CN114050234B - Negative plate and lithium ion battery comprising same - Google Patents
Negative plate and lithium ion battery comprising same Download PDFInfo
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- CN114050234B CN114050234B CN202111348702.5A CN202111348702A CN114050234B CN 114050234 B CN114050234 B CN 114050234B CN 202111348702 A CN202111348702 A CN 202111348702A CN 114050234 B CN114050234 B CN 114050234B
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a negative plate and a lithium ion battery comprising the same. In addition, the first negative electrode active material in the negative electrode sheet is selected from titanium carbide coated porous silicon spheres, which can greatly improve the capacity of the negative electrode sheet, meanwhile, the titanium carbide coating layer can relieve the lithium insertion tensile stress of a silicon material, so that the structure of the negative electrode sheet is more stable, and the titanium carbide coating layer has certain conductivity, therefore, the content of a binder in the first negative electrode active material layer can be properly increased, the expansion performance of a battery is improved, or the content of the first negative electrode active material is properly increased, and the energy density of the coating layer is improved; the second negative active material in the negative plate is selected from graphite, and the second negative active material can effectively control the overall charge-discharge cyclic expansion of the negative plate.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a negative plate, a preparation method and a lithium ion battery comprising the negative plate.
Background
With the rapid development of lithium ion battery technology, lithium ion batteries are more and more widely applied to portable mobile electronic devices such as notebook computers and smart phones. With the reduction of the volume and the increase of the power consumption of electronic devices, the design requirements of batteries are more and more stringent, and the demand of smaller volume and higher capacity products needs to be met by increasing the energy density of the batteries.
Disclosure of Invention
In order to increase the energy density of a lithium ion battery, measures such as increasing the compaction density of a graphite negative electrode sheet and using a silicon negative electrode material are generally adopted. Researches find that the porosity of the negative plate is reduced by improving the compaction density of the graphite negative plate, so that the dynamic performance of the negative plate is poor, and the problem of lithium precipitation is easy to occur; the silicon negative electrode material is easy to generate negative electrode active substance particle breakage in the battery charge-discharge cycle process, so that the battery cycle expansion rate is increased. In order to solve the above problems, the present invention provides a negative plate and a lithium ion battery comprising the negative plate, wherein a first negative active material in the negative plate is selected from a titanium carbide coated porous silicon sphere, which can greatly improve the capacity of the negative plate, and meanwhile, the titanium carbide coating can also relieve the lithium insertion tensile stress of a silicon material, so that the structure of the negative plate is more stable, and the titanium carbide coating has a certain conductivity, so that the content of a binder in the first negative active material layer can be properly increased, the expansion performance of the battery is improved, or the content of the first negative active material is properly increased, and the energy density of the coating is improved; the second negative active material in the negative plate is selected from graphite, and the second negative active material can effectively control the overall charge-discharge cycle expansion rate of the negative plate.
The purpose of the invention is realized by the following technical scheme:
a negative electrode sheet comprising a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer;
the second negative electrode active material layer is on the first surface of the negative electrode current collector, and the first negative electrode active material layer is on the surface of the second negative electrode active material layer;
the first negative electrode active material layer comprises a first negative electrode active material selected from titanium carbide coated porous silicon spheres;
the second negative active material layer includes a second negative active material selected from graphite.
According to the present invention, the median particle diameter Dv of the first negative electrode active material 1 50 Satisfies the following conditions: dv is not less than 100nm 1 50 Less than or equal to 600nm; for example, the median particle diameter Dv of the first negative electrode active material 1 50 Is 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 600nm or any point value in the range formed by the two endpoints.
According to the present invention, the median particle diameter Dv of the second negative electrode active material 2 50 Satisfies the following conditions: dv is less than or equal to 2 mu m 2 50 Less than or equal to 20 μm, preferably satisfying: dv is less than or equal to 3 mu m 2 50 Less than or equal to 19 mu m; for example, the median particle diameter Dv of the second negative electrode active material 2 50 Is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm or any point in the range formed by the two endpoints.
According to the present invention, the median particle diameter Dv of the first negative electrode active material 1 50 And a median particle diameter Dv of the second negative electrode active material 2 50 Ratio Dv of 1 50 /Dv 2 50 Satisfies the following conditions: 0.0053<Dv 1 50 /Dv 2 50 ≦ 0.2, e.g. the said Dv 1 50 /Dv 2 50 Is 0.006, 0.008, 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2 or any of the above two endpoints. When Dv is 1 50 /Dv 2 50 <When the capacity is 0.0053, the load density of the first negative electrode active material is low, the energy density is not obviously improved, the dynamic performance matching of the two layers of negative electrode active materials is poor, the lithium precipitation of the negative electrode sheet can be caused, and the cycle capacity retention rate of the battery can be reduced; when Dv is 1 50 /Dv 2 50 >At 0.2, the first negative electrode active material is more easily broken to form a new SEI film, so that the circulation capacity retention rate is low, the circulation expansion is large, and the porosity of the negative electrode plate is reduced, so that the lithium precipitation of the negative electrode plate is caused.
According to the inventionThickness d of the first negative electrode active material layer 1 Is 10 μm to 200 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm or any point in the range of the two endpoints.
According to the present invention, the thickness d of the first anode active material layer 1 And a thickness d of the second anode active material layer 2 Ratio d of 1 /d 2 Satisfies the following conditions: 0<d 1 /d 2 ≦ 0.5, e.g. d as described 1 /d 2 Is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any point in the range of any two of the above endpoints. When the thickness d of the first anode active material layer 1 And a thickness d of the second anode active material layer 2 Ratio d of 1 /d 2 Within this range (0)<d 1 /d 2 Less than or equal to 0.5), the energy density of the prepared lithium ion battery is greatly improved, the whole cyclic expansion meets the design requirement, and the capacity retention rate is good; when the ratio d 1 /d 2 When the expansion rate is more than 0.5, the titanium carbide-coated porous silicon spheres expand greatly, particles are easy to break relative to graphite, and a new SEI film is formed after the particles break, so that the cycle capacity retention rate is reduced, and the expansion rate of the battery is increased, so that the battery is failed.
According to the invention, the negative current collector is selected from copper foils.
According to the present invention, the thickness of the negative electrode current collector is 6 to 12 μm.
According to the present invention, the first negative electrode active material layer is also on a second surface of the negative electrode current collector opposite to the first surface, and the second negative electrode active material layer is on a surface of the first negative electrode active material layer.
According to the present invention, the titanium carbide-coated porous silicon spheres are prepared by a method known in the art, or are commercially available.
According to the invention, the titanium carbide coated porous silicon spheres comprise porous silicon spheres and titanium carbide, the titanium carbide is coated on the surfaces of the porous silicon spheres to form coating layers, wherein the thickness T of each coating layer is more than or equal to 1nm and less than or equal to 5nm; the aperture R of the porous silicon ball is not less than 5nm and not more than 20nm.
According to the invention, the titanium carbide comprises one or more of titanium carbide having the following chemical formula: ti (titanium) 2 C、Ti 3 C 2 、Ti 3 C 2 T x (T is O, F or OH, and x is a number between 1 and 10).
According to the invention, the titanium carbide coating layer in the titanium carbide coated porous silicon ball can relieve the lithium-embedded tensile stress of the silicon material, so that the structure of the negative plate is more stable, and the expansion of the negative plate is effectively improved.
According to the invention, the graphite is selected from at least one of artificial graphite, natural graphite and graphite coated with a modifier. Wherein the modifier is selected from soft carbon or hard carbon.
According to the present invention, the first anode active material layer further includes a first conductive agent and a first binder.
According to the present invention, the second anode active material layer further includes a second conductive agent and a second binder.
According to the present invention, the first anode active material layer includes the following components in mass fraction: 90 to 99.2 weight percent of first negative active material, 0.2 to 3.5 weight percent of first conductive agent and 0.6 to 6.5 weight percent of first binder.
According to the invention, the second anode active material layer comprises the following components in percentage by mass: 90 to 99.2 weight percent of second cathode active material, 0.2 to 4 weight percent of second conductive agent and 0.6 to 6 weight percent of second binder.
According to the present invention, the first conductive agent and the second conductive agent are the same or different and are independently selected from one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and conductive fiber.
According to the invention, the first binder and the second binder are the same or different and are independently selected from one or more of polyvinyl alcohol, polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene and polyethylene oxide.
The invention also provides a preparation method of the negative plate, which comprises the following steps:
1) Preparing slurry for forming a first negative electrode active material layer and slurry for forming a second negative electrode active material layer respectively;
2) And coating the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer on the first surface of the negative electrode current collector by using a double-layer coating machine to prepare the negative electrode sheet.
According to the present invention, in step 1), the slurry forming the first negative electrode active material layer and the slurry forming the second negative electrode active material layer have a solid content of 40 to 50wt% and a viscosity of 2000 to 7000mPa · s.
According to the invention, in step 2), the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer are coated on a second surface, opposite to the first surface, of the negative electrode current collector to prepare the negative electrode sheet.
The invention also provides a lithium ion battery which comprises the negative plate.
The invention has the beneficial effects that:
the invention provides a negative plate and a lithium ion battery comprising the same. In addition, the first negative electrode active material in the negative electrode sheet is selected from titanium carbide coated porous silicon spheres, which can greatly improve the capacity of the negative electrode sheet, and meanwhile, the titanium carbide coating can relieve the lithium insertion tensile stress of a silicon material, so that the structure of the negative electrode sheet is more stable, and the titanium carbide coating has certain conductivity, therefore, the content of a binder in the first negative electrode active material layer can be properly increased, the expansion performance of a battery is improved, or the content of the first negative electrode active material is properly increased, and the energy density of the coating layer is improved; the second negative active material in the negative plate is selected from graphite, and the second negative active material can effectively control the overall charge-discharge cyclic expansion of the negative plate.
In conclusion, the negative plate can effectively improve the energy density of the battery, control the cycle expansion rate and the capacity retention rate of the battery and improve the lithium separation problem of the battery.
Drawings
Fig. 1 is a schematic structural diagram of a negative electrode sheet according to a preferred embodiment of the present invention.
Reference numerals: 1 is a negative current collector; 2 is a second anode active material layer; and 3 is a first anode active material layer.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
Comparative example 1
(1) By the particle diameter Dv 50 Negative electrode slurry was prepared with artificial graphite of 14.8 μm as a negative electrode active material: mixing artificial graphite, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.8.
(2) Coating the slurry for forming the negative electrode active material layer on the surface of a negative electrode current collector, wherein the thickness of the formed negative electrode active material layer is d1+ d2, and the width of the formed negative electrode active material layer is L1; the coating work of the other side of the current collector is completed in the same manner.
(3) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96.
(4) And rolling, die cutting and cutting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the electrode plates with an aluminum-plastic film after the short circuit test is qualified, baking the electrode plates in an oven to remove moisture until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the electrode plates for 24 to 48 hours, and completing the first charging by a hot pressing process to obtain the activated lithium ion battery.
Comparative example 2
(1) By the particle diameter Dv 50 SiO of 400nm 2 Preparing cathode slurry by using the material as a cathode active material: mixing SiO 2 The material, the conductive agent SP, the binder styrene-butadiene latex (SBR) and the polyacrylic acid (PAA) are mixed according to the mass ratio of 96.2.
(2) Coating the slurry for forming the negative electrode active material layer on the surface of a negative electrode current collector, wherein the thickness of the formed negative electrode active material layer is d1+ d2, and the width of the formed negative electrode active material layer is L1; the coating work of the other side of the current collector is completed in the same manner.
(3) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96.
(4) And rolling, die-cutting and slitting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the roll core by using an aluminum-plastic film after the short circuit test is qualified, baking the roll core in an oven to remove moisture until the moisture standard required by liquid injection is achieved, injecting electrolyte, aging the electrolyte for 24 to 48 hours, and completing the first charging by using a hot pressing formation process to obtain the activated lithium ion battery.
Comparative example 3
(1) By the particle diameter Dv 50 Titanium carbide Ti of 400nm 3 C 2 T x Preparing a negative electrode slurry by using the coated porous silicon spheres (the thickness of the coating layer is 2.62nm, and the pore diameter of the porous silicon spheres is 8 nm) as a negative electrode active material: mixing titanium carbide coated porous silicon spheres, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.2.
The preparation process of the titanium carbide coated porous silicon ball comprises the following steps:
Ti 3 C 2 T x the synthesis of (2): mixing Ti 3 AlC 2 The powder sample was added to a mixture of lithium fluoride (LiF) and hydrochloric acid and stirred at 40 ℃ for 24 hours. The resulting product was then washed with deionized water and centrifuged several times and the sample was dried under vacuum at 60 ℃ for 8 hours.
Preparation of titanium carbide nanosheets (TNS): ti to be produced by argon gas 3 C 2 T x The powder was dispersed in oxygen free deionized water. The suspension was sonicated for 1 hour, then centrifuged for 1 hour and the supernatant collected for further use.
SiO 2 Preparing nano silicon spheres: adding ethanol and NH 3 ·H 2 O and deionized water were mixed for 15 minutes with vigorous stirring, then Tetraethylorthosilicate (TEOS) and deionized water were added dropwise and stirred at room temperature for a further 2 hours. The final product was washed repeatedly with water and ethanol and collected by centrifugation and vacuum drying.
Preparation of porous nano silicon spheres (Si p-NSs): siO to be prepared 2 Mixing the nano silicon spheres and magnesium powder and adding the mixture into an autoclave. The autoclave was heated continuously at 700 ℃ for 6 hours under an argon atmosphere. After cooling to room temperature, the resulting powder was dispersed in HCl solution for 5 hours. The powder was immersed in a solution of ethanol-based hydrofluoric acid (HF) for 30 minutes, then washed with ethanol and deionized water and dried at 80 ℃ for 12h, and finally magnesiothermic reduction was performed.
Preparing porous silicon spheres coated with titanium carbide: dispersing the porous nano silicon spheres in ethanol and NH at room temperature 3 ·H 2 And stirring the mixed solution of O, MPS and deionized water for 2 days. MPS modified porous nano silicon spheres, sodium Dodecyl Sulfate (SDS), polyvinylpyrrolidone (PVP) and deionized water were premixed in a three-necked flask at room temperature while stirring for 12h to form a uniform suspension a. Under nitrogen protection, potassium persulfate (KPS) solution was added to the flask. Dropping an emulsion B prepared from SDS, deionized water, MMA and KOH into a flask, then raising the temperature to 70 ℃, after polymerizing for 1 hour under argon, collecting PMMA-coated porous nano silicon sphere colloid and washing with water by centrifugation, and then dispersing a sample in deionized water by ultrasonic treatment. The TNS colloidal solution and the PMMA-coated porous nano silicon sphere dispersion were directly mixed together and kept under stirring for 10 minutes. The mixture was centrifuged, collected and dried at 80 ℃. Finally, after PMMA was removed by annealing at 500 ℃ for 2 hours under flowing argon gas, titanium carbide coated porous silicon spheres were obtained.
(2) Coating the slurry for forming the negative electrode active material layer on the surface of a negative electrode current collector, wherein the thickness of the formed negative electrode active material layer is d1+ d2, and the width of the formed negative electrode active material layer is L1; the coating work of the other side of the current collector is completed in the same manner.
(3) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96.
(4) And rolling, die cutting and cutting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the electrode plates with an aluminum-plastic film after the short circuit test is qualified, baking the electrode plates in an oven to remove moisture until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the electrode plates for 24 to 48 hours, and completing the first charging by a hot pressing process to obtain the activated lithium ion battery.
Example 1
(1) By the particle diameter Dv 1 50 Titanium carbide Ti of 400nm 3 C 2 T x Coated porous silicon spheres (thickness of coating layer 2.62nm, pore diameter of porous silicon spheres 8 nm) as a first negative active material negative slurry 1: mixing titanium carbide coated porous silicon spheres, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.2.
(2) By the particle diameter Dv 2 50 Negative electrode slurry 2 was prepared for 14.8 μm artificial graphite as a second negative electrode active material: mixing artificial graphite, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.8.
(3) Coating the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer on the surface of a negative electrode current collector, wherein the slurry for forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry for forming the first negative electrode active material layer is far away from the negative electrode current collector, the thickness of the formed first negative electrode active material layer is d1, the thickness of the formed second negative electrode active material layer is d2, and the width of the formed first negative electrode active material layer is the same as the width of the formed second negative electrode active material layer and is L1; the coating work of the other side of the current collector is completed in the same manner.
(4) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96.
(5) And rolling, die cutting and cutting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the electrode plates with an aluminum-plastic film after the short circuit test is qualified, baking the electrode plates in an oven to remove moisture until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the electrode plates for 24 to 48 hours, and finishing the first charging by a hot pressing process to obtain the activated lithium ion battery.
Example 2
(1) By the particle diameter Dv 1 50 Titanium carbide Ti of 79nm 3 C 2 T x Coated porous silicon spheres (thickness of coating layer 2.62nm, pore diameter of porous silicon spheres 8 nm) as a first negative active material negative slurry 1: mixing titanium carbide coated porous silicon spheres, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.2.
(2) By the particle diameter Dv 2 50 Negative electrode slurry 2 was prepared for 14.8 μm artificial graphite as a second negative electrode active material: mixing artificial graphite, a conductive agent SP, a binder styrene-butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.8.
(3) Coating the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer on the surface of a negative electrode current collector, wherein the slurry for forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry for forming the first negative electrode active material layer is far away from the negative electrode current collector, the thickness of the formed first negative electrode active material layer is d1, the thickness of the formed second negative electrode active material layer is d2, and the width of the formed first negative electrode active material layer is the same as the width of the formed second negative electrode active material layer and is L1; the coating work of the other side of the current collector is completed in the same manner.
(4) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96.
(5) And rolling, die-cutting and slitting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the roll core by using an aluminum-plastic film after the short circuit test is qualified, baking the roll core in an oven to remove moisture until the moisture standard required by liquid injection is achieved, injecting electrolyte, aging the electrolyte for 24 to 48 hours, and completing the first charging by using a hot pressing formation process to obtain the activated lithium ion battery.
Example 3
(1) By the particle diameter Dv 1 50 Titanium carbide Ti of 3000nm 3 C 2 T x Coated porous silicon spheres (thickness of coating layer 2.62nm, pore diameter of porous silicon spheres 8 nm) as a first negative active material negative slurry 1: mixing titanium carbide coated porous silicon spheres, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.2.
(2) By the particle diameter Dv 2 50 Negative electrode slurry 2 was prepared for 14.8 μm of artificial graphite as a second negative electrode active material: mixing artificial graphite, a conductive agent SP, a binder styrene-butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.8.
(3) Coating the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer on the surface of a negative electrode current collector, wherein the slurry for forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry for forming the first negative electrode active material layer is far away from the negative electrode current collector, the thickness of the formed first negative electrode active material layer is d1, the thickness of the formed second negative electrode active material layer is d2, and the width of the formed first negative electrode active material layer is the same as the width of the formed second negative electrode active material layer and is L1; the coating work of the other side of the current collector is completed in the same manner.
(4) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96:2.5, dispersing the mixture in N-methylpyrrolidone (NMP), uniformly stirring to prepare slurry, uniformly coating the slurry with the viscosity of 2000-7000 mPa & s and the solid content of 70-80 wt% on the two side surfaces of an aluminum foil of a positive electrode current collector, and baking for 4-8 h at 110-120 ℃ to prepare a positive electrode sheet.
(5) And rolling, die cutting and cutting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the electrode plates with an aluminum-plastic film after the short circuit test is qualified, baking the electrode plates in an oven to remove moisture until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the electrode plates for 24 to 48 hours, and finishing the first charging by a hot pressing process to obtain the activated lithium ion battery.
Example 4
(1) By the particle diameter Dv 1 50 Titanium carbide Ti of 400nm 3 C 2 T x Coated porous silicon spheres (thickness of coating layer 2.62nm, pore diameter of porous silicon spheres 8 nm) as a first negative active material negative slurry 1: mixing titanium carbide coated porous silicon spheres, a conductive agent SP, a binder styrene butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.2.
(2) By the particle diameter Dv 2 50 Negative electrode slurry 2 was prepared for 14.8 μm of artificial graphite as a second negative electrode active material: mixing artificial graphite, a conductive agent SP, a binder styrene-butadiene latex (SBR) and polyacrylic acid (PAA) according to a mass ratio of 96.8.
(3) Coating the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer on the surface of a negative electrode current collector, wherein the slurry for forming the second negative electrode active material layer is close to the negative electrode current collector, the slurry for forming the first negative electrode active material layer is far away from the negative electrode current collector, the thickness of the formed first negative electrode active material layer is d1, the thickness of the formed second negative electrode active material layer is d2, and the width of the formed first negative electrode active material layer is the same as the width of the formed second negative electrode active material layer and is L1; the coating work of the other side of the current collector is completed in the same manner.
(4) Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 96.
(5) And rolling, die cutting and cutting the obtained positive and negative electrode plates, winding and assembling the electrode plates in the thinning area into a roll core, packaging the electrode plates with an aluminum-plastic film after the short circuit test is qualified, baking the electrode plates in an oven to remove moisture until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the electrode plates for 24 to 48 hours, and finishing the first charging by a hot pressing process to obtain the activated lithium ion battery.
The lithium ion batteries prepared in the above examples and comparative examples are fully charged at 0.5C, and the ratio of the energy E of 0.5C discharge to the lithium ion battery volume V is the energy density ED.
The lithium ion batteries prepared in the above examples and comparative examples were charged at 4C rate, discharged at 1C rate, and subjected to a cycle expansion test for 300 cycles, and the negative electrode particle breakage rate was counted.
TABLE 1 composition and Performance test results for lithium ion batteries of comparative examples
Table 2 compositions and performance test results of the lithium ion batteries of the examples
The above results show that example 1 prepared according to the present invention significantly increases the energy density of the battery, is within design requirements despite a slightly higher cycle expansion ratio, and improves the lithium evolution problem, relative to comparative example 1; compared with the comparative example 3, the energy density of the comparative example 2 is not much different, but the cyclic expansion rate and the particle breakage rate are larger than those of the comparative example 3, which shows that the titanium carbide coated porous silicon spheres can obviously improve the cyclic expansion performance, but can not solve the problem of lithium precipitation caused by the reduction of the porosity due to expansion; in example 1, although the energy density was reduced compared with comparative example 3, the cycle expansion rate was greatly reduced, controlled within the requirements, and the problem of lithium deposition was improved. In example 2, compared with example 1, porous silicon spheres coated with titanium carbide having small particle sizes have the problems of low active material loading density, greatly reduced energy density, large specific surface area and poor matching with a graphite negative electrode coating layer, so that lithium precipitation is a problem; compared with the embodiment 1, the embodiment 3 has the advantages that the stress of the porous silicon spheres coated by the titanium carbide with large particle size is larger in the lithium ion de-intercalation process, the particle breakage rate is obviously increased, the new SEI film is formed to cause the loss of active lithium, the capacity retention rate is obviously reduced, and meanwhile, the problem of lithium precipitation caused by the reduction of the porosity due to expansion also exists; in example 4, the titanium carbide-coated porous silicon spheres had a coating layer thicker than that in example 1, and had a large cyclic expansion rate and a low capacity retention rate, and also had a problem of lithium precipitation due to a decrease in porosity due to expansion. In conclusion, the negative plate can effectively improve the energy density of the battery, control the cycle expansion rate and the capacity retention rate of the battery and improve the lithium separation problem of the battery.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. A negative electrode sheet comprising a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer;
the second negative electrode active material layer is on the first surface of the negative electrode current collector, and the first negative electrode active material layer is on the surface of the second negative electrode active material layer;
the first negative electrode active material layer comprises a first negative electrode active material selected from titanium carbide coated porous silicon spheres;
the second negative active material layer includes a second negative active material selected from graphite; the median particle diameter Dv of the first negative electrode active material 1 50 And a median particle diameter Dv of the second negative electrode active material 2 50 Ratio Dv of 1 50 /Dv 2 50 Satisfies the following conditions: 0.0053<Dv 1 50 /Dv 2 50 ≤0.2；
The median particle diameter Dv of the first negative electrode active material 1 50 Satisfies the following conditions: dv is not less than 100nm 1 50 Less than or equal to 600nm; the median particle diameter Dv of the second negative electrode active material 2 50 Satisfies the following conditions: dv is less than or equal to 2 mu m 2 50 ≤20μm；
Thickness d of the first anode active material layer 1 10 to 200 μm, the thickness d of the first negative electrode active material layer 1 And a thickness d of the second anode active material layer 2 Ratio d of 1 /d 2 Satisfies the following conditions: 0<d 1 /d 2 ≤0.5。
2. The negative plate according to claim 1, wherein the titanium carbide-coated porous silicon spheres comprise porous silicon spheres and titanium carbide, and the titanium carbide is coated on the surfaces of the porous silicon spheres to form coating layers, wherein the thickness T of the coating layers is 1nm or more and T or less and 5nm or less; the aperture R of the porous silicon ball is more than or equal to 5nm and less than or equal to 20nm.
3. The negative electrode sheet according to claim 1, wherein the graphite is selected from at least one of artificial graphite, natural graphite, and modifier-coated graphite; wherein the modifier is selected from soft carbon or hard carbon.
4. The negative electrode sheet of claim 1, wherein the first negative electrode active material layer further comprises a first conductive agent and a first binder; the second negative electrode active material layer further includes a second conductive agent and a second binder;
and/or the first negative electrode active material layer comprises the following components in percentage by mass: 90 to 99.2wt% of a first negative electrode active material, 0.2 to 3.5wt% of a first conductive agent, and 0.6 to 6.5wt% of a first binder;
the second negative electrode active material layer comprises the following components in percentage by mass: 90 to 99.2wt% of a second negative electrode active material, 0.2 to 4wt% of a second conductive agent, and 0.6 to 6wt% of a second binder.
5. A lithium ion battery comprising the negative electrode sheet of any one of claims 1 to 4.
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