CN113097427A - Negative plate and battery - Google Patents
Negative plate and battery Download PDFInfo
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- CN113097427A CN113097427A CN202110338907.9A CN202110338907A CN113097427A CN 113097427 A CN113097427 A CN 113097427A CN 202110338907 A CN202110338907 A CN 202110338907A CN 113097427 A CN113097427 A CN 113097427A
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Classifications
-
- 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
-
- 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
-
- 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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- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a negative plate and a battery, wherein the negative plate comprises a negative current collector, a negative pole tab, a first coating and a second coating, the first coating comprises a first part close to the empty foil area and a second part far away from the empty foil area, the second coating comprises a third part close to the empty foil area and a fourth part far away from the empty foil area, the thickness of the first part is smaller than that of the third part, and the median diameter D50 of an active material contained in the second coating is smaller than that D50 of the active material contained in the first coating, so that the second coating in a negative paste close to the negative pole tab occupies the main body, and the second coating is an active material with a smaller particle size, so that the second coating can present better ion diffusion dynamic performance and reduce the risk of lithium precipitation in the charging process.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a negative plate and a battery.
Background
With the development of lithium ion secondary batteries, consumers have increasingly high demands on charging speed, endurance time, and safety performance. For the negative electrode tab, the region where the current density is the greatest is generally concentrated in the region near the negative electrode tab, so that the current density in this region is large. Due to insufficient dynamic performance of the negative electrode, the polarization of the region is usually large and the potential is low, and during charging, the surface of the negative electrode plate can be more easily close to or reach a lithium precipitation potential in the region, so that lithium precipitation is caused, potential safety hazards are caused, and the safety performance of the battery is deteriorated.
Therefore, in the prior art, lithium is easy to precipitate near the negative pole tab of the negative pole piece, so that the safety performance of the battery is low.
Disclosure of Invention
The embodiment of the invention aims to provide a negative plate and a battery, and solves the problem that lithium is easy to precipitate near a negative electrode tab in the prior art.
In order to achieve the above object, in a first aspect, an embodiment of the present invention provides a negative electrode sheet, including a negative electrode current collector, a negative electrode tab, a first coating and a second coating, where the first coating is disposed on a surface of the negative electrode current collector, the second coating is disposed on a side of the first coating opposite to the negative electrode current collector, the surface of the negative electrode current collector further includes a blank foil region, and the negative electrode tab is disposed in the blank foil region;
wherein the first coating comprises a first portion proximate to the empty foil region and a second portion distal from the empty foil region, the second coating comprises a third portion proximate to the empty foil region and a fourth portion distal from the empty foil region, the first portion having a thickness less than a thickness of the third portion; the first coating comprises a first active material and the second coating comprises a second active material, the median diameter D50 of the first active material in the first coating being greater than the median diameter D50 of the second active material in the second coating.
Optionally, the thickness of the second portion is greater than the thickness of the fourth portion, and the compacted density of the second portion is greater than the compacted density of the fourth portion.
Optionally, the first coating further includes a fifth portion located on a side of the second portion facing away from the first portion, the second coating further includes a sixth portion located on a side of the fourth portion facing away from the third portion, and a thickness of the fifth portion is smaller than a thickness of the sixth portion.
Optionally, the width of the first portion is 1/10 to 1/2 of the width of the first coating, and the width of the third portion is 1/10 to 1/2 of the width of the second coating.
Optionally, the ratio of the thickness of the first portion to the thickness of the third portion is 1/9 to 2/3, the ratio of the thickness of the second portion to the thickness of the fourth portion is 3/2 to 9/1, and the sum of the maximum thickness of the first portion and the maximum thickness of the third portion is a first thickness, the sum of the maximum thickness of the second portion and the maximum thickness of the fourth portion is a second thickness, the first thickness is equal to the second thickness, and both the first thickness and the second thickness are less than 200 μm.
Optionally, the median diameter D50 of the first active material in the first coating layer is 12 μm to 18 μm, and the median diameter D50 of the second active material in the second coating layer is 5 μm to 8 μm.
Optionally, the first coating layer and the second coating layer satisfy at least one of the following conditions:
the content of the conductive agent in the first coating is less than that in the second coating;
the porosity of the first coating layer is less than the porosity of the second coating layer;
the coating amount of the first active material is less than the coating amount of the second active material;
the average particle size of the first active material is greater than the average particle size of the second active material;
the first active material has a graphite Orientation Index (OI) value greater than a graphite Orientation Index (OI) value of the second active material;
the impedance of the first coating is greater than the impedance of the second coating.
Optionally, the width of the first coating layer is equal to the width of the second coating layer, the width of the first portion is equal to the width of the third portion, and the width of the second portion is equal to the width of the fourth portion.
Optionally, the first portion includes a first thinned region and a first non-thinned region, and the thickness of the first thinned region gradually decreases from a side away from the empty foil region to a side close to the empty foil region; the third portion comprises a second thinned region and a second non-thinned region, the second thinned region having a thickness that gradually decreases from a side distal to the empty foil region to a side proximal to the empty foil region.
In a second aspect, an embodiment of the present invention provides a battery, including the negative electrode tab provided in the first aspect of the embodiment of the present invention.
One of the above technical solutions has the following advantages or beneficial effects:
the invention provides a negative plate and a battery, wherein the negative plate comprises a negative current collector, a negative pole tab, a first coating and a second coating, the first coating comprises a first part close to the empty foil area and a second part far away from the empty foil area, the second coating comprises a third part close to the empty foil area and a fourth part far away from the empty foil area, the thickness of the first part is smaller than that of the third part, and the median diameter D50 of an active material contained in the second coating is smaller than that D50 of the active material contained in the first coating, so that the second coating in a negative paste close to the negative pole tab occupies the main body, and the second coating is an active material with a smaller particle size, can present better ion diffusion dynamic performance, and reduces the risk of lithium precipitation in a charging process.
Drawings
Fig. 1 is one of schematic cross-sectional views of a negative electrode sheet before being cut according to an embodiment of the present invention;
fig. 2 is a schematic view of a negative electrode sheet before being cut according to an embodiment of the present invention;
fig. 3 is one of schematic cross-sectional views of a negative electrode sheet according to an embodiment of the present invention;
fig. 4 is a second schematic cross-sectional view of a negative electrode sheet according to an embodiment of the present invention;
fig. 5 is a second schematic cross-sectional view of the negative electrode sheet before being cut according to the embodiment of the present invention;
fig. 6 is a schematic flow chart of a method for preparing a negative electrode sheet according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 to 5, an embodiment of the present invention provides a negative electrode sheet.
As shown in fig. 1, the negative electrode sheet includes a negative electrode current collector 10, a negative electrode tab (not shown in the figure), a first coating 20 and a second coating 30, the first coating 20 is disposed on a surface of the negative electrode current collector 10, the second coating 30 is disposed on a side of the first coating 20 facing away from the negative electrode current collector 10, the surface of the negative electrode current collector 10 further includes a blank foil area 11, and the negative electrode tab is disposed on the blank foil area 11;
wherein the first coating layer 20 comprises a first portion close to the empty foil region 11 and a second portion far from the empty foil region 11, and the second coating layer 30 comprises a third portion close to the empty foil region 11 and a fourth portion far from the empty foil region 11, and the thickness of the first portion is smaller than that of the third portion; the first coating layer 20 comprises a first active material, the second coating layer 30 comprises a second active material, and the median diameter D50 of the first active material in the first coating layer 20 is greater than the median diameter D50 of the second active material in the second coating layer 30.
It should be noted that the negative electrode sheet shown in fig. 1 needs to be obtained by cutting along the central line shown in fig. 2. A cross-sectional view of the cut negative electrode sheet along a first plane is shown in fig. 3, where the first plane is parallel to the width direction of the negative electrode sheet and perpendicular to the length direction of the negative electrode sheet.
For the negative electrode tab, the region where the current density is the greatest is generally concentrated in the region near the negative electrode tab, i.e., the empty foil region 11, so that the empty foil region 11 has a greater current density. Due to insufficient anode kinetics, the polarization in this region is typically large and the potential is low, and during charging, the surface of the anode sheet may more easily approach or reach the lithium evolution potential in this region, causing lithium evolution to occur.
In the embodiment of the invention, as shown in fig. 1, two layers of coating pastes are coated on the surface of a negative current collector 10, and the negative electrode tab is arranged in a hollow foil area 11 on the negative current collector 10, and then is slit to form the negative electrode sheet shown in fig. 3. The negative plate comprises a first coating 20 and a second coating 30, and the second coating 30 is arranged on the side surface of the first coating 20, which faces away from the negative current collector 10.
Wherein the first portion may be understood as an edge portion of the first coating layer 20 on a side close to the empty foil region 11 as shown in fig. 3, and the second portion may be understood as an edge portion of the first coating layer 20 on a side away from the empty foil region 11 as shown in fig. 3. The third portion may be understood as an edge portion of the second coating 30 on the side close to the empty foil region 11 as shown in fig. 3, and the fourth portion may be understood as an edge portion of the second coating 30 on the side away from the empty foil region 11 as shown in fig. 3.
Since the median diameter D50 of the active material contained in the second coating layer 30 is smaller than the median diameter D50 of the active material contained in the first coating layer 20, the active material having a smaller particle size facilitates the movement of lithium ions inside the electrode material, and thus can exhibit better ion diffusion kinetics. Based on this, in the embodiment of the present invention, in the edge portion of the negative electrode coating layer near the empty foil region, the thickness d2 of the third portion is greater than the thickness d1 of the first portion, i.e., the second coating layer 30 with better dynamic performance occupies the main body, and the risk of lithium precipitation of the negative electrode sheet during the charging process is reduced. In addition, through double-layer coating, the energy density of the negative plate can be improved.
In particular, the first active material and the second active material may be one or more of artificial graphite, natural graphite, graphite coated with a modifier, a silicon negative electrode, a silicon-containing negative electrode material, and other negative electrodes suitable for lithium ion batteries. The present invention can be determined by practical situations, and the embodiments of the present invention are not limited herein.
Optionally, as shown in fig. 3, the thickness of the second portion is greater than the thickness of the fourth portion, and the compacted density of the second portion is greater than the compacted density of the fourth portion.
In this embodiment, the energy density of the second portion is higher than the energy density of the fourth portion because the compacted density of the second portion is higher than the compacted density of the fourth portion. In the part of the negative electrode coating far away from the empty foil area, the thickness d3 of the second part is greater than the thickness d4 of the fourth part, namely, the first coating 20 with higher energy density occupies the main body, and the overall energy density of the negative electrode plate is further improved.
Optionally, as shown in fig. 4, the first coating layer 20 further includes a fifth portion located on a side of the second portion facing away from the first portion, and the second coating layer 30 further includes a sixth portion located on a side of the fourth portion facing away from the third portion, where a thickness of the fifth portion is smaller than a thickness of the sixth portion.
In this embodiment, the first portion may be understood as an edge portion of the first coating layer 20 on a side close to the empty foil region 11 as shown in fig. 4, the second portion may be understood as a middle portion of the first coating layer 20 as shown in fig. 4, and the fifth portion may be understood as an edge portion of the first coating layer 20 on a side away from the empty foil region as shown in fig. 4. The third portion may be understood as an edge portion of the second coating layer 30 on a side close to the empty foil area as shown in fig. 4, the fourth portion may be understood as a middle portion of the second coating layer 30 as shown in fig. 4, and the sixth portion may be understood as an edge portion of the second coating layer 30 on a side away from the empty foil area as shown in fig. 4. In this way, in the region where the current density of the edge of the negative electrode sheet may be relatively high, the second coating 30 with relatively good dynamic performance in the negative electrode coating is taken as a main body, and further, the risk of lithium precipitation of the negative electrode sheet in the charging process is reduced.
In a specific implementation form, the first portion, the third portion, the fifth portion and the sixth portion have the same width, and the third portion and the fourth portion have the same width.
Optionally, as shown in fig. 3, the width L1 of the first portion is 1/10 to 1/2 of the width of the first coating 20, and the width L3 of the third portion is 1/10 to 1/2 of the width of the second coating 30.
Optionally, as shown in fig. 3, a ratio of a thickness d1 of the first portion to a thickness d2 of the third portion is 1/9 to 2/3, a ratio of a thickness d3 of the second portion to a thickness d4 of the fourth portion is 3/2 to 9/1, a sum of a maximum thickness of the first portion and a maximum thickness of the third portion is a first thickness, a sum of a maximum thickness of the second portion and a maximum thickness of the fourth portion is a second thickness, the first thickness is equal to the second thickness, and both the first thickness and the second thickness are smaller than 200 μm.
Optionally, the median diameter D50 of the first active material in the first coating layer 20 is 12 μm to 18 μm, and the median diameter D50 of the second active material in the second coating layer 30 is 5 μm to 8 μm.
Optionally, the first coating 20 and the second coating 30 satisfy at least one of the following conditions:
the content of the conductive agent in the first coating is less than that in the second coating;
the porosity of the first coating 20 is less than the porosity of the second coating 30;
the coating amount of the first active material is less than the coating amount of the second active material;
the average particle size of the first active material is greater than the average particle size of the second active material;
the first active material has a graphite Orientation Index (OI) value greater than a graphite Orientation Index (OI) value of the second active material;
the resistance of the first coating layer 20 is greater than the resistance of the second coating layer 30.
In this embodiment, in addition to the difference in the dynamic properties of the first coating layer 20 and the second coating layer 30 by controlling the median diameter D50 of the active material contained in the coating layers, the difference in the dynamic properties of the first coating layer 20 and the second coating layer 30 may be achieved by controlling at least one of the above to make the dynamic properties of the second coating layer 30 stronger than the dynamic properties of the first coating layer 20.
In particular, the porosity and resistance of the first coating layer 20 and the second coating layer 30 may be adjusted by adjusting the composition or content of the conductive agent and the binder in the coating slurry. For example, the content of the conductive agent in the first coating layer 20 may be made smaller than the content of the conductive agent in the second coating layer 30; alternatively, the resistance of the adhesive used in the first coating layer 20 may be greater than that of the adhesive used in the second coating layer 30, which may be determined according to actual conditions, and the embodiment of the present invention is not limited herein.
Alternatively, the empty foil region 11 is located on any one long side of the surface of the negative electrode collector 10.
In the present embodiment, as shown in fig. 2, the negative electrode current collector 10 is coated before slitting, and the empty foil region 11 may be a region a and a region B in fig. 2. After slitting, the part of the empty foil region 11 of the negative electrode sheet is located in the region a, and the part of the empty foil region 11 of the negative electrode sheet is located in the region B. In practical application, for a multi-tab negative plate, the empty foil regions 11 are generally distributed as shown in fig. 2, the number of the negative tabs of the multi-tab negative plate is multiple, and the negative tabs are generally formed by protruding the negative current collector 10 in the empty foil regions, and in one implementation form, the empty foil regions 11 extend to the direction regions departing from the first coating 20 and the second coating 30 to form the negative tabs.
In the first case, the number of the empty foil regions 11 before slitting is 1 in the present embodiment, and is located in the region a shown in fig. 2. In the present case, the edge of the second coating layer 30 on the side close to the a-region is flush with the edge of the first coating layer 20 on the side close to the a-region.
In the second case, the number of empty foil sections 11 before slitting is 1, located in the area B as shown in fig. 2. In the present case, the edge of the second coating layer 30 on the side close to the B region is flush with the edge of the first coating layer 20 on the side close to the B region.
In the third case, before slitting, the number of the empty foil areas is 2, which are respectively located in area a and area B as shown in fig. 2. In this case, the width of the first layer 20 is equal to the width of the second layer 30 before slitting, the width of the first portion is equal to the width of the third portion, and the width of the second portion is equal to the width of the fourth portion.
Optionally, the first portion includes a first thinned region and a first non-thinned region, and the thickness of the first thinned region gradually decreases from a side away from the empty foil region to a side close to the empty foil region; the third portion comprises a second thinned region and a second non-thinned region, the second thinned region having a thickness that gradually decreases from a side distal to the empty foil region to a side proximal to the empty foil region.
In the present embodiment, as shown in fig. 5, the thicknesses of the first coating layer 20 and the second coating layer 30 at the edges close to the empty foil area 11 are gradually reduced, and the orthographic projection of the first thinning area on the negative electrode current collector coincides with the orthographic projection of the second thinning area on the negative electrode current collector. On one hand, the thinning condition is determined based on the fluid mechanical property and the process characteristics of the cathode slurry; on the other hand, the negative electrode sheet can be prevented from having the problem of coiling and bulging in the subsequent use process by arranging a certain thinning area when the negative electrode slurry is coated on the surface of the negative electrode current collector 10.
Further, optionally, the width of the first thinning-out region is equal to the width of the second thinning-out region, and the width of the first thinning-out region is 1/10 to 2/3 of the width of the first portion, so as to ensure the energy density of the negative plate as a whole.
In summary, in the negative electrode sheet provided by the embodiment of the present invention, the first coating layer 20 and the second coating layer 30 are respectively formed by applying two layers of pastes on the coating region of the negative electrode current collector 10, and the thickness D2 of the third portion is greater than the thickness D1 of the first portion. Since the median diameter D50 of the active material contained in the second coating layer 30 is smaller than the median diameter D50 of the active material contained in the first coating layer 20, the active material having a smaller particle size facilitates the movement of lithium ions inside the electrode material, and thus can exhibit better ion diffusion kinetics. Based on this, the second coating 30 with better dynamic performance occupies the main body in the part of the negative electrode coating close to the empty foil area, and the risk of lithium precipitation of the negative electrode sheet in the charging process is reduced. In addition, through double-layer coating, the energy density of the negative plate can be improved.
The embodiment of the invention also provides a battery, and the battery comprises the negative plate provided by the embodiment of the invention. It should be noted that the battery includes all technical features of the negative electrode plate provided in the embodiment of the present invention, and can achieve all technical effects of the negative electrode plate provided in the embodiment of the present invention, and in order to avoid repetition, details are not described here.
Referring to fig. 6, fig. 6 is a flowchart of a method for manufacturing a negative electrode sheet according to an embodiment of the present invention. As shown in fig. 6, the method for preparing the negative electrode sheet includes:
601, forming a negative current collector, wherein the surface of the negative current collector comprises a coating area and a hollow foil area, and the hollow foil area is used for arranging a negative electrode tab;
wherein the first coating comprises a first portion proximate to the empty foil region and a second portion distal from the empty foil region, the second coating comprises a third portion proximate to the empty foil region and a fourth portion distal from the empty foil region, the first portion having a thickness less than a thickness of the third portion; the first coating comprises a first active material and the second coating comprises a second active material, the median diameter D50 of the first active material in the first coating being greater than the median diameter D50 of the second active material in the second coating.
In the embodiment of the present invention, the first coating layer 20 and the second coating layer 30 are formed by applying two layers of pastes on the coating region of the negative electrode current collector 10, respectively, and the thickness D2 of the third portion is made greater than the thickness D1 of the first portion. Since the median diameter D50 of the active material contained in the second coating layer 30 is smaller than the median diameter D50 of the active material contained in the first coating layer 20, the active material having a smaller particle size facilitates the movement of lithium ions inside the electrode material, and thus can exhibit better ion diffusion kinetics. Based on this, the second coating 30 with better dynamic performance occupies the main body in the part of the negative electrode coating close to the empty foil area, and the risk of lithium precipitation of the negative electrode sheet in the charging process is reduced. In addition, through double-layer coating, the energy density of the negative plate can be improved.
The first active material and the second active material can be one or more of artificial graphite, natural graphite, graphite coated with a modifier, a silicon negative electrode, a silicon-containing negative electrode material and other negative electrodes suitable for lithium ion batteries. The first conductive agent and the second conductive agent may be one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and conductive fiber. The first binder and the second binder may be one or more of polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.
In particular, the first coating slurry and the second coating slurry can be prepared and formed respectively by selecting active materials with different median diameters D50. In an implementation form, the dynamic performance of the second coating 30 may be stronger than that of the first coating 20 by adjusting the components or the contents of the first conductive agent and the second conductive agent, or by adjusting the components or the contents of the first binder and the second binder, which may be determined according to the actual situation, and the embodiment of the present invention is not limited herein.
On the basis of determining proper first active material, first binder and first conductive agent, the materials can be dissolved in a solvent according to a certain proportion, and the first coating slurry is prepared after uniform mixing. Specifically, the content of the first active material may be 90 to 98%, the content of the first conductive agent may be 0.2 to 4%, and the content of the first binder may be 0.6 to 6%, and the resultant first coating slurry has a viscosity of 2000-7000mpa.s and a solid content of 70 to 80%.
And on the basis of determining proper second active material, second binder and second conductive agent, dissolving the materials in a solvent according to a certain proportion, and uniformly mixing to obtain the second coating slurry. Specifically, the content of the second active material may be 90 to 98%, the content of the second conductive agent may be 0.2 to 4%, and the content of the second binder may be 0.6 to 6%, and the resultant second coating slurry has a viscosity of 2000-7000mpa.s and a solid content of 70 to 80%.
In the embodiment of the present invention, the coating steps of the two-layer coating slurry may be: and coating the first coating slurry on the surface of the negative current collector, drying to form the first coating, and then coating the second coating slurry on the first coating and drying to form the second coating. In other embodiments, the coating step of the two-layer coating slurry may also be: and simultaneously coating the first coating slurry and the second coating slurry on the surface of the negative current collector by using a double-layer coating technology, and drying to form the first coating and the second coating. The coating method may include one or more of gravure coating, transfer coating, and spray coating, which may be determined according to the actual situation, and the embodiments of the present invention are not limited herein.
The following are 5 specific examples and 3 comparative examples in example 1 of the present invention:
example 1
Step one, preparing anode coating slurry by lithium cobaltate: adding N-methylpyrrolidone (NMP) according to the mixture ratio of 96.9 wt% of lithium cobaltate, 1.8 wt% of conductive carbon black and 1.3 wt% of polyvinylidene fluoride (PVDF) to adjust to prepare anode coating slurry with proper solid content. And (3) coating the anode coating slurry on an anode current collector after passing through a screen, drying at 110-120 ℃, and rolling and cutting to obtain the anode sheet.
Step two, preparing a first coating slurry from artificial graphite 1(D50 ═ 15 um): mixing 96.9% of artificial graphite 1, 0.5 wt% of conductive carbon black and 1.3 wt% of CMC + SBR, and then adjusting the mixture into a first active material A by using deionized water; a second coating slurry was prepared with artificial graphite 2(D50 ═ 8 um): the mixture ratio of 96.9 percent of artificial graphite 1, 0.5 percent of conductive carbon black, 1.3 percent +1.3 percent of CMC + SBR is regulated into a second active material B by deionized water. Coating a first active material A of the negative electrode on the surface of a negative electrode current collector by coating equipment to form a first coating; and coating a second active material B of the negative electrode on the first coating by using double-layer coating equipment to form a second coating, and then drying, rolling, slitting and tabletting to obtain the negative electrode sheet. Wherein the area of the edge region of the first coating and the second coating is 1/5 and the area of the middle region is 4/5 of the total area of the coatings; and the thickness ratio of the edge region of the second coating to the edge region of the first coating is 7:3, and the ratio of the middle region is 3: 7; and the sum of the thicknesses of the first coating layer and the second coating layer is 100 μm.
And step three, stacking the positive plate prepared in the step one, the negative plate prepared in the step two and a diaphragm plate together, winding the positive plate and the diaphragm plate to prepare a winding core, packaging the winding core by using an aluminum plastic film to prepare a battery core, then performing the procedures of liquid injection, aging, formation, secondary packaging and the like, and finally testing the electrochemical performance of the battery.
Example 2
Example 2 differs from example 1 in that in step two, the area of the edge regions of the first and second coatings accounted for 1/2 and the area of the middle region accounted for 1/2 of the total area of the coatings.
Other steps may refer to the specific description in embodiment 1, and are not described herein again in order to avoid repetition.
Example 3
Example 3 differs from example 1 in that the composition of the first coating slip and the second coating slip is different in step two. Specifically, a first coating slurry was prepared from artificial graphite 1(D50 ═ 15 um): mixing 96.9% of artificial graphite 1, 0.5 wt% of conductive carbon black and 1.3 wt% of CMC + SBR, and then adjusting the mixture into a first active material A by using deionized water; a second coating slurry was prepared with artificial graphite 2(D50 ═ 8 um): the mixture ratio of 96.4 percent of artificial graphite 1, 1 percent of conductive carbon black, 1.3 percent +1.3 percent of CMC + SBR is regulated by deionized water to form a second active material B.
Other steps may refer to the specific description in embodiment 1, and are not described herein again in order to avoid repetition.
Example 4
Example 4 is different from example 1 in that the median diameter D50 of the anode first active material a and the anode second active material B is different in step two. Specifically, a first coating slurry was prepared from artificial graphite 1(D50 ═ 18 um): mixing 96.9% of artificial graphite 1, 0.5 wt% of conductive carbon black and 1.3 wt% of CMC + SBR, and then adjusting the mixture into a first active material A by using deionized water; a second coating slurry was prepared with artificial graphite 2(D50 ═ 5 um): the mixture ratio of 96.9 percent of artificial graphite 1, 0.5 percent of conductive carbon black, 1.3 percent +1.3 percent of CMC + SBR is regulated into a second active material B by deionized water.
Other steps may refer to the specific description in embodiment 1, and are not described herein again in order to avoid repetition.
Example 5
Example 5 differs from example 1 in that in step two, where there is edge thinning of the coating, the width of the first thinned region is in the range 1/10 to 2/3 of the width of the first portion, the sum of the thicknesses of the first and second coatings is reduced in a gradient from 1 μm to 15 μm, but the ratio of the thickness of the first coating to the thickness of the second coating is always maintained from 1:9 to 4: 6.
Other steps may refer to the specific description in embodiment 1, and are not described herein again in order to avoid repetition.
Comparative example 1
Comparative example 1 differs from example 1 in that the first coating slurry is applied in only a single layer.
Other steps may refer to the specific description in embodiment 1, and are not described herein again in order to avoid repetition.
Comparative example 2
Comparative example 2 differs from example 1 in that the second coating slurry is applied in only a single layer.
Other steps may refer to the specific description in embodiment 1, and are not described herein again in order to avoid repetition.
The lithium ion batteries prepared in the above examples and comparative examples were subjected to the following performance tests, the test procedures being:
1) 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.
2) 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 1.
TABLE 1 results of the Performance test of various examples and comparative examples
| Categories | Energy density Wh/L | Fast charge cycle life | Separating lithiumSituation(s) |
| Example 1 | 705 | Satisfy 1000T | Does not separate out lithium |
| Example 2 | 696 | Satisfy 1000T | Does not separate out lithium |
| Example 3 | 701 | Satisfy 1000T | Does not separate out lithium |
| Example 4 | 708 | Satisfy 1000T | Does not separate out lithium |
| Example 5 | 702 | Satisfy 1000T | Does not separate out lithium |
| Comparative example 1 | 720 | 621T | Severe lithium precipitation |
| Comparative example 2 | 630 | Satisfy 1000T | Does not separate out lithium |
As can be seen from table 1, by comparing example 1 with comparative example 1, the energy density of the battery cell can be significantly improved by only coating the first coating, but the quick charge performance is greatly reduced, and the current density near the tab is high, which causes serious lithium precipitation and serious capacity attenuation;
by comparing example 1 with comparative example 2, the fast charging capability is greatly improved but the energy density of the cell is severely reduced by only applying the second coating.
The conditions of different coating areas, different conductive agent contents and different negative electrode active material particle sizes are respectively considered through examples 2, 3 and 4, the total energy density is close, and the difference of the quick charging capacity is small. The proportion of the second active material B in the edge area is larger than that of the first active material A, the edge dynamics is improved, the polarization near a tab can be reduced, the potential near a negative electrode tab is improved, the safety problem caused by lithium precipitation near the tab is avoided, and the fast charging cycle life is favorably prolonged.
Example 5 considers the edge thinning of the double-layer coating technology, and the thickness ratio of the bottom layer to the top layer in the edge area is always consistent with that of example 1 in spite of the edge thinning, and the quick charging performance is not greatly different from the energy density.
It should be noted that, various optional implementations described in the embodiments of the present invention may be implemented in combination with each other or implemented separately, and the embodiments of the present invention are not limited thereto.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "left", "right", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation and a specific orientation configuration and operation, and thus, should not be construed as limiting the present invention. Furthermore, "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be directly connected or indirectly connected through an intermediate member, or they may be connected through two or more elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The embodiments described above are described with reference to the drawings, and various other forms and embodiments are possible without departing from the principle of the present invention, and therefore, the present invention should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of components may be exaggerated for clarity. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, components, and/or components, but do not preclude the presence or addition of one or more other features, integers, components, and/or groups thereof. Unless otherwise indicated, a range of values, when stated, includes the upper and lower limits of the range and any subranges therebetween.
While the preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
Claims (10)
1. A negative plate is characterized by comprising a negative current collector, a negative tab, a first coating and a second coating, wherein the first coating is arranged on the surface of the negative current collector, the second coating is arranged on the side, opposite to the negative current collector, of the first coating, the surface of the negative current collector further comprises a blank foil area, and the negative tab is arranged in the blank foil area;
wherein the first coating comprises a first portion proximate to the empty foil region and a second portion distal from the empty foil region, the second coating comprises a third portion proximate to the empty foil region and a fourth portion distal from the empty foil region, the first portion having a thickness less than a thickness of the third portion; the first coating comprises a first active material and the second coating comprises a second active material, the median diameter D50 of the first active material in the first coating being greater than the median diameter D50 of the second active material in the second coating.
2. The negative electrode sheet according to claim 1, wherein the thickness of the second portion is greater than the thickness of the fourth portion, and the compacted density of the second portion is greater than the compacted density of the fourth portion.
3. The negative electrode sheet of claim 1, wherein the first coating further comprises a fifth portion on a side of the second portion facing away from the first portion, and the second coating further comprises a sixth portion on a side of the fourth portion facing away from the third portion, the fifth portion having a thickness less than a thickness of the sixth portion.
4. The negative electrode sheet of claim 1, wherein the width of the first portion is 1/10-1/2 of the width of the first coating, and the width of the third portion is 1/10-1/2 of the width of the second coating.
5. The negative electrode sheet of claim 1, wherein the ratio of the thickness of the first portion to the thickness of the third portion is 1/9-2/3, the ratio of the thickness of the second portion to the thickness of the fourth portion is 3/2-9/1, and the sum of the maximum thickness of the first portion and the maximum thickness of the third portion is a first thickness and the sum of the maximum thickness of the second portion and the maximum thickness of the fourth portion is a second thickness, the first thickness is equal to the second thickness, and the first thickness and the second thickness are both less than 200 μm.
6. The negative electrode sheet of claim 1, wherein the median diameter D50 of the first active material in the first coating layer is 12-18 μm, and the median diameter D50 of the second active material in the second coating layer is 5-8 μm.
7. The negative electrode sheet according to claim 1, wherein the first coating layer and the second coating layer satisfy at least one of the following conditions:
the content of the conductive agent in the first coating is less than that in the second coating;
the porosity of the first coating layer is less than the porosity of the second coating layer;
the coating amount of the first active material is less than the coating amount of the second active material;
the average particle size of the first active material is greater than the average particle size of the second active material;
the first active material has a graphite Orientation Index (OI) value greater than a graphite Orientation Index (OI) value of the second active material;
the impedance of the first coating is greater than the impedance of the second coating.
8. The negative electrode sheet according to any one of claims 1 to 7, wherein the width of the first coating layer is equal to the width of the second coating layer, the width of the first portion is equal to the width of the third portion, and the width of the second portion is equal to the width of the fourth portion.
9. The negative plate of claim 8, wherein the first portion comprises a first thinned region and a first non-thinned region, the first thinned region having a thickness that gradually decreases from a side away from the empty foil region to a side closer to the empty foil region; the third portion comprises a second thinned region and a second non-thinned region, the second thinned region having a thickness that gradually decreases from a side distal to the empty foil region to a side proximal to the empty foil region.
10. A battery comprising the negative electrode sheet according to any one of claims 1 to 9.
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