Negative electrode sheet, secondary battery, battery module, battery pack and power-consuming device

Abstract

The present application relates to a negative electrode plate, comprising: a negative electrode current collector; and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a middle coating region and side coating regions located on opposite sides of the middle coating region, the side coating regions having a thickness of A1 in a fully discharged state, a thickness of B1 in a fully charged state, the middle coating region having a thickness of A2 in a fully discharged state, and a thickness of B2 in a fully charged state; wherein A1, A2, B1, and B2 satisfy the following conditions: (B1-A1) / A1>(B2-A2) / A2, B2<B1. The present application also relates to a secondary battery comprising the negative electrode plate, a battery module comprising the secondary battery, a battery pack, and an electrical device.

Description

Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a negative electrode plate, a secondary battery, a battery module, a battery pack, and an electrical device. Background Art

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding features such as light weight, no pollution, and no memory effect.

[0003] In order to pursue high energy density, current secondary batteries set the negative electrode plate to a higher compaction density and a higher load. However, such a design will result in a lower overall porosity of the negative electrode plate and poor wettability to the electrolyte. The process of electrolyte infiltration of the plate follows the basic law of diffusion, diffusing from the outer edge of the negative electrode plate to the middle. In this case, the electrolyte infiltration of the middle area of ​​the negative electrode plate will be insufficient, resulting in lithium metal precipitation during the formation or circulation process due to the large ion diffusion resistance, affecting the safety and cycle performance of the battery. Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a negative electrode plate, aiming to make the secondary battery containing the negative electrode plate have better safety performance and cycle performance.

[0005] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a negative electrode sheet, comprising:

[0006] negative electrode current collector; and

[0007] A negative electrode film layer is located on at least one surface of the negative electrode current collector, the negative electrode film layer includes a middle coating area and side coating areas located on opposite sides of the middle coating area, the side coating areas have a thickness of A1 in a fully discharged state, a thickness of B1 in a fully charged state, a thickness of A2 in a fully discharged state, and a thickness of B2 in a fully charged state; wherein A1, A2, B1, and B2 meet the following conditions:

[0008] (B1-A1) / A1>(B2-A2) / A2, B2<B1.

[0009] Compared with the prior art, this application has at least the following beneficial effects:

[0010] The above-mentioned negative electrode plate of the present application forms a middle coating area and a side coating area with different thickness rebound rates in different areas on the negative electrode current collector. Specifically, the thickness rebound rate of the side coating area of ​​the negative electrode film layer is greater than the thickness rebound rate of the middle coating area. In this way, when the negative electrode plate is in a fully charged state, the thickness B2 of the middle coating area is lower than the thickness B1 of the side coating area. In this way, when the negative electrode plate is in a fully charged state, the electrolyte in the central area of ​​the negative electrode plate will not be completely squeezed out, and the electrolyte will not be difficult to be absorbed back to the middle area of ​​the negative electrode plate after the battery cell expands. Moreover, since the thickness B2 of the middle coating area is low, the electrolyte is easily absorbed back to the middle area, thereby improving the problem of lithium plating caused by less electrolyte in the middle and difficult diffusion of lithium ions, thereby improving the safety performance and cycle performance of the secondary battery using the negative electrode plate.

[0011] In any embodiment of the present application, B1 and B2 satisfy the following conditions:

[0012] 0<(B1-B2) / B2≤65%;

[0013] Optionally, 0%≤(B1-B2) / B2≤25%; more optionally, 6%≤(B1-B2) / B2≤15%.

[0014] In any embodiment of the present application, A1 and A2 satisfy the following conditions:

[0015] 0≤|A2-A1| / A1≤10%;

[0016] Optionally, 0≤|A2-A1| / A1≤5%;

[0017] In any embodiment of the present application, A1=30-300 μm, more preferably, A1=40-160 μm. In any embodiment of the present application, A2=30-300 μm, more preferably, A2=40-160 μm.

[0018] In any embodiment of the present application, 12%≤(B1-A1) / A1≤70%, 1%≤(B2-A2) / A2≤40%;

[0019] Optionally, 15%≤(B1-A1) / A1≤40%, 3%≤(B2-A2) / A2≤20%;

[0020] Optionally, 18%≤(B1-A1) / A1≤22%, and 6%≤(B2-A2) / A2≤12%.

[0021] In any embodiment of the present application, A1, A2, B1 and B2 satisfy the following conditions:

[0022] 1<(B1*A2) / (B2*A1)≤10;

[0023] Optionally, 1.6≤(B1*A2) / (B2*A1)≤3.5.

[0024] In any embodiment of the present application, in the extension direction from the edge coating area to the middle coating area, the size of the edge coating area is D1, and the size of the middle coating area is D2; D1 and D2 meet the following conditions:

[0025] 0.05≤D2 / (D2+D1)≤0.95;

[0026] Optionally, 0.1≤D2 / (D2+D1)≤0.4.

[0027] In any embodiment of this application,

[0028] The side coating area contains a first negative electrode active material, the middle coating area contains a second negative electrode active material, and the volume expansion rate of the first negative electrode active material is greater than the volume expansion rate of the second negative electrode active material;

[0029] Optionally, the mass content of the first negative electrode active material in the side coating area is greater than or equal to the mass content of the second negative electrode active material in the middle coating area;

[0030] Optionally, the types of the negative electrode active materials in the middle coating area and the side coating area are at least partially different.

[0031] In any embodiment of the present application, the negative electrode active material in the edge coating area is the first negative electrode active material;

[0032] Optionally, the middle coating area further comprises a third negative electrode active material of a type different from that of the second negative electrode active material, and the volume expansion rate of the third negative electrode active material is less than or equal to the volume expansion rate of the first negative electrode active material.

[0033] In any embodiment of the present application, the negative electrode active material in the edge coating area is selected from at least one of artificial graphite, first natural graphite and silicon-based material;

[0034] The negative electrode active material in the middle coating area is selected from at least one of a second natural graphite, hard carbon and soft carbon;

[0035] Wherein, the volume expansion rate of the first natural graphite is greater than the volume expansion rate of the second natural graphite.

[0036] In any embodiment of the present application, the orientation value of the first natural graphite is smaller than the orientation value of the second natural graphite.

[0037] A second aspect of the present application provides a secondary battery comprising the negative electrode sheet according to the first aspect of the present application.

[0038] A third aspect of the present application provides a battery module comprising the secondary battery according to the second aspect of the present application.

[0039] The fourth aspect of the present application provides a battery pack comprising the battery module of the third aspect of the present application.

[0040] The fifth aspect of the present application provides an electrical device comprising at least one of the secondary battery according to the second aspect of the present application, the battery module according to the third aspect of the present application, and the battery pack according to the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0042] Figure 1 This is a schematic diagram of the partitioned coating structure on one surface of an embodiment of the negative electrode plate of the present application.

[0043] Figure 2 This is a schematic diagram of the partitioned coating structure on one surface of another embodiment of the negative electrode plate of the present application.

[0044] Figure 3 This is a schematic diagram of one embodiment of a secondary battery.

[0045] Figure 4 yes Figure 3 Exploded diagram of .

[0046] Figure 5 is a schematic diagram of one embodiment of a battery module.

[0047] Figure 6 is a schematic diagram of one embodiment of a battery pack.

[0048] Figure 7 yes Figure 6 Exploded diagram of .

[0049] Figure 8 This is a schematic diagram of an embodiment of an electric device using a secondary battery as a power source.

[0050] Description of reference numerals:

[0051] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module; 5. Secondary battery; 51. Shell; 52. Electrode assembly; 53. Cover; 6. Electrical device; 7. Negative electrode sheet; 71. Side coating area; 72. Middle coating area; 73. Blank area. DETAILED DESCRIPTION

[0052] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0053] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0054] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” include the number itself, and “several” in “one or several” means two or more.

[0055] In the description herein, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist). Unless otherwise stated, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0056] secondary batteries

[0057] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0058] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to provide isolation. The electrolyte conducts ions between the positive and negative electrodes.

[0059] [Negative electrode]

[0060] As described in the background art, in order to improve the safety and cycle performance of a secondary battery, an embodiment of the present application provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0061] The negative electrode film layer includes a middle coating area and side coating areas located on two opposite sides of the middle coating area.

[0062] The thickness of the side coating area in a fully discharged state is A1, and the thickness of the side coating area in a fully charged state is B1.

[0063] The thickness of the middle coating area in a fully discharged state is A2, and the thickness of the middle coating area in a fully charged state is B2.

[0064] Among them, A1, A2, B1 and B2 meet the following conditions:

[0065] (B1-A1) / A1>(B2-A2) / A2, B2<B1.

[0066] It can be understood that (B1-A1) / A1 and (B2-A2) / A2 represent the thickness rebound rates of the side coating area and the middle coating area, respectively, when fully charged relative to the fully discharged state. In other words, the negative electrode film material in the side coating area and the material in the middle coating area have different thickness rebound rates; specifically, the thickness rebound rate of the material in the side coating area is greater than that of the material in the middle coating area.

[0067] like Figure 1 FIG. 1 shows a schematic diagram of the structure of the negative electrode film layer on one surface of the negative electrode plate 7, which includes a middle coating area 72 located in the middle area and side coating areas 71 located on opposite sides of the middle coating area 72; further, a blank area 73 without a negative electrode film layer is included on one side of the side coating area 71 away from the middle coating area 72, which serves as a tab area. Specifically, Figure 1 The blank area 73 is shown to be continuous and can be used to form a full tab.

[0068] like Figure 2 As shown, from Figure 2 It can be seen that Figure 1 The structure of the negative electrode plate 7 shown is basically the same, with the only difference being that the blank area 73 is discontinuous, which can be used to form split tabs.

[0069] exist Figure 1 and Figure 2 In the specific example shown, the contact surface between the middle coating area 72 and the side coating area 71 is a plane. It can be understood that in other embodiments, the contact surface can also be an inclined surface, a curved surface, etc.

[0070] Without wishing to be limited to any theory, the above-mentioned negative electrode plate of the present application forms a middle coating area and a side coating area with different thickness rebound rates in different areas on the negative electrode current collector. Specifically, the thickness rebound rate of the side coating area of ​​the negative electrode film layer is greater than the thickness rebound rate of the middle coating area. In this way, when the negative electrode plate is in a fully charged state, the thickness B2 of the middle coating area is lower than the thickness B1 of the side coating area. In this way, when the negative electrode plate is in a fully charged state, the electrolyte in the central area of ​​the negative electrode plate will not be completely squeezed out, and the electrolyte will not be difficult to be absorbed back to the middle area of ​​the negative electrode plate after the battery cell expands. Moreover, since the thickness B2 of the middle coating area is low, the electrolyte is easily absorbed back to the middle area, thereby improving the problem of lithium plating caused by less electrolyte in the middle and difficult diffusion of lithium ions, thereby improving the safety performance and cycle performance of the secondary battery using the negative electrode plate.

[0071] In the negative electrode film layer of the above-mentioned negative electrode plate, since the thickness rebound rate of the material used in the side coating area is greater than the thickness rebound rate of the material used in the middle coating area, the coating thickness of the side coating area and the middle coating area can be controlled to be the same or equivalent during the coating stage, and then the materials of the side coating area and the middle coating area have different thickness rebound rates, so that when the negative electrode plate is in a fully charged state, the thickness B2 of the middle coating area is lower than the thickness B1 of the side coating area.

[0072] However, the method of using materials with the same thickness rebound rate and directly constructing side coating areas and middle coating areas with different thicknesses requires, on the one hand, the thickness of multiple areas to be controlled during coating, which increases processing costs; on the other hand, in the preparation process of the negative electrode plate, such as the cold pressing process, due to the uneven coating thickness of the negative electrode film layer, overpressure may occur in some areas, causing the negative electrode collector to expand and increase, thereby worsening the strength of the negative electrode plate. It is easy for the plate to collapse in the middle due to the uneven initial thickness during subsequent processing such as hot pressing, which leads to an increase in the defective rate of the battery cell. In addition, it is easy to break during the battery cycle, affecting the processing performance.

[0073] The above-mentioned negative electrode plate of the present application can maintain uniform thickness during the coating process, reducing processing costs; in addition, it can avoid the above-mentioned problem of using materials with the same thickness rebound rate and directly constructing side coating areas and middle coating areas with different thicknesses.

[0074] In any embodiment of the present application, A1 and A2 satisfy the following condition: 0 ≤ |A2 - A1| / A1 ≤ 10%. In other words, the thickness of the side coating area and the middle coating area in the fully discharged state is the same or not much different. In this way, it is only necessary to control the coating thickness of the side coating area and the middle coating area to be the same or equivalent.

[0075] Optionally, 0≤|A2-A1| / A1≤5%. Optionally, A2=A1.

[0076] In any embodiment of the present application, A1 = 30-300 μm; A2 = 30-300 μm. Alternatively, A1 = 40-160 μm. Alternatively, A2 = 40-160 μm. This allows the thickness of the side coating and the middle coating to be within a given range when fully discharged, achieving a moderate thickness, neither too thick nor too thin, thereby facilitating the processing of the negative electrode sheet.

[0077] In any embodiment of the present application, B1 and B2 satisfy the following conditions: 0<(B1-B2) / B2≤65%; optionally, 0%≤(B1-B2) / B2≤25%; more optionally, 6%≤(B1-B2) / B2≤15%, or 10%≤(B1-B2) / B2≤15%. Furthermore, on the basis of controlling the thickness B2 of the middle coating area to be lower than the thickness B1 of the side coating area when the negative electrode plate is in a fully charged state, further limiting the difference between the thickness B2 of the middle coating area and the thickness B1 of the side coating area is conducive to further promoting the electrolyte of the negative electrode plate to be smoothly sucked back to the middle area of ​​the negative electrode plate when fully charged, further improving the problem of lithium plating caused by insufficient electrolyte in the middle area and difficulty in lithium ion diffusion.

[0078] In any embodiment of the present application, 12%≤(B1-A1) / A1≤70%, and 1%≤(B2-A2) / A2≤40%.

[0079] If the thickness rebound rate of the side coating area is too large, the electrolyte in the edge area will also be difficult to reabsorb. First, it is not conducive to improving lithium precipitation. Second, the group margin during battery design will be reduced, which is not conducive to improving the overall energy density of the battery. Among them, the group margin refers to the ratio of the actual internal cross-sectional area of ​​the battery to the maximum internal cross-sectional area. The thickness rebound rate of the middle coating area cannot be set too small, because the active material with a smaller thickness rebound often has a lower capacity. The use of such materials is also not conducive to improving the energy density of the battery cell. In this way, on the basis of limiting (B1-A1) / A1>(B2-A2) / A2, the range of the thickness rebound rate of the side coating area and the middle coating area is further limited, which is conducive to improving the wetting and preservation ability of the middle part of the negative electrode sheet to the electrolyte, thereby ensuring the cycle performance and energy density of the battery.

[0080] Optionally, 12%≤(B1-A1) / A1≤60%. Optionally, 15%≤(B1-A1) / A1≤40%. Further optionally, 18%≤(B1-A1) / A1≤22%.

[0081] Optionally, 3%≤(B2-A2) / A2≤20%. Further optionally, 4%≤(B2-A2) / A2≤12%. Still further optionally, 6%≤(B2-A2) / A2≤12%.

[0082] It can be understood that (B1-A1) / A1>(B2-A2) / A2; that is, B1 / A1-1>B2 / A2-1. Furthermore, B1 / A1>B2 / A2, and further, (B1*A2) / (B2*A1)>1.

[0083] In any embodiment of the present application, A1, A2, B1 and B2 satisfy the following conditions:

[0084] 1<(B1*A2) / (B2*A1)≤10. Further limiting (B1*A2) / (B2*A1) to a given range is equivalent to limiting the difference in thickness rebound rate between the side coating area and the middle coating area. If the difference in thickness rebound rate is too small, the improvement of the electrolyte resorption problem will be ineffective. If the difference in thickness rebound rate is too large, the full-charge thickness of the negative electrode sheet as a whole, especially in the side coating area, will be too large, reducing the group margin during battery design and hindering the improvement of energy density. Therefore, limiting the difference in thickness rebound rate between the side coating area and the middle coating area to a given range helps improve the negative electrode sheet's ability to wet the electrolyte and ensure the battery's energy density.

[0085] Optionally, 1.6≤(B1*A2) / (B2*A1)≤3.5.

[0086] In any embodiment of the present application, in the extension direction from the edge coating area to the middle coating area, the size of the edge coating area is D1, and the size of the middle coating area is D2; D1 and D2 meet the following conditions:

[0087] 0.05≤D2 / (D2+D1)≤0.95.

[0088] This defines the relative dimensions of the side and middle coating regions, and thus their relative areas. Because the thickness rebound rate of the middle coating region is lower than that of the side coating region, the volume expansion rate of the material used in the middle coating region is generally lower than that of the material used in the side coating region. Since the volume expansion rate of a material is positively correlated with its true density, the true density of the material used in the middle coating region is lower than that of the material used in the side coating region. True density, relative to the bulk density of the particle group, refers to the actual mass of solid matter per unit volume in an absolutely dense state, i.e., the density after removing internal pores or voids between particles. Therefore, using a material with a lower true density as the base of the middle coating region, which has more internal pores, can significantly improve the material's ability to wet the electrolyte. However, if the width or area of ​​the middle coating region is too large, the overall electrolyte requirement for the battery will increase significantly, reducing the battery's energy density. If the width or area of ​​the middle coating region is too small, the area of ​​improved electrolyte wetting is limited, and during charge and discharge, the innermost layer may still be unable to be wetted by the electrolyte, resulting in lithium deposition. Therefore, taking all factors into consideration, the relative sizes of the side coating area and the middle coating area are preferably within the above range to simultaneously meet the safety performance, cycle performance and energy density requirements of the battery.

[0089] Optionally, 0.1≤D2 / (D2+D1)≤0.4.

[0090] The negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector may be a copper foil.

[0091] In any embodiment of the present application, the negative electrode film layer contains a negative electrode active material, and the total mass content of the negative electrode active material in the middle coating area and the side coating area is the same.

[0092] In any embodiment of the present application, the types of the negative electrode active materials in the middle coating area and the side coating area are at least partially different, that is, completely different or partially different.

[0093] Furthermore, the side coating region contains a first negative electrode active material, the middle coating region contains a second negative electrode active material, and the volume expansion rate of the first negative electrode active material is greater than the volume expansion rate of the second negative electrode active material. This makes the thickness rebound rate of the side coating region greater than the thickness rebound rate of the middle coating region.

[0094] Optionally, the mass content of the first negative electrode active material in the side coating area is greater than or equal to the mass content of the second negative electrode active material in the middle coating area.

[0095] In any embodiment of the present application, the negative electrode active material in the edge coating area is the first negative electrode active material.

[0096] Optionally, the negative electrode active materials in the middle coating area are all second negative electrode active materials. In other embodiments, the middle coating area may further include a third negative electrode active material of a different type from the second negative electrode active material, and the volume expansion rate of the third negative electrode active material is less than or equal to the volume expansion rate of the first negative electrode active material.

[0097] The above-mentioned negative electrode active materials include at least one of hard carbon, soft carbon, artificial graphite, natural graphite, expanded graphite, silicon-based materials, and lithium titanate materials. Silicon-based materials include but are not limited to silicon particles, silicon dioxide, silicon carbon, and other materials.

[0098] The above-mentioned negative electrode active materials are commonly used active materials for the negative electrode of secondary batteries. The design of the negative electrode plate described in the present invention is based on the types of these negative electrode active materials and has obvious effects on these negative electrode active materials. Using preferred active materials makes it easier to achieve the designed technical effects.

[0099] In any embodiment of the present application, the negative electrode active material in the side coating region is selected from at least one of artificial graphite, a first natural graphite, and a silicon-based material; these materials have a relatively large volume expansion rate. The negative electrode active material in the middle coating region is selected from at least one of a second natural graphite, hard carbon, and soft carbon; these materials have a relatively small volume expansion rate. The volume expansion rate of the first natural graphite is greater than the volume expansion rate of the second natural graphite.

[0100] Furthermore, the orientation value of the first natural graphite is smaller than the orientation value of the second natural graphite. The smaller the orientation value of the natural graphite, the greater its volume expansion rate.

[0101] In addition to the negative electrode active material, the negative electrode film layer generally further includes a binder, a conductive agent and other optional auxiliary agents.

[0102] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] As an example, the binder can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0104] As an example, other optional auxiliary agents may be thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0105] The present application also provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0106] The negative electrode film layer is formed on at least one surface of the negative electrode current collector.

[0107] It is understood that the negative electrode film layer can be applied to the negative electrode current collector in zones to form a mid-coat region and a side-coat region. Coating methods include, but are not limited to, spraying, brushing, and the like. The composition and thickness control of the slurry used to form the mid-coat region and the side-coat region of the negative electrode film layer are as described above and will not be repeated here.

[0108] Unless otherwise specified, the above raw materials can be obtained commercially.

[0109] [Positive electrode]

[0110] In a secondary battery, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0111] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may be an aluminum foil.

[0112] The specific type of the positive electrode active material is not limited, and any active material known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select it according to actual needs.

[0113] As an example, the positive electrode active material may include, but is not limited to, at least one of a lithium ion positive electrode active material and a sodium ion positive electrode active material. Specifically, the positive electrode active material includes, but is not limited to, one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates and their respective modified compounds, layered sodium-containing oxides, sodium iron sulfate, and sodium-containing Prussian blue analogs. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their modified compounds. These materials can all be obtained through commercial channels.

[0114] In some embodiments, the modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0115] The positive electrode film layer may also optionally include a binder, a conductive agent and other optional additives.

[0116] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0117] As an example, the binder can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0118] [Isolation film]

[0119] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0120] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0121] [Electrolyte]

[0122] A secondary battery may include an electrolyte that conducts ions between a positive electrode and a negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0123] As an example, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0124] As an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0125] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0126] In some embodiments, the secondary battery of the present application is a lithium ion secondary battery or a sodium ion secondary battery.

[0127] Secondary batteries can be prepared according to conventional methods in the art, for example, the positive electrode sheet, the separator, and the negative electrode sheet are wound (or stacked) in sequence, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, to obtain a battery cell, which is placed in an outer package, injected with electrolyte and sealed to obtain a secondary battery.

[0128] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. Figure 3 The secondary battery 5 is a square structure as an example.

[0129] In some embodiments, the secondary battery may include an outer packaging for encapsulating a positive electrode sheet, a negative electrode sheet, and an electrolyte.

[0130] In some embodiments, reference Figure 4 The outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates together form a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to seal the receiving cavity.

[0131] The positive electrode sheet, the negative electrode sheet, and the separator can be wound or laminated to form an electrode assembly 52. ​​The electrode assembly 52 is enclosed in the housing. The electrolyte is infiltrated into the electrode assembly 52. ​​The secondary battery 5 can contain one or more electrode assemblies 52, which can be adjusted according to needs.

[0132] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0133] In some embodiments, secondary batteries can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0134] Figure 5 This is an example of a battery module 4. In the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0135] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0136] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0137] Figure 6 and Figure 7 The battery pack 1 is shown as an example. The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0138] [Electrical devices]

[0139] The present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack. The secondary battery, battery module, or battery pack can be used as a power source for the device, or as an energy storage unit for the device. The device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0140] The device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0141] Figure 8 The power consumption device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0142] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0143] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0144] Example

[0145] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit this application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0146] The materials used in the examples of this application can all be obtained commercially.

[0147] 1. Preparation of negative electrode sheet

[0148] Example 1:

[0149] 95% by mass of negative electrode active material 2 (see Table 1 for details), 1.74% of conductive carbon black (SP), 2.3% of styrene-butadiene rubber latex (SBR), and 0.96% of sodium carboxymethyl cellulose were mixed and dissolved in deionized water to prepare a slurry, which was then coated on the middle position of the two surfaces of a copper foil with a width of 206 mm and a thickness of 6 μm. This coating is the middle coating area.

[0150] Next, 962% by mass of negative electrode active material 1 (see Table 1 for details), 0.8% conductive carbon black (SP), 1.8% styrene-butadiene rubber latex (SBR), and 12% sodium carboxymethyl cellulose were mixed to prepare a slurry, which was then applied to both sides of the middle coating area to obtain two side coating areas of the same area and shape.

[0151] The coated electrode sheets are dried and cold pressed, and then cut into the negative electrode sheets.

[0152] Example 2-3 is basically the same as Example 1, except that the composition of the negative electrode active material 2 is different, so B2 is different (see Table 1).

[0153] Examples 4-5 are basically the same as Example 2, except that the composition of the negative electrode active material 1 is different, so B1 is different (see Table 1).

[0154] Examples 6-7 are basically the same as Example 2, except that the width of the mid-coat area is different (see Table 1).

[0155] Examples 8-10 are substantially the same as Example 2, except that the thicknesses of A1 and A2 and the widths of the intermediate coating regions are different, as shown in Table 1.

[0156] Example 11 is basically the same as Example 1, except that the width ratio of the middle coating area is different (see Table 1).

[0157] Examples 12-13 are basically the same as Example 2, except that the width of the mid-coat area is different (see Table 1).

[0158] Examples 14-18 are substantially the same as Example 1 or Example 2, with the differences shown in Table 1.

[0159] Comparative Example 1 is substantially the same as Example 1, except that negative electrode active material 2 is replaced by negative electrode active material 1.

[0160] Comparative Examples 2-3 are substantially the same as Example 1, with the differences shown in Table 1.

[0161] Some parameters of the negative electrode sheets prepared in various embodiments and comparative examples are shown in Table 1 below.

[0162] 2. Preparation of batteries

[0163] 1. Positive electrode: active material LiNi 0.8 Co 0.1 Mn 0.1O2, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96.8:2.2:1, dissolved in N-methylpyrrolidone (NMP), and the slurry is mixed to obtain a positive electrode slurry, which is coated on a 400mm wide aluminum foil, dried, cold pressed, and cut to obtain a positive electrode sheet.

[0164] 2. Isolation membrane: Use polyethylene (PE) porous polymer membrane as isolation membrane

[0165] 3. Negative electrode sheet: The negative electrode sheet prepared in the above embodiments or comparative examples is used.

[0166] 4. Electrolyte: Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:6:1. Dissolve fully dried lithium salt (LiPF6) at a ratio of 1 mol / L in the mixed organic solvent to obtain the desired electrolyte.

[0167] 5. Full Battery Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to form a bare cell. The bare cell is then placed in an aluminum casing. The prepared electrolyte is injected into the dry cell after high-temperature drying. After vacuum packaging, resting, formation, and shaping, a lithium-ion secondary cylindrical battery is obtained.

[0168] 3. Battery Performance Evaluation

[0169] The performance evaluation of each embodiment and comparative example was carried out according to the following method.

[0170] 1. Cycle performance test:

[0171] Under a constant temperature environment of 25°C, the first charge and discharge were carried out. Constant current and constant voltage charging (charging to a current of 0.05C) was performed at a charging current of 1.0C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) until the upper limit voltage reached 4.25V. After standing for 5 minutes, constant current discharge was performed at a discharge current of 1.0C until the final voltage was 2.8V. The discharge capacity of the first cycle was recorded; then continuous charge and discharge cycles were carried out.

[0172] Capacity retention rate at the nth cycle = (discharge capacity at the nth cycle / discharge capacity at the first cycle) × 100%

[0173] 2. Thickness test

[0174] Test environment and test method: Place it in an environment with a humidity of 2%, use a micrometer to measure its thickness, record the data of 15 points, take the average value, and get the corresponding thickness.

[0175] Among them, the test sample with 0% SOC thickness is to discharge the battery cell to zero charge state (i.e. full discharge state, 0% SOC), place the battery in a dry environment at 20°C and 2% humidity for disassembly, and separate the negative electrode sheet.

[0176] The test sample with 100% SOC thickness is a battery cell charged to a fully charged state (i.e., fully charged state, 100% SOC) after a corresponding number of cycles. The battery is placed in a dry environment at 20°C and 2% humidity for disassembly, and the negative electrode sheet is separated.

[0177] 3. Lithium deposition test

[0178] After the corresponding number of cycles, the battery cell is charged to a fully charged state (i.e., fully charged state, 100% SOC), and the battery is disassembled in a dry environment at 20°C and 2% humidity. The negative electrode of the disassembled battery cell is unfolded, and the lithium deposition in the coated area is observed, photographed, and recorded.

[0179] The lithium plating situation is defined as follows:

[0180] Level 0: Lithium deposition cannot be observed with the naked eye

[0181] Level 1: Trace lithium deposition (lithium deposition area is less than 20% of the middle coating area)

[0182] Level 2: Small area lithium deposition (lithium deposition area is 20%-40% of the middle coating area)

[0183] Level 3: Large area lithium deposition (lithium deposition area > 40% of the middle coating area)

[0184] In Table 1, negative electrode active material 1 is the negative electrode active material in the side coating layer, and negative electrode active material 2 is the negative electrode active material in the middle coating layer;

[0185] Graphite a is artificial graphite with an average particle size Dv50 of 14 μm, an orientation value (OI) of 20, and a gram capacity of 345 mAh / g;

[0186] Graphite b is artificial graphite with an average particle size Dv50 of 11 μm, an orientation value (OI) of 41, and a gram capacity of 350 mAh / g;

[0187] Graphite c is natural graphite with an average particle size Dv50 of 15 μm, an orientation value (OI) of 11, and a gram capacity of 350 mAh / g;

[0188] Graphite d is artificial graphite with an average particle size Dv50 of 8.9 μm, an orientation value (OI) of 55, and a gram capacity of 340 mAh / g;

[0189] Graphite e is artificial graphite with an average particle size Dv50 of 14.1 μm, an orientation index (OI) of 5, and a gram capacity of 355 mAh / g;

[0190] The average particle size Dv50 of the hard carbon material is 5 μm, and the gram capacity is 320 mAh / g;

[0191] Taking the negative electrode active material 2 in Example 2 as 80% hard carbon + 20% graphite d as an example, it means that in the negative electrode active material in the midcoat layer, 80 wt% is hard carbon and 20 wt% is graphite d. The following are similar.

[0192] A1 and B1 are the 0% SOC thickness and 100% SOC thickness of the edge coating, respectively;

[0193] A2 and B2 are the 0% SOC thickness and 100% SOC thickness of the midcoat, respectively;

[0194] D1 and D2 are the dimensions of the side coating area and the middle coating area in the extension direction from the side coating area to the middle coating area respectively;

[0195] (D2 / 2D1+D2) is the width ratio of the middle coating area.

[0196] 4. Volumetric Energy Density: This is a well-known definition in the industry and can be obtained using methods known in the industry. Herein, the volumetric energy density of a cell is calculated as: cell plateau potential x cell plateau voltage / cell volume. The volumetric energy density in Table 2 is relative, based on the volumetric energy density of Example 1. The volumetric energy density of each Example and Comparative Example is the ratio relative to the volumetric energy density of Example 1.

[0197] Table 1

[0198]

[0199]

[0200]

[0201] Table 2

[0202]

[0203] It can be seen from Tables 1 and 2 above that each embodiment controls (B1-A1) / A1>(B2-A2) / A2, B2<B1. Compared with Comparative Examples 1-3 which control (B1-A1) / A1≤(B2-A2) / A2), each embodiment has improved cycle performance and greatly improved the lithium plating problem while basically maintaining the volume energy density.

[0204] Examples 2-3 are essentially the same as Example 1, differing in that the composition of negative electrode active material 2 differs, resulting in a different B2 ratio. Consequently, (B2-A2) / A2 and (B1-B2) / B2 differ. While maintaining comparable volumetric energy density and lithium plating levels, Examples 1-2 exhibit superior cycling performance.

[0205] Examples 4-5 are essentially the same as Example 2, differing in that the composition of negative electrode active material 1 differs, resulting in a different B1 and, consequently, different (B1-A1) / A1 and (B1-B2) / B2. Given comparable volumetric energy density and lithium plating levels, Examples 2 and 5 exhibit superior cycling performance.

[0206] Examples 6-7, 12-13, and 18 are basically the same as Example 2, except that the width of the mid-coat area accounts for a different proportion. Examples 8-10 are basically the same as Example 2, except that the thickness of A1 and A2 and the width of the mid-coat area are different. Example 11 is basically the same as Example 1, except that the width of the mid-coat area accounts for a different proportion. When the volume energy density and lithium precipitation level are equivalent, the cycle performance of Examples 2 and 6-10 is better than that of Examples 11-13 and 18. That is, preferably 0.1≤D2 / (D2+D1)≤0.4.

[0207] Examples 14-15 and 17 are essentially the same as Example 1, differing in that the composition of negative electrode active material 1 differs, resulting in a different B1 and, consequently, different (B1-A1) / A1 and (B1-B2) / B2. While maintaining comparable volumetric energy density and lithium plating levels, Example 1 exhibits superior cycling performance.

[0208] Example 16 is basically the same as Example 1, with the only difference being (B1-B2) / B2. The volume energy density and lithium plating level of Example 1 and Example 16 are comparable, and both have superior cycle performance.

[0209] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A negative electrode sheet, wherein: include: negative electrode current collector; and A negative electrode film layer is located on at least one surface of the negative electrode current collector, the negative electrode film layer includes a middle coating area and side coating areas located on opposite sides of the middle coating area, the side coating areas have a thickness of A1 in a fully discharged state, a thickness of B1 in a fully charged state, a thickness of A2 in a fully discharged state, and a thickness of B2 in a fully charged state; wherein A1, A2, B1, and B2 meet the following conditions: (B1-A1) / A1>(B2-A2) / A2, B2<B1; 6%≤(B1-B2) / B2≤25%; In the extension direction from the edge coating area to the middle coating area, the size of the edge coating area is D1, and the size of the middle coating area is D2; D1 and D2 meet the following conditions: 0.1≤D2 / (2D1+D2)≤0.4; The negative electrode active material in the edge coating area is selected from at least one of artificial graphite, a first natural graphite and a silicon-based material; the negative electrode active material in the middle coating area is selected from at least one of a second natural graphite, hard carbon and soft carbon; wherein the volume expansion rate of the first natural graphite is greater than the volume expansion rate of the second natural graphite.

2. The negative electrode sheet according to claim 1, wherein: B1 and B2 meet the following conditions: 6%≤(B1-B2) / B2≤15%.

3. The negative electrode sheet according to claim 1, wherein: B1 and B2 meet the following conditions: 10%≤(B1-B2) / B2≤15%.

4. The negative electrode sheet according to claim 1, wherein: A1 and A2 meet the following conditions: 0≤|A2-A1| / A1≤10%.

5. The negative electrode sheet according to claim 4, wherein: 0≤|A2-A1| / A1≤5%.

6. The negative electrode sheet according to claim 4, wherein: A1=30~300μm.

7. The negative electrode sheet according to claim 6, wherein: A1=40~160μm.

8. The negative electrode sheet according to claim 4, wherein: A2=30~300μm.

9. The negative electrode sheet according to claim 8, wherein: A2=40~160μm.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein: 12%≤(B1-A1) / A1≤70%, 1%≤(B2-A2) / A2≤40%.

11. The negative electrode sheet according to claim 10, wherein: 15%≤(B1-A1) / A1≤40%, 3%≤(B2-A2) / A2≤20%.

12. The negative electrode sheet according to claim 11, wherein: 18%≤(B1-A1) / A1≤22%, 6%≤(B2-A2) / A2≤12%.

13. The negative electrode sheet according to any one of claims 1 to 9, wherein: The side coating area contains a first negative electrode active material, and the middle coating area contains a second negative electrode active material. The volume expansion rate of the first negative electrode active material is greater than the volume expansion rate of the second negative electrode active material.

14. The negative electrode sheet according to claim 13, wherein: The mass content of the first negative electrode active material in the side coating region is greater than or equal to the mass content of the second negative electrode active material in the middle coating region.

15. The negative electrode sheet according to claim 13, wherein: The types of negative electrode active materials in the middle coating area and the side coating area are at least partially different.

16. The negative electrode sheet according to claim 13, wherein: The negative electrode active materials in the edge coating area are all the first negative electrode active materials.

17. The negative electrode sheet according to claim 16, wherein: The middle coating region further includes a third negative electrode active material of a type different from the second negative electrode active material, and the volume expansion rate of the third negative electrode active material is less than or equal to the volume expansion rate of the first negative electrode active material.

18. The negative electrode sheet according to claim 1, wherein: The orientation value of the first natural graphite is smaller than the orientation value of the second natural graphite.

19. A secondary battery, wherein: Comprising the negative electrode sheet according to any one of claims 1 to 18.

20. A battery module, characterized in that: The secondary battery according to claim 19 is included.

21. A battery pack, characterized in that: Comprising the battery module as claimed in claim 20.

22. An electrical device, characterized in that: The battery comprises at least one selected from the group consisting of the secondary battery according to claim 19, the battery module according to claim 20, and the battery pack according to claim 21.

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