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CN116885105A - Lithium ion battery and electronic device of silicon negative electrode system - Google Patents

Lithium ion battery and electronic device of silicon negative electrode system Download PDF

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Publication number
CN116885105A
CN116885105A CN202310984066.8A CN202310984066A CN116885105A CN 116885105 A CN116885105 A CN 116885105A CN 202310984066 A CN202310984066 A CN 202310984066A CN 116885105 A CN116885105 A CN 116885105A
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active layer
lithium ion
ion battery
silicon
negative electrode
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Inventor
彭冲
陈博
李俊义
韦世超
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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Priority to CN202310984066.8A priority Critical patent/CN116885105A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • 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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Composite Materials (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention provides a lithium ion battery and an electronic device of a silicon negative electrode system. The first aspect of the invention provides a lithium ion battery of a silicon anode system, which comprises an anode current collector and a first anode active layer arranged on at least one functional surface of the anode current collector, wherein the first anode active layer comprises a carbon material and a silicon material; in the thickness direction of the first anode active layer, the silicon materials are distributed in the first anode active layer in N linear arrangements, and the average particle number of the silicon materials in each linear arrangement is 1.5-5.5; when the lithium ion battery is subjected to constant-current discharge at the temperature of 45 ℃, constant-current and constant-voltage charge at the temperature of 0.7 ℃ and the temperature of 1.5 ℃, the cut-off current is 0.05 ℃, after 600T of circulation, the thickness of a reaction layer on the surface of the silicon material is less than or equal to 600nm, and the gap between the silicon material and the surrounding materials of the silicon material is less than or equal to 900nm. The lithium ion battery provided by the invention has relatively excellent cycle performance.

Description

Lithium ion battery and electronic device of silicon negative electrode system
The present disclosure is a divisional application of the invention patent application with the name of "lithium ion battery and electronic device of a silicon negative electrode system" filed to China patent office with the application number 202111051207.8 and the application date 2021, 09 and 08.
Technical Field
The invention relates to a lithium ion battery and an electronic device of a silicon negative electrode system, and relates to the technical field of secondary batteries.
Background
The lithium ion battery has the advantages of high energy density, long cycle life, environmental protection and the like, and is widely applied to industries such as 3C consumer products (mobile phone pen-powered, intelligent wearing), electric tools, electric automobiles and the like. However, with the continuous improvement of the requirements of people on the endurance mileage and safety of lithium ion batteries, the development of lithium ion batteries with high energy density has become the focus of attention of researchers.
The negative electrode is one of key factors determining the performance of the lithium ion battery, however, the limited gram capacity of the conventional negative electrode active material, such as graphite, severely limits the improvement of the energy density of the lithium ion battery, and the silicon material, as an emerging negative electrode active material, has a higher gram capacity and can remarkably improve the energy density of the lithium ion battery.
However, silicon materials have serious expansion problems during cycling, affecting the cycling performance of lithium ion batteries. Therefore, there is increasing interest in improving the cycle performance of lithium ion batteries.
Disclosure of Invention
The invention provides a lithium ion battery of a silicon anode system, which has lower SEI impedance R by controlling the particle number of a silicon material, the thickness and the gap of a reaction layer on the surface of the silicon material after circulation within a preset range SEI Charge transfer resistor R ct The capacity retention rate of the lithium ion battery is improved, so that the lithium ion battery has excellent cycle performance.
The invention provides a lithium ion battery of a silicon anode system, which comprises an anode current collector and a first anode active layer arranged on at least one functional surface of the anode current collector, wherein the first anode active layer comprises a carbon material and a silicon material;
in the thickness direction of the first anode active layer, the silicon materials are distributed in the first anode active layer in N linear arrangements, and the average particle number of the silicon materials in each linear arrangement is 1.5-5.5;
when the lithium ion battery is subjected to constant-current discharge at the temperature of 45 ℃, constant-current and constant-voltage charge at the temperature of 0.7 ℃ and the temperature of 1.5 ℃ and the cut-off current is 0.05 ℃, after 600T of circulation, the thickness of a reaction layer on the surface of the silicon material is less than or equal to 600nm, and the gap between the silicon material and the surrounding materials of the silicon material is less than or equal to 900nm.
The invention provides a lithium ion battery, which comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a first negative electrode active layer arranged on at least one functional surface of the negative electrode current collector, the functional surface of the negative electrode current collector refers to two opposite surfaces with larger area for bearing the negative electrode active layer in the negative electrode current collector, in particular to the upper surface and the lower surface of the negative electrode current collector, for example, fig. 1 is a negative electrode provided by an embodiment of the inventionThe structure of the pole piece is schematically shown in fig. 1, the negative pole piece comprises a negative pole current collector 1 and a first negative pole active layer 2-1 arranged on one functional surface of the negative pole current collector 1, a diaphragm 3 is arranged above the first negative pole active layer 2-1 and is used for separating the positive pole piece and the negative pole piece in the lithium ion battery, the first negative pole active layer 2-1 comprises a carbon material 4 and a silicon material 5, and the lithium ion battery has lower SEI impedance R by limiting the average particle number of the silicon material in the thickness direction of the first negative pole active layer and the reaction layer thickness on the surface of the silicon material and the gap between the silicon material and surrounding materials SEI Charge transfer resistor R ct The lithium ion battery is further provided with excellent cycle performance, specifically, in the thickness direction of the first anode active layer, silicon materials are distributed in the first anode active layer in N linear arrangements, namely N straight lines are made from one side of the anode current collector 1 along the direction perpendicular to the anode current collector to the separator 3, the particle number of the silicon materials on each straight line is subjected to statistical calculation, and the average value obtained by dividing the total particle number by N is the average particle number of the silicon materials in the thickness direction of the first anode active layer, wherein the average particle number is 1.5-5.5; FIG. 2 is a SEM diagram of a reaction layer on the surface of a silicon material according to an embodiment of the present invention, wherein the thickness of the reaction layer on the surface of the silicon material is shown in FIG. 2, which means that the silicon material and the electrolyte react electrochemically in a solid-liquid phase section during the cycle of the lithium ion battery to form a passivation layer covering the surface of the silicon material, and the reaction product (such as Li 2 CO 3 LiF, ROLi, etc.) is deposited on the surface of the silicon material, namely a reaction layer on the surface of the silicon material, and the thickness of the reaction layer is less than or equal to 600nm; fig. 3 is an SEM image of a gap between a silicon material and a surrounding material, as shown in fig. 3, in which the gap is a gap between the silicon material and the surrounding material, for example, a portion circled in fig. 3, is smaller than or equal to 900nm, and the surrounding material is mainly a carbon material, but other materials are not excluded. The lithium ion battery has lower SEI resistance by controlling the average particle number of the silicon material in the thickness direction of the first anode active layer, the thickness of the surface reaction layer of the circulated silicon material and the gap between the surface reaction layer and surrounding materialsanti-R SEI Charge transfer resistor R ct The capacity retention rate of the lithium ion battery is improved, so that the lithium ion battery has excellent cycle performance.
In order to further alleviate the problem of poor cycling performance of the lithium ion battery caused by volume expansion of the silicon material, the silicon material may be concentrated on the side of the negative electrode active layer close to the current collector, and the active material on the side far away from the current collector is mainly a carbon material, i.e. the lithium ion battery comprises a second negative electrode active layer, wherein the second negative electrode active layer is disposed on the surface of the first negative electrode active layer far away from the negative electrode current collector, and the second negative electrode active layer comprises a carbon material.
Fig. 4 is a schematic structural diagram of a negative electrode sheet according to another embodiment of the present invention, as shown in fig. 4, the negative electrode sheet includes a negative electrode current collector 1, a first negative electrode active layer 2-1, and a second negative electrode active layer 2-2, where the first negative electrode active layer 2-1 and the second negative electrode active layer 2-2 are sequentially stacked on the upper surface of the negative electrode current collector 1, the first negative electrode active layer 2-1 includes a carbon material 4 and a silicon material 5, and the second negative electrode active layer 2-2 includes a carbon material 4, that is, does not include a silicon material 5.
In order to further consider the energy density on the basis of improving the cycle performance of the lithium ion battery, the D50 of the carbon material Carbon (C) D50 of the silicon material Silicon (Si) Mass m of the carbon material 1 Mass m of the silicon material 2 The thickness H of the negative electrode active layer satisfies the relationship 1:
D50 carbon (C) 、D50 Silicon (Si) And H has the same unit, m 1 And m is equal to 2 Is the same in units of (a);
for convenience of explanation, the invention relates to the particle size and quality of carbon material and silicon materialThe numerical value calculated from the formula shown in formula 1 is defined as the M value, which can reflect the ratio of the particle number of the silicon material to the particle number of the carbon material in the anode active layer, specifically, D50 Carbon (C) And D50 Silicon (Si) The particle size values corresponding to the cumulative distribution of the carbon material and the silicon material reaching 50% are respectively the same as the unit of the carbon material and the silicon material, and can be μm for example, and the particle size can be measured by a laser particle sizer; the mass ratio of the carbon material to the silicon material means a ratio of the mass of the carbon material to the mass of the silicon material in the anode active layer, and the units of the two are the same, for example, gram; the thickness H of the anode active layer refers to the thickness of the anode active layer on one functional surface of the anode current collector, and the unit thereof is the same as the D50 unit.
When the anode sheet includes an anode current collector and a first anode active layer, substituting D50 of a carbon material, D50 of a silicon material, mass of the carbon material and the silicon material, and thickness of the first anode active layer into a formula shown in formula 1 to calculate; when the negative electrode sheet further comprises a second negative electrode active layer, in the formula shown in formula 1, when D50 of carbon materials in the first negative electrode active layer and the second negative electrode active layer are the same, the D50 is directly substituted into formula 1 for calculation, when D50 of carbon materials in the first negative electrode active layer and the second negative electrode active layer are different, D50 average value (calculated formula is D50A% +D50B% B) is substituted into formula 1 for calculation, A% and B% are the proportion of two different carbon materials in the negative electrode active layer, the thickness H of the negative electrode active layer is the total thickness of the first negative electrode active layer and the second negative electrode active layer, and the mass m of the carbon materials is calculated 1 The mass m of the silicon material is the total mass of the carbon materials in the first anode active layer and the second anode active layer 2 Is the total mass of silicon material in the first anode active layer and the second anode active layer.
The lithium ion battery can be prepared by combining a conventional technical means by a person skilled in the art, for example, firstly mixing a carbon material and a silicon material according to a certain mass ratio to obtain a negative electrode active material, matching a conductive agent, a binder and a dispersing agent to obtain a negative electrode active layer slurry, and then coating the negative electrode active layer slurry on at least one functional surface of a negative electrode current collector to obtain a negative electrode plate; when the negative electrode sheet comprises a first negative electrode active layer and a second negative electrode active layer, the difference is that the first negative electrode active layer slurry and the second negative electrode active layer slurry are respectively prepared and coated according to the structure shown in fig. 4, so as to obtain the negative electrode sheet, and the double-layer coating can be carried out by matching a double-cavity die head for simplifying the coating process; the lithium ion battery is prepared by the steps of filling liquid, packaging, forming, sorting and the like after the prepared negative electrode plate is matched with the positive electrode plate and the diaphragm to obtain the battery core, and in order to meet the requirements of average particle number, thickness of a reaction layer and gaps, a person skilled in the art can reasonably set the formula of the lithium ion battery with a silicon negative electrode system and prepare the lithium ion battery meeting the use requirements according to the method.
In a specific embodiment, the carbon material and the silicon material used in the present invention are conventional materials in the art, for example, the carbon material is one or two of natural graphite and artificial graphite, the silicon material is one or more of silicon, silica and silicon-carbon, and it is understood that parameters such as the size of the particle diameter, the mass ratio and the like of the carbon material and the silicon material all affect the average particle number, the thickness of the reaction layer and the gap, and the present invention further provides the ranges of the parameters, specifically: in the first negative electrode active layer, the D50 of the carbon material is 10-20 mu m, and the D50 of the carbon material is 5-15 mu m.
When the lithium ion battery includes the second anode active layer, the particle diameter of the carbon material may be performed according to conventional technical means in the art, for example, the D50 of the carbon material in the second anode active layer is 5 to 20 μm.
When the anode active layer includes a first anode active layer and a second anode active layer, a mass ratio of the first anode active layer to the second anode active layer is (1:9) - (7:3).
In addition, since the conductivity of the silicon material is poor, when the first negative electrode active layer includes the silicon material, the conductivity of the active layer should be properly improved, and since the conductivity of the carbon tube in the conventional conductive agent in the art is far greater than that of the conventional carbon black conductive agent, the negative electrode active layer including the silicon material further includes the carbon tube, and as the content of the silicon material increases, the content of the carbon tube also needs to be correspondingly increased, but the dispersion property of the carbon tube is poor, the lithium ion battery has a risk of gassing, and in order to balance the conductivity of the silicon material and the safety of the lithium ion battery, the carbon tube and the carbon black may be mixed as the conductive agent.
When the second anode active layer is included, the present invention is not limited to the kind of the conductive agent in the second anode active layer, and one skilled in the art may set according to actual needs, for example, the conductive agent may include only carbon black.
As a result of the studies by the inventors, it was found that the binder PAA (polyacrylic acid) helps to alleviate the volume expansion of the silicon material, and therefore, when the first anode active layer includes the silicon material, PAA may be preferable as the binder, i.e., the first anode active layer includes the binder PAA.
When the second anode active layer is included, the present invention is not limited in the kind of binder in the second anode active layer, and one skilled in the art may set according to actual needs, for example, the binder is SBR.
In addition, the negative electrode active layer further includes a dispersing agent, that is, the negative electrode active layer includes a negative electrode active material, a conductive agent, a binder and a dispersing agent, the negative electrode active material includes a silicon material and a carbon material, or includes only a carbon material, to which the present invention further defines the contents of each component in the first negative electrode active layer and the second negative electrode active layer, specifically, the first negative electrode active layer includes 85% -99% of the negative electrode active material, 0% -2% of the conductive agent, 0% -2% of the binder and 1% -2% of the dispersing agent by mass percent; the second negative electrode active layer comprises, by mass, 95% -99% of a carbon material, 0% -2% of a conductive agent, 1% -2% of a binder and 1% -2% of a dispersing agent.
In summary, the invention provides the average particle number of the silicon material in the thickness direction of the first anode active layer, the thickness of the silicon material surface reaction layer and the gap between the silicon material surface reaction layer and surrounding materials, and the proper formula of the silicon anode system lithium ion battery is set according to the definition of the parameters, so that the accurate improvement of the performance of the silicon anode system can be realized, and the lithium ion battery has excellent cycle performance.
The second aspect of the invention provides an electronic device comprising the lithium ion battery provided in the first aspect of the invention. The invention is not limited to the type of electronic device, and may specifically include, but not limited to, mobile phones, notebook computers, electric automobiles, electric bicycles, digital cameras, and the like.
The implementation of the invention has at least the following advantages:
1. the invention controls the average particle number of the silicon material in the thickness direction of the first anode active layer, the thickness of the surface reaction layer of the circulated silicon material and the clearance between the surface reaction layer and surrounding materials, so that the lithium ion battery has lower SEI impedance R SEI Charge transfer resistor R ct The capacity retention rate of the lithium ion battery is improved, so that the lithium ion battery has excellent cycle performance.
2. According to the invention, the double-layer anode active layer is arranged, so that the carbon material arranged on the surface of the anode plate can provide a buffer channel for the bottom silicon material in the cycle process of the lithium ion battery, thereby being beneficial to relieving the volume expansion of the silicon material and further improving the cycle performance of the lithium ion battery.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments or the description of the prior art will be briefly described below, it will be obvious that the drawings in the following description are some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort to a person skilled in the art.
Fig. 1 is a schematic structural diagram of a negative plate according to an embodiment of the present invention;
FIG. 2 is an SEM image of a surface reaction layer of a silicon material according to one embodiment of the present invention;
FIG. 3 is an SEM diagram of a gap between a silicon material and surrounding materials according to one embodiment of the present invention;
fig. 4 is a schematic structural diagram of a negative electrode sheet according to another embodiment of the present invention.
Reference numerals illustrate:
1-a negative electrode current collector;
2-1-a first anode active layer;
2-2-a second anode active layer;
3-a separator;
4-carbon material;
5-silicon material.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The lithium ion battery provided by the embodiment comprises a positive plate and a negative plate, wherein:
the negative plate comprises a negative current collector copper foil and a first negative active layer arranged on two functional surfaces of the negative current collector copper foil, wherein the thickness of the first negative active layer is 54 mu m;
the first anode active layer includes 96.5 parts by mass of an anode active material, 0.5 part by mass of a conductive agent, 1.5 parts by mass of a binder PAA, and 1.5 parts by mass of a dispersant CMC-Na, the anode active material includes graphite and silicon, and the mass ratio of graphite to silicon is 80:20, the conductive agent comprises carbon black and carbon tubes;
the graphite had a D10 of 7.5 μm, a D50 of 14.3 μm and a D90 of 27.6. Mu.m;
silicon has a D10 of 3.4 μm, a D50 of 10.6 μm and a D90 of 22.3 μm;
the positive plate comprises a positive current collector aluminum foil and a positive active layer arranged on two functional surfaces of the positive current collector aluminum foil, wherein the positive active layer comprises 98 parts by mass of lithium cobaltate, 1 part by mass of conductive agent carbon black and 1 part by mass of binder PVDF.
The preparation method of the lithium ion battery provided by the invention comprises the following steps: preparing a negative plate according to the parameters, preparing a battery cell by matching the positive plate and a diaphragm, welding a tab, and then winding the battery cell with the diaphragm, wherein the diaphragm adopts a Xudi 5+2+2 oil system diaphragm; and then packaging, injecting liquid, forming and sorting to obtain the lithium ion battery.
In a vacuum glove box, the lithium ion battery is disassembled, a proper amount of negative plates with good surfaces are taken, and the sample is subjected to section cutting by adopting an argon ion mill CP, so that a section sample is obtained. Taking a picture of the section sample by adopting a back scattering electron microscope (BSE) to obtain 5.5 average particle numbers of the silicon material in the thickness direction of the first anode active layer; and discharging the lithium ion battery at a constant temperature of 45 ℃ under the conditions of 0.7C constant current and 1.5C constant current and constant voltage, charging with a cut-off current of 0.05C, and after 600T circulation, the thickness of a reaction layer on the surface of the silicon material is less than or equal to 600nm, the gap between the silicon material and the surrounding materials is less than or equal to 900nm, the SEI film impedance of the lithium ion battery is 125.5mΩ, and the charge transfer impedance is 84.9mΩ.
Each parameter in the first anode active layer was substituted into formula 1 to calculate, and the calculated M value was 1.59.
Example 2
The lithium ion battery provided in this embodiment can refer to embodiment 1, and is different in that:
the anode active layer includes a first anode active layer and a second anode active layer, wherein the first anode active layer includes 96.5 parts by mass of an anode active material, 1.5 parts by mass of a dispersant CMC-Na, 1.5 parts by mass of a binder PAA, and 0.5 parts by mass of a conductive agent, wherein the anode active material includes graphite and silicon, and the mass ratio of graphite to silicon is 80:20, a step of;
the second anode active layer included 96.5 parts by mass of graphite, 1.5 parts by mass of dispersant CMC-Na, 1.5 parts by mass of binder PVDF, and 0.5 parts by mass of conductive agent carbon black.
The mass ratio of the first anode active layer to the second anode active layer is 7:3.
the total thickness of the first anode active layer and the second anode active layer was 54 μm;
in the lithium ion battery provided in this example, the average particle number of the silicon material in the thickness direction of the first negative electrode active layer was 4.3, the thickness of the reaction layer on the surface of the silicon material was 430nm or less, the gap between the silicon material and the surrounding materials was 670nm or less, the SEI film resistance of the lithium ion battery was 103.4mΩ, and the charge transfer resistance was 79.3mΩ.
The calculated M value of this example was 1.16.
Example 3
The lithium ion battery provided in this embodiment can refer to embodiment 2, and the difference is that:
the mass ratio of the first anode active layer to the second anode active layer is 5:5.
in the lithium ion battery provided in this example, the average particle number of the silicon material in the thickness direction of the first negative electrode active layer was 3.5, the thickness of the reaction layer on the surface of the silicon material was 290nm or less, the gap between the silicon material and the surrounding materials was 440nm or less, the SEI film resistance of the lithium ion battery was 98.6mΩ, and the charge transfer resistance was 73.8mΩ.
The calculated M value of this example was 0.86.
Example 4
The lithium ion battery provided in this embodiment can refer to embodiment 2, and the difference is that:
the mass ratio of the first anode active layer to the second anode active layer is 3:7.
in the lithium ion battery provided in this example, the average particle number of the silicon material in the thickness direction of the first negative electrode active layer was 2.8, the thickness of the reaction layer on the surface of the silicon material was 220nm or less, the gap between the silicon material and the surrounding materials was 360nm or less, the SEI film resistance of the lithium ion battery was 79.5mΩ, and the charge transfer resistance was 62.3mΩ.
The calculated M value of this example was 0.53.
Example 5
The lithium ion battery provided in this embodiment can refer to embodiment 2, and the difference is that:
the mass ratio of the first anode active layer to the second anode active layer is 1:9.
in the lithium ion battery provided in this example, the average particle number of the silicon material in the thickness direction of the first negative electrode active layer was 1.5, the thickness of the reaction layer on the surface of the silicon material was 130nm or less, the gap between the silicon material and the surrounding materials was 310nm or less, the SEI film resistance of the lithium ion battery was 59.9mΩ, and the charge transfer resistance was 67.3mΩ, as tested by the same method as in example 1.
The calculated M value of this example was 0.18.
Comparative example 1
The lithium ion battery provided in this comparative example can be referred to example 1, with the difference that:
the anode active layer included 96.5 parts by mass of an anode active material including graphite and silicon in a mass ratio of 7, 0.5 parts by mass of a conductive agent, 1.5 parts by mass of a binder, and 1 part by mass of a dispersing agent: 3.
in the lithium ion battery provided in this comparative example, the average particle number of the silicon material in the thickness direction of the anode active layer was 6.5, the thickness of the reaction layer on the surface of the silicon material was 800nm or less, the gap between the silicon material and the surrounding materials was 1200nm or less, the SEI film resistance of the lithium ion battery was 135.6mΩ, and the charge transfer resistance was 110.4mΩ, as tested by the same method as in example 1.
The M value calculated in this comparative example was 2.23.
Comparative example 2
The lithium ion battery provided in this comparative example can be referred to example 2, with the difference that:
the mass ratio of graphite to silicon in the first anode active layer was 5:5.
In the lithium ion battery provided in this comparative example, the average particle number of the silicon material in the thickness direction of the first negative electrode active layer was 8, the thickness of the reaction layer on the surface of the silicon material was 1200nm or less, the gap between the silicon material and the surrounding materials was 1600nm or less, the SEI film resistance of the lithium ion battery was 154.6mΩ, and the charge transfer resistance was 119.3mΩ, as tested by the same method as in example 1.
The M value calculated in this comparative example was 2.57.
Comparative example 3
The lithium ion battery provided in this comparative example can be referred to example 2, with the difference that:
the mass ratio of graphite to silicon in the first anode active layer is 5:5;
the mass ratio of the first anode active layer to the second anode active layer is 5:5.
in the lithium ion battery provided in this comparative example, the average particle number of the silicon material in the thickness direction of the first negative electrode active layer was 7.2, the thickness of the reaction layer on the surface of the silicon material was 1000nm or less, the gap between the silicon material and the surrounding materials was 1300nm or less, the SEI film resistance of the lithium ion battery was 149.6mΩ, and the charge transfer resistance was 121.2mΩ, as tested by the same method as in example 1.
The M value calculated in this comparative example was 1.96.
Table 1-2 list description of the negative electrode sheets of examples 1-5 and comparative examples 1-3 to make the difference of the negative electrode sheets provided in examples 1-5 and comparative examples 1-3 more intuitive.
Table 1 description of the negative electrode sheet provided in example 1 and comparative example 1
TABLE 2 description of negative plates provided in examples 2-5 and comparative examples 2-3
The lithium ion batteries provided in examples 1 to 5 and comparative examples 1 to 3 above were tested for energy density, and capacity retention and cyclic expansion rates, and the test methods and test results were as follows:
1. the energy density testing method comprises the following steps: at 25 ℃, 0.2C charge, 0.5C discharge and 0.025C cut-off charge and discharge system are adopted to measure the lithium ion battery; the plateau voltage of the lithium ion battery is the plateau voltage under 0.2C rate discharge. The Energy Density (ED) of a lithium ion battery is calculated according to the following formula:
ed=capacity plateau voltage/(cell length×cell width×cell thickness).
2. The method for testing the retention rate of the cyclic capacity and the cyclic expansion rate at 25 ℃ comprises the following steps: the lithium ion batteries of the examples and the comparative examples were cycled at 25 ℃ for 800T with a cycle regime of 2C charge and 0.7C discharge; capacity retention = discharge capacity (per turn)/initial capacity; cyclic expansion ratio= (thickness after cycle-initial thickness)/initial thickness.
3. The method for testing the cyclic capacity retention rate and cyclic expansion rate at 45 ℃ comprises the following steps: the lithium ion batteries of examples and comparative examples were cycled for 600T at 45 ℃ with a cycle regime of 1.5C charge and 0.7C discharge; capacity retention = discharge capacity (per turn)/initial capacity; cyclic expansion ratio= (thickness after cycle-initial thickness)/initial thickness.
Table 3 test results of lithium ion batteries provided in examples 1 to 5 and comparative examples 1 to 3
From the data provided in examples 1-5 and comparative examples 1-3, the present invention provides lithium ion batteries with lower SEI impedance R by defining the particle count of the silicon material, the reaction layer thickness and the gap between the silicon material and the surrounding materials SEI Charge transfer resistor R ct Thereby improving the capacity retention rate of the lithium ion battery and the cycle performance of the lithium ion battery; according to the data provided in the embodiment 1 and the embodiments 2 to 5, the lithium ion battery with the double-layer structure is more beneficial to relieving the volume expansion of the silicon material and further improving the cycle performance of the lithium ion battery; from the data provided in examples 2-5, it can be seen that when the D50 of the carbon material Carbon (C) D50 of silicon material Silicon (Si) Mass m of carbon material 1 Mass m of silicon material 2 The thickness H of the negative electrode active layer is calculated according to formula 1 to have a value M in the range of 0.5-12, which is helpful for the energy density and cycle performance of the lithium ion battery。
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (13)

1. The lithium ion battery of the silicon negative electrode system is characterized by comprising a negative electrode current collector and a first negative electrode active layer arranged on at least one functional surface of the negative electrode current collector, wherein the first negative electrode active layer comprises a carbon material and a silicon material;
when the lithium ion battery is subjected to constant-current discharge at the temperature of 45 ℃, constant-current and constant-voltage charge at the temperature of 0.7 ℃ and the temperature of 1.5 ℃ and the cut-off current is 0.05 ℃, after 600T of circulation, the thickness of a reaction layer on the surface of the silicon material is less than or equal to 600nm, and the gap between the silicon material and the surrounding materials of the silicon material is less than or equal to 900nm.
2. The lithium ion battery according to claim 1, wherein the silicon material is distributed in the first anode active layer in N linear arrangements in the layer thickness direction of the first anode active material, and the average particle number of the silicon material in each linear arrangement is 1.5 to 5.5.
3. The lithium ion battery of claim 1 or 2, wherein the carbon material has a D50 of Carbon (C) D50 of the silicon material Silicon (Si) Mass m of the carbon material 1 Mass m of the silicon material 2 The thickness H of the negative electrode active layer satisfies the relationship 1:
D50 carbon (C) 、D50 Silicon (Si) And H has the same unit, m 1 And m is equal to 2 Is the same in units of (a).
4. A lithium ion battery according to any of claims 1-3, wherein the lithium ion battery comprises a second anode active layer disposed on a surface of the first anode active layer remote from the anode current collector, the second anode active layer comprising a carbon material.
5. The lithium ion battery according to any one of claims 1 to 3, wherein the first anode active layer comprises, in mass%, 85% to 99% of an anode active material, 0% to 2% of a conductive agent, 0% to 2% of a binder, and 1% to 2% of a dispersing agent.
6. The lithium ion battery according to claim 4, wherein the second anode active layer comprises, by mass, 95% -99% of a carbon material, 0% -2% of a conductive agent, 1% -2% of a binder, and 1% -2% of a dispersing agent.
7. The lithium ion battery according to any one of claims 1 to 6, wherein in the first anode active layer, the D50 of the carbon material is 10 to 20 μm and the D50 of the silicon material is 5 to 15 μm.
8. The lithium ion battery of claim 4, wherein the D50 of the carbon material in the second anode active layer is 5-20 μιη.
9. The lithium ion battery of claim 1, wherein the carbon material comprises one or both of natural graphite and artificial graphite;
and/or the silicon material comprises one or more of silicon, silicon oxygen and silicon carbon.
10. The lithium ion battery of claim 4, wherein the mass ratio of the first negative electrode active layer to the second negative electrode active layer is (1:9) - (7:3).
11. The lithium ion battery of any of claims 1-10, wherein the first negative active layer comprises a binder PAA.
12. The lithium ion battery of any of claims 1-10, wherein the first negative active layer comprises carbon tubes and carbon black.
13. An electronic device comprising a lithium-ion battery according to any one of claims 1-12.
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