A lithium ion battery cell, a preparation method thereof and a lithium ion battery containing the same

Abstract

A battery cell of a lithium-ion battery, comprising a straight section and a bent section, the battery cell being wound from a laminate including a positive electrode sheet, a negative electrode sheet, and a separator; wherein, the total number of winding turns of the battery cell is N, the thickness of the laminate in the straight section of the battery cell is m1 millimeters, and a reserved space is provided inside at least one specified turn in the bent section of the battery cell, so that the distance g between two points at the maximum curvature of the innermost layer and the outermost layer of the bent section of the battery cell satisfies m1N < g < 1.87m1N; wherein the at least one specified turn is in the range of N / 4 to 3N / 4; the unit volume capacity of the negative electrode sheet is a mAh / cm 3 , and 619

Description

Technical Field

[0001] The present application relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery cell, a preparation method thereof, and a lithium ion battery comprising the cell. Background Art

[0002] The battery cell of a soft-package lithium-ion battery is made of wound pole sheets. During the lithium insertion process, there is usually varying degrees of volume expansion, which causes the pole sheets to wrinkle and deform. The wrinkling and deformation of the pole sheets can cause lithium deposition during charging, posing a safety hazard. Summary of the invention

[0003] The present application provides a lithium-ion battery cell to reduce the probability of pole piece deformation, thereby at least improving the problem of lithium deposition in the battery cell caused by pole piece deformation.

[0004] In a first aspect, the present application provides a lithium-ion battery cell, comprising a straight section and a bent section, wherein the cell is formed by winding a stacked body comprising a positive electrode sheet, a negative electrode sheet and a separator;

[0005] The total number of windings of the battery core is N, and the thickness of the stack in the straight section of the battery core is m. 1 mm, a reserved space is provided inside at least one designated circle of the bending section of the battery cell, so that the distance g between the two points where the curvature of the innermost layer and the outermost layer of the bending section of the battery cell is the largest satisfies m 1 N<g<1.87m 1 N; wherein the at least one designated circle is in the range of N / 4 to 3N / 4; the unit volume capacity of the negative electrode plate is a mAh / cm 3 , and 619<a<3000.

[0006] In some embodiments of the first aspect of the present application, a and g satisfy: 0.55m 1 N<1000g / a<1.90m 1 N.

[0007] In some embodiments of the first aspect of the present application, the number of the designated circles is 2 or 3, and the interval between two adjacent reserved spaces is 2-5 circles of the stack.

[0008] In some embodiments of the first aspect of the present application, 5≤N≤30.

[0009] In some embodiments of the first aspect of the present application, the negative electrode active material on the negative electrode plate comprises a silicon-based material.

[0010] In some embodiments of the first aspect of the present application, the silicon-based material comprises nano-silicon particles, SiO x, at least one of a silicon-carbon composite material or a silicon alloy, wherein 0.5≤x<1.6.

[0011] In some embodiments of the first aspect of the present application, the average particle size of SiOx, silicon-carbon composite material or silicon alloy in the silicon-based material is 500nm-30μm; and the average particle size of the nano-silicon particles is less than 100nm.

[0012] In some embodiments of the first aspect of the present application, the silicon-based material further contains lithium and / or magnesium.

[0013] The second aspect of the present application provides a method for preparing the battery cell provided in the first aspect of the present application, comprising:

[0014] Winding the laminated body;

[0015] After the previous circle of the designated circle is wound, a spacer is inserted into the bending section where a reserved space is required, and the designated circle is wound;

[0016] After winding is completed, the spacer is removed to form a reserved space.

[0017] The third aspect of the present application provides a lithium ion battery comprising the battery cell provided in the first aspect of the present application, wherein the lithium ion battery further comprises an electrolyte and a packaging film, wherein the battery cell is immersed in the electrolyte and encapsulated in the packaging film.

[0018] A fourth aspect of the present application provides an electronic device, comprising the lithium-ion battery provided in the third aspect of the present application.

[0019] The terms used in this application are generally terms commonly used by those skilled in the art. If there is any inconsistency with commonly used terms, the terms in this application shall prevail.

[0020] In this article, the term “wrinkle” refers to the phenomenon of continuous bending of the separator and the pole piece;

[0021] Herein, the term “deformation” refers to a cell Ripple>2, where Ripple=planar surface thickness of the full cell (PPG) / point thickness of the full cell (MMC)-1;

[0022] The lithium-ion battery cell provided in the embodiment of the present application can improve the wrinkling or deformation caused by the expansion of the battery cell by setting an appropriate reserved space in the bending section of the battery cell, and thus at least improve the problem of lithium deposition in the battery cell caused by deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application and the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of a cell structure of a lithium-ion battery according to an embodiment of the present application;

[0025] Figure 2 A top view of a cell of a lithium-ion battery of Example 4;

[0026] Figure 3 A thickness plane view of a cell of a lithium-ion battery of Example 4;

[0027] Reference numerals:

[0028] 1: straight section; 2: bent section; 3: reserved space; 4: winding corner; 5: center line of the battery cell in the thickness direction; 6: positive electrode sheet; 7: negative electrode sheet. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme, and advantages of the present application more clearly understood, the present application is further described in detail with reference to the accompanying drawings and examples. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0030] The first aspect of the present application provides a lithium ion battery cell, such as Figure 1-3 As shown, it includes a straight section 1 and a bent section 2; the battery cell is formed by winding a stack including a positive electrode sheet 6, a negative electrode sheet 7 and a separator,

[0031] The total number of windings of the battery core is N, and the thickness of the stack in the straight section of the battery core is m. 1 mm, a reserved space 3 is provided inside at least one designated circle of the bending section of the battery cell, so that the distance g between the two points at the maximum curvature of the innermost layer and the outermost layer of the bending section 2 of the battery cell satisfies m 1 N<g<1.87m 1 N; wherein the at least one designated circle is in the range of N / 4 to 3N / 4; the unit volume capacity of the negative electrode plate is a mAh / cm 3 , and 619<a<3000.

[0032] In the present application, the straight section 1 of the battery cell refers to two areas in the battery cell where the stack does not bend or bends slightly, and the bent section 2 of the battery cell refers to the two ends of the stack in the battery cell where the stack bends; wherein the bent section 2 also includes a winding corner 4, and the winding corner 4 refers to a range within each bending section, on the cross section of the battery cell, centered on the center line 5 in the thickness direction of the battery cell, with a width of approximately 1 / 2 of the thickness of the battery cell.

[0033] In the present application, the laminate may specifically include a positive electrode sheet, a negative electrode sheet and two layers of separators, one of the two layers of separators being located between the positive electrode sheet and the negative electrode sheet, and the other layer of separator being located on the other side of the positive electrode sheet. When the laminate is wound to form a battery cell, the two layers of separators are used to isolate the positive electrode sheet and the negative electrode sheet in each winding, and to isolate the positive electrode sheet and the negative electrode sheet that are close to each other in two adjacent windings, so as to prevent the positive and negative electrodes in the battery from short-circuiting. The composition of the laminate and the positional relationship of the various parts in the laminate may be determined by conventional technical means by those skilled in the art, and this application does not limit this. Exemplarily, the layers in the stack can be arranged in the order of isolation membrane, positive electrode sheet, isolation membrane, and negative electrode sheet. When the stack is wound into a battery cell, the isolation membrane is located at the innermost layer and the negative electrode sheet is located at the outermost layer in each winding. At this time, "a reserved space is provided on the inner side of the designated circle" means that a reserved space is provided between the innermost isolation membrane of the designated circle and the negative electrode sheet of the previous circle of the designated circle.

[0034] The distance between the two points with the largest curvature between the innermost and outermost layers of the bending section of the battery cell can be understood as the distance between the two points with the largest curvature between the inner isolation film of the innermost layer of the battery cell stack and the outer positive electrode sheet of the outermost layer of the stack in a bending section.

[0035] In the present application, the reserved space is set so that the line connecting the two points where the innermost and outermost layers of the bending section of the wound battery cell have the largest curvature passes through the reserved space; the two points where the innermost and outermost layers of the bending section of the wound battery cell have the largest curvature can be two points on the center line 5 where the innermost and outermost layers of the stack on the cross section of the battery cell are located in the thickness direction of the battery cell; at this time, the reserved space 3 can be set in the winding corner 4.

[0036] In the present application, the thickness of the stack can be understood as the sum of the thicknesses of the positive electrode sheet, the negative electrode sheet and the two layers of isolation membranes. When the stack is wound into a battery cell, it can be considered that the thickness of the straight section of the stack does not change before and after winding.

[0037] The inventors found in their research that the reserved space 3 cannot effectively suppress lithium deposition and deformation of the electrode if it is too large or too small. Without being limited to any theory, it can be considered that when g≤m 1 N, it is not enough to relieve volume expansion and inhibit wrinkling and deformation; and when g ≥ 1.87m1 N, the reserved space inside the battery cell is too large, causing the battery cell to deform and the solid electrolyte interface (SEI) to deteriorate, thereby affecting the degree of lithium insertion in the negative electrode and the diffusion rate of lithium ions, thus causing lithium precipitation.

[0038] In some embodiments of the first aspect of the present application, a and g satisfy: 0.55m 1 N<1000g / a<1.90m 1 N; The inventors found in their research that when g and a satisfy the above-mentioned proportional relationship, a better effect of suppressing deformation and lithium precipitation can be obtained.

[0039] In the present application, the total number of winding turns N is usually an integer; in “at least one designated turn is in the range of N / 4 to 3N / 4”, the “designated turn” is an integer turn, and the designated turn is in the range of N / 4 to 3N / 4; when N / 4 or 3N / 4 is not an integer, it is rounded to the nearest integer, and the rounded value should be in the range of N / 4 to 3N / 4.

[0040] In some embodiments of the first aspect of the present application, 5≤N≤30.

[0041] In some embodiments of the first aspect of the present application, the number of the designated circles is 2 or 3, and the interval between two adjacent reserved spaces is 2-5 circles of stacked bodies; preferably, the interval between two adjacent reserved spaces is 2-3 circles of stacked bodies; more preferably, the interval between two adjacent reserved spaces is 2 circles of stacked bodies. The inventors unexpectedly found in the study that when the number of the designated circles is 2 or 3, and the interval between two adjacent reserved spaces is 2-5 circles of stacked bodies, the effect of preventing battery cell deformation and lithium precipitation is better.

[0042] Without being limited to any theory, the inventors also found in their research that in lithium-ion batteries, the battery cells will have different degrees of volume expansion during the process of lithium insertion. For example, silicon-based negative electrode materials have a gram capacity of up to 1500 to 4200 mAh / g, which is much higher than the carbon-based negative electrode materials in the prior art, and are therefore considered to be the next generation of lithium-ion battery negative electrode materials with the most application prospects; however, silicon-based negative electrode materials have a volume expansion of about 300% during the process of lithium insertion and extraction, and the existing technologies for preventing deformation of negative electrode materials and inhibiting lithium precipitation are almost not applicable to such negative electrode materials with high gram capacity and high expansion rate; however, by using the method of the present application, by setting a reserved space, further, the unit volume capacity a (mAh / cm 3 ) and the distance g between the two points where the curvature of the innermost and outermost layers of the bending section of the battery cell is the largest is 0.55m 1 N<1000g / a<1.90m 1 N, it can effectively reduce the probability of battery cell deformation and improve the problem of battery cell lithium plating.

[0043] The battery cell of the present application includes a positive electrode plate, a negative electrode plate and a separator. The negative electrode plate includes a negative electrode collector and a negative electrode coating. The negative electrode coating is formed by coating a negative electrode material on the negative electrode collector. The negative electrode coating contains a negative electrode active substance. In some embodiments of the first aspect of the present application, the negative electrode active substance on the negative electrode plate contains a silicon-based material.

[0044] The silicon-based materials used in this application are materials known in the art; they can be prepared according to existing technologies or obtained through commercial channels. In some embodiments of the first aspect of this application, the silicon-based materials include at least one of nano-silicon particles, silicon oxide (SiOx, where 0.5≤x<1.6), silicon-carbon composite materials or silicon alloys; the particle size of the silicon-based materials can be conventional in the art. In some embodiments of the first aspect of this application, the average particle size of SiOx, silicon-carbon composite materials or silicon alloys in the silicon-based materials is 500nm-30μm; the average particle size of the nano-silicon particles is less than 100nm. In other embodiments of the first aspect of this application, the silicon-based materials may also contain elements such as lithium and magnesium.

[0045] In the present application, the materials and preparation of the positive electrode plate and the separator are not particularly limited, and can be prepared by any method known to those skilled in the art or purchased from commercial sources. For example, the positive electrode plate includes a positive electrode collector and a positive electrode coating, and the positive electrode coating is formed by coating a positive electrode material on a positive electrode collector, and the positive electrode coating contains a positive electrode active substance, and the positive electrode active substance contains at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel oxide or lithium nickel cobalt oxide; the material of the separator is selected from at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0046] The second aspect of the present application provides a method for preparing the battery cell provided in the first aspect of the present application, comprising:

[0047] Winding the laminated body;

[0048] After the previous circle of the designated circle is wound, a spacer is inserted into the bending section where a reserved space is required, and the designated circle is wound;

[0049] After winding is completed, the spacer is removed to form a reserved space.

[0050] The third aspect of the present application provides a lithium ion battery comprising the battery cell provided in the first aspect of the present application, wherein the lithium ion battery further comprises an electrolyte and a packaging film, wherein the battery cell is immersed in the electrolyte and encapsulated in the packaging film.

[0051] The electrolyte and packaging film used in the present application are all materials known in the art; for example, the electrolyte can be prepared by the following method: in a dry argon environment, lithium hexafluorophosphate (LiPF4) is added to a solvent solution of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1. 6 ) are mixed evenly, wherein LiPF 6 The concentration of the electrolyte is about 1.15 mol / L, and 12 wt % of fluoroethylene carbonate (FEC) is added and mixed evenly to obtain an electrolyte.

[0052] The packaging film may be an aluminum-plastic film; this application does not limit this.

[0053] A fourth aspect of the present application provides an electronic device, comprising the lithium-ion battery provided in the third aspect of the present application.

[0054] Hereinafter, the present application will be specifically described based on examples, but the present application is not limited to these examples.

[0055] Negative electrode capacity detection:

[0056] The negative electrode sheet (single-sided area) obtained in the embodiment was measured with a micrometer to measure the thickness of the single-sided electrode sheet and the corresponding copper foil (t 1 and t 2 ), dried in a vacuum oven at 85°C for 12 hours, cut into discs with a diameter of 1.4 cm using a punch in a dry environment, and assembled into button cells in a glove box using a metal lithium sheet as the counter electrode and a ceglard composite membrane as the isolation membrane. The battery was charged and discharged using the LAND series battery test to test its charge and discharge performance. The capacity obtained is set to C1 (mAh), then the unit volume capacity a = C1 / coated area*(t 1 -t 2 ).

[0057] Lithium deposition test:

[0058] The test temperature was 25°C. The full batteries prepared in the embodiments and comparative examples were charged to 4.4V at a constant current of 0.7C, charged to 0.05C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes. A 0.7C charge / 0.5C discharge cycle test was then performed. After 10 cycles, the battery cells were removed and disassembled to observe the lithium precipitation phenomenon.

[0059] The judgment is based on the state of the fully charged electrode. If the electrode is golden yellow, there is no lithium deposition. If the electrode is gray, there is lithium deposition. The degree of lithium deposition is judged based on the ratio of the area of ​​lithium deposition (gray) on the fully charged electrode to the area of ​​the entire electrode:

[0060] <3% is slight lithium deposition

[0061] 3% to 5% is lithium precipitation

[0062] >5% is severe

[0063] The results are shown in Table 1.

[0064] Full battery preparation example

[0065] In the following examples and comparative examples, the positive electrode sheet was prepared by the following method:

[0066] The active material LiCoO 2 , conductive carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system in a weight ratio of 96.7:1.7:1.6. The solid content of the slurry is 30 vol%, and then it is coated on an Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0067] In the following examples and comparative examples, a PE porous polymer film is used as the isolation membrane.

[0068] Example 1

[0069] Preparation of negative electrode: Graphite and the silicon oxide material (SiOx, where 0.5≤x<1.6) in the embodiment are mixed in a certain ratio to obtain a unit volume capacity of 619.8 mAh / cm 3 The mixed powder, the conductive agent acetylene black, and polyacrylic acid (PAA) are fully stirred and mixed in a deionized water solvent system according to a weight ratio of 95:1.2:3.8, wherein the solid content of the slurry is 30 vol%, and then the negative electrode material is coated on a Cu foil, dried, and cold pressed to obtain a negative electrode sheet; wherein the coating weight per unit area is 9.74 mg / cm 2 , the coating thickness is 0.115mm.

[0070] Full battery preparation:

[0071] The positive electrode sheet, the negative electrode sheet and the separator are included, and the thickness is m 1 =0.260mm laminated body is wound 13 times to obtain a battery cell; wherein, in the two bending sections of the 5th turn, a spacer is inserted to set a reserved space so that the thickness of each bending section of the battery cell at the center line of the cross section is g = 3.41mm = 1.01m 1 N.

[0072] The battery cell is placed in a packaging film, injected with the prepared electrolyte and packaged, and a complete battery is obtained through a process of formation, degassing, trimming and other processes.

[0073] Example 2

[0074] The laminate was wound 25 times, and a spacer was inserted in the 17th turn to make g = 6.63 mm = 1.02 m 1 N, and the rest is the same as in Example 1.

[0075] Example 3

[0076] The laminate was wound 25 times, and spacers were inserted in the 10th and 12th turns to make g = 12.09 mm = 1.86 m 1 N, and the rest is the same as in Example 1.

[0077] Example 4

[0078] The unit volume capacity of the mixed powder in Example 1 is 957.8 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 7.27 mg / cm 2 ; coating thickness becomes 0.091mm; thickness m 1 = 0.27mm laminate was wound 5 times, and a spacer was inserted in the second turn to make g = 2.84mm = 1.05m 1 N, and the rest is the same as in Example 1.

[0079] Example 5

[0080] In addition to winding the laminate 11 times, spacers were inserted into the bending sections of the 3rd and 5th turns to form two reserved spaces in each bending section, and g = 1.72m 1 N=4.64 mm, and the rest is the same as in Example 4.

[0081] Example 6

[0082] In addition to winding the laminate 10 times, spacers were inserted into the bending sections of the 4th and 6th turns to form two reserved spaces in each bending section, and g = 1.75m 1 N=4.72 mm, and the rest is the same as in Example 4.

[0083] Example 7

[0084] The unit volume capacity of the mixed powder in Example 1 was adjusted to 1151.3 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 5.324 mg / cm 2 ; coating thickness becomes 0.070mm; thickness m 1 = 0.212mm laminate was wound 30 times, and a spacer was inserted in the 15th turn to make g = 1.56m 1 N=9.92 mm, and the rest is the same as in Example 1.

[0085] Example 8

[0086] In addition to the bending sections of the 9th, 14th and 19th circles, spacers are inserted to form three reserved spaces in each bending section, and g = 1.58m 1 N=10.05 mm and the rest is the same as in Example 7.

[0087] Example 9

[0088] The method is the same as that of Example 8 except that spacers are inserted into the bending segments of the 9th, 15th and 21st turns to form three reserved spaces in each bending segment.

[0089] Example 10

[0090] The method is the same as that of Example 8 except that spacers are inserted into the bending segments of the 9th, 12th, 15th and 18th turns to form four reserved spaces in each bending segment.

[0091] Embodiment 11

[0092] The unit volume capacity of the mixed powder in Example 1 was adjusted to 1336.7 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 5.194 mg / cm 2 ; coating thickness becomes 0.0698mm; thickness m 1 = 0.202mm laminate was wound 20 times, and spacers were inserted in the 6th, 8th and 10th turns to make g = 1.47m 1 N=5.94 mm, and the rest is the same as in Example 1.

[0093] Example 12

[0094] The designed unit volume capacity of the mixed powder in Example 1 was adjusted to 1671.8 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 4.181 mg / cm 2 ; coating thickness becomes 0.0575mm; thickness m 1 = 0.192mm laminate was wound 20 times, and spacers were inserted in the 12th and 15th turns to make g = 1.49m 1 N=5.72 mm, and the rest is the same as in Example 1.

[0095] Embodiment 13

[0096] The designed unit volume capacity of the mixed powder in Example 1 was adjusted to 2422.2 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 2.642 mg / cm 2 ; coating thickness becomes 0.04mm; thickness m 1= 0.180 mm laminate was wound 15 times, and a spacer was inserted in the fourth turn to make g = 1.64 m 1 N=4.43 mm, and the rest is the same as in Example 1.

[0097] Embodiment 14

[0098] The designed unit volume capacity of the mixed powder in Example 1 was adjusted to 2839.0 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 2.434 mg / cm 2 ; coating thickness becomes 0.038mm; thickness m 1 = 0.166 mm laminate was wound 10 times, and spacers were inserted in the 3rd and 5th turns to make g = 1.66 m 1 N=2.76 mm, and the rest is the same as in Example 1.

[0099] Embodiment 15

[0100] By inserting spacers at the 4th and 6th turns, g = 1.86m 1 N=3.09mm, and the rest is the same as Example 14.

[0101] Comparative Example 1

[0102] By winding the laminate, g = m 1 N, and the rest is the same as in Example 2.

[0103] Comparative Example 2

[0104] By inserting a spacer, g = 1.87m 1 N, and the rest is the same as in Example 2.

[0105] Comparative Example 3

[0106] The laminate was wound so that g = 0.95 m 1 N, and the rest is the same as Example 6.

[0107] Comparative Example 4

[0108] By inserting a spacer, g = 1.88m 1 N, and the rest is the same as Example 6.

[0109] Comparative Example 5

[0110] The laminate was wound 20 times, and spacers were inserted in the 5th, 7th, 9th, and 11th turns to make g = 1.89m 1 N, and the rest is the same as Example 6.

[0111] Comparative Example 6

[0112] The laminate was wound so that g = 0.85 m1 N, and the rest is the same as Example 7.

[0113] Comparative Example 7

[0114] The laminate was wound so that g = 0.80 m 1 N, and the rest is the same as Example 11.

[0115] Comparative Example 8

[0116] The laminate was wound so that g = 0.79 m 1 N, and the rest is the same as Example 12.

[0117] Comparative Example 9

[0118] The laminate was wound so that g = 0.73 m 1 N, and the rest is the same as Example 13.

[0119] Comparative Example 10

[0120] The laminate was wound so that g = 0.95 m 1 N, and the rest is the same as Example 14.

[0121] Comparative Example 11

[0122] By inserting a spacer at the fifth turn, g = 1.88 m 1 N, and the rest is the same as Example 14.

[0123] Comparative Example 12

[0124] The unit volume capacity of the mixed powder in Example 14 was adjusted to 3000.0 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 2.279 mg / cm 2 ; coating thickness becomes 0.0364mm; laminate thickness m 1 Changes to 0.162mm; the rest is the same as Example 14.

[0125] Comparative Example 13

[0126] The unit volume capacity of the mixed powder in Example 15 was adjusted to 3000.0 mAh / cm 3 ; The negative electrode coating weight per unit area becomes 2.279 mg / cm 2 ; coating thickness becomes 0.0364mm; laminate thickness m 1 Changes to 0.162mm; the rest is the same as Example 15.

[0127] Comparative Example 14

[0128] The designed unit volume capacity of the mixed powder in Example 1 was adjusted to 3600 mAh / cm3 ; The negative electrode coating weight per unit area becomes 2.253 mg / cm 2 ; coating thickness becomes 0.0356; thickness m 1 = 0.163 mm laminate was wound 15 times, and spacers were inserted in the 4th, 6th, and 8th turns to make g = 2 m 1 N=4.89 mm, and the rest is the same as in Example 1.

[0129] Table 1

[0130]

[0131]

[0132] "-" indicates that no reserved space is set.

[0133] By comparing Examples 1-3 with Comparative Examples 1-2, and Examples 14 and 15 with Comparative Examples 10 and 11, it is shown that for the same negative electrode plate unit volume capacity, by controlling different g values, that is, controlling the size of the reserved space, the battery cell has different lithium deposition conditions. 1 N<g<1.87m 1 N, the battery cells did not show lithium precipitation. This shows that although the pole piece has repeated expansion and contraction processes during the process of lithium insertion and extraction, and the volume expansion of the pole piece is greater when the negative electrode active material contains silicon-based materials, if the corresponding space is reserved inside the battery cell to alleviate the expansion and contraction and inhibit the pole piece from wrinkling and deformation, the CB value [cell balance, (negative electrode reversible capacity × negative electrode active material ratio) / (anode reversible capacity × anode active material ratio)] can be suppressed, thereby improving the lithium precipitation phenomenon. As can be seen from Comparative Examples 2, 4, 5, and 11, when g ≥ 1.87m 1 N, the cells all showed lithium deposition or severe lithium deposition. Without being limited to any theory, this may be because the g value is too large, the reserved gap inside the cell becomes larger, causing the cell to deform, and the solid electrolyte interface (SEI) becomes worse, affecting the degree of lithium insertion and Li+ diffusion rate of the negative electrode, thus causing lithium deposition. It can be seen from Comparative Examples 1, 3, 6-10 that when g≤m 1 N, the battery cell also began to show lithium deposition. Not limited to any theory, this may be because there is no reserved space, which cannot alleviate the volume expansion. Therefore, the electrode is deformed after the cycle and serious lithium deposition occurs.

[0134] By comparing Examples 11-13 and Comparative Examples 7-9, it is found that as the unit volume capacity of the negative electrode sheet increases, if the g value is gradually increased and the reserved space at the winding corner is increased, the battery cell will not have the phenomenon of lithium precipitation, while if the g value is further reduced, the battery cell will have serious lithium precipitation. As the unit volume capacity of the negative electrode sheet increases, the content of active material silicon in the negative electrode also increases, and thus the degree of volume expansion caused by it also increases significantly. Only by increasing the reserved space within a certain range can the volume expansion be effectively alleviated, thereby suppressing the lithium precipitation caused by the deformation of the electrode sheet. If there is no corresponding reserved space, it is difficult to alleviate the volume expansion to suppress deformation, and the battery cell will have serious lithium precipitation.

[0135] Compared with Comparative Examples 12 and 13, when the g value is the same, different phenomena occur in the electrode sheet after cycling as the unit volume capacity of the negative electrode sheet increases. When the unit volume capacity of the negative electrode sheet is less than 3000 mAh / cm 3 When the negative electrode has a capacity per unit volume higher than 3000mAh / cm 3 When the g value is increased, serious lithium deposition occurs on the battery cell electrode; it can also be seen from Comparative Example 14 that if the capacity per unit volume is too large, increasing the g value will still lead to serious lithium deposition; without being limited to any theory, this may be because the setting of the g value should match the corresponding unit volume capacity of the negative electrode electrode. If the unit volume capacity is too large, it will cause excessive volume expansion. Even if a large reserved space is set, the deformation of the electrode cannot be effectively suppressed, thereby failing to effectively improve the lithium deposition phenomenon.

[0136] In summary, the size of the reserved space has a great influence on the lithium deposition of the battery cell. Different silicon contents can provide different unit volume capacities of the negative electrode sheet, but will also cause different degrees of volume expansion. Therefore, different unit volume capacities should match different g values. When the reserved space is set in the bending section of the battery cell to meet the m 1 N<g<1.87m 1 N, it can effectively alleviate the volume expansion and reduce the deformation probability of the electrode, thereby improving the lithium deposition phenomenon of the battery cell; this improvement is at least applicable to the negative electrode unit volume capacity of 619mAh / cm 3 ~3000mAh / cm 3 of negative electrode material.

[0137] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A lithium-ion battery cell, comprising a straight section and a bent section, wherein the cell is formed by winding a laminate comprising a positive electrode sheet, a negative electrode sheet and a separator; in, The total number of windings of the battery cell is N, the thickness of the laminate in the straight section of the battery cell is m1 mm, and a reserved space is provided inside at least one designated circle of the bent section of the battery cell, so that the distance g between the two points at the maximum curvature of the innermost layer and the outermost layer of the bent section of the battery cell satisfies m1N<g<1.87m1N; wherein the at least one designated circle is in the range of N / 4 to 3N / 4; the unit volume capacity of the negative electrode plate is a mAh / cm 3 , and 619<a<3000.

2. The battery cell according to claim 1, wherein: a and g satisfy: 0.55m1N<1000g / a<1.90m1N.

3. The battery cell according to claim 1, wherein: The number of the designated circles is 2 or 3, and the interval between two adjacent reserved spaces is 2-5 circles of the stack.

4. The battery cell according to claim 1, wherein: 5≤N≤30。 5. The battery cell according to any one of claims 1 to 4, wherein: The negative electrode active material on the negative electrode plate comprises a silicon-based material.

6. The battery cell according to claim 5, wherein: The silicon-based material comprises at least one of nano silicon particles, SiOx, a silicon-carbon composite material or a silicon alloy, wherein 0.5≤x<1.

6.

7. The battery cell according to claim 6, wherein: The average particle size of SiOx, silicon-carbon composite material or silicon alloy in the silicon-based material is 500nm-30μm; the average particle size of the nano silicon particles is less than 100nm.

8. The battery cell according to claim 5, wherein: The silicon-based material also contains lithium and / or magnesium.

9. The method for preparing the battery cell according to any one of claims 1 to 8, comprising: Winding the laminated body; After the previous circle of the designated circle is wound, a spacer is inserted into the bending section where a reserved space is required, and the designated circle is wound; After winding is completed, the spacer is removed to form a reserved space.

10. A lithium ion battery comprising the battery cell according to any one of claims 1 to 8, the lithium ion battery further comprising an electrolyte and a packaging film, the battery cell being immersed in the electrolyte and encapsulated in the packaging film.

11. An electronic device comprising the lithium ion battery according to claim 10.

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