Lithium ion battery

Abstract

The invention provides a lithium ion battery which comprises a battery shell, an electrolyte and a roll core, and the roll core comprises a positive plate, a diaphragm and a negative plate which are sequentially stacked; the positive plate comprises a positive current collector and positive active material layers formed on two sides of the positive current collector; the negative plate comprises a negative current collector and negative active material layers formed on two sides of the negative current collector; the positive plate and the negative plate meet the relational expression: # imgabs0 #; the tensile strength of the positive / negative current collector, the compaction density of the positive / negative active material layer and the expansion rate of the negative plate in the state of 25-35% of charge are set, so that when the formula is met, the four corners of the aluminum-plastic film are not easy to damage, and meanwhile, the improvement of the energy density of the product and the reliability of long-term use can be taken into consideration.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a lithium-ion battery. Background Art

[0002] In order to pursue higher energy density, technical elements such as thinner current collectors, higher compaction density, and anode materials with higher specific capacity are continuously introduced into lithium-ion batteries. Thinner current collectors (such as copper foil and aluminum foil) will lead to a reduction in the mechanical strength of the current collector, and higher material compaction density will further negatively affect the mechanical tensile strength of the current collector. Anode materials with higher specific capacity often exhibit higher material expansion characteristics (such as SiOx, silicon-carbon materials, etc.). When pursuing energy density, these factors will cause the width of the electrode sheet to extend during the cycling process, resulting in interference between the electrode sheet and the four corners of the aluminum-plastic film, and easily causing excessive stress at the corners of the battery, leading to battery damage, leakage, and inability to be used. Therefore, how to overcome the above-mentioned technical problems and defects has become a key issue to be solved. Summary of the Invention

[0003] Aiming at the problem that in high-energy density batteries, the width of the electrode sheet extends during the cycling process and is prone to interference with the four corners of the aluminum-plastic film, resulting in excessive stress at the corners of the battery, leading to battery damage, leakage, and inability to be used, the present invention provides a lithium-ion battery.

[0004] The technical solutions adopted by the present invention to solve the above technical problems are as follows: On the one hand, the present invention provides a lithium-ion battery, including a battery housing, an electrolyte, and a wound core. The material of the battery housing is aluminum-plastic film. The wound core is placed inside the battery housing, and the electrolyte is injected into the battery housing. The wound core includes a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence. The positive electrode sheet, the separator, and the negative electrode sheet are wound to form the wound core. The two sides of the negative electrode sheet in the width direction protrude from the two sides of the positive electrode sheet in the width direction correspondingly. The positive electrode sheet includes a positive current collector and positive active material layers formed on both sides of the positive current collector. The negative electrode sheet includes a negative current collector and negative active material layers formed on both sides of the negative current collector. The positive electrode sheet and the negative electrode sheet satisfy the following relationship: ; Wherein, PA-gap mm is the difference between the width of the negative electrode sheet and the length of the punch for punching the aluminum-plastic film in the length direction of the battery; TC MPa is the tensile strength of the positive current collector; Ta MPa is the tensile strength of the negative current collector; Pc g / cm 3is the tap density of the positive electrode active material layer; Pa g / cm 3 is the tap density of the negative electrode active material layer; as% is the swelling rate of the negative electrode sheet in the state of 25%-35% state of charge; Optionally, the value range of the PA-gap is 1.0 mm - 1.6 mm.

[0005] Optionally, as% is the swelling rate of the negative electrode sheet in the state of 30% state of charge, and 12% ≤ as ≤ 25%.

[0006] Optionally, the T C has a value range of 180 MPa ≤ T C ≤ 350 MPa; and / or, the value range of the Pc is 3.2 g / cm 3 ≤ Pc ≤ 4.35 g / cm 3 .

[0007] Optionally, the T a has a value range of 300 MPa ≤ T a ≤ 650 MPa; and / or, the value range of the Pa is 1.6 g / cm 3 ≤ Pa ≤ 1.85 g / cm 3 .

[0008] Optionally, the material of the positive electrode current collector is aluminum foil, the aluminum foil includes Al element, which is 100% based on the mass of the aluminum foil, and the mass percentage of the Al element in the aluminum foil is 99% - 100%.

[0009] Optionally, the aluminum foil further includes one or more elements of Fe, Si, Cu, Zn, Mn, Mg, N, Ti and Gr; based on the mass of the aluminum foil being 100%, the total mass percentage of the Fe element and the Si element in the aluminum foil is 0% - 1%; the mass percentage of the Cu element in the aluminum foil is 0% - 0.3%; the mass percentages of the Zn element, the Mn element, the Mg element, the N element, the Ti element and the Gr element in the aluminum foil are 0% - 0.1% respectively.

[0010] Optionally, the positive electrode active material layer includes a positive electrode active material, a first conductive agent, and a first binder. Based on the total mass of the positive electrode active material layer being 100%, the percentage of the positive electrode active material in the mass of the positive electrode active material layer is 94.5% - 98.7%; the percentage of the first conductive agent in the mass of the positive electrode active material layer is 0.3 - 2.5%; the percentage of the first binder in the mass of the positive electrode active material layer is 0.9 - 2.5%.

[0011] Optionally, the positive electrode active material includes one or more of lithium cobaltate, ternary LiNi x Co y Mn z O 2 materials (where x + y + z = 1, x ≥ y); and / or, the first conductive agent includes one or more of conductive carbon black, conductive carbon nanotubes; and / or, the first binder includes one or more of PVDF, PTFE.

[0012] Optionally, when the positive electrode active material is lithium cobaltate material, the tap density of the positive electrode active material layer is 4.1 - 4.35 g / cm 3 ; when the positive electrode active material simultaneously uses lithium cobaltate material and ternary material, the tap density of the positive electrode active material layer is 3.6 - 4.1 g / cm 3 ; when the positive electrode active material is ternary material, the tap density of the positive electrode active material layer is 3.2 - 3.6 g / cm 3 .

[0013] Optionally, the material of the negative electrode current collector is copper foil, the copper foil includes Cu element, based on the mass of the copper foil being 100%, the percentage of the Cu element in the mass of the copper foil is 99.5% - 100%.

[0014] Optionally, the copper foil further includes one or more elements of Fe, Cr, Zn; based on the mass of the copper foil being 100%, the mass fraction of the Fe element in the copper foil is 0 ppm - 50 ppm; the mass fraction of the Cr element in the copper foil is 0 ppm - 300 ppm; the mass fraction of the Zn element in the copper foil is 0 ppm - 200 ppm.

[0015] Optionally, the negative electrode active material layer comprises a negative electrode active material, a second conductive agent, and a second binder. Based on the total mass of the negative electrode active material layer being 100%, the percentage of the negative electrode active material in the mass of the negative electrode active material layer is 95-98%; the percentage of the second conductive agent in the mass of the negative electrode active material layer is 0.5-1.5%; the percentage of the second binder in the mass of the negative electrode active material layer is 1.5-3.5%.

[0016] Optionally, the negative electrode active material comprises one or more of graphite material, silicon oxide material, and silicon carbon material; and / or, the second conductive agent comprises one or more of conductive carbon black, conductive carbon nanotubes, graphene, and conductive carbon fibers; and / or, the second binder comprises one or more of CMC, SBR, and PAA.

[0017] Optionally, when the negative electrode active material is graphite material, at a state of charge of 25%-35%, the expansion rate of the negative electrode sheet is 12% - 18%; when the negative electrode active material is silicon-containing material, at a state of charge of 25%-35%, the expansion rate of the negative electrode sheet is 18% - 25%.

[0018] According to the lithium-ion battery provided by the present invention, when the value of PA-gap is smaller, the energy density of the product is larger; however, the PA-gap value is closely related to the tensile strength of the positive current collector, the tensile strength of the negative current collector, the tap density of the positive active material layer, the tap density of the negative active material layer, and the swelling rate of the negative electrode sheet. Therefore, it is necessary to precisely control each parameter to ensure that while improving the energy density, the material stability and safety are also taken into account. By experimentally verifying the influence of different PA-gap values on the performance and optimizing the design scheme, it is aimed to achieve the best comprehensive performance at the minimum PA-gap value to meet the needs of the high-end market; when the tensile strength of the foil is weak, during the charge and discharge process of the battery, the swelling of the material will cause the foil to deform and extend in the width direction, resulting in a continuous decrease in the PA-gap value during the battery cycle, and the extrusion degree at the four corners of the electrode sheet and the outer packaging aluminum-plastic film will increase, which is likely to cause the battery to be damaged. When the tensile strength of the foil is large, the rigidity of the foil has a good ability to inhibit the deformation of the electrode sheet, but too high strength will increase the manufacturing cost (such as burrs are likely to be generated during the slitting process, and the life of the slitting knife decreases, etc.); when the tap density of the active material is high, a higher energy density can be obtained, but too high a tap density will increase the internal stress in the electrode sheet, resulting in an increase in material swelling during the cycle, further exacerbating the foil deformation and the reduction of the distance between the positive and negative electrode sheets and the corner area and the corners of the aluminum-plastic film, affecting the battery stability. Therefore, while ensuring the energy density, it is necessary to reasonably control the tap density, balance the internal stress and material swelling, and ensure the long-term cycle performance of the battery. If the selected active material has a large swelling (such as silicon oxide, silicon carbon, etc.), the excessive swelling rate of the active material itself during the lithium intercalation process will also cause the deformation of the electrode sheet and the reduction of the distance between the positive and negative electrode sheets and the corner area and the corners of the aluminum-plastic film, further exacerbating the internal stress of the battery and affecting the overall structural stability. Therefore, the combination among the tensile strength of the foil, the tap density of the active material, and the self-swelling characteristics of the active material is closely related and has an obvious synergistic effect: when a high-swelling negative electrode + high tap density design is adopted, if a foil with high mechanical strength is actually matched, a small PA-gap value can be used; if a foil with low strength is matched, a large PA-gap value needs to be used to achieve the best balance between energy density and stability, and ensure that the battery still maintains excellent performance under high cycle life. Detailed implementation manners

[0019] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clear and understandable, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] Unless otherwise specified, the test methods used in the following examples are conventional methods; the materials, reagents, etc. used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0021] In one embodiment, the present invention provides a lithium-ion battery on the one hand, including a battery case, an electrolyte, and a wound core. The material of the battery case is an aluminum-plastic film. The wound core is placed inside the battery case, and the electrolyte is injected into the battery case. The wound core includes a positive electrode sheet, a separator, and a negative electrode sheet that are stacked in sequence. The positive electrode sheet, the separator, and the negative electrode sheet are wound to form the wound core. On both sides in the width direction of the negative electrode sheet, they correspondingly protrude beyond both sides in the width direction of the positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and positive electrode active material layers formed on both sides of the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and negative electrode active material layers formed on both sides of the negative electrode current collector. The positive electrode sheet and the negative electrode sheet satisfy the relational expression: ; Wherein, PA-gap mm is the difference between the width of the negative electrode sheet and the length of the punch for punching the aluminum-plastic film in the battery length direction. TC MPa is the tensile strength of the positive electrode current collector. Ta MPa is the tensile strength of the negative electrode current collector. Pc g / cm 3 is the tap density of the positive electrode active material layer. Pa g / cm 3 is the tap density of the negative electrode active material layer. as% is the swelling rate of the negative electrode sheet in the state of 25%-35% state of charge.

[0022] In this application, is the recommended value of PA-gap, and PA-gap is the design value; When the value of PA-gap is smaller, the energy density of the product is larger. If the PA-gap value is too small, the swelling of the wound core after cycling will cause the four corners of the electrode sheet and the outer packaging aluminum-plastic film to squeeze each other, which is likely to cause damage to the aluminum-plastic film or the electrode sheet of the battery, resulting in battery failure. Therefore, for a battery with a large degree of wound core swelling, the PA-gap needs to be designed larger, and for a battery with a small degree of wound core swelling, the PA-gap can be designed smaller. The swelling of the wound core is closely related to the tensile strength of the positive current collector, the tensile strength of the negative current collector, the compaction density of the positive active material layer, the compaction density of the negative active material layer, and the swelling rate of the negative electrode sheet. Therefore, it is necessary to precisely control each parameter to ensure that while improving the energy density, the material stability and safety are taken into account, the reliability of the battery is guaranteed, and the service life is extended. Through experimental verification of the influence of different PA-gap values on the performance, the design scheme is optimized to strive for the best comprehensive performance at the minimum PA-gap value to meet the needs of the high-end market.

[0023] When the tensile strength of the foil is weak, during the charge and discharge process of the battery, the expansion of the material will cause the foil to deform and extend in the width direction, which will further cause the distance between the positive and negative electrode sheets and the corner areas and corners of the aluminum-plastic film to continuously decrease during the battery cycling process. The overhang area of the swollen negative electrode sheet can deform in the battery case to release stress. If the swollen positive electrode sheet abuts against the battery case through the negative electrode sheet, mutual extrusion will occur between the four corners of the electrode sheet and the outer packaging aluminum-plastic film. As the positive and negative electrode sheets further expand, the degree of mutual extrusion increases, causing battery damage (if the aluminum-plastic film has high strength, the positive and negative electrode sheets will be damaged; if the positive and negative electrode sheets have high strength, the aluminum-plastic film will be damaged). When the tensile strength of the foil is large, the rigidity of the foil has a good ability to inhibit the deformation of the electrode sheet, but too high strength will increase the manufacturing cost (such as burrs are easily generated in the slitting process, and the life of the slitting knife decreases, etc.); When the compaction density of the active material is relatively high, a relatively high energy density can be obtained, but too high a compaction density will increase the internal stress of the electrode sheet, resulting in an increase in material expansion during cycling, which will further exacerbate the foil deformation and the reduction of the distance between the positive and negative electrode sheets and the corner areas and corners of the aluminum-plastic film, affecting the battery stability. Therefore, while ensuring the energy density, it is necessary to reasonably control the compaction density, balance the internal stress and material expansion, and ensure the long-term cycling performance of the battery.

[0024] If the selected active material has a large expansion (such as silicon oxide, silicon carbon, etc.), the excessive expansion rate of the active material itself during the lithium insertion process will also cause electrode sheet deformation and the reduction of the distance between the positive and negative electrode sheets and the corner areas and corners of the aluminum-plastic film, further exacerbating the internal stress of the battery and affecting the overall structural stability.

[0025] Therefore, the combination among the tensile strength of the foil, the compaction density of the active material, and the self-expansion characteristics of the active material is closely related and has an obvious synergistic effect: when a high-expansion anode and a high-compaction design are adopted, if a foil with high mechanical strength is actually used, a small PA-gap value can be used; if a foil with low strength is used, a large PA-gap value is required to achieve the best balance between energy density and stability, ensuring that the battery still maintains excellent performance under high cycle life.

[0026] When the difference between the PA-gap value and is between 0.06 and 0.6, the four corners of the aluminum-plastic film are not prone to corner breakage problems, and at the same time, the improvement of the product energy density and the reliability of long-term use can be taken into account.

[0027] In one embodiment, the value range of the PA-gap is 1.0 mm - 1.6 mm.

[0028] Specifically, the value range of the PA-gap is any one value or a range value composed of any two point values among 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, or 1.6 mm; in a preferred embodiment, the value range of the PA-gap is 1.2 mm - 1.4 mm.

[0029] When the value range of the PA-gap is 1.0 mm - 1.6 mm, the battery has a high energy density; when the value range of the PA-gap is greater than 1.6 mm, the energy density of the battery decreases.

[0030] In one embodiment, the value range of TC is 180 MPa ≤ TC ≤ 350 MPa.

[0031] Specifically, the value range of TC is any one value or a range value composed of any two point values among 180 MPa, 190 MPa, 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa, 310 MPa, 320 MPa, 330 MPa, 340 MPa, or 350 MPa; in a preferred embodiment, the value range of TC is 250 MPa ≤ TC ≤ 300 MPa.

[0032] When the value range of TC is 180 MPa ≤ TC ≤ 350 MPa, the tensile strength of the positive current collector is relatively large. At this time, the stronger the ability to inhibit the widening of the positive electrode sheet width, so a smaller PA-gap value can be set; when the value range of TC is less than 180 MPa, it will cause the inability to effectively inhibit the widening of the positive electrode sheet width, resulting in the PA-gap value gradually decreasing with the progress of cycling and interfering with the four corners of the aluminum-plastic film, causing corner breakage or liquid leakage. To avoid this situation, it is necessary to ensure that the initial PA-gap design value remains at a relatively large value, but this will affect the battery energy density; when the value range of TC is greater than 350 MPa, the too high strength of the aluminum foil will lead to an increase in the processing difficulty of the process, thus having an adverse impact on production efficiency. Due to the relatively high mechanical strength, the aluminum foil is prone to cracks, fractures or uneven deformation during slitting, cutting and winding, etc., which increases the scrap rate during the manufacturing process. In addition, the harder aluminum foil will cause more serious wear to the production equipment, resulting in a shorter service life of components such as molds and cutting tools, and correspondingly increasing the maintenance cost.

[0033] In one embodiment, the value range of Pc is 3.2 g / cm 3 ≤ Pc ≤ 4.35 g / cm 3 .

[0034] Specifically, the value range of PC is 3.2 g / cm 3 , 3.25 g / cm 3 , 3.3 g / cm 3 , 3.35 g / cm 3 , 3.4 g / cm 3 , 3.45 g / cm 3 , 3.5 g / cm 3 , 3.55 g / cm 3 , 3.6 g / cm 3 , 3.65 g / cm 3 , 3.7 g / cm 3 , 3.75 g / cm 3 , 3.8 g / cm 3 , 3.85 g / cm 3 , 3.9 g / cm 3 , 3.95 g / cm 3 , 4 g / cm 3 , 4.05 g / cm 3 , 4.1 g / cm 3 , 4.15 g / cm 3 , 4.2 g / cm 3 , 4.25 g / cm 3 , 4.3 g / cm 3 or 4.35 g / cm 3Any point value or the range value formed by any two point values therein; in a preferred embodiment, the value range of PC is 3.7 g / cm 3 ≤Pc≤4 g / cm 3 .

[0035] When the value range of PC is 3.2 g / cm 3 ≤Pc≤4.35 g / cm 3 , the mechanical properties of the positive current collector are less damaged, and because the compaction density is low, the mechanical stress generated during the rolling process is small, and the material is not easy to expand during the cycling process, and the battery also has a high energy density; when the value range of PC is less than 3.2 g / cm 3 , the mechanical properties of the positive current collector are less damaged and the material is not easy to expand, but it will result in a low energy density of the battery; when the value range of PC is greater than 4.35 g / cm 3 , the mechanical properties of the positive current collector are more damaged and the material is prone to accumulate a large mechanical stress during rolling. During the subsequent charge and discharge cycles, it is easy to generate a large expansion, which in turn affects the cycle life and safety of the battery. Therefore, reasonably controlling the value range of PC is a key factor in optimizing battery performance. By precisely regulating the PC value, not only can the energy density of the battery be improved, but also mechanical damage and material expansion can be effectively reduced, ensuring the stability and safety of the battery during long-term use, thereby extending its service life.

[0036] In one embodiment, the value range of Ta is 300 MPa ≤ Ta ≤ 650 MPa.

[0037] Specifically, the value range of Ta is any point value or the range value formed by any two point values among 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa or 650 MPa; in a preferred embodiment, the value range of Ta is 400 MPa ≤ Ta ≤ 550 MPa.

[0038] When the value range of Ta is 300 MPa ≤ Ta ≤ 650 MPa, the tensile strength of the negative current collector is relatively large. At this time, the stronger the ability to inhibit the widening of the negative electrode sheet width, so that a smaller PA-gap value can be set; when the value range of Ta is less than 300 MPa, it will cause the inability to effectively inhibit the widening of the negative electrode sheet width, resulting in a large initial PA-gap value, which in turn affects the battery energy density; when the value range of Ta is greater than 650 MPa, similar to the positive aluminum foil, it will lead to an increase in the processing difficulty of the process. The too high strength of the copper foil is prone to produce slitting burrs during slitting and causes greater wear on the slitting knife. As the strength increases, its flexibility will decrease, and the electrode sheet is prone to become brittle, and may break during the later stage of cycling due to weak flexibility.

[0039] In one embodiment, the value range of Pa is 1.6 g / cm 3 ≤ Pa ≤ 1.85 g / cm 3 .

[0040] Specifically, the value range of Pa is 1.6 g / cm 3 , 1.61 g / cm 3 , 1.62 g / cm 3 , 1.63 g / cm 3 , 1.64 g / cm 3 , 1.65 g / cm 3 , 1.66 g / cm 3 , 1.67 g / cm 3 , 1.68 g / cm 3 , 1.69 g / cm 3 , 1.7 g / cm 3 , 1.71 g / cm 3 , 1.72 g / cm 3 , 1.73 g / cm 3 , 1.74 g / cm 3 , 1.75 g / cm 3 , 1.76 g / cm 3 , 1.77 g / cm 3 , 1.78 g / cm 3 , 1.79 g / cm 3 , 1.8 g / cm 3 , 1.81 g / cm 3 , 1.82 g / cm 3 , 1.83 g / cm 3 , 1.84 g / cm 3 or 1.85 g / cm 3 and any range value composed of any one point value or any two point values among them; in a preferred embodiment, the value range of Pa is 1.7 g / cm 3 ≤ Pa ≤ 1.83 g / cm 3 .

[0041] When the value range of Pa is 1.6 g / cm 3 ≤ Pa ≤ 1.85 g / cm 3 , the mechanical property damage to the negative electrode current collector is small and the material is not easy to expand, and the battery also has a high energy density; when the value range of Pa is less than 1.6 g / cm 3 , the mechanical property damage to the negative electrode current collector is small and the material is not easy to expand, but it will cause the battery energy density to be low; when the value range of Pa is greater than 1.85 g / cm 3When the value is large, it causes greater mechanical property damage to the negative current collector and the material is prone to expansion. When the PA-gap value is small, it will cause corner breakage problems at the four corners of the aluminum-plastic film. Moreover, a high compaction density will cause greater mechanical stress concentration to occur more easily in the single-sided fabric area of the negative electrode sheet during rolling, resulting in the head of the electrode sheet being prone to folding during winding, which in turn affects the interface contact of the electrode sheet and ultimately affects the reliability and safety of the battery.

[0042] In one embodiment, the value range of as is 12% ≤ as ≤ 25%.

[0043] Specifically, the value range of as is any one value or the range value composed of any two point values among 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%; in a preferred embodiment, the value range of as is 15% ≤ as ≤ 20%.

[0044] When the value range of as is 12% ≤ as ≤ 25%, this technical solution can effectively balance the deformation problem during the battery cycle, improve the lithium deposition phenomenon in the arc area of the battery, and increase the energy density of the battery; if the as value is lower than 12%, it may lead to too low porosity of the electrode sheet, hindering the penetration of the electrolyte into the micropores of the electrode sheet, thereby weakening the charge-discharge kinetic performance of the electrode sheet and affecting the stability of the battery during long-term use; if the as value exceeds 25%, it may cause excessive expansion of the battery, resulting in a decrease in energy density, and the excessive volume expansion may cause the battery to deform, compress the electrolyte in the arc area, resulting in insufficient electrolyte in this area during the later stage of the cycle, and then leading to a rapid decrease in battery capacity.

[0045] In one embodiment, the material of the positive current collector is aluminum foil, the aluminum foil contains Al element, which is 100% based on the mass of the aluminum foil, and the mass percentage of the Al element in the aluminum foil is 99% - 100%.

[0046] Specifically, the mass percentage of the Al element in the aluminum foil is any one value or the range value composed of any two point values among 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or 100%; in a preferred embodiment, the mass percentage of the Al element in the aluminum foil is 99.2% - 100%.

[0047] In one embodiment, the aluminum foil further comprises one or more elements of Fe, Si, Cu, Zn, Mn, Mg, N, Ti, and Gr; based on 100% of the mass of the aluminum foil, the total mass percentage of Fe element and Si element in the aluminum foil is 0% - 1%, that is, when the aluminum foil contains Fe element or Si element, the mass percentage of Fe element or Si element in the aluminum foil is 0% - 1%, and when the aluminum foil contains Fe element and Si element, the total mass percentage of Fe element and Si element in the aluminum foil is 0% - 1%; the mass percentage of Cu element in the aluminum foil is 0% - 0.3%; the mass percentages of Zn element, Mn element, Mg element, N element, Ti element, and Gr element in the aluminum foil are 0% - 0.1% respectively.

[0048] Specifically, the total mass percentage of Fe element and Si element in the aluminum foil is any one value or a range value composed of any two values among 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%; in a preferred embodiment, the total mass percentage of Fe element and Si element in the aluminum foil is 0.2% - 0.5%.

[0049] Specifically, the mass percentage of Cu element in the aluminum foil is any one value or a range value composed of any two values among 0.1%, 0.2%, or 0.3%; in a preferred embodiment, the mass percentage of Cu element in the aluminum foil is 0.1% - 0.2%.

[0050] Specifically, the mass percentage of any one of the elements of Zn element, Mn element, Mg element, N element, Ti element, and Gr element in the aluminum foil is any one value or a range value composed of any two values among 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1%; in a preferred embodiment, the mass percentages of Zn element, Mn element, Mg element, N element, Ti element, and Gr element in the aluminum foil are 0.02% - 0.05% respectively.

[0051] Introducing elements such as Fe, Si, and Cu into the aluminum foil is beneficial to improving the tensile strength of the aluminum foil. The higher the tensile strength of the aluminum foil, the stronger the ability of the aluminum foil to inhibit the widening of the width of the positive electrode sheet; thus, a smaller PA - gap value can be set.

[0052] In one embodiment, the positive electrode active material layer comprises a positive electrode active material, a first conductive agent, and a first binder. Based on 100% of the total mass of the positive electrode active material layer, the mass percentage of the positive electrode active material in the positive electrode active material layer is 94.5% - 98.7%; the mass percentage of the first conductive agent in the positive electrode active material layer is 0.3 - 2.5%; the mass percentage of the first binder in the positive electrode active material layer is 0.9 - 2.5%.

[0053] Specifically, the percentage of the positive electrode active material in the mass of the positive electrode active material layer is any one value among 94.5%, 94.7%, 94.9%, 95.1%, 95.3%, 95.5%, 95.7%, 95.9%, 96.1%, 96.3%, 96.5%, 96.7%, 96.9%, 97.1%, 97.3%, 97.5%, 97.7%, 97.9%, 98.1%, 98.3%, 98.5% or 98.7%, or a range value composed of any two of these values; in a preferred embodiment, the percentage of the positive electrode active material in the mass of the positive electrode active material layer is 95% - 98%.

[0054] Specifically, the percentage of the first conductive agent in the mass of the positive electrode active material layer is any one value among 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3% or 2.5%, or a range value composed of any two of these values; in a preferred embodiment, the percentage of the first conductive agent in the mass of the positive electrode active material layer is 1% - 2%.

[0055] Specifically, the percentage of the first binder in the mass of the positive electrode active material layer is any one value among 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3% or 2.5%, or a range value composed of any two of these values; in a preferred embodiment, the percentage of the first binder in the mass of the positive electrode active material layer is 1.5% - 2%.

[0056] When the mass ratios of various materials in the positive electrode active material layer are within the above ranges, the positive electrode sheet can have a relatively high lithium deintercalation and intercalation capacity, and the battery can have a relatively high capacity.

[0057] In one embodiment, the positive electrode active material includes one or more of lithium cobalt oxide, ternary LiNixCoyMnzO2 materials (where x + y + z = 1, x ≥ y); and / or, The first conductive agent includes one or more of conductive carbon black, conductive carbon nanotubes; and / or, The first binder includes one or more of PVDF, PTFE.

[0058] In some embodiments, the positive electrode active material further includes, but is not limited to, one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium manganese oxide (LMO), lithium nickel oxide (LNO), lithium-rich manganese-based (LMR), lithium nickel manganese oxide (LNMO), lithium vanadium phosphate (Li 3 V 2 (PO 4 ) 3 ,LiVOPO 4 ).

[0059] In some embodiments, the first conductive agent further includes, but is not limited to, one or more of graphite, superconducting carbon, carbon black, graphene, carbon nanofibers, metal powder, metal fibers, and polyphenylene derivatives.

[0060] In some embodiments, the first binder further includes, but is not limited to, one or more of polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0061] The positive electrode sheet can be prepared by conventional methods in the art. For example, the positive electrode active material layer is usually formed by coating a positive electrode paste made of a positive electrode active material, a first conductive agent, a first binder, and any other components on a positive electrode current collector, and then drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0062] In one embodiment, when the positive electrode active material is a lithium cobaltate material, the tap density of the positive electrode active material layer is 4.1~4.35 g / cm 3 ; when the positive electrode active material simultaneously uses a lithium cobaltate material and a ternary material, the tap density of the positive electrode active material layer is 3.6~4.1 g / cm 3 ; when the positive electrode active material is a ternary material, the tap density of the positive electrode active material layer is 3.2~3.6 g / cm 3 .

[0063] When the positive electrode active material uses a lithium cobaltate material as the positive electrode material and the tap density of the positive electrode active material layer is 4.1~4.35 g / cm 3 , the mechanical properties of the positive electrode current collector are less damaged, and because the tap density is low, the mechanical stress generated during the rolling process is small, the material is not easily expanded during the cycling process, and the battery also has a high energy density; when the tap density of the positive electrode active material layer is less than 4.1 g / cm 3 , the mechanical properties of the positive electrode current collector are less damaged and the material is not easily expanded, but this will result in a lower energy density of the battery; when the tap density of the positive electrode active material layer is greater than 4.35 g / cm 3 , the mechanical properties of the positive electrode current collector are more damaged and the material is prone to accumulate a large mechanical stress during rolling. During the subsequent charge and discharge cycling process, it is easy to generate a large expansion, which will affect the cycle life and safety of the battery.

[0064] When the positive electrode active material simultaneously uses a lithium cobaltate material and a ternary material and the tap density of the positive electrode active material layer is 3.6~4.1 g / cm 3When the value is within a certain range, the mechanical properties of the positive current collector are less damaged. And because the compaction density is relatively low, the mechanical stress generated during the rolling process is small. During the cycling process, the material is not prone to expansion, and the battery also has a relatively high energy density. When the compaction density of the positive active material layer is less than 3.6 g / cm 3 When the value is within a certain range, the mechanical properties of the positive current collector are less damaged and the material is not prone to expansion, but this will result in a relatively low energy density of the battery. When the compaction density of the positive active material layer is greater than 4.1 g / cm 3 When the value is within a certain range, the mechanical properties of the positive current collector are more damaged, and during rolling, the material is prone to accumulate a large amount of mechanical stress. During the subsequent charge-discharge cycling process, it is prone to generate a large amount of expansion, which in turn affects the cycle life and safety of the battery.

[0065] When the ternary material is simultaneously selected as the positive active material, and the compaction density of the positive active material layer is 3.2 - 3.6 g / cm 3 When the value is within a certain range, the mechanical properties of the positive current collector are less damaged. And because the compaction density is relatively low, the mechanical stress generated during the rolling process is small. During the cycling process, the material is not prone to expansion, and the battery also has a relatively high energy density. When the compaction density of the positive active material layer is less than 3.2 g / cm 3 When the value is within a certain range, the mechanical properties of the positive current collector are less damaged and the material is not prone to expansion, but this will result in a relatively low energy density of the battery. When the compaction density of the positive active material layer is greater than 3.6 g / cm 3 When the value is within a certain range, the mechanical properties of the positive current collector are more damaged, and during rolling, the material is prone to accumulate a large amount of mechanical stress. During the subsequent charge-discharge cycling process, it is prone to generate a large amount of expansion, which in turn affects the cycle life and safety of the battery.

[0066] In one embodiment, the material of the negative current collector is copper foil, which includes Cu element, accounting for 100% by the mass of the copper foil, and the mass percentage of Cu element in the copper foil is 99.5% - 100%.

[0067] Specifically, the mass percentage of Cu element in the copper foil is any one value or the range value composed of any two values among 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or 100%; in a preferred embodiment, the mass percentage of Cu element in the copper foil is 99.7% - 100%.

[0068] In one embodiment, the copper foil further includes one or more elements of Fe, Cr, Zn; accounting for 100% by the mass of the copper foil, the mass fraction of Fe element in the copper foil is 0 ppm - 50 ppm; the mass fraction of Cr element in the copper foil is 0 ppm - 300 ppm; the mass fraction of Zn element in the copper foil is 0 ppm - 200 ppm.

[0069] Specifically, the mass fraction of Fe element in the copper foil is any one value or a range value composed of any two point values among 0 ppm, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm or 50 ppm; in a preferred embodiment, the mass fraction of Fe element in the copper foil is 5 ppm to 20 ppm.

[0070] Specifically, the mass fraction of Cr element in the copper foil is any one value or a range value composed of any two point values among 0 ppm, 30 ppm, 60 ppm, 90 ppm, 120 ppm, 150 ppm, 180 ppm, 210 ppm, 240 ppm, 270 ppm or 300 ppm; in a preferred embodiment, the mass fraction of Cr element in the copper foil is 100 ppm to 200 ppm.

[0071] Specifically, the mass fraction of Zn element in the copper foil is any one value or a range value composed of any two point values among 0 ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm, 160 ppm, 180 ppm or 200 ppm; in a preferred embodiment, the mass fraction of Zn element in the copper foil is 50 ppm to 100 ppm.

[0072] Among them, the addition of Fe, Cr, and Zn elements can enhance the hardness and strength of the copper foil, improve its wear resistance and tensile strength, and improve the ductility and toughness of the copper foil, making it easy to process and form the copper foil.

[0073] In one embodiment, the negative electrode active material layer includes a negative electrode active material, a second conductive agent, and a second binder. Taking the total mass of the negative electrode active material layer as 100%, the percentage of the negative electrode active material in the mass of the negative electrode active material layer is 95 - 98%; the percentage of the second conductive agent in the mass of the negative electrode active material layer is 0.5 - 1.5%; the percentage of the second binder in the mass of the negative electrode active material layer is 1.5 - 3.5%.

[0074] Specifically, the percentage of the negative electrode active material in the mass of the negative electrode active material layer is any one value or a range value composed of any two point values among 95%, 95.2%, 95.4%, 95.6%, 95.8%, 96%, 96.2%, 96.4%, 96.6%, 96.8%, 97%, 97.2%, 97.4%, 97.6%, 97.8% or 98%; in a preferred embodiment, the percentage of the negative electrode active material in the mass of the negative electrode active material layer is 96% to 97%.

[0075] Specifically, the percentage of the second conductive agent in the mass of the negative electrode active material layer is any value among 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5% or a range value composed of any two of these values; in a preferred embodiment, the percentage of the second conductive agent in the mass of the negative electrode active material layer is 0.8% - 1.2%.

[0076] Specifically, the percentage of the second binder in the mass of the negative electrode active material layer is any value among 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3% or 3.5% or a range value composed of any two of these values; in a preferred embodiment, the percentage of the second binder in the mass of the negative electrode active material layer is 2% - 3%.

[0077] When the mass ratios of various materials in the negative electrode active material layer are within the above ranges, the battery can have excellent long - cycle performance at both room temperature and high - temperature environments.

[0078] In one embodiment, the negative electrode active material includes one or more of graphite materials, silicon - oxygen materials, and silicon - carbon materials; and / or, the second conductive agent includes one or more of conductive carbon black, conductive carbon nanotubes, graphene, and conductive carbon fibers; and / or, the second binder includes one or more of CMC, SBR, and PAA.

[0079] In one embodiment, the negative electrode active material further includes, but is not limited to, one or more of silicon negative electrode materials, tin negative electrode materials, tin oxide negative electrode materials, tin alloy negative electrode materials (such as Sn - Fe, Sn - Co, Sn - Cu, etc.), lithium metal negative electrode materials, lithium alloy negative electrode materials (such as Li - Ag, Li - Al, Li - Sn, Li - Mg, Li - Zn, Li - In, Li - Ga, etc.), and lithium - free negative electrode materials.

[0080] In some embodiments, the second conductive agent further includes, but is not limited to, one or more of graphite, superconducting carbon, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0081] In some embodiments, the second binder further includes, but is not limited to, one or more of polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and polymethacrylic acid.

[0082] The negative electrode sheet can be prepared by conventional methods in the art. For example, the negative electrode active material layer is usually formed by making a negative electrode slurry of the negative electrode active material, the second conductive agent, the second binder, and any other components, coating it on the negative electrode current collector, and then drying and cold - pressing. The solvent can be an aqueous solvent, but is not limited thereto.

[0083] In one embodiment, when the negative electrode active material is a graphite material, the expansion rate of the negative electrode sheet is 12% - 18% in the state of 25% - 35% charge; when the negative electrode active material is a silicon-containing material, the expansion rate of the negative electrode sheet is 18% - 25% in the state of 25% - 35% charge.

[0084] When the negative electrode active material is a graphite material, the expansion rate of the negative electrode sheet is 12% - 18%. This technical solution can effectively balance the deformation problem during the battery cycle, improve the lithium deposition phenomenon in the arc region of the battery, and increase the energy density of the battery; when the expansion rate of the negative electrode sheet is less than 12%, it may lead to too low porosity of the electrode sheet, hindering the penetration of the electrolyte into the micropores of the electrode sheet, thereby weakening the charge-discharge kinetic performance of the electrode sheet and affecting the stability of the battery during long-term use; when the expansion rate of the negative electrode sheet is greater than 18%, it may cause excessive expansion of the battery, resulting in a decrease in energy density, and the excessive volume expansion may cause the battery to deform, compress the electrolyte in the arc region, resulting in insufficient electrolyte in this region in the later stage of the cycle, and then leading to a rapid decrease in the battery capacity.

[0085] When the negative electrode active material is a silicon-containing material, the expansion rate of the negative electrode sheet is 18% - 25%. This technical solution can effectively balance the deformation problem during the battery cycle, improve the lithium deposition phenomenon in the arc region of the battery, and increase the energy density of the battery; when the expansion rate of the negative electrode sheet is less than 18%, it may lead to too low porosity of the electrode sheet, hindering the penetration of the electrolyte into the micropores of the electrode sheet, thereby weakening the charge-discharge kinetic performance of the electrode sheet and affecting the stability of the battery during long-term use; when the expansion rate of the negative electrode sheet is greater than 23%, it may cause excessive expansion of the battery, resulting in a decrease in energy density, and the excessive volume expansion may cause the battery to deform, compress the electrolyte in the arc region, resulting in insufficient electrolyte in this region in the later stage of the cycle, and then leading to a rapid decrease in the battery capacity. The beneficial effects of the present invention are further described below with reference to embodiments.

[0086] In order to make the invention purpose, technical solution and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of the present invention are only for explaining the present invention, not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. For the embodiments where specific experimental conditions or operation conditions are not specified, they are made according to conventional conditions or according to the conditions recommended by the material suppliers.

[0087] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between the explicitly mentioned steps, unless otherwise stated; it should also be understood that the combined connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before and after the combined devices / apparatuses or the insertion of other devices / apparatuses between the two explicitly mentioned devices / apparatuses, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is only a convenient tool for identifying each method step, rather than restricting the arrangement order of each method step or limiting the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present invention.

[0088] In the following examples, the reagents, materials, and instruments used, unless otherwise specified, can be commercially purchased or obtained by synthetic methods well-known in the art.

[0089] Table 1 Design of the battery cells of Examples 1-56 and Comparative Examples 1-7;

[0090] Example 1: This example is used to illustrate the battery cell and battery disclosed in the present invention; it includes the following operation steps: Preparation of the positive electrode sheet: Mix the positive electrode active material lithium cobaltate and ternary material, the first conductive agent carbon black and carbon nanotubes, and the first binder PVDF in a mass ratio of 48.8%:48.8%:0.5%:0.4%:1.5% and stir well in NMP solvent to form a uniform positive electrode paste.

[0091] Coat this paste on both sides of the positive electrode current collector aluminum foil, dry, roll, and then cut into strips to obtain positive electrode sheets of appropriate size.

[0092] The tensile strength of the positive electrode current collector is 170 MPa, and the tap density of the positive electrode active material layer is 3.8 g / cm 3 .

[0093] Preparation of the negative electrode sheet: Mix the negative electrode active material graphite and silicon carbide (the mass ratio of silicon carbide in the active material is 7%), the second conductive agent single-walled carbon nanotubes, and the second binders CMC, SBR, and PAA in a mass ratio of 96.8%:0.2%:0.4%:1.2%:1.4% and stir well in deionized water to form a uniform negative electrode paste.

[0094] Coat the negative electrode paste on both sides of the negative electrode current collector copper foil, dry, roll, and then cut into strips to obtain negative electrode sheets of appropriate size.

[0095] The tensile strength of the negative current collector is 500 MPa, and the tap density of the positive active material layer is 1.7 g / cm 3 ; at a state of 30% charge, the swelling rate of the negative electrode sheet is 22%.

[0096] Manufacture of the separator: Use a PE porous polymer film as the separator substrate; Manufacture of the battery: Stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role. Then wind the stacked electrode sheets and the separator and place them in a 76-micron aluminum-plastic film bag formed by punching the shell. Inject the electrolyte into the baked and dried battery cell, and after processes such as vacuum packaging, standing, and formation, a lithium-ion battery is obtained.

[0097] Example 2-56 Example 2-56 is used to illustrate the lithium-ion battery disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows: Adopt the parameters of the positive electrode sheet and the negative electrode sheet shown in Table 1.

[0098] Comparative Example 1-7 Comparative Example 1-7 is used to illustrate the lithium-ion battery disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows: Adopt the parameters of the positive electrode sheet and the negative electrode sheet shown in Table 1.

[0099] Performance test Performance test: Conduct capacity tests on the batteries of Examples 1-56 and Comparative Examples 1-7: Test methods and steps: Corner breakage ratio test: Under the environmental conditions of 45°C and an environmental humidity of 90% RH, discharge at a given current of 0.5C to 3.0V; let it stand for 5 min; charge at a constant current and constant voltage of 1.2C to the upper limit voltage, with a cut-off current of 0.05C; after standing for 10 min, discharge at 0.5C to 3.0V, and cycle 200 times in sequence. There are 50 batteries in each group. After the test is completed, check the breakage conditions at the four corners of the battery. The purpose of the high-temperature and high-humidity cycle test is to fully accelerate the expansion in the width direction of the battery electrode sheet and display it in advance, which can provide early warning for the battery design in mass production.

[0100] Volume energy density test: The prepared lithium-ion battery was tested under standard conditions of 25 ± 2 °C (charging current 1.2C, charging cut-off voltage 4.5V, charging cut-off current 0.05C, discharging rate of 0.2C to 3.0V). Record the discharging capacity C1 and the plateau voltage V1 at a discharging rate of 0.2C. Subsequently, at a state of 30% SOC, use a flat thickness gauge with a force of 600 gf to measure the thickness of the lithium-ion battery. The volume energy density of the battery was calculated according to the following formula: Volume energy density (Wh / L) = (C1 * V1) / (thickness * width * length of the battery).

[0101] Battery cycle life test: After the battery in the angular position breakage ratio test was cycled 200 times, calculate the capacity retention rate of the lithium-ion battery after cycling. The calculation formula is as follows: Capacity retention rate at the 200th cycle (%) = (discharging capacity at the 200th cycle) / (discharging capacity at the first cycle) * 100%.

[0102] Battery swelling performance test: When the battery was in the initial shipment state at 30% SOC, use a flat thickness gauge with a force of 600 gf to measure the thickness of the battery. When the battery in the angular position breakage test reached 200 cycles of the cycle life test, measure it with the same flat thickness gauge in the fully charged state, and calculate the thickness swelling rate of the battery. The calculation formula is as follows: Thickness swelling rate (%) = (fully charged thickness after the 200th cycle) / (thickness at 30% SOC in the initial state).

[0103] Table 2 Test results of the battery cores of Examples 1 - 56 and Comparative Examples 1 - 7;

[0104] It can be seen from Table 2 that by comparing Examples 1 - 56 with Comparative Examples 1 - 7, the actual PA-gap value ≥ the recommended PA-gap value, indicating that the initially reserved PPA-gap value is sufficient, and no angular position breakage was found in the accelerated 200-cycle test. When the actual PA-gap value < the recommended PA-gap value, it indicates that the initially reserved space is insufficient, and after the high-temperature and high-humidity accelerated test, angular position breakage occurred in different proportions; Comparing Comparative Examples 1-5, when the value range of TC is 180 MPa ≤ TC ≤ 350 MPa, the tensile strength of the positive current collector is relatively large. At this time, the ability to suppress the widening of the width of the positive electrode sheet is stronger, so a smaller PA-gap value can be set, and it will not affect the energy density, cycle capacity retention rate, and battery expansion rate of the battery; when the value range of TC is less than 180 MPa, the recommended value of PA-gap is relatively large, resulting in a relatively low energy density of the battery; when the value range of TC is less than 180 MPa or greater than 350 MPa, the cycle capacity retention rate of the battery will be reduced and the battery expansion rate will be increased, affecting the safety performance of the battery.

[0105] Comparing Comparative Example 3 and Examples 6-9, when the positive active material uses lithium cobaltate material and ternary material, and the value range of PC is 3.6 g / cm 3 ≤ Pc ≤ 4.1 g / cm 3 , the mechanical properties of the positive current collector are less damaged, and because the compaction density is relatively low, the mechanical stress generated during the rolling process is small, and the material is not easily expanded during the cycling process, and the battery also has a relatively high energy density; when the value range of PC is less than 3.6 g / cm 3 , the energy density of the battery is relatively low, but the cycle capacity retention rate of the battery is relatively high and the battery expansion rate is relatively low; when the value range of PC is greater than 4.1 g / cm 3 , the energy density of the battery is relatively high, but the cycle capacity retention rate of the battery is relatively short and the battery expansion rate is relatively high.

[0106] Comparing Comparative Examples 10-14, when the positive active material uses ternary material, and the value range of PC is 3.2 g / cm 3 ≤ Pc ≤ 3.6 g / cm 3 , the mechanical properties of the positive current collector are less damaged, and because the compaction density is relatively low, the mechanical stress generated during the rolling process is small, and the material is not easily expanded during the cycling process, and the battery also has a relatively high energy density; when the value range of PC is less than 3.2 g / cm 3 , the energy density of the battery is relatively low, but the cycle capacity retention rate of the battery is relatively high and the battery expansion rate is relatively low; when the value range of PC is greater than 3.6 g / cm 3 , the energy density of the battery is relatively high, but the cycle capacity retention rate of the battery is relatively short and the battery expansion rate is relatively high.

[0107] Comparing Comparative Example 3 and Examples 15-19, when the positive active material uses lithium cobaltate material, and the value range of PC is 4.1 g / cm 3 ≤ Pc ≤ 4.35 g / cm 3When it is, the mechanical properties of the positive current collector are less damaged, and because the compaction density is low, the mechanical stress generated during the rolling process is small, and the material is not easily expanded during the cycling process, and the battery also has a high energy density; when the value range of PC is less than 4.1 g / cm 3 When it is, the energy density of the battery is low, but the cycle capacity retention rate of the battery is high and the battery expansion rate is low; when the value range of PC is greater than 4.35 g / cm 3 When it is, the energy density of the battery is high, but the cycle capacity retention rate of the battery is short and the battery expansion rate is high.

[0108] Comparing Example 3 with Examples 20-23, when the value range of Ta is 300 MPa ≤ Ta ≤ 650 MPa, the tensile strength of the negative current collector is large. At this time, the stronger the ability to suppress the widening of the negative electrode sheet width, so a smaller PA-gap value can be set, and it will not affect the energy density, cycle capacity retention rate and battery expansion rate of the battery; when the value range of Ta is less than 300 MPa, it will cause the inability to effectively suppress the widening of the negative electrode sheet width, resulting in a large initial PA-gap value, which will lead to a low energy density of the battery; when the value range of Ta is less than 300 MPa or greater than 650 MPa, it will reduce the cycle capacity retention rate of the battery and increase the battery expansion rate, affecting the battery safety performance.

[0109] Comparing Example 3 with Examples 24-27, when the value range of Pa is 1.6 g / cm 3 ≤ Pa ≤ 1.85 g / cm 3 When it is, the mechanical properties of the negative current collector are less damaged and the material is not easily expanded, and the battery also has a high energy density; when the value range of Pa is less than 1.6 g / cm 3 When it is, the energy density of the battery is low, but the cycle capacity retention rate of the battery is high and the battery expansion rate is low; when the value range of Pa is greater than 1.85 g / cm 3 When it is, the energy density of the battery is high, but the cycle capacity retention rate of the battery is short and the battery expansion rate is high.

[0110] Comparing Comparative Example 3 with Examples 28 - 31, when the positive electrode active material is lithium cobaltate material and ternary material; or, comparing Comparative Examples 32 - 36, when the positive electrode active material is ternary material; or, comparing Comparative Examples 37 - 41, when the positive electrode active material is lithium cobaltate material; at this time, when the negative electrode active material is a silicon-graphite composite material and the value range of as is 18% ≤ as < 25%, this technical solution can effectively balance the deformation problem during the battery cycle, improve the lithium deposition phenomenon in the arc region of the battery, and enhance the cycle capacity retention rate of the battery and reduce the battery swelling rate; if the as value is lower than 18%, it may lead to too low porosity of the electrode sheet, hindering the infiltration of the electrolyte into the micropores of the electrode sheet, thereby weakening the charge and discharge kinetic performance of the electrode sheet, reducing the cycle capacity retention rate of the battery and increasing the battery swelling rate. When the as value exceeds 25%, it may cause excessive swelling of the battery, resulting in a decrease in energy density, and the excessive volume expansion may cause the battery to deform, compress the electrolyte in the arc region, resulting in insufficient electrolyte in this region in the later stage of the cycle, and further leading to a rapid decrease in the battery capacity.

[0111] Comparing Comparative Examples 42 - 46, when the positive electrode active material is lithium cobaltate material and ternary material; or, comparing Comparative Examples 47 - 51, when the positive electrode active material is ternary material; or, comparing Comparative Examples 52 - 56, when the positive electrode active material is lithium cobaltate material; at this time, when the negative electrode active material is graphite material and the value range of as is 12% ≤ as < 18%, this technical solution can effectively balance the deformation problem during the battery cycle, improve the lithium deposition phenomenon in the arc region of the battery, and enhance the cycle capacity retention rate of the battery and reduce the battery swelling rate; if the as value is lower than 12%, it may lead to too low porosity of the electrode sheet, hindering the infiltration of the electrolyte into the micropores of the electrode sheet, thereby weakening the charge and discharge kinetic performance of the electrode sheet, reducing the cycle capacity retention rate of the battery and increasing the battery swelling rate. When the as value exceeds 18%, it may cause excessive swelling of the battery, resulting in a decrease in energy density, and the excessive volume expansion may cause the battery to deform, compress the electrolyte in the arc region, resulting in insufficient electrolyte in this region in the later stage of the cycle, and further leading to a rapid decrease in the battery capacity.

[0112] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: The invention comprises a battery case, an electrolyte and a winding core, wherein the material of the battery case is an aluminum-plastic film, the winding core is placed in the battery case, and the electrolyte is injected into the battery case; the winding core comprises a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence; the positive electrode sheet, the separator and the negative electrode sheet are wound to form the winding core, and the two sides of the negative electrode sheet in the width direction protrude from the two sides of the positive electrode sheet in the width direction accordingly; The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on both sides of the positive electrode current collector; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer formed on both sides of the negative electrode current collector; The positive electrode sheet and the negative electrode sheet satisfy the relationship: ； Wherein, PA-gap mm is the difference between the width of the negative electrode sheet and the length of the punch used to punch the aluminum-plastic film in the length direction of the battery; T C MPa is the tensile strength of the positive electrode current collector; Ta MPa is the tensile strength of the negative electrode current collector; Pc g / cm 3 is the compaction density of the positive electrode active material layer; Pa g / cm 3 is the compaction density of the negative electrode active material layer; as% is the expansion rate of the negative electrode sheet when the charge level is 25%-35%.

2. The lithium-ion battery according to claim 1, characterized in that: The PA-gap value range is 1.0 mm-1.6 mm.

3. The lithium-ion battery according to claim 1, characterized in that: The as% refers to the expansion rate of the negative electrode sheet when the charge is 30%, which is 12%≤as≤25%.

4. The lithium-ion battery according to claim 1, characterized in that: The T C The value range is 180MPa≤T C ≤350MPa; and / or, The value range of Pc is 3.2 g / cm 3 ≤Pc≤4.35g / cm 3 .

5. The lithium-ion battery according to claim 1, characterized in that: The T a The value range is 300MPa≤T a ≤650MPa; and / or, The value range of Pa is 1.6 g / cm 3 ≤Pa≤1.85g / cm 3 .

6. The lithium-ion battery according to claim 1, characterized in that: The material of the positive electrode current collector is aluminum foil, and the aluminum foil includes Al element. Based on the mass of the aluminum foil being 100%, the mass percentage of the Al element in the aluminum foil is 99% to 100%.

7. The lithium-ion battery according to claim 6, characterized in that: The aluminum foil also includes one or more elements selected from Fe, Si, Cu, Zn, Mn, Mg, N, Ti and Gr; taking the mass of the aluminum foil as 100%, the mass percentage of the Fe element and the Si element in total of the aluminum foil is 0% to 1%; the mass percentage of the Cu element in the aluminum foil is 0% to 0.3%; the mass percentage of the Zn element, the Mn element, the Mg element, the N element, the Ti element and the Gr element in each of the aluminum foil is 0% to 0.1%.

8. The lithium-ion battery according to claim 1, characterized in that: The positive electrode active material layer includes a positive electrode active material, a first conductive agent and a first binder. Taking the total mass of the positive electrode active material layer as 100%, the positive electrode active material accounts for 94.5% to 98.7% of the mass of the positive electrode active material layer; the first conductive agent accounts for 0.3-2.5% of the mass of the positive electrode active material layer; and the first binder accounts for 0.9-2.5% of the mass of the positive electrode active material layer.

9. The lithium-ion battery according to claim 8, characterized in that: The positive electrode active material includes lithium cobalt oxide, ternary LiNi x Co y Mn z One or more of O2 materials (where x+y+z=1, x≥y); and / or, The first conductive agent includes one or more of conductive carbon black and conductive carbon nanotubes; and / or, The first binder includes one or more of PVDF and PTFE.

10. The lithium-ion battery according to claim 9, characterized in that: When the positive electrode active material is lithium cobalt oxide, the compaction density of the positive electrode active material layer is 4.1-4.35 g / cm 3 ; When the positive electrode active material is selected from lithium cobalt oxide material and ternary material at the same time, the compaction density of the positive electrode active material layer is 3.6-4.1 g / cm 3 ; When the positive electrode active material is a ternary material, the compaction density of the positive electrode active material layer is 3.2-3.6 g / cm 3 .

11. The lithium-ion battery according to claim 1, characterized in that: The negative electrode current collector is made of copper foil, which includes a Cu element. Based on the mass of the copper foil being 100%, the mass percentage of the Cu element in the copper foil is 99.5% to 100%.

12. The lithium-ion battery according to claim 11, characterized in that: The copper foil also includes one or more elements of Fe, Cr, and Zn; taking the mass of the copper foil as 100%, the mass fraction of the Fe element in the copper foil is 0ppm~50ppm; the mass fraction of the Cr element in the copper foil is 0ppm~300ppm; and the mass fraction of the Zn element in the copper foil is 0ppm~200ppm.

13. The lithium-ion battery according to claim 1, characterized in that: The negative electrode active material layer includes a negative electrode active material, a second conductive agent and a second binder. Taking the total mass of the negative electrode active material layer as 100%, the negative electrode active material accounts for 95-98% of the mass of the negative electrode active material layer; the second conductive agent accounts for 0.5-1.5% of the mass of the negative electrode active material layer; and the second binder accounts for 1.5-3.5% of the mass of the negative electrode active material layer.

14. The lithium ion battery according to claim 13, characterized in that: The negative electrode active material includes one or more of graphite material, silicon-oxygen material, and silicon-carbon material; and / or, The second conductive agent includes one or more of conductive carbon black, conductive carbon nanotubes, graphene, and conductive carbon fibers; And / or, the second binder includes one or more of CMC, SBR, and PAA.

15. The lithium ion battery according to claim 14, characterized in that: When graphite is used as the negative electrode active material, the expansion rate of the negative electrode sheet is 12%~18% when the charge is 25%-35%; when silicon-containing material is used as the negative electrode active material, the expansion rate of the negative electrode sheet is 18%~25% when the charge is 25%-35%.

Images