to the range of 20°-40° is I ₁ , and the maximum intensity of the broad peak belonging to the range of 40°-60° The maximum intensity of the broad peak I ₂ , I ₁ >I ₂ .

Fig. 2 is a SEM cross-sectional view of the homogeneous SiC material in Example 1 of the present disclosure. It can be seen from Fig. 2 that the inside of the particle is a homogeneous structure at a magnification of 50K, and there is no phase separation structure of silicon and carbon. That is, there is no obvious boundary between the two components in the microstructure, and the homogeneous SiC material has a double continuous phase structure.

The negative electrode binder is carboxymethylcellulose lithium (CMC-Li) and styrene-butadiene rubber (SBR), water is a solvent, and the conductive agent is super P (SP) and single-walled carbon nanotubes (SWCNTs), The mass ratio of the negative electrode active material: CMC-Li:SBR:SP:SWCNTs is 96:1.5:1.5:0.9:0.1, and the negative electrode current collector is copper foil.

A method for preparing a negative pole piece, comprising the following steps:

Step 1: Add the negative electrode active material, negative electrode binder and negative electrode conductive agent into the dispersant according to the proportioning amount and stir at 20°C for 18 hours to prepare a negative electrode slurry with a solid content of 30%-50%;

Step 2: coating the negative electrode slurry on the surface of the negative electrode current collector, drying and rolling to obtain a negative electrode sheet.

A battery containing the negative pole piece includes a positive pole piece, a diaphragm, an electrolyte, an aluminum-plastic film and the above-mentioned negative pole piece.

The positive electrode sheet contains a positive electrode active material, the positive electrode active material is a 4.45V lithium cobaltate positive electrode (LiCoO ₂ ), the first charge and discharge efficiency is 95%, polyvinylidene fluoride (PVDF) is used as a binder, and N-formazan Pyrrolidone (NMP) is a solvent, SP (super P) and carbon nanotubes (CNTs) are composite conductive agents, and the mass ratio of the positive electrode active material: PVDF:SP:CNTs is 96:2:1.5:0.5, after stirring , coating, rolling, slitting, and sheeting to prepare positive electrode sheets.

The diaphragm is a polyethylene diaphragm, the electrolyte is a non-aqueous electrolyte, and the non-aqueous electrolyte includes a carbonate solvent and a lithium salt, and the carbonate solvent is ethylene carbonate (EC), and the lithium The salt is LiPF ₆ .

The size of the negative electrode sheet is larger than that of the positive electrode sheet, and the reversible capacity per unit area is 5% higher than that of the positive electrode.

The positive and negative electrodes are stacked and assembled, the tabs are welded, aluminum-plastic film is packaged, the top and side are sealed, and the moisture is baked in vacuum. After the moisture reaches the standard, liquid injection, standing, and chemical formation are performed.

Under the charging and discharging conditions of 25°C and 0.5C, the sorting energy density of the battery reaches 820Wh/L, the capacity retention rate after 500 cycles at 0.5C is 83.3%, and the battery expansion rate is 8.3%.

Comparative example 1

Other operations are the same as embodiment 1, the difference is only in:

The negative electrode slurry includes a negative electrode active material (the first charge and discharge efficiency is 88%, and the reversible gram capacity is 500mAh/g), wherein the negative electrode active material is a mixture of conventional SiC and graphite, and the mass ratio of the conventional SiC and graphite is 12:88.

The size of the negative electrode sheet is larger than that of the positive electrode sheet, and the reversible capacity per unit area is 6% higher than that of the positive electrode.

Under the charging and discharging conditions of 25°C and 0.5C, the sorting energy density of the battery reaches 820Wh/L, the capacity retention rate after 500 cycles at 0.5C is 71.3%, and the battery expansion rate is 16%.

Example 2

Other operations are the same as embodiment 1, the difference is only in:

The negative electrode slurry includes negative electrode active material (the first charge and discharge efficiency is 88%, and the reversible gram capacity is 550mAh/g), negative electrode binder and negative electrode conductive agent, wherein, the negative electrode active material is homogeneous SiC material and artificial graphite mixture, the mass ratio of the homogeneous SiC material and artificial graphite is 3:7.

Wherein, the homogeneous SiC is obtained by the following method:

Using the purchased Yoshikura nanoporous carbon material MC-1, after continuously feeding silane gas (SiH ₄ ) at 450°C under 20kPa vacuum condition for 15h, then raising the temperature to 600°C, feeding acetylene gas for 25min, and cooling under the protection of argon to obtain .

The homogeneous SiC material is a silicon-carbon material with a bicontinuous phase structure formed by Si and C elements, with a median particle diameter D _v50 of 10 μm and a specific surface area of 8.1 m ² /g. In the homogeneous SiC material The mass percent content of C element is 45.3wt%.

The mass ratio of the negative electrode active material: CMC-Li:SBR:SP:SWCNTs is 95:1.5:2:1.3:0.2.

The positive electrode active material is a ternary material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the first charge and discharge efficiency is 89%.

The size of the negative electrode sheet is larger than that of the positive electrode sheet, and the reversible capacity per unit area is 12% higher than that of the positive electrode.

Under 25°C 0.5C charging and discharging conditions, the sorting energy density of the battery can reach 320Wh/kg, the capacity retention rate after 800 cycles at 0.5C is 82.6%, and the battery expansion rate is 11.3%.

Comparative example 2

Other operations are the same as embodiment 2, the difference is only in:

The negative electrode slurry includes a negative electrode active material (the first charge and discharge efficiency is 79%, and the reversible gram capacity is 550mAh/g), and the negative electrode active material is a mixture of SiO _1.1 and artificial graphite, and the mass of the SiO _1.1 and artificial graphite The ratio is 3:7, and the SiO _1.1 is a nanoscale composite of silicon and SiO ₂ .

Under the charge and discharge condition of 25°C and 0.5C, the sorting energy density of the battery is 300Wh/kg, the capacity retention rate after 800 cycles at 0.5C is 70.5%, and the battery expansion rate is 17.4%.

Example 3

Other operations are the same as embodiment 1, the difference is only in:

The negative electrode slurry includes a negative electrode active material (the first charge and discharge efficiency is 90%, and the reversible gram capacity is 450mAh/g), wherein the negative electrode active material is a mixture of homogeneous SiC material and artificial graphite, and the homogeneous SiC material and The mass ratio of artificial graphite is 7:93.

Wherein, the homogeneous SiC is obtained by the following method:

The purchased mesoporous carbon material CMK-3 was obtained by continuously feeding silane gas (SiH ₄ ) at 450°C for 12h under a vacuum condition of 10kPa, then raising the temperature to 650°C and feeding ethylene gas for 30min, and cooling under the protection of argon.

The homogeneous SiC material is a silicon-carbon material with a bicontinuous phase structure formed by Si and C elements, with a median particle size D _v50 of 11 μm and a specific surface area of 9.1 m ² /g. In the homogeneous SiC material The mass percent content of C element is 47.2wt%.

The electrolytic solution is a non-aqueous electrolytic solution, and the non-aqueous electrolytic solution includes a carbonate solvent and a lithium salt, the carbonate solvent is ethylene carbonate (EC), and the lithium salt is LiTFSI and LiPF ₆ .

Under the condition of 3C charge/0.5C discharge at 25°C, the sorting energy density of the battery can reach 730Wh/L, the capacity retention rate is 80.3% after 600 cycles at 3C, and the battery expansion rate is 9.3%.

Comparative example 3

Other operations are the same as embodiment 3, the difference is only in:

The negative electrode slurry includes a negative electrode active material (the first charge and discharge efficiency is 90%, and the reversible gram capacity is 450mAh/g), wherein the negative electrode active material is a mixture of conventional SiC material and artificial graphite, and the conventional SiC material and artificial graphite The mass ratio is 7:93.

Under the condition of 25°C 3C charge/0.5C discharge, the sorting energy density of the battery reaches 730Wh/L, the capacity retention rate after 600 cycles of 3C is 68.3%, and the battery expansion rate is 14.5%.

Table 1 is the performance test result of negative electrode active material and battery of embodiment and comparative example

It can be seen from Table 1 that, compared with conventional SiC materials, the homogeneous SiC material of the present disclosure has better cycle performance and high gram capacity, can reduce electrolyte consumption, reduce side reactions, reduce cycle expansion, and can also It effectively solves the problems of low first efficiency, fast cycle attenuation, and large cycle expansion of high-ratio mixed negative electrodes, thereby significantly improving the energy density and cycle life of the battery, and is suitable for large-scale commercial production.

To sum up, the energy density of the battery disclosed in the present disclosure is significantly improved, and the problems of cycle attenuation and large expansion can be effectively improved, and the service life is longer.

The embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the above-mentioned embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included within the protection scope of the present disclosure.

Claims

A negative electrode active material, characterized in that the negative electrode active material includes a homogeneous SiC material and graphite; wherein the homogeneous SiC material is a silicon-carbon material composed of Si and C elements and has a dual continuous phase structure.
Negative electrode active material according to claim 1, is characterized in that, described graphite is artificial graphite or natural graphite;

Preferably, the graphite has a median diameter D v50 of 5 μm˜20 μm.
The negative electrode active material according to claim 1 or 2, characterized in that, the median particle diameter D v50 of the homogeneous SiC material is 5 μm to 15 μm;

Preferably, the specific surface area of the homogeneous SiC material is 3m 2 /g˜10m 2 /g.
The negative electrode active material according to any one of claims 1-3, wherein the graphite accounts for 45wt% to 99wt% of the total mass of the negative electrode active material, and the homogeneous SiC material accounts for 45wt% to 99wt% of the negative electrode active material 1 wt% to 55 wt% of the total mass.
The negative electrode active material according to any one of claims 1-4, characterized in that, the maximum intensity of the broad peak in the X-ray diffraction pattern of the homogeneous SiC material that 2θ belongs to within the range of 20°-40° is 1 1 , the maximum intensity I 2 assigned to the broad peak in the range of 40°-60°, I 1 >I 2 .
The negative electrode active material according to any one of claims 1-5, characterized in that the mass percentage of C element in the homogeneous SiC material is 30wt%-70wt%.
The negative electrode active material according to any one of claims 1-6, characterized in that, within the homogeneous SiC material, in the region 100 nm away from the surface of the homogeneous SiC material, the C element at any two points A and B The mass proportions of C A and C B satisfy: |C A -C B |≤15%, preferably, |C A -C B |≤10%.
The negative electrode active material according to any one of claims 1-7, characterized in that the specific surface area of the phase formed by C element in the homogeneous SiC material is 900m 2 /g˜1500m 2 /g.
The negative electrode active material according to any one of claims 1-8, characterized in that the phase formed by C element in the homogeneous SiC material has a porosity of 0.4 cc/g˜1.1 cc/g.
The negative electrode active material according to any one of claims 1-9, wherein the phase formed by the C element in the homogeneous SiC material is a porous structure, and the porous structure is a mixed structure of mesopores and micropores;

Preferably, the mesopore diameter is concentrated in the range of 4 nm to 14 nm, and the mesoporosity of the phase formed by C element in the homogeneous SiC material is 0.1 cc/g to 0.4 cc/g;

Preferably, the pore size of the micropores is distributed in the range of less than or equal to 1 nm, and the micropore porosity of the phase formed by C element in the homogeneous SiC material is 0.3 cc/g˜0.9 cc/g.
A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, characterized in that the negative electrode active material layer comprises any one of claims 1-10 The negative electrode active material described in the item.
The negative electrode sheet according to claim 11, wherein the negative electrode active material layer also includes a negative electrode binder and a negative electrode conductive agent, based on the total mass of the negative electrode active material layer, the negative electrode active material layer The mass percentages of negative electrode active material, negative electrode binder and negative electrode conductive agent in the material layer are:

80wt%-99.8wt% negative electrode active material, 0.1wt%-10wt% negative electrode conductive agent, 0.1wt%-10wt% negative electrode binder.
According to the negative electrode sheet according to claim 11 or 12, the negative electrode conductive agent is selected from one or more combinations of conductive carbon black, carbon fiber, activated carbon, acetylene black, graphene, superP, and carbon nanotubes;

Preferably, the negative electrode binder is selected from styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyurethane, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, sodium alginate, CMC-Na, A combination of one or more of CMC-Li and PVP;

Preferably, the negative electrode current collector is copper foil or porous copper foil.
A battery, characterized in that the battery comprises the negative electrode active material according to any one of claims 1-10, or comprises the negative electrode sheet according to any one of claims 11-13.
The battery according to claim 14, wherein the battery is a lithium ion battery.