CN117913218A

CN117913218A - Pole piece and lithium ion battery

Info

Publication number: CN117913218A
Application number: CN202410075970.1A
Authority: CN
Inventors: 赵伟; 杨帆
Original assignee: Zhuhai Cosmx Battery Co Ltd
Current assignee: Zhuhai Cosmx Battery Co Ltd
Priority date: 2024-01-18
Filing date: 2024-01-18
Publication date: 2024-04-19

Abstract

The invention relates to a pole piece and a lithium ion battery containing the pole piece. The pole piece comprises a current collector, wherein the current collector comprises a first section and a second section which are connected along a first direction, active layers are arranged on two side surfaces of the first section of the current collector, an active layer is arranged on one side or two side surfaces of the second section of the current collector, and a safety layer is arranged on at least part of the surface of one side of the active layer; the active layer includes active material particles and the security layer includes inorganic particles. The lithium ion battery can realize excellent thermal safety performance on the premise of keeping better energy density and electrochemical performance.

Description

Pole piece and lithium ion battery

Technical Field

The invention relates to the technical field of batteries, in particular to a pole piece and a lithium ion battery containing the pole piece.

Background

Lithium ion batteries have numerous advantages and are used in large scale applications. In order to reduce the occurrence of instability in the interior of the cell under high voltage electrochemical systems, it is desirable to conduct a furnace temperature (Hotbox) test on the cell.

The battery is characterized in that the graphite has poor thermal stability, the heat and gas production of the whole battery core are larger in the furnace temperature testing process, the battery core is easier to blow out and deform, the edge of the positive plate of the outermost ring is lapped with the negative plate, internal short circuit occurs, and the thermal safety problem of the battery core is caused.

In order to improve the thermal stability of a battery in the prior art, the common practice is to thicken a diaphragm ceramic layer, use a low-melting-point tab, optimize electrolyte and the like, and researches show that the thickening of the diaphragm ceramic layer can cause the loss of energy density of the battery cell, the use of the low-melting-point tab can reduce the packaging reliability of the battery cell, and the optimization of the electrolyte can increase the impedance of the battery cell, so that the electrochemical performance of the battery cell is affected.

Therefore, the prior art is difficult to combine the thermal safety of the battery cell with the energy density and the electrochemical performance.

Disclosure of Invention

The invention aims to provide a pole piece and a lithium ion battery comprising the pole piece. The lithium ion battery can realize excellent thermal safety performance on the premise of keeping better energy density and electrochemical performance.

In order to solve the above problems, a first aspect of the present invention provides a pole piece, including a current collector, the current collector including a first section and a second section connected along a first direction, wherein active layers are disposed on both side surfaces of the first section of the current collector, an active layer is disposed on one or both side surfaces of the second section of the current collector, and a safety layer is disposed on at least a portion of a surface of one side active layer; the active layer includes active material particles and the security layer includes inorganic particles.

The second aspect of the invention provides a lithium ion battery, which comprises a positive plate, a diaphragm and a negative plate, wherein the positive plate is the plate in the first aspect, and/or the negative plate is the plate in the first aspect.

Through the setting, can effectively avoid because of graphite thermal stability is poor, the battery core air-blowing that leads to warp, and then the short circuit that the positive pole of outer lane that leads to and negative pole overlap joint initiate, through the setting of this technical security layer, reduce the short circuit risk, improve the thermal stability of battery, improve the passing rate of furnace temperature test to fine energy density and electrochemical performance have been maintained.

Drawings

Fig. 1 is a schematic structural view of a pole piece according to the present invention, wherein a and b are two examples.

Fig. 2 is a schematic view of a winding core structure of a wound lithium ion battery according to an embodiment of the present invention.

Fig. 3 is a schematic view of a winding core structure of a wound lithium ion battery according to another embodiment of the present invention.

Description of the reference numerals

10 Is a current collector, 11 is a positive current collector, and 12 is a negative current collector;

20 is an active layer, 21 is a positive electrode active layer, and 22 is a negative electrode active layer;

31 is a security layer, 32 is an active layer + a security layer;

40 is a tab, 41 is a positive tab, and 42 is a negative tab;

50 is a diaphragm.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

1-3, The first direction refers to the pole piece length direction; the second direction refers to the thickness direction of the pole piece; the third direction refers to the width direction of the pole piece; the fourth direction refers to the width direction of the winding core; the fifth direction refers to the thickness direction of the winding core.

The first aspect of the present invention provides a pole piece, as shown in fig. 1, comprising a current collector, wherein the current collector comprises a first section and a second section connected along a first direction, wherein active layers 20 are arranged on two side surfaces of the first section of the current collector 10, an active layer 20 is arranged on one side or two side surfaces of the second section of the current collector, and a safety layer 31 is arranged on at least part of the surface of one side active layer 20; the active layer 20 includes active material particles and the security layer 31 includes inorganic particles.

In order to solve the problem that heat safety and energy density and electrochemical performance are difficult to be compatible, the inventor of the invention discovers that by coating a safety coating on one side of an A surface (the A surface in the text refers to the surface facing the winding center of two sides of a current collector of a pole piece) at the tail part of the pole piece, the positive and negative short circuits caused by gas expansion, deformation of the pole piece at the outermost ring, diaphragm contraction and other reasons of the battery cell in the process of testing the furnace temperature can be greatly avoided, and the overall heat stability of the battery cell is further improved.

In one example, the pole piece is a pole piece in a wound battery.

As shown in fig. 1, the pole piece is divided into a first section and a second section connected along a first direction (winding direction in a wound battery); one end of the first section far away from the connecting part (of the first section and the second section) is called a head part and corresponds to the winding center of the winding battery; the second segment corresponds to the winding tail of the wound cell as shown in fig. 2.

The first section is provided with pole pieces in a conventional manner, i.e. active layers are provided on both side surfaces of the first section of the current collector.

The second section is provided with a security layer on one side surface of the current collector. There are two embodiments:

In the first embodiment, one side surface of the current collector is provided with an active layer and a safety layer in sequence, and the other side surface is not provided with an active layer or a safety layer, but is an empty foil, as shown in fig. 1 (a). When wound, the side on which the active layer and the security layer are disposed faces the winding center.

In the second embodiment, the active layers are disposed on both side surfaces of the current collector, and the safety layer is disposed on only one side of the active layer surface, as shown in fig. 1 (b). When winding, the side provided with the security layer faces the winding center.

According to the invention, the safety layer is arranged at the tail part of the pole piece, so that short circuit heat generation caused by contact of the positive electrode and the negative electrode due to expansion, shrinkage, deformation and the like when the battery core heats can be effectively avoided, the thermal stability of the battery is effectively improved, and good energy density and electrochemical performance are maintained. To further enhance the effect, the present invention may further satisfy one or more of the following features.

The active layer includes active material particles, a first binder, and optionally a first conductive agent. As used herein, "optional" means that it may or may not be present.

In one example, the active material particles are present in an amount of 90wt% to 99.5wt% (e.g., 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%9, 6wt%, 97wt%, 98wt%, 99wt%, 99.5wt% and any two end point range), the first binder is present in an amount of 0.5wt% to 5wt% (0.5 wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt% and any two end point range), and the first conductive agent is present in an amount of 0wt% to 5wt% (i.e., no, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt% and any two end point range) based on the total weight of the active layer.

The security layer includes inorganic particles, a second binder, and optionally a second conductive agent.

In one example, the inorganic particles are present in an amount of 40-99.5wt% (e.g., 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, 99.5wt%, and a range of any two endpoints), the second conductive agent is present in an amount of 0-10wt% (i.e., no), 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, and a range of any two endpoints), and the second binder is present in an amount of 0.5-50wt% (0.5 wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, and a range of any two endpoints), based on the total weight of the security layer.

The active material particles are positive electrode active material particles (when the electrode sheet is a positive electrode sheet) or negative electrode active material particles (when the electrode sheet is a negative electrode sheet), and the selection of specific materials may be performed in a manner conventional in the art, and will not be described herein.

In one example, the inorganic particles include one or more of silica, magnesia, and alumina.

In one example, the first and second conductive agents each independently include one or more of conductive carbon black (SP), acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

In one example, the first binder and the second binder each independently comprise an aqueous binder or an oil-based binder. The aqueous binder includes, for example, one or more of polyacrylic acid (PAA), polyacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and Polyacrylonitrile (PAN). The oil-based binder includes, for example, one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE) polyolefin (PP, PE and other copolymers), fluorinated rubber, polyimide (PI), and perfluorosulfonic acid ionomer (Nafion).

In one example, the average particle size of the active material particles is greater than the average particle size of the inorganic particles.

In one example, the ratio of the particle diameter Dv50 of the active material particles to the particle diameter Dv50 of the inorganic particles is (50-600): 1, for example, 50:1, 80:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, 550:1, 600:1, and ranges of any two endpoints. In one example (100-400): 1.

In the invention, the pole piece can be a positive pole piece or a negative pole piece. In more examples, a positive plate.

In one example, the active material particles are positive electrode active material particles (i.e., the electrode sheet is a positive electrode sheet), and the ratio of the particle diameter Dv50 of the positive electrode active material particles to the particle diameter Dv50 of the inorganic particles is (50-500): 1, for example, 50:1, 80:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, and ranges of any two endpoints. Since the anode active material is lithiated (lithium-intercalated anode active material), thermal stability is worse; by limiting the particle size of the inorganic particles in the security layer to the above range, the security layer can be made thinner, thereby reducing energy density loss and achieving security. In one example (100-400): 1.

In one example, the active material particles are anode active material particles (i.e., the electrode sheet is an anode sheet), and the ratio of the particle diameter Dv50 of the anode active material particles to the particle diameter Dv50 of the inorganic particles is (50-600): 1, for example, 50:1, 100:1, 150:1, 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, and ranges of any two endpoints. The particles with the particle size of the safety layer in the ratio range can move along with the needle tip in the needling process, so that the needle tip is wrapped, the contact between the positive electrode current collector (such as aluminum foil) and the negative electrode active substance (such as graphite) is avoided, the short circuit heat generation is prevented, and the safety is improved. In one example (100-400): 1.

Through the particle size matching, the porosity can further meet a certain relation.

In one example, the average porosity A2 of the active layer and the active layer on the side of the safety layer and the safety layer arranged in the second section is less than or equal to the average porosity A1 of the active layer of the first section. The active layer has larger porosity, which is beneficial to increasing the contact area with the opposite pole piece during short circuit, thereby reducing short circuit current and heat generation.

Herein, porosity is measured by a true density tester and is used to indicate how tight the coated particles are. The method adopts an Archimedes principle-gas expansion displacement method, utilizes the Boyle's law (PV=nRT) of inert gas with small molecular diameter under certain conditions, and accurately determines the real volume of a sample by measuring the reduction of the gas capacity of the sample testing cavity caused by the sample testing cavity being placed into the sample, thereby obtaining the real density, the real density=mass/the real volume of the sample. The porosity can be calculated by the bulk density of the coating, the mass percent of each component of the coating and the true density of the coating component, and the calculation formula is as follows: epsilon=1- ρcoat (ω _AM/ρ_AM+ω_CA/ρ_CA+ω_B/ρ_B) where epsilon is the porosity of the pole piece coating, ρ _coat is the bulk density of the coating, ω is the mass percent of the coating components, and ρ is the true density of the coating components. Subscripts AM, CA, B represent the active material, the conductive agent, and the binder, respectively.

In one example, A2: a1 = (0.5-0.9): 1, e.g., 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, and ranges of any two endpoints. In one example A2: a1 = (0.6-0.8): 1

In one example, R2> R1, where R1 is the resistivity of the current collector and one side active layer (i.e., current collector + active layer) of the first segment in the second direction, and R2 is the resistivity of the current collector and one side active layer and safety layer (i.e., current collector + active layer + safety layer) of the second segment in the second direction.

In one example, R2/r1=1.5-9, e.g., 1.5, 2, 3, 4, 5, 6, 7, 8, 9, and ranges of any two endpoints. In one example, R2/r1=2-7.

In one example, r2=300-900 mΩ, for example, 300mΩ, 350mΩ, 400mΩ, 450mΩ, 500mΩ, 550mΩ, 600mΩ, 650mΩ, 700mΩ, 750mΩ, 800mΩ, 850mΩ, 900mΩ, and ranges of any two endpoints. In one example, r2=400-700 mΩ.

In the present invention, the resistivity is measured by a resistivity tester to represent the magnitude of the impedance between the current collector and the coating. The testing method comprises the following steps: and (3) placing the pole piece with the diameter not smaller than 20mm between an upper terminal and a lower terminal of the resistance tester, closing the two terminals of the resistance tester, applying force to the pole piece, and outputting resistance data by the resistance tester.

In one example, R2> R1H 2, wherein H2 is the thickness of the security layer in μm. The arrangement is beneficial to avoiding the deformation of the pole piece caused by the heat generation gas, and the heat release caused by the contact short circuit with the opposite pole piece.

In one example, R2/(r1×h2) =0.5-25, e.g., 0.5, 1, 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, and ranges of any two endpoints. In one example, R2/(r1×h2) =0.8-20.

In one example, h2=0.1-5 μm, e.g., 0.1, 0.2, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, and ranges of any two endpoints. In one example, h2=0.3-3 μm.

In one example, H1/h2=5-150, where H1 is the thickness of the active layer and H2 is the thickness of the security layer, e.g., H1/h2=5, 10, 20, 50, 80, 100, 120, 150. In one example, H1/h2=10-100.

In one example, R2/Δt=7.5-500. The delta T is the temperature rise amplitude, namely the difference between the highest temperature and the target temperature in the furnace temperature test, and the unit is the temperature. For example, R2/Δt=7.5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, 180, 200, 250, 300, 350, 400, 450, 500, and ranges of any two endpoints. In one example, R2/Δt=10-150. The safety layer can increase the impedance of the positive plate, so that the outer-most ring electrode plate (such as the positive plate) can not generate short circuit when being contacted with the opposite-side electrode plate (such as the negative electrode) after being heated and gas-generating deformed in the furnace temperature testing process, thereby avoiding short circuit heat generation, reducing the temperature rise of the battery cell and improving the safety.

In one example, Δt=1 to 40 ℃, e.g. 1℃、2℃、3℃、4℃、5℃、6℃、7℃、8℃、9℃、10℃、11℃、12℃、13℃、14℃、15℃、16℃、17℃、18℃、19℃、20℃、21℃、22℃、23℃、24℃、25℃、26℃、27℃、28℃、29℃、30℃、31℃、32℃、33℃、34℃、35℃、36℃、37℃、38℃、39℃、40℃ and ranges consisting of any two endpoints.

In one example, R2/Δt _130℃ = 20-500; deltaT _130℃ in this relation refers to the difference between the highest temperature in the furnace temperature test and the target temperature of 130 ℃ (national standard test temperature); r2 has the unit of mΩ. For example, R2/Δt _130℃ =20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150, 180, 200, 250, 300, 350, 400, 450, 500, and ranges of any two endpoints. In one example, R2/. DELTA.T _130℃ = 40-100.

In one example, Δt _130℃ =1-25 ℃, e.g., 1 ℃,2 ℃, 3 ℃, 4 ℃,5 ℃,6 ℃,7 ℃,8 ℃,9 ℃,10 ℃,11 ℃,12 ℃,13 ℃, 14 ℃,15 ℃, 16 ℃,17 ℃,18 ℃,19 ℃, 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, and ranges of any two endpoints.

In the present invention, the furnace temperature test is performed by: the cells were charged to the upper usage limit voltage recommended by the battery manufacturer (typically 4.45V and above), then placed in an oven, warmed to the target temperature at a rate of 5±2 ℃/min, then held for 60min, and the test ended. The battery cell is not ignited and does not explode. In the furnace temperature test, the target temperature to be tested is firstly set on a test instrument, then the temperature is started to rise, when the temperature rises to the target temperature, the battery cell does not stop rising but continues rising to the highest temperature (of the battery cell), and then the temperature is slowly reduced to the target temperature (of the furnace); it is generally believed that a smaller difference in the maximum temperature of the cell from the target temperature of the furnace (i.e., the temperature rise amplitude Δt) characterizes a better battery stability, while when the battery stability is poor, it may heat up until a fire explosion, i.e., a failure to pass the test. Thus, in this context, the maximum temperature refers to the maximum temperature reached by the temperature rise of the cell in the furnace temperature test, and the target temperature refers to the steady temperature of the furnace set in the furnace temperature test (i.e., the furnace temperature remains unchanged after the temperature rise to the target temperature).

In one example, the second binder content in the security layer is greater than the first binder content in the active layer. The content of the safety coating binder is increased, so that the adhesion between the diaphragm and the safety coating is improved, and the contact short circuit between the anode and the cathode caused by the contraction of the diaphragm is avoided, so that the stripping force between the safety layer and the diaphragm is also larger than that between the active layer and the diaphragm.

In one example, the swelling ratio of the security layer is greater than the swelling ratio of the active layer. The increase of the swelling rate of the safety coating is beneficial to absorbing electrolyte and avoiding lithium precipitation caused by local barren solution.

In the invention, the swelling ratio test method is to weigh a pole piece with an area of 25mm by 25mm, and record the weight as M1; the pole piece was then immersed in the electrolyte for 48 hours at 60 c, and the immersed weight was measured after removal of the pole piece and drying, and recorded as M2. The calculation method of the swelling ratio comprises the following steps: (M2-M1)/M1 x 100%.

In one example, the security layer is continuously or discontinuously distributed over the second segment.

In one example, the security layer is continuously distributed over the second segment. The continuous distribution may cover the second section for the whole of the security layer or for part of the security layer, but only one coating block is formed.

In one example, the security layer is discontinuously distributed over the second segment, i.e., forming 2 or more patches. The discontinuous distribution may be discontinuous in either the first direction or the third direction.

In one example, the area of the security layer comprises 1-100% of the area of the second segment, such as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99.9%, 100%, and ranges of any two endpoints. In one example, the length of the security layer comprises 1-100% of the length of the second segment, such as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99.9%, 100%, and ranges of any two endpoints. When the safety layer exceeds the second section, the internal impedance of the battery cell is overlarge, the electrical performance of the battery cell is affected, the thickness of the battery cell is obviously increased, and the energy density of the battery cell is further affected.

In one example, the area of the security layer comprises 4-20%, such as 4%, 10%, 15%, 20%, 25%, 30%, 35%, 40% and any two end point ranges of the single-sided area of the active layer on the same side of the security layer. In one example, the length of the security layer is 4-20%, such as 4%, 10%, 15%, 20%, 25%, 30%, 35%, 40% and ranges of any two endpoints, of the length of the single side of the active layer on the same side of the security layer. When the safety layer occupies too large an active layer, the internal resistance of the battery core is easily caused to be large, the electric performance and the energy density are influenced, and the effect of safety improvement cannot be achieved if the safety layer occupies too small amount.

The second aspect of the invention provides a lithium ion battery, which comprises a positive plate, a diaphragm and a negative plate, wherein the positive plate is the plate of the first aspect, and/or the negative plate is the plate of the first aspect.

In one example, the lithium ion battery is a stacked lithium ion battery.

In one example, the lithium ion battery is a laminated secondary lithium ion battery.

In one example, the lithium ion battery is formed by sequentially stacking a positive electrode sheet, a separator and a negative electrode sheet. The number of the positive electrode sheet, the separator, and the negative electrode sheet is not limited, and may include one or more positive electrode sheets, one or more separators, and one or more negative electrode sheets.

In one example, the lithium ion battery is a wound lithium ion battery. The lithium ion battery is formed by sequentially laminating and winding a positive plate, a diaphragm and a negative plate; the pole piece is arranged in such a way that the side, provided with the safety layer, of the first section, which is close to the winding center, faces the winding center.

In one example, the lithium ion battery is a wound secondary lithium ion battery.

Fig. 2 is a schematic diagram of a cell structure of a wound secondary lithium ion battery according to an embodiment of the invention.

Wherein 11 is a positive electrode current collector, 12 is a negative electrode current collector, 21 is a positive electrode active layer, 22 is a negative electrode active layer, 32 is an active layer+a safety layer, 41 is a positive electrode tab, 42 is a negative electrode tab, and 50 is a diaphragm. As can be seen from the figure, the positive electrode sheet, the separator and the negative electrode sheet are sequentially laminated and wound to form the battery cell, and at the wound outermost ring, the positive electrode sheet is provided with a single-sided coated tail section (i.e. the second section) which at least partially wraps the outermost ring of the battery cell. Thus in one example, the length of the second segment is no shorter than the core width L of the lithium ion battery (core width L is the perpendicular distance of the core from one bend to another, as shown in fig. 2). In one example, the length of the second segment is 1-3 times the width L of the winding core of the lithium ion battery. In one example, the length of the second segment is not shorter than one outermost winding cycle (i.e., 2 times the winding core width L) of the lithium ion battery.

In an example, the positive electrode sheet is the sheet according to the first aspect, the positive electrode sheet is divided into a first section (i.e. a double-sided active layer section, 11 is shown in fig. 2) and a second section (i.e. a single-sided active layer+safety layer section, 15 is shown in fig. 2), wherein the head of the first section is used as a winding center, the first section is laminated with the separator and the negative electrode sheet and wound, the winding is performed until the end point of the negative electrode sheet (usually the positive electrode active layer area is shorter than the negative electrode active layer area), the winding is switched to the second section, and the side provided with the safety layer on the second section is continuously wound towards the winding center so that the second section is wound around the battery core to complete at least one winding core width L.

According to one embodiment of the invention, the security layer on the second section is provided with a continuous coating, as described above.

According to one embodiment of the invention, the security layer on the second section is provided as a discontinuous coating. In one example, the area of the security layer comprises at least 1% of the area of the second active layer, such as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99.9% and ranges of any two endpoints. In one example, the length of the security layer comprises 1-100% of the length of the second segment, such as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99.9%, 100%, and ranges of any two endpoints. The length of the security layer is the dimension of the security layer in the first direction as shown in fig. 1. When the safety layer exceeds the second section, the internal impedance of the battery cell is overlarge, the electrical performance of the battery cell is affected, the thickness of the battery cell is obviously increased, and the energy density of the battery cell is further affected.

In an example, a safety layer is disposed at a position corresponding to the tab slot on the second segment, as shown in fig. 3.

One or more tab grooves are usually arranged on the pole piece, and tabs are arranged in the tab grooves. After the winding core is formed, in the fifth direction, the tab slot forms a projection area on each layer of the pole piece, wherein the projection areas comprise two or more projection areas on the outermost ring (namely, the second section) and a plurality of projection areas on the inner ring (except the outermost ring, namely, the first section). The "tab slot corresponding position" refers to a projection area of the tab slot formed on the pole piece in the fifth direction. The area of the safety layer is not smaller than the projection area of the tab slot.

That is, in an example, the tab slot and the tab located in the tab slot are formed on the pole piece, the safety layer is discontinuously distributed on the first segment and/or the second segment, and the projection of the safety layer in the fifth direction covers the projection of the tab slot on the safety layer, as shown in fig. 3.

In an example, the pole piece is a positive pole piece, the tab slot is a positive tab slot, and the tab is a positive tab, that is, the above-mentioned setting is performed on the positive pole piece, and no safety layer is provided on the negative pole piece, because the short-circuit point generally appears on the negative pole piece corresponding to the positive tab, and the safety coating is provided at the projection position of the positive tab, which is favorable for avoiding the short circuit at the position.

In one example, the length of the safety layer is 1-3 times the length of the tab slot, such as 1 time, 1.2 times, 1.5 times, 1.8 times, 2 times, 2.2 times, 2.5 times, 2.8 times, 3 times, and any two end point formed ranges. The length of the safety coating is not too large or too small, so that the performance and the energy density of the battery core are affected, and the safety coating cannot be improved. The length of the security layer is the dimension of the security layer in the first direction shown in fig. 1, i.e. in the fourth direction shown in fig. 2. The length of the tab slot is the dimension of the tab slot along the first direction shown in fig. 1, that is, along the fourth direction shown in fig. 2.

In one example, the lithium ion battery is a monopolar ear battery.

In one example, the trailing end of the second section of the positive electrode sheet does not exceed the trailing end of the negative electrode sheet.

In an example, the stripping force N1 between the safety layer and the diaphragm is greater than or equal to the stripping force N2 between the active layer and the diaphragm, so that the adhesion between the diaphragm and the safety coating is increased, and the contact short circuit between the anode and the cathode caused by the shrinkage of the diaphragm is avoided.

In one example, N1/n2=1.05-10, e.g., 1.5, 2,3, 4, 5, 6, 7, 8, 9, 10, and ranges of any two endpoints. In one example, N1/n2=1.2-8.

In the present invention, the peel force is measured by a tension meter to indicate the magnitude of the adhesion force between the two phases. The testing method comprises the following steps: and (3) adhering the pole piece on the adhesive tape by using the pole piece with the area not smaller than 20mm and 200mm, peeling one ends of the current collector and the active substance, respectively clamping the current collector and the active substance layer at two ends of the tension meter, respectively pulling the current collector and the active substance layer by the tension meter when the test starts, and finally outputting the peeling force value by the tension meter. The numerical value of the adhesive strength between the current collector and the active substance is shown.

In one example, the lithium-ion battery is a fast-charging battery. The fast-charging battery has the meaning and characteristics conventional in the art. The judgment standard of the quick-charging battery can be as follows: assuming that the capacity of the battery is C Ah, charging/discharging the battery by using a current of 1.5C/0.5C, and disassembling after 30 circles of circulation, wherein the surface of the negative electrode plate is free of lithium precipitation, so that the battery is a quick-charging battery.

With the arrangement of the first aspect and the second aspect described above, the present invention can realize:

(1) The safety performance of the lithium ion battery is effectively improved, the passing rate of a furnace temperature test is greatly improved, and particularly when the lithium ion battery is a quick-charging battery, the improvement effect is more obvious;

(2) The lithium ion battery can keep good electrochemical performance;

(3) The pole piece and the lithium ion battery can maintain good energy density.

It should be understood that the term "and/or" is merely an association relationship describing the associated object, and means that three relationships may exist, for example, a and/or B may mean: there are three cases, a alone, a and B together, and B alone, wherein a, B may be singular or plural. In addition, the character "/" herein generally indicates that the associated object is an "or" relationship, but may also indicate an "and/or" relationship, and may be understood by referring to the context.

In the present invention, "a plurality of" means two or more. It should be understood that, in various embodiments of the present invention, the sequence numbers of the foregoing processes do not mean the order of execution, and the order of execution of the processes should be determined by the functions and internal logic thereof, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

The present invention will be described in detail by examples. The described embodiments of the invention are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. Those skilled in the art can, with the benefit of this disclosure, suitably modify the process parameters to achieve this. It is expressly noted that all such similar substitutions and modifications will be apparent to those skilled in the art, and are deemed to be included in the present invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those skilled in the relevant art that variations and modifications can be made in the methods and applications described herein, and in the practice and application of the techniques of this invention, without departing from the spirit or scope of the invention.

Example 1

The pole piece and the wound lithium ion battery were arranged in the manner shown in fig. 1 (a) and 2.

The method specifically comprises the following steps:

(1) Preparing positive electrode active layer slurry: adding a first conductive agent (conductive carbon black and carbon nano tubes in a weight ratio of 1:1 in the embodiment) into a first binder (PVDF in the embodiment) glue solution, uniformly stirring, and then adding positive electrode active material particles (lithium cobaltate in the embodiment) and uniformly stirring to prepare the positive electrode active layer slurry. The mass content of the positive electrode active material particles was 97.6%, the mass content of the first binder was 1.05%, and the mass content of the first conductive agent was 1.35% on a dry weight basis.

(2) Preparing a safety layer slurry: inorganic particles (SiO ₂ in the embodiment), a second conductive agent (conductive carbon black and carbon nano tubes in the weight ratio of 1:1 in the embodiment) and a second binder (PAA in the embodiment) are uniformly stirred in a glue solution to prepare the safe layer slurry. The mass content of the inorganic particles was 90% and the mass content of the second binder was 5% and the mass content of the second conductive agent was 5% on a dry weight basis.

(3) Preparing a positive plate: as shown in fig. 1 (a), a current collector (aluminum foil in this embodiment) is divided into a first section and a second section, the positive electrode active layer slurry is coated on both sides of the first section, the positive electrode active layer slurry (empty foil on the other side) is coated on one side of the second section, and baking is performed; coating the safety layer slurry on the surface of the positive electrode active layer of the second section of the baked pole piece, and then baking; and then rolling to obtain the positive plate.

(4) Preparing a negative plate: uniformly mixing 97.3% of graphite, 0.5% of conductive carbon black, 1.3% of adhesive and 0.9% of dispersing agent, adding a proper amount of deionized water, uniformly dispersing to prepare negative electrode slurry, coating the negative electrode slurry on a carbon-coated copper foil, baking and rolling to obtain the negative electrode plate.

(5) The positive and negative pole pieces are cut, flaked and coiled by a diaphragm to obtain a coiled core, and the coiled core is packaged, baked and injected with liquid (the electrolyte is commercially available conventional electrolyte, wherein lithium salt is LiFP ₆), formed, sealed twice, separated and OCV to obtain the lithium ion battery shown in figure 2.

Other parameters of the positive plate and the lithium ion battery are shown in table 1.

Example 2

The procedure of example 1 was repeated, except that the particle diameter of the positive electrode active material particles, the particle diameter of the inorganic particles, the content of the first binder, the content of the second binder, the thickness of the safety layer, and the like were adjusted in steps (1), (2), and (3), and the relevant parameters were measured or calculated and recorded in table 1.

Example 3

TABLE 1

Example 4 group

This set of embodiments is intended to illustrate the effect of the thickness of the active layer and/or the security layer.

This set of examples is performed with reference to example 1, except that the thickness of the active layer and/or the security layer, respectively, is changed such that H2, H1 or H1/H2 is changed, in particular:

example 4a, h2= 0.4 μm, H1/h2=100;

Example 4b, h23 μm, h1/h2=19;

example 4c, h2= 0.25 μm, H1/h2=142;

Example 4d, h2=5 μm, h1/h2=7.5.

Example 5 group

This set of examples is intended to illustrate the effect of particle size.

This group of examples is carried out with reference to example 1, except that the particle diameter (Dv 50) of the positive electrode active particles in the active layer and/or the particle diameter (Dv 50) of the inorganic particles in the safety layer are changed, respectively, such that the positive electrode active particles Dv 50/inorganic particles Dv50 (abbreviated as ID/IID) are changed; or A2/A1 change. Specifically:

example 5a, id/iid=112;

example 5b, id/iid=389;

example 5c, id/iid=82;

Example 5d, id/iid=524;

example 5e, a2/a1=0.53;

example 5f, a2/a1=0.86.

Example 6 group

This set of examples is intended to illustrate the effect of resistivity.

This set of examples is performed with reference to example 1, except that by varying one or more of the parameters R1, R2, H2, Δt, the change in R2/R1, R2/(R1H 2) or R2/Δt, in particular:

Example 6a, r2/r1=2.8, r2=406 mΩ;

Example 6b, r2/r1=7, r2=769mΩ;

Example 6c, r2/r1=1.6, r2=321 mΩ;

Example 6d, r2/r1=8.8, r2=856 mΩ;

Example 6e, R2/(r1×h2) =10.7, h2=0.3 μm;

example 6f, R2/(r1×h2) =2.3, h2=3 μm;

example 6g, R2/(r1×h2) =0.5, h2=3.2 μm;

Example 6H, R2/(r1×h2) =23.8, h2=0.29 μm;

example 6i, r2/Δt=39.6;

Example 6j, r2/Δt=102;

Example 6k, r2/Δt=25.8;

example 6l, r2/. DELTA.T=398.7.

Example 7 group

This set of examples is intended to illustrate the effect of peel force.

This set of examples is carried out with reference to example 1, except that by varying the binder content in the active layer and/or the security layer, N1/N2 is varied, in particular:

example 7a, n1/n2=1.6;

example 7b, n1/n2=9.8.

Example 8 group

This set of embodiments is used to verify the specific choice of binder in the security layer.

This set of examples is carried out with reference to example 1, except that the specific composition of the binder in the security layer is changed (the content is kept unchanged), in particular:

example 8a, the security layer binder was changed to PVDF;

example 8b, the security layer binder was changed to SBR;

Example 8c, the security layer binder was changed to PI;

example 8d, the security layer binder was changed to PTFE.

Example 9

With reference to example 1, except that the second segment was not entirely continuous with the safety layer, but the safety layer was provided only on two projected areas of the positive electrode tab on the second segment as shown in fig. 3, and the length of the safety layer was 2 times the tab slot length.

Comparative example 1

Reference is made to example 1 except that the second segment is not coated with a security layer.

Test case

The resulting pole piece or lithium ion battery was tested in the following manner, respectively.

(1) Furnace temperature test: full-charging the battery cell to the upper limit voltage of 4.5V, then placing the battery cell in an oven, heating to the set target temperature (130 ℃, 132 ℃, 135 ℃ or 140 ℃) at the temperature rise rate of 5+/-2 ℃/min, then keeping for 60min, and ending the test; the electric core is not ignited and is not exploded; recording the maximum temperature reached during the temperature rise (typically, rising to the maximum temperature and then falling back to the target temperature), and calculating the temperature rise amplitude Δt=maximum temperature-target temperature; if the temperature of the battery cells continuously rises until the battery cells are on fire or explode, the test is failed.

(2) Electrochemical performance test

The battery was placed in a constant temperature room at 45C, the battery was discharged to a lower limit voltage (3.0V) of the battery at 1C, the battery was charged to an upper limit voltage (4.5V) of the battery at 1.5C, and then the battery was discharged to the lower limit voltage at 1C, and the above-mentioned one charge-discharge operation was one test period, and thus the discharge capacity retention rate of the battery was calculated 800 times. When the initial discharge capacity is Q1 and the discharge capacity after 800 cycles is Q2, the discharge capacity retention rate= (Q2/Q1) is 100%.

(3) Energy density testing

Constant-current charging the lithium ion battery to 4.5V at a multiplying power of 0.2C, and then constant-voltage charging to 0.025C to finish full charge of the lithium ion battery; then constant-current discharge is carried out by using multiplying power of 0.2C until the voltage of the lithium ion battery is reduced to 3.0V, the total capacity discharged in the discharge process is recorded as C, and the actual volume V of the lithium ion battery is calculated;

ED = discharge capacity C voltage plateau/cell volume V;

the 4.5V system plateau voltage is typically 3.9V;

ED loss = ED difference/comparative example 1 cell ED 100%.

The results obtained are shown in Table 2.

TABLE 2

/>

As can be seen from table 2, the lithium ion battery of the present invention can achieve excellent thermal safety performance while maintaining good energy density and electrochemical performance.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. The pole piece is characterized by comprising a current collector, wherein the current collector comprises a first section and a second section which are connected along a first direction, active layers are arranged on two side surfaces of the first section of the current collector, an active layer is arranged on one side or two side surfaces of the second section of the current collector, and a safety layer is arranged on at least part of the surface of one side of the active layer; the active layer includes active material particles and the security layer includes inorganic particles.

2. The pole piece of claim 1, wherein the ratio of the particle diameter Dv50 of the active material particles to the particle diameter Dv50 of the inorganic particles is (50-600): 1, preferably (100-400): 1.

3. The pole piece according to claim 1 or 2, wherein the average porosity A2 of the active layer and the safety layer on the side of the active layer and the safety layer arranged in the second section is smaller than or equal to the average porosity A1 of the active layer of the first section;

preferably, A2: a1 = (0.5-0.9): 1, more preferably (0.6-0.8): 1.

4. The pole piece of claim 1, wherein the inorganic particles comprise one or more of silica, magnesia, and alumina; and/or the number of the groups of groups,

The active layer further comprises a first binder, the security layer further comprises a second binder, the first binder and the second binder each independently comprise an aqueous binder comprising one or more of polyacrylic acid, polyacrylate, styrene-butadiene rubber, carboxymethyl cellulose, and polyacrylonitrile, or an oil binder comprising one or more of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyolefin, fluorinated rubber, polyimide, and perfluorosulfonic acid ionomer; and/or the number of the groups of groups,

The active layer further comprises a first conductive agent, the security layer further comprises a second conductive agent, and the first conductive agent and the second conductive agent each independently comprise one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fibers, carbon nanotubes, metal powder and carbon fibers.

5. The pole piece of claim 1, wherein the pole piece satisfies: r2> R1, wherein R1 is the resistivity of the current collector and the active layer on one side of the first section in the second direction, and R2 is the resistivity of the current collector and the active layer on one side of the second section and the safe layer in the second direction;

Preferably, R2/r1=1.5-9, more preferably 2-7;

preferably, r2=300-900 mΩ.

6. The pole piece of claim 1, wherein the pole piece satisfies: r2> R1 is H2, wherein H2 is the thickness of the security layer, and the unit is mu m;

Preferably, R2/(r1×h2) =0.5-25, more preferably 0.8-20; and/or h2=0.1-5 μm.

7. The pole piece of claim 1, wherein the pole piece satisfies: h1/h2=5-150, where H1 is the thickness of the active layer and H2 is the thickness of the security layer;

Preferably, H1/h2=10-100.

8. The pole piece of claim 1, wherein the pole piece satisfies:

r2/Δt=7.5-500, the Δt being the difference between the maximum temperature in the furnace temperature test and the target temperature in degrees celsius and R2 in mΩ; preferably R2/Δt=10-150; preferably Δt=1-40 ℃; and/or the number of the groups of groups,

R2/. DELTA.T _130℃ = 20-500, preferably R2/. DELTA.T _130℃ = 40-100, preferably DeltaT _130℃ = 1-25 ℃; the DeltaT _130℃ is the difference between the highest temperature in the furnace temperature test and the target temperature of 130 ℃, in degrees Celsius.

9. The pole piece of claim 4, wherein the second binder content in the security layer is greater than the first binder content in the active layer; and/or the number of the groups of groups,

The swelling ratio of the security layer is greater than the swelling ratio of the active layer.

10. The pole piece of claim 1, wherein the security layer is continuously or discontinuously distributed over the second segment; and/or the number of the groups of groups,

The length of the safety layer accounts for 1-100% of the length of the second section; and/or the number of the groups of groups,

The length of the safety layer accounts for 4-20% of the single-sided length of the active layer on the same side of the safety layer.

11. A lithium ion battery, characterized in that the lithium ion battery is formed by sequentially laminating a positive electrode plate, a diaphragm and a negative electrode plate, wherein the positive electrode plate is the electrode plate according to any one of claims 1-10, and/or the negative electrode plate is the electrode plate according to any one of claims 1-10.

12. The lithium ion battery according to claim 11, wherein the lithium ion battery is formed by sequentially laminating and winding a positive electrode sheet, a separator and a negative electrode sheet; the pole piece is arranged in such a way that the side, provided with the safety layer, of the first section, which is close to the winding center, faces the winding center.

13. The lithium ion battery of claim 11 or 12, wherein a peel force N1 between the safety layer and the separator is greater than or equal to a peel force N2 between the active layer and the separator;

preferably, N1/n2=1.05-10.

14. The lithium ion battery of claim 12, wherein the length of the second segment is no shorter than a winding core width L of the lithium ion battery; preferably, the length of the second section is 1-3 times of the width L of the winding core of the lithium ion battery;

And/or the length of the safety layer accounts for 1-100% of the length of the second section.

15. The lithium ion battery of claim 12, wherein tab grooves and tabs located in the tab grooves are formed on the pole pieces, and a projection of the safety layer in a fifth direction covers a projection of the tab grooves on the safety layer.

16. The lithium ion battery of claim 15, wherein the length of the safety layer is 1-3 times the length of the tab slot.