CN112018326A - Negative plate and lithium ion battery comprising same - Google Patents

Negative plate and lithium ion battery comprising same Download PDF

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CN112018326A
CN112018326A CN202010983983.0A CN202010983983A CN112018326A CN 112018326 A CN112018326 A CN 112018326A CN 202010983983 A CN202010983983 A CN 202010983983A CN 112018326 A CN112018326 A CN 112018326A
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active material
negative electrode
electrode active
material layer
negative
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欧长志
彭冲
李俊义
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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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
    • H01M4/133—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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/65—Means for temperature control structurally associated with the cells
    • H01M10/653—Means for temperature control structurally associated with the cells characterised by electrically insulating or thermally conductive materials
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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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Abstract

The invention provides a negative plate and a lithium ion battery comprising the same. The negative plate is characterized in that a first negative active material layer and a second negative active material layer are respectively coated on a negative current collector by a double-layer coating technology; the first negative electrode active material layer is arranged between the second negative electrode active material layer and the negative electrode current collector, the first negative electrode active material layer uses the first negative electrode active material with a large heat conductivity coefficient, heat is not easy to accumulate due to the use of the first negative electrode active material with the large heat conductivity coefficient, negative polarization is reduced, and the energy density of the electrode can be effectively improved; the second negative electrode active material layer is in contact with the electrolyte on the surface, so that the surface heat dissipation is relatively simple, the migration rate of lithium ions can be improved by proper heat, and the migration rate of the lithium ions can be promoted by using the second negative electrode active material with a slightly smaller heat conductivity coefficient under the condition that the heat cannot be locally accumulated.

Description

Negative plate and lithium ion battery comprising same
Technical Field
The invention belongs to the technical field of polymer lithium ion batteries, and particularly relates to a negative plate and a lithium ion battery comprising the same.
Background
At present, the lithium ion battery develops rapidly in the fields of high energy density and quick charge, and meanwhile, the safety performance of the lithium ion battery is also concerned. When the lithium ion battery is charged or overcharged quickly, if the heat conductivity coefficient of graphite on the negative plate is insufficient, heat accumulation is easy to occur, the diffusion rate and the embedding rate of local lithium ions are not matched, so that local polarization is large, and local lithium precipitation is easy to occur, so that the safety problem is caused; if the graphite heat conductivity coefficient is larger, the corresponding volume density is larger, and the quick charging performance cannot be considered while the high energy density and the safety are met. Therefore, it is currently required to design a lithium ion negative electrode sheet having high energy density and fast charge performance, and at the same time, having high safety.
Disclosure of Invention
The invention aims to provide a negative plate and a lithium ion battery comprising the same. According to the invention, a first negative active material layer with high heat conductivity coefficient is uniformly coated on a negative current collector by adopting a double-layer coating technology, so that the negative plate can be rapidly cooled in the charging and discharging process, the polarization is reduced, the volume density of the negative plate is improved, and the volume energy density of the lithium ion battery is improved; and a second negative active material layer with a slightly lower heat conductivity coefficient is uniformly coated on the first negative active material layer, so that the heat is not easy to accumulate locally, and the quick charging performance of the pole piece is ensured to be more than 1.5 ℃. Through the arrangement of the double-layer negative active material layers with different heat conductivity coefficients, the requirements of high energy density and quick charging are both considered, and the safety performance of the lithium ion battery can be improved.
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 first negative electrode active material layer is arranged on the first surface of the negative electrode current collector, and the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer;
the first negative electrode active material layer includes a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material, and a thermal conductivity λ of the first negative electrode active material1A thermal conductivity lambda larger than that of the second negative electrode active material2。
According to the present invention, the first negative active material has a thermal conductivity λ1Is 150W/mK<λ1<600W/mK, e.g. 180W/mK ≦ λ1550W/mK or less, and further 200W/mK or less1Less than or equal to 500W/mK; the second negative electrode active material layer includes a second negative electrode active material having a thermal conductivity lambda2Is 20W/mK<λ1<200W/mK, e.g. 30W/mK ≦ λ1180W/mK or less, further for example 50W/mK or less lambda2≤150W/mK。
In the invention, the thermal conductivity is measured by a rapid thermal conductivity tester, and a hot wire method is mainly adopted, namely, the material is locally heated by current with constant power, and the thermal conductivity of the material is measured by the function relation of temperature rise and time.
According to the invention, the negative current collector is a copper foil, and further is a common copper foil.
According to the invention, the thickness of the negative electrode current collector is 6-12 μm.
According to the present invention, the first negative electrode active material layer is further provided on a second surface of the negative electrode current collector opposite to the first surface, and the second negative electrode active material layer is provided on a surface of the first negative electrode active material layer.
According to the invention, the first negative electrodeMedian particle diameter D of the active Material1 50≤30μm。
According to the present invention, the median particle diameter D of the second negative electrode active material2 50≤15μm。
According to the present invention, the median particle diameter of the first negative electrode active material is larger than the median particle diameter of the second negative electrode active material. In the present invention, the porosity between the first negative electrode active material and the second negative electrode active material particles can be adjusted by adjusting the median particle diameter of the first negative electrode active material and the second negative electrode active material, thereby achieving adjustment of the thermal conductivity of the negative electrode active material, for example, the larger the median particle diameter of the negative electrode active material, the lower the porosity between the negative electrode active material particles, and the larger the thermal conductivity.
According to the present invention, the thickness of the first anode active material layer is 10 to 100 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.
According to the present invention, the thickness of the second anode active material layer is 10 to 100 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.
According to the present invention, the first anode active material layer further includes a first conductive agent, a first binder, and a first thickener.
According to the present invention, the second anode active material layer further includes a second conductive agent, a second binder, and a second thickener.
According to the present invention, the first anode active material layer includes the following components in mass fraction:
95-97.5 wt% of a first negative active material, 0.5-2 wt% of a first conductive agent, 1-1.5 wt% of a first binder, and 1-1.5 wt% of a first thickener.
According to the present invention, the second anode active material layer includes the following components in mass fraction:
95-97.5 wt% of a second negative active material, 0.5-2 wt% of a second conductive agent, 1-1.5 wt% of a second binder, and 1-1.5 wt% of a second thickener.
According to the present invention, the first negative active material is selected from artificial graphite and/or natural graphite.
According to the present invention, the second negative active material is selected from one or more of artificial graphite, natural graphite, and porous carbon microspheres.
According to the 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, Super P, graphene and carbon nano-tube.
According to the invention, the first binder and the second binder are the same or different and are selected from one or more of Styrene Butadiene Rubber (SBR), Nitrile Butadiene Rubber (NBR), polyvinylidene fluoride (PVDF) and sodium polyacrylate (PAA-Na) independently from each other.
According to the invention, the first and second thickening agents are selected from sodium carboxymethylcellulose (CMC).
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 solid contents of the slurry for forming the first anode active material layer and the slurry for forming the second anode active material layer are 40 wt% to 45 wt%.
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.
According to the invention, the lithium ion battery further comprises a positive plate, a diaphragm and electrolyte.
The invention has the beneficial effects that:
the invention provides a negative plate and a lithium ion battery comprising the same. The negative plate is characterized in that a first negative active material layer and a second negative active material layer are respectively coated on a negative current collector by a double-layer coating technology; the first negative electrode active material layer is arranged between the second negative electrode active material layer and the negative electrode current collector, the first negative electrode active material layer uses the first negative electrode active material with a large heat conduction coefficient, heat is not easy to accumulate due to the use of the first negative electrode active material with the large heat conduction coefficient, negative polarization is reduced, the volume density of the first negative electrode active material with the large heat conduction coefficient is relatively large, and the energy density of the electrode can be effectively improved; the second negative electrode active material layer has relatively simple surface heat dissipation due to the fact that the surface of the second negative electrode active material layer is in contact with the electrolyte, the migration rate of lithium ions can be improved by proper heat, and the migration rate of the lithium ions can be promoted by the second negative electrode active material with a small heat conductivity coefficient under the condition that the heat cannot be locally accumulated; however, the second negative active material having too small a thermal conductivity may not be used, preventing the heat from being excessively accumulated to cause side reactions at the surface.
In conclusion, the negative plate disclosed by the invention has high energy density, safety performance and quick charging performance, the energy density of the prepared lithium ion battery reaches above 700Wh/L, the long cycle life at the rate of 1.5C can reach above 1000 times, and lithium is not separated out. The lithium ion battery has higher application value and practicability and can meet the requirement of industrial application.
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 first anode active material layer; and 3 is a second 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.
Example 1:
(1) preparing a positive plate:
LiCoO as positive electrode active material2PVDF as a binder and Super P as a conductive agent in a mass ratio of 97%: 1.5%: 1.5 percent of the components are mixed, dispersed in N-methyl pyrrolidone (NMP) and evenly stirred to prepare slurry, evenly coated on the two side surfaces of an aluminum foil of a positive current collector, baked for 4-8h at the temperature of 100 ℃ and 150 ℃, and then cold pressed and cut to prepare a positive plate of a lithium ion battery, wherein the compaction density is 4.1g/cm3The thickness of the single-sided positive electrode active material layer was 60 μm.
(2) Preparation of first negative electrode active material layer slurry:
mixing artificial graphite, SP as a conductive agent, SBR and CMC in a mass ratio of 97:0.5:1.5:1, dispersing the mixture in water, and uniformly stirring to prepare first negative electrode active material layer slurry, wherein the particle size D of the artificial graphite50Less than or equal to 25 mu m and heat conductivity coefficient lambda1350W/mK, the slurry solids content was 48%.
(3) Preparation of second negative electrode active material layer slurry:
mixing natural graphite, a conductive agent SP, SBR and CMC according to a mass ratio of 97:0.5:1.5:1, dispersing the mixture in water, and uniformly stirring to prepare second negative electrode active material layer slurry, wherein the particle size D of the natural graphite is50Less than or equal to 15 mu m and heat conductivity coefficient lambda2120W/mK, slurry solids content 45%.
(4) Preparing a negative plate:
on the first surface of a 6 μm thick copper foil, 0.00403g/cm, respectively2And 0.00272g/cm2Simultaneously uniformly coating the first negative electrode active material layer and the second negative electrode active material layerAnd two negative electrode active material layers, wherein the first negative electrode active material layer is positioned between the second negative electrode active material layer and the negative electrode current collector. The coating speed is 5m/min, and after coating, drying treatment is carried out by 5 sections of ovens, wherein the temperature of each section of oven is 60 ℃, 80 ℃, 110 ℃ and 100 ℃; coating the second surface of the copper foil opposite to the first surface by repeated coating, and pressurizing by a roller press to obtain a compact density of 1.65g/cm3The negative electrode sheet of (1) having a thickness of 80 μm after roll-pressing, wherein the thickness of the first negative electrode active material layer is 53. + -.2 μm, and the thickness of the second negative electrode active material layer is 27. + -.2 μm.
(5) Preparing a lithium ion battery:
the prepared positive plate, the diaphragm (the composite diaphragm with the substrate, the single-sided ceramic and the double-sided glue coating) and the negative plate are stacked together, then a winding core of a winding structure with the positive plate wrapped is manufactured by winding through a winding machine, the winding core is packaged through an aluminum plastic film, the winding core is baked for 48 hours in a vacuum state to remove moisture, then electrolyte is injected, and then the battery is subjected to conventional formation and sorting to obtain the square soft package lithium ion battery. The electrolyte is prepared by adopting a conventional electrolyte formula: LiPF6+ solvent (EC + FEC + DEC + DMC + PS).
Example 2:
this example differs from example 1 in that:
the first negative active material in the first negative active material layer is natural graphite, D50Less than or equal to 30 mu m and heat conductivity coefficient lambda1400W/mK; the second negative active material in the second negative active material layer is porous carbon microspheres, D50Less than or equal to 10 mu m and heat conductivity coefficient lambda2＝150W/mK。
Example 3:
this example differs from example 1 in that:
the first negative electrode active material in the first negative electrode active material layer is artificial graphite, D50Less than or equal to 20 mu m and heat conductivity coefficient lambda1200W/mK; the second negative active material in the second negative active material layer is natural graphite, D50Less than or equal to 10 mu m and heat conductivity coefficient lambda2＝50W/mK。
Example 4:
this example differs from example 1 in that:
the thicknesses of the coating layers on the surface of the negative current collector are different, and are specifically shown in table 1; the compacted density of the negative plate is 1.75g/cm3。
Example 5:
this example differs from example 1 in that:
the thicknesses of the coating layers on the surface of the negative current collector are different, and are specifically shown in table 1; the compacted density of the negative plate is 1.55g/cm3。
Example 6:
this example differs from example 1 in that:
the first negative electrode active material layer and the second negative electrode active material layer are both 0.00338g/cm2The surface density of the negative electrode sheet after rolling is 1.65g/cm3And the thickness of the first negative electrode active material layer and the second negative electrode active material layer is 40 +/-2 microns.
Example 7:
this example differs from example 1 in that:
on the first surface of a 6 μm thick copper foil, 0.00473g/cm, respectively2And 0.00203g/cm2The first negative active material layer and the second negative active material layer are simultaneously and uniformly coated, wherein the first negative active material layer is positioned between the second negative active material layer and the negative current collector. The coating speed is 5m/min, and after coating, drying treatment is carried out by 5 sections of ovens, wherein the temperature of each section of oven is 60 ℃, 80 ℃, 110 ℃ and 100 ℃; coating the second surface of the copper foil opposite to the first surface by repeated coating, and pressurizing by a roller press to obtain a compact density of 1.65g/cm3The negative electrode sheet of (1) has a thickness of 80 μm after roll-pressing, wherein the thickness of the first negative electrode active material layer is 56 ± 2 μm, and the thickness of the second negative electrode active material layer is 24 ± 2 μm.
Comparative example 1:
this comparative example differs from example 1 in that:
the first negative active material in the first negative active material layer is natural graphite, D50Less than or equal to 15 mu m and heat conductivity coefficient lambda1120W/mK; the second negative active material in the second negative active material layer is artificial graphite, D50Less than or equal to 25 mu m and heat conductivity coefficient lambda2＝350W/mK。
Comparative example 2:
this comparative example differs from example 1 in that:
the first negative active material in the first negative active material layer is porous carbon microspheres, D50Less than or equal to 10 mu m and heat conductivity coefficient lambda1150W/mK; the second negative active material in the second negative active material layer is natural graphite, D50Less than or equal to 30 mu m and heat conductivity coefficient lambda2＝400W/mK。
Comparative example 3:
this comparative example differs from example 1 in that:
the first anode active material layer was not coated while the thickness of the second anode active material layer was 80 μm.
Comparative example 4:
this comparative example differs from example 1 in that:
the second anode active material layer was not coated while the thickness of the first anode active material layer was 80 μm.
Example 8:
this example differs from example 1 in that:
on the first surface of a 6 μm thick copper foil, 0.00203g/cm, respectively2And 0.00473g/cm2The first negative active material layer and the second negative active material layer are simultaneously and uniformly coated, wherein the first negative active material layer is positioned between the second negative active material layer and the negative current collector. The coating speed is 5m/min, and after coating, drying treatment is carried out by 5 sections of ovens, wherein the temperature of each section of oven is 60 ℃, 80 ℃, 110 ℃ and 100 ℃; coating the second surface of the copper foil opposite to the first surface by repeated coating, and pressurizing by a roller press to obtain a compact density of 1.65g/cm3The thickness of the negative plate after rolling is 80 muAnd m, wherein the first negative electrode active material layer has a thickness of 24 + 2 μm, and the second negative electrode active material layer has a thickness of 56 + 2 μm.
Example 9:
this example differs from example 1 in that:
the first negative electrode active material in the first negative electrode active material layer is artificial graphite, D50Less than or equal to 30 mu m and heat conductivity coefficient lambda1500W/mK; the second negative active material in the second negative active material layer is natural graphite, D50Less than or equal to 15 mu m and heat conductivity coefficient lambda2＝120W/mK。
Example 10:
this example differs from example 1 in that:
the first negative electrode active material in the first negative electrode active material layer is artificial graphite, D50Less than or equal to 25 mu m and heat conductivity coefficient lambda1350W/mK; the second negative active material in the second negative active material layer is natural graphite, D50Less than or equal to 10 mu m and heat conductivity coefficient lambda2＝30W/mK。
Table 1 compositions of negative electrode sheets of examples and comparative examples
Figure BDA0002688498210000091
The following tests were carried out on the batteries of the above examples and comparative examples:
(1) energy density:
cell energy density (first discharge capacity of cell) average voltage/cell thickness in Wh L-1。
(2) And (3) testing the quick charge cycle life:
the batteries of examples and comparative examples were constant-current charged at a rate of 1.5C to 4.45V at 25C, then constant-voltage charged at 4.45V with a cutoff current of 0.025C, and then constant-current discharged at a rate of 0.5C with a cutoff voltage of 3V, which is a charge-discharge cycle process, and the charge-discharge cycle process was repeated until the capacity retention ratio of the battery was less than 80% or the number of cycles reached 1000.
(3) And (3) lithium separation:
the batteries of the examples and comparative examples were charged at 25 ℃ at a constant current of 1.5C rate to 4.45V, then charged at a constant voltage of 4.45V with a cutoff current of 0.025C, and then discharged at a constant current of 0.5C rate with a cutoff voltage of 3V, which is a charge-discharge cycle, and the charge-discharge cycle was repeated 10 times, after which the batteries were fully charged, the cells were disassembled in a dry room environment, and the lithium deposition on the surface of the negative electrode was observed.
The degree of lithium separation is classified into no lithium separation, slight lithium separation and serious lithium separation. Slight lithium deposition means that the lithium deposition region on the surface of the negative electrode is 1/10 or less of the entire region, and severe lithium deposition means that the lithium deposition region on the surface of the negative electrode exceeds 1/3 of the entire region. The test results are shown in table 2.
Table 2 results of performance test of batteries of examples and comparative examples
Categories Energy Density/Wh L-1 Fast charge cycle life Case of lithium evolution
Example 1 732 Meet 1000 times Does not separate out lithium
Example 2 741 Meet 1000 times Does not separate out lithium
Example 3 719 Meet 1000 times Does not separate out lithium
Example 4 755 Meet 1000 times Does not separate out lithium
Example 5 714 Meet 1000 times Does not separate out lithium
Example 6 709 Meet 1000 times Does not separate out lithium
Example 7 738 Meet 1000 times Does not separate out lithium
Comparative example 1 635 508 times Severe lithium precipitation
Comparative example 2 645 467 times Severe lithium precipitation
Comparison ofExample
3 587 Meet 1000 times Does not separate out lithium
Comparative example 4 748 454 times Severe lithium precipitation
Example 8 598 Meet 1000 times Does not separate out lithium
Example 9 754 376 times Severe lithium precipitation
Example 10 657 Meet 1000 times Does not separate out lithium
From the above test results it can be seen that:
compared with the embodiment 1, in the embodiments 2 to 3, the heat conductivity coefficient is changed correspondingly after the first negative electrode active material and the second negative electrode active material are replaced, but the heat conductivity coefficient of the first negative electrode active material is still kept to be larger than that of the second negative electrode active material, so that the first negative electrode active material layer is positioned between the second negative electrode active material layer and the negative electrode current collector, the first negative electrode active material with the larger heat conductivity coefficient is used, heat is not easy to accumulate, negative electrode polarization is reduced, the volume density of the first negative electrode active material with the larger heat conductivity coefficient is relatively larger, and the energy density of the electrode can be effectively improved; the second negative electrode active material layer is in contact with the electrolyte on the surface, so that the surface heat dissipation is relatively simple, the migration rate of lithium ions can be improved by proper heat, the migration rate of the lithium ions can be promoted by using the second negative electrode active material with a slightly smaller heat conductivity coefficient under the condition that the heat cannot be locally accumulated, the quick charge cycle performance of the negative electrode plate is improved, and the safety is improved.
Examples 4-5 compared with example 1, the compaction density of the negative electrode sheet was changed, the cycle performance of the negative electrode sheet was not significantly changed, but the thickness of the negative electrode sheet was changed due to the change in compaction, and thus the volumetric energy density of the battery was changed.
Examples 6 to 7, in comparison with example 1, varied the areal densities of the first negative electrode active material layer and the second negative electrode active material layer, resulting in different thickness ratios of the two in the negative electrode sheet. The cycle performance of the negative plate is not obviously changed, and the volumetric energy density of the battery is changed along with the change of the proportion of the first negative active material layer with larger volumetric density in the whole negative electrode.
Compared with the embodiment 2-3, the comparative example 1-2 is equivalent to the replacement of the distribution positions of the first negative electrode active material layer and the second negative electrode active material layer in the negative plate, the negative electrode active material on the surface of the negative plate has high heat conductivity coefficient, the spacing between the negative electrode active material particles is smaller, and in the 1.5C quick charge cycle process, the lithium embedding rate is slowed down, the polarization is increased, the lithium precipitation phenomenon is easy to occur, so that the capacity is sharply attenuated, even lithium dendrite is formed, and the safety problem is caused.
Comparative examples 3 to 4 compare with example 1, the first negative active material layer or the second negative active material layer is not coated, and if the first negative active material layer is not coated, the second negative active material of a single layer has a low thermal conductivity, the pores between the negative active material particles are large, the performance is excellent during the 1.5C fast charge cycle, but the battery volume energy density is small; if the second negative electrode active material layer is not coated, the single-layer first negative electrode active material has high heat conductivity coefficient, small pores among negative electrode active material particles and large battery volume energy density, but lithium intercalation is blocked in the 1.5C quick charge cycle process, polarization is large, cycle performance is poor, and lithium precipitation is easy to occur.
Compared with example 1, in example 8, the content ratio of the negative active material with the high thermal conductivity in the negative plate is reduced, which is reflected by a smaller thickness, so that the 1.5C quick charge cycle performance of the negative plate is excellent, but since the negative active material with the low thermal conductivity in the negative plate occupies most of the negative active material, the space between the negative active material particles in the negative plate is larger, the porosity is larger, and thus the volumetric energy density of the battery is reduced.
Example 9 compared with example 1, the thermal conductivity of the first negative electrode active material was as high as 500W/mK, the pores between the corresponding negative electrode active material particles were small, the energy density of the battery was large, but intercalation of lithium during the 1.5C fast charge cycle was severely hindered, leading to rapid decay of the cycle capacity, and severe lithium evolution occurred.
Example 10 in comparison with example 1, the second negative active material has a thermal conductivity as low as 30W/mK, and the pores between the corresponding negative active material particles are large, and although it is advantageous for the cycle performance of the battery, the volumetric energy density of the battery is greatly reduced.
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 (10)

1. A negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer, and a second negative electrode active material layer; the first negative electrode active material layer is arranged on the first surface of the negative electrode current collector, and the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer;
the first negative electrode active material layer includes a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material, and a thermal conductivity λ of the first negative electrode active material1A thermal conductivity lambda larger than that of the second negative electrode active material2。
2. The negative electrode sheet of claim 1, wherein the first negative active material has a thermal conductivity λ1Is 150W/mK<λ1<600W/mK; and/or the presence of a gas in the gas,
the second negative electrode active material layer includes a second negative electrode active material having a thermal conductivity lambda2Is 20W/mK<λ1<200W/mK。
3. The negative electrode sheet according to claim 1 or 2, wherein the first negative electrode active material layer is further provided on a second surface of the negative electrode current collector opposite to the first surface, and the second negative electrode active material layer is provided on a surface of the first negative electrode active material layer.
4. The negative electrode sheet according to any one of claims 1 to 3, wherein the median particle diameter D of the first negative electrode active material1 50Less than or equal to 30 mu m; and/or the presence of a gas in the gas,
a median particle diameter D of the second negative electrode active material2 50Less than or equal to 15 mu m; and/or the presence of a gas in the gas,
the median particle diameter of the first negative electrode active material is larger than the median particle diameter of the second negative electrode active material.
5. The negative electrode sheet according to any one of claims 1 to 4, wherein the thickness of the first negative electrode active material layer is 10 to 100 μm; and/or the presence of a gas in the gas,
the thickness of the second negative electrode active material layer is 10 to 100 μm.
6. The negative electrode sheet according to any one of claims 1 to 5, wherein the first negative electrode active material layer further comprises a first conductive agent, a first binder, and a first thickener, and the first negative electrode active material layer comprises the following components in parts by mass:
95-97.5 wt% of a first negative active material, 0.5-2 wt% of a first conductive agent, 1-1.5 wt% of a first binder, and 1-1.5 wt% of a first thickener.
7. The negative electrode sheet according to any one of claims 1 to 6, wherein the second negative electrode active material layer further comprises a second conductive agent, a second binder, and a second thickener, and the second negative electrode active material layer comprises the following components in parts by mass:
95-97.5 wt% of a second negative active material, 0.5-2 wt% of a second conductive agent, 1-1.5 wt% of a second binder, and 1-1.5 wt% of a second thickener.
8. Negative electrode sheet according to any one of claims 1 to 7, wherein the first negative active material is selected from artificial graphite and/or natural graphite.
9. The negative electrode sheet according to any one of claims 1 to 8, wherein the second negative electrode active material is selected from one or more of artificial graphite, natural graphite, and porous carbon microspheres.
10. A lithium ion battery comprising the negative electrode sheet of any one of claims 1 to 9.
CN202010983983.0A 2020-09-17 2020-09-17 Negative plate and lithium ion battery comprising same Pending CN112018326A (en)

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