CN111180657A - Negative pole piece, preparation method thereof and lithium ion battery - Google Patents
Negative pole piece, preparation method thereof and lithium ion battery Download PDFInfo
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- CN111180657A CN111180657A CN201811339192.3A CN201811339192A CN111180657A CN 111180657 A CN111180657 A CN 111180657A CN 201811339192 A CN201811339192 A CN 201811339192A CN 111180657 A CN111180657 A CN 111180657A
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- 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
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Abstract
The invention provides a negative pole piece which comprises a current collector and a silicon-graphene coating, wherein the silicon-graphene coating comprises a silicon layer and a graphene layer, the silicon layer is in direct contact with the current collector, the silicon-graphene coating is coated on two sides of the current collector, the porosity of the silicon-graphene coating is 27% -33%, and the large porosity can realize the quick charging of a battery and also can improve the volume expansion of silicon in charging and discharging. In addition, the invention also provides a method for preparing the negative pole piece and a lithium ion battery assembled by adopting the negative pole piece, and the battery can be charged with large current and has good cycle performance and high battery capacity.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a negative pole piece, a preparation method thereof and a lithium ion battery.
Background
The lithium ion battery is widely applied to 3C digital products, such as personal computers, mobile phones, portable CD machines and other personal wireless electronic devices, due to the characteristics of high energy density, long cycle life, no memory effect, adjustable shape and size and the like. Along with the national advocation of energy conservation and emission reduction, the lithium ion battery is more and more important to the new energy industry and is widely applied to automobiles as a new energy source. However, compared with the conventional fuel-powered vehicle, the lithium ion battery has a slower charging speed, which limits the popularization of electric vehicles, and therefore, research and application of a rapid charging technology are necessary.
When the lithium ion battery is charged, lithium ions are extracted from the positive electrode, enter the electrolyte, pass through the diaphragm to reach the surface of the negative electrode, and then are embedded into micropores of the negative electrode. When large current charging is adopted, a large amount of lithium ions are extracted from the positive electrode and reach the negative electrode, and if the lithium ion embedding path in the negative electrode is long, a large amount of lithium ions are deposited on the surface of the negative electrode to form lithium dendrites, so that the capacity of the battery is reduced, and potential safety hazards exist in short circuit of the battery. The diffusion path of lithium ions can be shortened by thinning the negative plate, so that the lithium ions can be rapidly embedded into the negative electrode micropores, the occurrence of side reactions in diffusion is avoided, and the rapid charging of the battery can be realized. However, the thin negative electrode sheet contains less negative active material, so that the battery capacity is low.
The silicon negative electrode has higher theoretical gram capacity (4200 mAh/g), so that the negative plate can be thinned while the high battery capacity is met, and the quick charging of the battery is facilitated. However, the silicon negative electrode has large volume change in the process of lithium ion desorption and intercalation, which easily causes silicon cracking and pulverization, and affects the performance and safety of the battery. Therefore, the performance and safety of the lithium ion battery should be ensured while the quick charge of the lithium ion battery is realized.
Disclosure of Invention
The invention provides a negative pole piece, a preparation method thereof and a lithium ion battery, aiming at realizing the quick charge of the lithium ion battery and solving the problem of volume expansion of a silicon negative pole. The silicon-graphene composite material is used as a negative active material, so that the rapid charging of the battery is realized, and the problem of silicon volume expansion in battery circulation is solved.
To achieve the object of the present invention, in a first aspect of the present invention, there is provided a negative electrode tab, including:
the silicon-graphene coating comprises a silicon layer and a graphene layer, the silicon layer is in direct contact with the current collector, the silicon-graphene coating is coated on two sides of the current collector, the porosity of the silicon-graphene coating is 27% -33%, the mass proportion of silicon in the silicon-graphene coating is 83% -90%, and the mass proportion of graphene in the silicon-graphene coating is 8% -12%.
Through a large number of experiments, the inventor of the invention discovers that when the negative pole piece obtained by forming the silicon-graphene coating on the current collector and enabling the porosity of the silicon-graphene coating to be 27% -33% is applied to a lithium ion battery, lithium ions can be rapidly charged, and the silicon volume expansion is small in the charge-discharge cycle of the lithium ion battery. The porosity of the negative active material of the negative pole piece is 27% -33%, so that a path is provided for the diffusion of lithium ions in the negative pole, the desorption of the lithium ions is accelerated, the rapid charging of the battery is realized, a space is provided for the change of silicon volume caused by the intercalation and desorption of the lithium ions in the battery circulation, the problems of silicon layer cracking and pulverization are solved, and the safety performance and the cycle performance of the battery are improved; and the high porosity also increases the specific surface area of the coating material and increases the quantity of lithium ions inserted into the negative electrode, so that on the premise of meeting the requirement of high battery capacity, the pole piece can be thinned, the thin negative pole piece can shorten the diffusion path of the lithium ions, and the lithium ions can be inserted into the negative pole piece to realize the rapid charging of the battery. In addition, the graphene on the surface of the silicon layer has good flexibility, and the problem of large volume change of silicon is buffered; the graphene layer is in direct contact with the electrolyte, so that an SEI film is mainly generated on the surface of the graphene, and the electrolyte is prevented from being consumed due to the fact that the SEI film is formed again after the silicon layer is pulverized; moreover, the good conductivity of the graphene can accelerate the diffusion of lithium ions in the coating material, thereby being beneficial to the exertion of battery capacity and quick charging.
In a second aspect of the present invention, a method for preparing the negative electrode plate is provided, which includes the following steps:
(1) preparing silicon layer slurry: silicon, nano silicon dioxide, a conductive agent and a binder are mixed according to the mass ratio of (85-91%): (8% -10%): (0.5% -2.5%): (0.5% -2.5%) and dispersing into an organic solvent to obtain silicon layer slurry;
(2) preparing graphene layer slurry: the graphene/conductive material composite material is prepared by mixing (97.5-99.5%) graphene particles and a conductive agent in a mass ratio of: (0.5% -2.5%) and dispersing into an organic solvent to obtain graphene layer slurry;
(3) immersing a current collector into the silicon layer slurry obtained in the step (1), taking out and drying to obtain a current collector with silicon and nano silicon dioxide coated on both sides, immersing the current collector into the graphene layer slurry obtained in the step (2), taking out and drying to obtain a current collector with silicon, nano silicon dioxide and graphene coated together;
(4) immersing the current collector obtained in the step (3) into hydrofluoric acid, taking out and drying to obtain a current collector coated with the silicon-graphene coating;
(5) compacting the current collector obtained in the step (4) to obtain a negative pole piece;
the porosity of the silicon-graphene coating is 27% -33%, wherein the mass percentage of silicon in the silicon-graphene coating is 83% -90%, and the mass percentage of graphene is 8% -12%.
The inventor of the invention discovers through a large number of experiments that silicon dioxide is added when a negative active coating is formed, and hydrofluoric acid is used for reacting with the silicon dioxide to generate gas and water at a later stage, so that a pore channel is left in a coating material, the porosity of a negative pole piece is increased, the diffusion of lithium ions is facilitated, the quick charge is realized, a space is provided for the silicon volume change caused by the deintercalation of the lithium ions, and the phenomena of silicon layer cracking and pulverization are improved. Meanwhile, the manufacturing method of the negative pole piece provided by the invention adopts a dip-coating mode to coat the electrode active substance on the surface of the current collector, and the negative pole pieces with coatings of different thicknesses can be obtained by controlling the immersion time and the immersion times, so that the operation is simple and flexible, and the cost is low. In addition, the method can obtain a thinner negative pole piece, and is beneficial to the diffusion of lithium ions and the realization of the quick charge of the battery. The graphene layer in the negative pole piece prepared by the method has good flexibility and conductivity, so that on one hand, the change of silicon volume can be improved, the consumption of electrolyte caused by the generation of a new SEI film formed by silicon pulverization is avoided, and on the other hand, the diffusion of lithium ions can be accelerated, and the quick charge of a battery can be realized.
The third aspect of the invention provides the negative pole piece prepared by the preparation method of the negative pole piece.
In a fourth aspect of the present invention, a lithium ion battery is provided, which includes a positive electrode plate, a diaphragm, an electrolyte and a negative electrode plate, wherein the negative electrode plate is the negative electrode plate according to the first and third aspects of the present invention.
Compared with the existing lithium ion battery, the lithium ion battery provided by the invention can realize the quick charging of the battery on the premise of meeting the requirement of high battery capacity, and has good battery cycle performance, so that the time wasted in the charging aspect of the conventional battery can be saved, and the lithium ion battery is used for an electric automobile, can enable the automobile to run in a full charge within a short time, and is beneficial to the propaganda and popularization of the electric automobile.
Drawings
FIG. 1 is a graph comparing the cycle performance of a battery at 8C charge and 1C discharge according to example one and comparative example one of the present invention;
FIG. 2 is a graph comparing the cycle performance of the batteries at 1C charge and 1C discharge for example one and comparative example one of the present invention;
FIG. 3 is a graph of battery cycle performance at 8C charge 1C discharge and 1C charge 1C discharge for example two of the present invention;
fig. 4 is a graph of battery cycle performance at 8C charge 1C discharge and 1C charge 1C discharge for example three of the present invention.
Detailed Description
In order to better understand the technical scheme and the beneficial effects of the invention, the invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides a negative pole piece which comprises a current collector and a silicon-graphene coating, wherein the silicon-graphene coating comprises a silicon layer and a graphene layer, the silicon layer is in direct contact with the current collector, the silicon-graphene coating is coated on two sides of the current collector, the porosity of the silicon-graphene coating is 27% -33%, the mass percentage of silicon in the silicon-graphene coating is 83% -90%, and the mass percentage of graphene in the silicon-graphene coating is 8% -12%.
Wherein the compacted density of the negative pole piece is 1.0-1.65g/cm3And the thickness of the negative pole piece is 30-60 microns.
Preferably, the silicon layer is nano silicon, the particle size of the nano silicon is 100-400 nm, and the change of the silicon volume in lithium ion deintercalation can be effectively slowed down;
before the negative pole piece is compacted, the thickness of single-layer silicon in the silicon-graphene coating is 10-20 microns, the thickness of single-layer graphene is 1-5 microns, and preferably the thickness of the single-layer graphene is 3 microns.
The silicon-graphene coating comprises a plurality of silicon layers and a plurality of graphene layers, wherein the silicon layers and the graphene layers are arranged in a staggered mode, the number of layers of the silicon layers is the same as that of the graphene layers, and namely the graphene layers are coated outside the silicon layers.
The current collector is made of one of copper, nickel and stainless steel, and is in a shape of a screen mesh or a foil;
the current collector is a copper foil, the thickness of the copper foil is 6-12 microns, and further the thickness of the copper foil is 10 microns;
the embodiment of the invention provides a preparation method of the negative pole piece, which comprises the following steps:
(1) preparing silicon layer slurry: silicon, nano silicon dioxide, a conductive agent and a binder are mixed according to the mass ratio of (85-91%): (8% -10%): (0.5% -2.5%): (0.5% -2.5%) and dispersing into an organic solvent to obtain silicon layer slurry;
(2) preparing graphene layer slurry: the graphene/conductive material composite material is prepared by mixing (97.5-99.5%) graphene particles and a conductive agent in a mass ratio of: (0.5% -2.5%) and dispersing into an organic solvent to obtain graphene layer slurry;
(3) immersing a current collector into the silicon layer slurry obtained in the step (1), taking out and drying to obtain a current collector with silicon and nano silicon dioxide coated on both sides, immersing the current collector into the graphene layer slurry obtained in the step (2), taking out and drying to obtain a current collector with silicon, nano silicon dioxide and graphene coated together;
(4) immersing the current collector obtained in the step (3) into hydrofluoric acid, taking out and drying to obtain a current collector coated with the silicon-graphene coating;
(5) compacting the current collector obtained in the step (4) to obtain a negative pole piece;
preferably, the silicon in the step (1) is nano silicon, the particle size of the nano silicon is 100-400 nm, and the change of the volume of the silicon in lithium ion deintercalation can be effectively slowed down;
in the step (4), hydrofluoric acid can react with silicon dioxide in the coating layer in the step (3) to generate gas and water, so that pores can be left in the coating layer, the porosity of the coating layer of the negative pole piece is increased, the volume change of silicon in charge and discharge can be effectively improved, and the capacity and performance of the battery can be exerted.
The porosity of the silicon-graphene coating in the negative pole piece is 27% -33%, wherein the mass percentage of silicon in the silicon-graphene coating is 83% -90%, the mass percentage of graphene is 8% -12%, and the compaction density of the obtained negative pole piece is 1.0-1.65g/cm3And the thickness is 30-60 microns.
The thickness of the single-layer silicon in the silicon-graphene coating before compaction of the negative pole piece is 10-20 microns, and the thickness of the single-layer graphene is 1-5 microns, preferably 3 microns.
Before the step (5), repeating the step (3) and the step (4) at least once to obtain a current collector coated with a plurality of silicon layers and a plurality of graphene layers in an interlaced manner, wherein the number of the layers of the silicon layers is the same as that of the graphene layers, and the number of the repetitions affects the thickness of the silicon-graphene coating, namely the amount of active materials, so that the battery capacity and other properties are affected, and therefore the number of the repetitions can be selected according to specific practical situations.
The conductive agent is one of carbon black, carbon nano tubes, graphene and graphite carbon materials, the binder is one of fluorine-containing resin, polyethylene and polyvinyl alcohol, the conductive agent is further carbon nano tubes, and the binder is polyvinylidene fluoride.
The organic solvent also comprises a surfactant, the surfactant is cetyl trimethyl ammonium bromide, and the addition of the surfactant can better disperse and mix the silicon layer slurry and the graphene layer slurry, so that the subsequent coating of the current collector is facilitated.
The current collector is made of one of copper, nickel and stainless steel, and is in a screen shape or a foil shape.
The current collector is a copper foil, the thickness of the copper foil is 6-12 microns, and further the thickness of the copper foil is 10 microns.
The embodiment of the invention also provides the negative pole piece prepared according to the preparation method of the negative pole piece.
The embodiment of the invention also provides a lithium ion battery, which comprises a positive pole piece, a diaphragm, electrolyte and a negative pole piece, wherein the negative pole piece is the negative pole piece.
The positive pole piece comprises a current collector and a coating material which is coated on the current collector and contains an active substance, a conductive agent and a binder, the formula of the coating material, the solvent used and the preparation process of the pole piece are the same as those of a conventional lithium ion battery, furthermore, the current collector is an aluminum foil, the thickness of the current collector is 12 microns, and the active substance is nickel cobalt lithium manganate (Li (Ni)0.6Co0.2Mn0.2)1.15O2) The conductive agent is Carbon Nano Tube (CNT), the binder is polyvinylidene fluoride (PVDF), and the solvent is N-methyl pyrrolidone (NMP).
The diaphragm is a diaphragm commonly used in a conventional lithium ion battery, and further is a polyethylene film coated with alumina ceramic, and the thickness of the diaphragm is 12 micrometers.
The electrolyte comprises a lithium salt, a nonaqueous organic solvent and an additive, the formula of the electrolyte is the same as that of the electrolyte in a conventional lithium ion battery, further, the lithium salt is lithium hexafluorophosphate, the concentration of the lithium salt is 1M, the nonaqueous organic solvent is a mixture of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 2% to 3% to 2%, the additive comprises a negative film forming additive of vinylene carbonate (Vc) and a positive film forming additive of methylene methanedisulfonate, and the additive accounts for 2% of the total weight of the electrolyte.
Further, the lithium ion battery is prepared by assembling the positive pole piece, the diaphragm and the negative pole piece in a winding manner, injecting the electrolyte, and then carrying out formation, sealing and capacity grading.
The following is a further description with reference to specific examples.
Example one
Preparing a silicon-graphene composite material negative pole piece:
(1) uniformly mixing 86 mass percent to 10 mass percent to 2 mass percent of nano-silicon, nano-silicon dioxide, carbon nano-tubes (CNT) and polyvinylidene fluoride (PVDF), and dispersing the mixture into acetone containing 1 mass percent of cetyltrimethylammonium bromide (CTAB) to obtain silicon layer slurry;
(2) uniformly mixing graphene particles and polyvinylidene fluoride (PVDF) according to a mass ratio of 98% to 2%, and dispersing the mixture into N, N-dimethylformamide containing 1% of cetyltrimethylammonium bromide (CTAB) to obtain graphene layer slurry;
(3) immersing a copper foil with the thickness of 10 microns into the silicon layer slurry for 5min, then taking out, drying in a drying oven at the temperature of 80 ℃ for 30min, cooling to room temperature, immersing into the silicon layer slurry again for 20s, then taking out, drying under the same condition, and repeating the process steps of immersing the silicon layer slurry for 20s and drying for 30min for 5 times to obtain the copper foil with the double-sided coating of nano silicon and nano silicon dioxide; soaking the copper foil into graphene layer slurry for 20s, taking out, drying in a drying oven at 80 ℃ for 30min, repeating the steps of dip coating and drying for 3 times to obtain copper foil coated with nano silicon, nano silicon dioxide and graphene together, soaking the copper foil into hydrofluoric acid with the mass concentration of 25% to react for 48h, taking out, washing with deionized water, and drying in a vacuum drying oven at 200 ℃ for 16h to obtain the dressing with the surface density of 2.06mg/cm2The pole piece is pressed into a sheet to obtain the compact density of 1.58g/cm3And the negative pole piece with the thickness of 36 micrometers, wherein the porosity of the pole piece coating is 29%, the mass proportion of silicon is 77%, and the mass proportion of graphene is 19%. Cutting the obtained negative pole piece into 544 multiplied by 44.5mm for later use.
Preparing a nickel cobalt lithium manganate positive pole piece: lithium nickel cobalt manganese (Li (Ni))0.6Co0.2Mn0.2)1.15O2) Uniformly mixing the powder, polyvinylidene fluoride (PVDF) and Carbon Nano Tubes (CNT) according to the mass ratio of 96% to 2%, adding the mixture into N-methylpyrrolidone (NMP), and uniformly stirring and mixing to obtain the anode slurry. Uniformly coating the prepared slurry on an aluminum foil with the thickness of 12 microns by adopting a squeezing coating mode, and drying to obtain the dressing with the surface density of 20.06mg/cm2The pole piece is pressed into a pole piece with the thickness of 126 microns and the compacted density of 3.52g/cm3Cutting the positive pole piece into 551X 44mm for standby.
Preparing electrolyte: mixing Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) at a mass ratio of 2%:3%:2%, adding 1M lithium hexafluorophosphate (LiPF)6) And adding vinylene carbonate (Vc) accounting for 1 percent of the total weight of the electrolyte and methylene methanedisulfonate additive accounting for 1 percent of the total weight of the electrolyte to prepare the electrolyte for later use.
A diaphragm: an alumina ceramic coated polyethylene film with the thickness of 12 microns is selected as the battery diaphragm.
And winding the prepared positive pole piece, diaphragm and negative pole piece, putting the wound positive pole piece, diaphragm and negative pole piece into a square aluminum-shell battery with the size of 5.5 multiplied by 34 multiplied by 50mm, injecting 4.1g of the electrolyte, and then forming, sealing and grading according to a conventional mode to obtain the lithium ion battery.
Example two
The preparation of the negative pole piece was carried out according to the method of example 1, wherein the time for re-immersing the silicon layer slurry after the first time was 40s, and the process steps of 40s dip-coating and drying were repeated 5 times, and the areal density of the pole piece dressing finally obtained was 2.4mg/cm2And the compacted density is 1.20g/cm after tabletting3And the negative pole piece with the thickness of 50 microns, wherein the porosity of the coating is 32%, the mass ratio of silicon is 86%, and the mass ratio of graphene is 10%. Push buttonA positive electrode sheet was prepared in the same manner as in example 1, wherein the areal density of the dressing was 23.12mg/cm2And the compacted density is 3.48g/cm after tabletting3And the thickness of the positive pole piece is 145 microns. The prepared electrode plate was assembled into a battery by the method of example 1, wherein the injection amount of the electrolyte was 4.8 g.
EXAMPLE III
Preparing a negative pole piece according to the method of the embodiment 1, wherein the time for immersing the silicon layer slurry again for the first time is 40s, the process steps of dipping for 40s and drying are repeated for 5 times, and the surface density of the pole piece dressing obtained finally is 2.4mg/cm2And the compacted density is 1.60g/cm after tabletting3And the negative pole piece with the thickness of 40 microns, wherein the porosity of the coating is 28%, the mass proportion of silicon is 86%, and the mass proportion of graphene is 10%. A positive electrode sheet was produced in accordance with the method of example 1, wherein the areal density of the dressing was 23.12mg/cm2And the compacted density is 3.48g/cm after tabletting3And the thickness of the positive pole piece is 145 microns. The prepared electrode plate was assembled into a battery by the method of example 1, wherein the injection amount of the electrolyte was 4.8 g.
Comparative example 1
Graphite is used as a negative active substance, the negative formula and the manufacturing process are the conventional lithium ion battery manufacturing process, wherein the mass ratio of the graphite to Styrene Butadiene Rubber (SBR) to carboxymethylcellulose (CMC) in the negative slurry is 96.6 to 1.8 to 1.6 percent, deionized water is used as a solvent, and the surface density of dressing coated on the obtained pole piece is 7.43mg/cm2The compacted density of the negative pole piece obtained after compaction is 1.52 g/cm3And a thickness of 108 microns, wherein the coating porosity is 22%. The preparation method of the positive pole piece is the same as that of the embodiment 1, wherein the surface density of the pole piece dressing is 16.05mg/cm2The compacted density is 3.49g/cm after compaction3And the thickness of the positive pole piece is 104 microns. And assembling the prepared electrode plates into a battery, wherein the electrolyte amount is 3.2 g.
The amounts of the positive electrode and the electrolyte are adjusted according to the amount of the negative electrode active material, so that the capacities of both the positive electrode active material and the negative electrode active material can be exhibited to a large extent.
Testing equipment: blue and odd BK7128 battery performance test cabinet.
The test method comprises the following steps:
and (3) capacity testing: (1) discharging the battery to be tested to 3.0V at a constant current of 0.5C, and standing for 5 minutes; (2) charging to the upper limit voltage of 4.2V at a constant current and a constant voltage of 0.5C, taking 0.02C as a cut-off current, and standing for 5 minutes; (3) and discharging to the lower limit voltage of 3.0V at the current of 0.2C, wherein the obtained capacity is the discharge capacity of the battery, namely the battery capacity.
1C, charge-discharge cycle test: (1) discharging the battery 1C to be tested to 3.0V at constant current at normal temperature, and standing for 5 minutes; (2) charging to 4.2V at constant current and constant voltage at 1C, stopping current at 0.02C, and standing for 5 minutes; (3) discharging the 1C at constant current to 3.0V, and standing for 5 minutes; (4) the second and third steps are repeated, and the cycle is repeated 500 times.
8C charge 1C discharge cycle test: (1) discharging the battery 1C to be tested to 3.0V at constant current at normal temperature, and standing for 5 minutes; (2) charging to 4.2V at constant current and constant voltage of 8C, stopping current at 0.02C, and standing for 5 minutes; (3) discharging the 1C at constant current to 3.0V, and standing for 5 minutes; (4) the second and third steps are repeated, and the cycle is repeated 500 times.
The batteries prepared in examples and comparative examples were tested for battery capacity and large current charge cycle performance according to the above test methods, and the results are shown in table 1 and fig. 1 to 4.
TABLE 1
As can be seen from the results of the battery capacity test in table 1, the batteries in examples one to three showed higher battery capacity than the battery in comparative example one, and as can be seen from the above description of examples and comparative examples, the negative electrode sheet in examples was thinner than comparative example, and the negative active material used was also less than comparative example, thus demonstrating that the negative electrode sheet provided by the present invention can provide higher battery capacity even when the sheet was thinner and the amount of the electrode active material used was less. As can be seen from the battery cycle performance graph of fig. 2, the batteries of example one and comparative example one each exhibited good battery cycle performance when subjected to the 1C charge-discharge cycle test; however, as can be seen from fig. 2, when the 8C charge-1C discharge test, i.e., the fast charge test, was performed, the battery in example one still exhibited similar cycle performance to that of the 1C charge test, i.e., the fast charge did not affect the cycle stability of the battery, and the battery was suitable for the fast charge, whereas the cycle stability of the battery in comparative example one was deteriorated at the time of the large current charge, and the battery capacity continued to fade, i.e., the battery was not suitable for the fast charge. As can be seen from the battery cycle performance graphs of fig. 3 and 4, examples two and three exhibited similar cycle performance to that of 1C charging when a large 8C current was applied, i.e., the batteries were applicable to rapid charging. The battery assembled by the negative pole piece provided by the invention can realize the quick charging of the battery under the condition of meeting the requirement of high battery capacity.
Claims (16)
1. The negative pole piece is characterized by comprising a current collector and a silicon-graphene coating, wherein the silicon-graphene coating comprises a silicon layer and a graphene layer, the silicon layer is in direct contact with the current collector, the silicon-graphene coating is coated on two sides of the current collector, the porosity of the silicon-graphene coating is 27% -33%, the mass percentage of silicon in the silicon-graphene coating is 83% -90%, and the mass percentage of graphene in the silicon-graphene coating is 8% -12%.
2. The negative pole piece of claim 1, wherein the negative pole piece has a compacted density of 1.0 to 1.65g/cm3And the thickness of the negative pole piece is 30-60 microns.
3. The negative pole piece of claim 1, wherein the silicon layer is nano silicon, the particle size of the nano silicon is 100-400 nm, the thickness of the single layer silicon in the silicon-graphene coating before compaction of the negative pole piece is 10-20 microns, and the thickness of the single layer graphene is 1-5 microns.
4. The negative electrode plate of claim 1, wherein the silicon-graphene coating comprises a plurality of silicon layers and a plurality of graphene layers, the silicon layers and the graphene layers are arranged in a staggered manner, and the number of the silicon layers is the same as that of the graphene layers.
5. The negative pole piece of claim 1, wherein the current collector is made of one of copper, nickel and stainless steel, and the current collector is one of a mesh and a foil.
6. The negative pole piece of claim 1, wherein the current collector is a copper foil, and the copper foil has a thickness of 6 to 12 microns.
7. A preparation method of a negative pole piece is characterized by comprising the following steps:
(1) preparing silicon layer slurry: silicon, nano silicon dioxide, a conductive agent and a binder are mixed according to the mass ratio of (85-91%): (8% -10%): (0.5% -2.5%): (0.5% -2.5%) and dispersing into an organic solvent to obtain silicon layer slurry;
(2) preparing graphene layer slurry: the graphene/conductive material composite material is prepared by mixing (97.5-99.5%) graphene particles and a conductive agent in a mass ratio of: (0.5% -2.5%) and dispersing into an organic solvent to obtain graphene layer slurry;
(3) immersing a current collector into the silicon layer slurry obtained in the step (1), taking out and drying to obtain a current collector with silicon and nano silicon dioxide coated on both sides, immersing the current collector into the graphene layer slurry obtained in the step (2), taking out and drying to obtain a current collector with silicon, nano silicon dioxide and graphene coated together;
(4) immersing the current collector obtained in the step (3) into hydrofluoric acid, taking out and drying to obtain a current collector coated with the silicon-graphene coating;
(5) compacting the current collector obtained in the step (4) to obtain a negative pole piece;
the porosity of the silicon-graphene coating in the negative electrode plate is 27% -33%, wherein the mass ratio of silicon in the silicon-graphene coating is 83% -90%, and the mass ratio of graphene is 8% -12%.
8. The preparation method of the negative pole piece according to claim 7, wherein the compacted density of the negative pole piece is 1.0-1.65g/cm3And the thickness of the negative pole piece is 30-60 microns.
9. The preparation method of the negative pole piece according to claim 7, wherein the silicon in the step (1) is nano silicon, the particle size of the nano silicon is 100-400 nm, the thickness of the single-layer silicon in the silicon-graphene coating before the negative pole piece is compacted is 10-20 microns, and the thickness of the single-layer graphene is 1-5 microns.
10. The preparation method of the negative electrode plate according to claim 7, wherein the step (3) and the step (4) are repeated at least once before the step (5), so that a current collector with multiple silicon layers and multiple graphene layers coated in a staggered manner can be obtained, and the number of the layers of the silicon layers is the same as that of the graphene layers.
11. The method for preparing the negative electrode plate of claim 7, wherein the conductive agent is one of carbon black, carbon nanotubes, graphene and graphite-like carbon materials, and the binder is one of fluorine-containing resin, polyethylene and polyvinyl alcohol.
12. The method for preparing the negative electrode plate of claim 7, wherein the organic solvent further contains a surfactant.
13. The method for preparing the negative pole piece according to claim 7, wherein the current collector is made of one of copper, nickel and stainless steel, and the shape of the current collector is one of a mesh shape and a foil shape.
14. The method for preparing the negative electrode plate of claim 13, wherein the current collector is a copper foil, and the thickness of the copper foil is 6-12 microns.
15. A negative pole piece is characterized in that the negative pole piece is prepared by the preparation method of the negative pole piece according to any one of claims 7 to 14.
16. A lithium ion battery is characterized by comprising a positive pole piece, a diaphragm, electrolyte and a negative pole piece, wherein the negative pole piece is the negative pole piece of any one of claims 1 to 6 or the negative pole piece of claim 15.
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| CN117174829A (en) * | 2023-11-03 | 2023-12-05 | 溧阳中科海钠科技有限责任公司 | Negative electrode of sodium ion battery and preparation method thereof |
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