CN113097428A - Negative plate, battery and preparation method of negative plate - Google Patents
Negative plate, battery and preparation method of negative plate Download PDFInfo
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- CN113097428A CN113097428A CN202110338909.8A CN202110338909A CN113097428A CN 113097428 A CN113097428 A CN 113097428A CN 202110338909 A CN202110338909 A CN 202110338909A CN 113097428 A CN113097428 A CN 113097428A
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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
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- 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
- H01M4/139—Processes of manufacture
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Abstract
The invention provides a negative plate, a battery and a preparation method of the negative plate, wherein the negative plate comprises a negative current collector, a negative pole lug, a first coating and a second coating, the edge of the second coating is closer to the negative pole lug than the edge of the first coating, and the median diameter D50 of an active material contained in the second coating is smaller than the median diameter D50 of the active material contained in the first coating, so that a negative paste closer to the negative pole lug is an active material with a smaller particle size, better ion diffusion dynamic performance can be presented, and the risk of lithium precipitation in a charging process is reduced.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a negative plate, a battery and a preparation method of the negative plate.
Background
With the development of lithium ion secondary batteries, consumers have increasingly high demands on charging speed, endurance time, and safety performance. Because of the fluid mechanics characteristic and the processing characteristics of the negative pole slurry, the thickness of the edge part of the coating paste is smaller than that of the middle part, and because the current density of the position of the negative pole piece close to the negative pole lug is relatively larger, when the negative pole piece is prepared into an electric core, the head part of the electric core has insufficient negative pole allowance, and lithium is separated out in the charging process, so that the performance of the battery is deteriorated.
Disclosure of Invention
The embodiment of the invention aims to provide a negative plate, a battery and a preparation method of the negative plate, and solves the problem that lithium is separated out in the charging process due to insufficient negative allowance at the head of a battery cell 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 includes a first portion and a second portion, the first portion is disposed on the first coating, the second portion is disposed on the negative electrode current collector, the surface of the negative electrode current collector further includes a hollow foil region, and the negative electrode tab is disposed in the hollow foil region;
the distance between the edge of the second coating layer close to the negative pole lug and the negative pole lug is a first distance, the distance between the edge of the first coating layer close to the negative pole lug and the negative pole lug is a second distance, and the first distance is smaller than the second distance;
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 hollow foil region is located on any one long side of the surface of the negative electrode current collector.
Optionally, the second coating completely covers the first coating, the first coating having a width less than a width of the second coating.
Optionally, the first coating layer comprises a first thinned region and a first non-thinned region, and the thickness of a portion of the first thinned region adjacent to the empty foil region is less than the thickness of a portion adjacent to the first non-thinned region;
the second coating comprises a second thinning area and a second non-thinning area, and the thickness of the part, close to the empty foil area, of the second thinning area is smaller than that of the part, close to the second non-thinning area.
Optionally, an orthographic projection of the first thinning area on the negative electrode current collector is not coincident with an orthographic projection of the second thinning area on the negative electrode current collector.
Optionally, the maximum thickness of the second portion is greater than or equal to the sum of the thickness of the first coating and the thickness of the first portion.
Optionally, the median diameter D50 of the first active material in the first coating layer is 5 μm to 19 μm, and the median diameter D50 of the second active material in the second coating layer is 3 μm to 15 μm.
Optionally, the first coating and the second coating 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.
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.
In a third aspect, an embodiment of the present invention provides a method for preparing a negative electrode sheet, including:
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;
coating a first coating slurry on the coating area to form a first coating, wherein the first coating slurry is formed by mixing a first conductive agent, a first binder and a first active material;
coating a second coating slurry on the first coating to form a second coating, wherein the second coating slurry is formed by mixing a second conductive agent, a second binder and a second active material;
the distance between the edge of the second coating layer close to the negative pole lug and the negative pole lug is a first distance, the distance between the edge of the first coating layer close to the negative pole lug and the negative pole lug is a second distance, and the first distance is smaller than the second distance; the median diameter D50 of the first active material in the first coating layer is greater than the median diameter D50 of the second active material in the second coating layer.
One of the above technical solutions has the following advantages or beneficial effects:
the negative plate comprises a negative current collector, a negative tab, a first coating and a second coating, wherein the edge of the second coating is closer to the negative tab than the edge of the first coating, and the median diameter D50 of an active material contained in the second coating is smaller than the median diameter D50 of the active material contained in the first coating. Therefore, the negative electrode paste closer to the negative electrode tab is an active material with a smaller particle size, so that lithium ions can move in the electrode material more conveniently, better ion diffusion dynamic performance can be presented, and the risk of lithium precipitation in the charging process is reduced. In addition, through double-layer coating, the energy density of the negative plate can be improved.
Drawings
Fig. 1 is a schematic cross-sectional view of a negative electrode sheet before being cut according to an embodiment of the present invention;
fig. 2 is a schematic cross-sectional view of a negative electrode sheet before being cut according to an embodiment of the present invention;
fig. 3 is a schematic cross-sectional view of a negative electrode sheet according to an embodiment of the present invention;
fig. 4 is a schematic view of a negative electrode sheet before slitting, not shown, of a second coating according to an embodiment of the present invention;
fig. 5 is a schematic view of a negative electrode sheet before slitting, not shown, of the first coating according to an 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.
The negative plate comprises a negative current collector 10, a negative tab (not shown in the figure), a first coating 20 and a second coating 30, wherein the first coating 20 is arranged on the surface of the negative current collector 10, the second coating 30 comprises a first part and a second part, the first part is arranged on the first coating 20, the second part is arranged on the negative current collector 10, the surface of the negative current collector 10 further comprises a hollow foil area, and the negative tab is arranged in the hollow foil area;
the distance between the edge of the second coating 30 close to the negative electrode tab and the negative electrode tab is a first distance, the distance between the edge of the first coating 20 close to the negative electrode tab and the negative electrode tab is a second distance, and the first distance is smaller than the second distance;
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.
Due to the fluid mechanics characteristics and the processing characteristics of the negative electrode slurry, the thickness of the edge part of the negative electrode paste coating is smaller than that of the middle part, and the current density of the part, close to the negative electrode lug, of the negative electrode piece is relatively larger, so that when the negative electrode piece is prepared into an electric core, the head part of the electric core, namely the part, close to the negative electrode lug, of the electric core is subjected to lithium separation in the charging process, and the performance of the battery is deteriorated.
In the embodiment of the invention, as shown in fig. 1, two layers of coating pastes are coated on the surface of the negative current collector 10, the negative electrode tab is arranged in a hollow foil area on the negative current collector 10, and then the negative electrode sheet shown in fig. 3 is formed by slitting. The negative electrode tab includes a first coating layer 20 and a second coating layer 30, and the second coating layer 30 includes a first portion covering the first coating layer 20 and a second portion covering the negative electrode collector 10.
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. Therefore, in the embodiment of the present invention, the edge of the portion of the second coating 30 covering the negative electrode current collector 10 is closer to the negative electrode tab than the edge of the first coating 20. In this way, the use of a second, more kinetically active material in the region close to the negative tab, i.e. where the active material thickness is relatively thin but the current density is relatively high, reduces the risk of lithium deposition during charging. 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, the median diameter D50 of the first active material in the first coating layer 20 is 5 μm to 19 μm, and the median diameter D50 of the second active material in the second coating layer 30 is 3 μm to 15 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 is located on any one long side of the surface of the negative electrode current 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 regions may be a region a and a region B in fig. 2. After slitting, the empty foil area of part of the negative electrode sheet is positioned in the area A, and the empty foil area of part of the negative electrode sheet is positioned in the area B. In practical application, for a multi-tab negative plate, the empty foil regions 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. It is understood that the hollow foil region located on any one long side of the surface of the negative electrode current collector 10 is not limited to be applied to the multi-tab battery, and may be determined according to practical situations, and the embodiment of the present invention is not limited thereto.
In the first case, the number of the empty foil regions before slitting is 1, and the empty foil regions are located in the region a shown in fig. 2. In this case, the edge of the second coating layer 30 on the side close to the a region is closer to the anode tab than the edge of the first coating layer 20 on the side close to the a region.
In the second case, before slitting, the number of said empty foil zones is 1, located in the area B as shown in fig. 2. In this case, the edge of the second coating layer 30 on the side close to the B region is closer to the anode tab than the edge of the first coating layer 20 on the side close to the B region.
In the third case, the number of the empty foil areas before slitting is 2, which are located in area a and area B as shown in fig. 3. In the present case, as shown in fig. 2, 4 and 5, the second coating layer 30 completely covers the first coating layer 20, and the width L1 of the first coating layer 20 is smaller than the width L2 of the second coating layer 30. In a particular implementation, the line of symmetry of the first coating 20 in the length direction coincides with the line of symmetry of the second coating 30 in the length direction before slitting. Therefore, the integral uniformity of the negative electrode coating can be improved, and the integral energy density balance of the negative electrode plate is ensured.
Optionally, the first coating 20 comprises a first thinned region and a first non-thinned region, the thickness of the portion of the first thinned region adjacent to the empty foil region being less than the thickness of the portion adjacent to the first non-thinned region;
the second coating 30 comprises a second thinned region and a second non-thinned region, the thickness of the portion of the second thinned region adjacent to the free foil region being less than the thickness of the portion adjacent to the second non-thinned region.
In the present embodiment, as shown in fig. 3, the thicknesses of the first coating layer 20 and the second coating layer 30 at the edges are gradually reduced. 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.
In this embodiment, in one implementation form, an orthographic projection of the first thinning-out area on the negative electrode current collector and an orthographic projection of the second thinning-out area on the negative electrode current collector are not coincident. This implementation form can guarantee that the non-thinned area of second coating 30 completely covers first coating 20, can further reduce the risk of educing lithium in the charging process.
Optionally, the maximum thickness of the second portion is greater than or equal to the sum of the thickness of the first coating 20 and the thickness of the first portion.
In the present embodiment, as shown in fig. 3, the first coating layer 20 has a thickness d1, and the second coating layer 30 includes a first portion covering the first coating layer 20, i.e., the left portion as shown in fig. 3, the first portion having a thickness d 2; the second coating layer 30 also includes the second portion that is not covered with the first coating layer 20 but directly covered on the negative electrode collector 10, i.e., the right portion as shown in fig. 3. The thickness d3 of the second part is greater than or equal to the sum of the thickness d1 of the first coating 20 and the thickness d2 of the first part, so that the paste content of the part, close to the negative pole tab, of the second coating 30 is increased, the risk of lithium precipitation of the negative pole piece during charging is further reduced, and the energy density of the negative pole piece is ensured.
In summary, in the negative electrode sheet provided 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 coating pastes on the coating region of the negative electrode current collector 10, and the edge of the second coating layer 30 is closer to the negative electrode tab. 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. In this way, the use of a second, more kinetically active material in the region close to the negative tab, i.e. where the active material thickness is relatively thin but the current density is relatively high, reduces the risk of lithium deposition during charging. 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;
the distance between the edge of the second coating layer close to the negative pole lug and the negative pole lug is a first distance, the distance between the edge of the first coating layer close to the negative pole lug and the negative pole lug is a second distance, and the first distance is smaller than the second distance; the median diameter D50 of the first active material in the first coating layer is greater than the median diameter D50 of the second active material in the second coating layer.
In the embodiment of the invention, the first coating and the second coating are respectively formed by coating two layers of coating pastes on the coating area of the negative electrode current collector, and the edge of the second coating is closer to the negative electrode tab. Since the median diameter D50 of the active material contained in the second coating layer is smaller than the median diameter D50 of the active material contained in the first coating layer, the active material with a smaller particle size facilitates the movement of lithium ions inside the electrode material, and thus can exhibit better ion diffusion kinetics. In this way, the use of a second, more kinetically active material in the region close to the negative tab, i.e. where the active material thickness is relatively thin but the current density is relatively high, reduces the risk of lithium deposition during charging. 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 layer may be stronger than that of the first coating layer 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 actual situations, 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 3 specific examples and 3 comparative examples in 1 of the examples of the present invention:
example 1
Step one, preparing first coating slurry by using a first active material: the first coating slurry is prepared according to the mixture ratio of 96.8% of the first active material, 1.2% of the first conductive agent and 2% of the first binder based on a certain mixing process, the viscosity of the first coating slurry is 2000-5000mPa.s, and the solid content of the first coating slurry is 40% -50%.
Step two, preparing a second coating slurry by using a second active material: the second coating slurry is prepared according to the mixture ratio of 96.8% of the second active material, 1.2% of the second conductive agent and 2% of the second binder based on a certain mixing process, the viscosity of the second coating slurry is 2000-5000mPa.s, and the solid content is 40-50%.
And step three, after the first coating slurry prepared in the step one passes through a screen, coating the first coating slurry and a coating area of the negative current collector to form a first coating, and then, after the second coating slurry prepared in the step two passes through a screen, coating the second coating slurry on the first coating to form a second coating, so that the coating width of the first coating slurry is L1, the coating thickness is d1, the coating width of the second coating slurry is L2, and the coating thickness is d 2. Drying, rolling and slitting to obtain the negative plate.
Step four, preparing anode coating slurry by using a third active material: the anode coating slurry is prepared based on a certain mixing process according to the mixture ratio of 96% of the third active material, 2.5% of the third conductive agent and 1.5% of the third binder, the viscosity of the anode coating slurry is 2000-7000mPa.s, and the solid content is 70-80%. 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.
And step five, assembling the obtained positive and negative pole pieces into a winding core by winding, packaging the winding core by using an aluminum plastic film after the short circuit test is qualified, baking the winding core in an oven to remove water until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the winding core for 24 to 48 hours, and completing primary charging by using a hot pressing formation process to obtain the activated battery cell.
In this embodiment, the median diameter D50 of the first active material is 15.5, the median diameter D50 of the second active material is 5.6, the coating width L1 is 2L to 10mm, L is the width of the negative electrode sheet, the coating thickness is D1, the coating width L2 is 2L, the thickness is D2, the edge thickness is D3, and D3 is equal to D1+ D2.
Comparative example 1
Step one, preparing first coating slurry by using a first active material: the first coating slurry is prepared according to the mixture ratio of 96.8% of the first active material, 1.2% of the first conductive agent and 2% of the first binder based on a certain mixing process, the viscosity of the first coating slurry is 2000-5000mPa.s, and the solid content of the first coating slurry is 40% -50%.
And step two, after the first coating slurry prepared in the step one passes through a screen, coating the first coating slurry and a coating area of the negative current collector to form a first coating, ensuring that the coating width of the first coating slurry is L1 and the coating thickness is d1, and drying, rolling and slitting to obtain the negative plate.
Step three, preparing anode coating slurry by using a third active material: the anode coating slurry is prepared based on a certain mixing process according to the mixture ratio of 96% of the third active material, 2.5% of the third conductive agent and 1.5% of the third binder, the viscosity of the anode coating slurry is 2000-7000mPa.s, and the solid content is 70-80%. 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.
And step four, winding and assembling the obtained positive and negative pole pieces into a winding core, packaging the winding core by using an aluminum plastic film after the short circuit test is qualified, baking the winding core in an oven to remove water until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the winding core for 24-48 hours, and completing primary charging by using a hot pressing formation process to obtain the activated battery cell.
In this comparative example, the median diameter D50 of the first active material was 7.3, the coating width L1 was 2L, L was the width of the negative electrode sheet, and the coating thickness was D1.
Comparative example 2
Step one, preparing a second coating slurry by using a second active material: the second coating slurry is prepared according to the mixture ratio of 96.8% of the second active material, 1.2% of the second conductive agent and 2% of the second binder based on a certain mixing process, the viscosity of the second coating slurry is 2000-5000mPa.s, and the solid content is 40-50%.
And step two, coating the second coating slurry prepared in the step one on a coating area of the negative current collector to form a second coating after passing through a screen, ensuring that the coating width of the second coating slurry is L2 and the coating thickness is d2, and drying, rolling and slitting to obtain the negative plate.
Step three, preparing anode coating slurry by using a third active material: the anode coating slurry is prepared based on a certain mixing process according to the mixture ratio of 96% of the third active material, 2.5% of the third conductive agent and 1.5% of the third binder, the viscosity of the anode coating slurry is 2000-7000mPa.s, and the solid content is 70-80%. 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.
And step four, winding and assembling the obtained positive and negative pole pieces into a winding core, packaging the winding core by using an aluminum plastic film after the short circuit test is qualified, baking the winding core in an oven to remove water until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the winding core for 24-48 hours, and completing primary charging by using a hot pressing formation process to obtain the activated battery cell.
In this comparative example, the median diameter D50 of the second active material was 5.6, the coating width L2 was 2L, L was the width of the negative electrode sheet, and the coating thickness was D2.
Comparative example 3
Step one, preparing first coating slurry by using a first active material: the first coating slurry is prepared according to the mixture ratio of 96.8% of the first active material, 1.2% of the first conductive agent and 2% of the first binder based on a certain mixing process, the viscosity of the first coating slurry is 2000-5000mPa.s, and the solid content of the first coating slurry is 40% -50%.
Step two, preparing a second coating slurry by using a second active material: the second coating slurry is prepared according to the mixture ratio of 96.8% of the second active material, 1.2% of the second conductive agent and 2% of the second binder based on a certain mixing process, the viscosity of the second coating slurry is 2000-5000mPa.s, and the solid content is 40-50%.
And step three, after the first coating slurry prepared in the step one passes through a screen, coating the first coating slurry and a coating area of the negative current collector to form a first coating, and then, after the second coating slurry prepared in the step two passes through a screen, coating the second coating slurry on the first coating to form a second coating, so that the coating width of the first coating slurry is L1, the coating thickness is d1, the coating width of the second coating slurry is L2, and the coating thickness is d 2. Drying, rolling and slitting to obtain the negative plate.
Step four, preparing anode coating slurry by using a third active material: the anode coating slurry is prepared based on a certain mixing process according to the mixture ratio of 96% of the third active material, 2.5% of the third conductive agent and 1.5% of the third binder, the viscosity of the anode coating slurry is 2000-7000mPa.s, and the solid content is 70-80%. 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.
And step five, assembling the obtained positive and negative pole pieces into a winding core by winding, packaging the winding core by using an aluminum plastic film after the short circuit test is qualified, baking the winding core in an oven to remove water until the moisture reaches the moisture standard required by liquid injection, injecting electrolyte, aging the winding core for 24 to 48 hours, and completing primary charging by using a hot pressing formation process to obtain the activated battery cell.
In this comparative example, the median diameter D50 of the first active material was 15.5, the median diameter D50 of the second active material was 5.6, the coating width L1 was 2L, L was the width of the negative electrode sheet, the coating thickness was D1, the coating width L2 was 2L, i.e., L2 ═ L1, the thickness was D2, the edge thickness was D3, and D3 was equal to D1+ D2.
The cells prepared in the above examples and comparative examples were fully charged at 0.5C, and the energy E of 0.5C discharge was compared with the cell volume V to obtain the energy density. The battery cell prepared above was charged at 4C rate, and discharged at 1C rate for a life test of 700 cycles. The prepared cell is fully charged at 5.5C, discharged at 0.5C, and dissected after 15 times of charging and discharging to check the lithium separation condition, and the table 1 shows the lithium separation condition of the above examples and comparative examples in the charging process. It should be noted that, L in table 1 is the width L ± 1mm of the positive electrode plate, and the ED value is the ratio of the discharge energy to the volume of the battery cell.
TABLE 1 lithium deposition for different examples and comparative examples
As can be seen from table 1, example 1 of the present invention can solve the problem of lithium precipitation at the cell head due to insufficient negative electrode paste at the edge of the negative electrode sheet, compared to comparative example 1; compared with the comparative example 2, the embodiment 1 of the invention can improve the energy density of the battery cell on the premise of ensuring no lithium precipitation; compared with the comparative example 3, the lithium-ion battery can solve the problem of lithium precipitation at the head of the battery cell caused by insufficient negative pole paste at the edge of the negative pole piece on the premise of keeping proper energy density in the embodiment 1 of the invention.
In summary, in the preparation method of the negative electrode sheet provided by the embodiment of the present invention, the first coating layer and the second coating layer may be formed respectively by coating two layers of coating pastes on the coating region of the negative electrode current collector, and the edge of the second coating layer is closer to the negative electrode tab. Since the median diameter D50 of the active material contained in the second coating layer is smaller than the median diameter D50 of the active material contained in the first coating layer, the region of 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. In this way, even if the second coating layer has a relatively small thickness and a large current density near the anode tab, the risk of lithium deposition during charging can be reduced due to its relatively strong dynamic properties. In addition, through double-layer coating, the energy density of the negative plate can be improved.
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 comprises a first part and a second part, the first part is arranged on the first coating, the second part is arranged on the negative current collector, the surface of the negative current collector further comprises a hollow foil area, and the negative tab is arranged in the hollow foil area;
the distance between the edge of the second coating layer close to the negative pole lug and the negative pole lug is a first distance, the distance between the edge of the first coating layer close to the negative pole lug and the negative pole lug is a second distance, and the first distance is smaller than the second distance;
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 empty foil region is located on any one long side of the surface of the negative electrode current collector.
3. The negative electrode sheet according to claim 1, wherein the second coating layer completely covers the first coating layer, and the width of the first coating layer is smaller than the width of the second coating layer.
4. The negative electrode sheet according to any one of claims 1 to 3, wherein the first coating layer comprises a first thinned region and a first non-thinned region, and the thickness of a portion of the first thinned region adjacent to the empty foil region is less than the thickness of a portion adjacent to the first non-thinned region;
the second coating comprises a second thinning area and a second non-thinning area, and the thickness of the part, close to the empty foil area, of the second thinning area is smaller than that of the part, close to the second non-thinning area.
5. The negative electrode sheet of claim 4, wherein an orthographic projection of the first thinning area on the negative electrode current collector is not coincident with an orthographic projection of the second thinning area on the negative electrode current collector.
6. Negative electrode sheet according to any one of claims 1 to 3, characterized in that the maximum thickness of the second portion is greater than or equal to the sum of the thickness of the first coating and the thickness of the first portion.
7. The negative electrode sheet of claim 1, wherein the median diameter D50 of the first active material in the first coating layer is 5-19 μm, and the median diameter D50 of the second active material in the second coating layer is 3-15 μm.
8. 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.
9. A battery comprising the negative electrode sheet according to any one of claims 1 to 8.
10. A preparation method of a negative plate is characterized by comprising the following steps:
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;
coating a first coating slurry on the coating area to form a first coating, wherein the first coating slurry is formed by mixing a first conductive agent, a first binder and a first active material;
coating a second coating slurry on the first coating to form a second coating, wherein the second coating slurry is formed by mixing a second conductive agent, a second binder and a second active material;
the distance between the edge of the second coating layer close to the negative pole lug and the negative pole lug is a first distance, the distance between the edge of the first coating layer close to the negative pole lug and the negative pole lug is a second distance, and the first distance is smaller than the second distance; the median diameter D50 of the first active material is greater than the median diameter D50 of the second active material.
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