CN115039268A

CN115039268A - Battery cell of lithium ion battery, preparation method of battery cell and lithium ion battery comprising battery cell

Info

Publication number: CN115039268A
Application number: CN202080094446.9A
Authority: CN
Inventors: 章婷; 姜道义; 陈志焕; 崔航
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2022-09-09
Also published as: WO2021184262A1

Abstract

The battery cell of the lithium ion battery comprises a straight section and a bent section, and is formed by winding a laminated body comprising a positive pole piece, a negative pole piece and a separation film; the total number of winding turns of the battery cell is N, and the thickness of the laminated body in the straight section of the battery cell is m ₁ A reserved space is arranged on the inner side of at least one designated circle of the bending 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 bending section of the battery cell meets the requirement of 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 pole piece is a mAh/cm ³ And 619 (i) and<a<3000. by adopting the battery core provided by the embodiment of the application, through arranging the proper reserved space at the bending section of the battery core,the phenomenon of wrinkling or deformation caused by cell expansion can be improved, and the problem of lithium precipitation of the cell is solved.

Description

Battery cell of lithium ion battery, preparation method of battery cell and lithium ion battery comprising battery cell

Technical Field

The present disclosure relates to the field of lithium ion battery technologies, and in particular, to a battery cell of a lithium ion battery, a method for manufacturing the battery cell, and a lithium ion battery including the battery cell.

Background

The electric core of the flexible package lithium ion battery is formed by winding a pole piece, and volume expansion with different degrees usually exists in the lithium embedding process, so that the pole piece is wrinkled and deformed, and the wrinkling and deformation of the pole piece can cause lithium precipitation in the charging process, thereby causing potential safety hazards.

Disclosure of Invention

The application provides a lithium ion battery's electric core to reduce the probability that the pole piece takes place to warp, thereby improve the problem that the electric core that causes by pole piece deformation is analysed lithium at least.

The first aspect of the application provides a battery cell of a lithium ion battery, which comprises a straight section and a bent section, wherein the battery cell is formed by winding a laminated body comprising a positive pole piece, a negative pole piece and an isolating membrane;

the total number of winding turns of the battery cell is N, and the thickness of the laminated body in the straight section of the battery cell is m ₁ A reserved space is arranged on the inner side of at least one designated circle of the bending section of the battery cell, so that the distance g between two points at the maximum curvature position of the innermost layer and the outermost layer of the bending section of the battery cell meets m ₁ N<g<1.87m ₁ N; it is composed ofWherein the at least one specified circle is in the range of N/4 to 3N/4; the unit volume capacity of the negative pole piece is a mAh/cm ³ And 619<a<3000。

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。

In some embodiments of the first aspect of the present application, the number of the designated turns is 2 or 3, and the interval between two adjacent head spaces is 2 to 5 turns of the laminate.

In some embodiments of the first aspect of the present application, 5 ≦ N ≦ 30.

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

In some embodiments of the first aspect of the present application, the silicon-based material comprises nano-sized silicon particles, SiO _x At least one of silicon-carbon composite material or silicon alloy, wherein x is more than or equal to 0.5<1.6。

In certain embodiments of the first aspect of the present application, the SiOx, silicon carbon composite, or silicon alloy in the silicon-based material has an average particle size of 500nm to 30 μm; the average particle diameter of the nano silicon particles is less than 100 nm.

In certain embodiments of the first aspect of the present application, the silicon-based material further comprises lithium and/or magnesium.

A second aspect of the present application provides a method for preparing a battery cell provided in the first aspect of the present application, including:

winding the laminated body;

after the front circle of the appointed circle is wound, inserting a spacer at a bending section needing to be provided with a reserved space, and winding the appointed circle;

after the winding is completed, the spacer is taken out to form a reserved space.

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, the lithium ion battery further comprises an electrolyte and a packaging film, and the battery cell is immersed in the electrolyte and is packaged in the packaging film.

The fourth aspect of the present application provides an electronic device including the lithium ion battery provided by the third aspect of the present application.

The terms used in the present application are generally terms commonly used by those skilled in the art, and if they are not consistent with the commonly used terms, the terms in the present application shall control.

Herein, the term "wrinkle" refers to a phenomenon in which the separator and the pole piece are continuously bent;

herein, the term "deformation" refers to a cell Ripple >2, wherein Ripple is the flat sheet face thickness of a full cell (PPG)/point thickness of a full cell (MMC) -1;

the lithium ion battery's that this application embodiment provided electric core sets up suitable headspace through the bending segment at electric core, can improve the fold or the deformation phenomenon that electric core inflation arouses, and then can improve the electric core lithium problem of educing that arouses by the deformation at least.

Drawings

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 the embodiments and the prior art, and obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic diagram of a cell structure of a lithium ion battery according to an embodiment of the present application;

fig. 2 is a top view of a cell of the lithium ion battery of example 4;

fig. 3 is a thickness plan view of a cell of the lithium ion battery of example 4;

reference numerals:

1: a straight section; 2: bending the section; 3: reserving a space; 4: winding a corner; 5: the center line of the thickness direction of the battery cell; 6: a positive electrode plate; 7 negative pole piece.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below by referring to the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

A first aspect of the present application provides a battery cell of a lithium ion battery, as shown in fig. 1 to 3, including a straight section 1 and a bent section 2; the battery cell is formed by winding a laminated body comprising a positive pole piece 6, a negative pole piece 7 and an isolating membrane,

the total number of winding turns of the battery cell is N, and the thickness of the laminated body in the straight section of the battery cell is m ₁ Millimeter, a reserved space 3 is arranged on the inner side of at least one designated circle of the bending section of the battery cell, so that the distance g between two points at the maximum curvature position of the innermost layer and the outermost layer of the bending section 2 of the battery cell meets 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 pole piece is a mAh/cm ³ And 619 (i) and<a<3000。

in the application, the straight section 1 of the battery cell refers to two sections of areas where the laminated body in the battery cell is not bent or is bent less, and the bent section 2 of the battery cell refers to two ends where the laminated body in the battery cell is bent; the bending section 2 further includes a winding corner 4, where the winding corner 4 is a width of about the range of the cell thickness 1/2, on the cross section of the cell, and is centered on a center line 5 in the cell thickness direction in each bending section.

In this application, the stack specifically can include positive pole piece, negative pole piece and two-layer barrier film, one deck in two-layer barrier film is located between positive pole piece and the negative pole piece, and another layer barrier film is located the opposite side of positive pole piece, works as when the stack forms electric core through the coiling, positive pole piece and negative pole piece in every round of coiling are kept apart respectively to the effect of two-layer barrier film to and keep apart in adjacent two rounds of coiling positive pole piece and the negative pole piece that are close, in order to prevent the inside positive negative pole short circuit of battery. The structure of the laminate and the positional relationship of the respective parts in the laminate can be determined by a person skilled in the art by conventional techniques, and the present application is not limited thereto. For example, each layer in the laminated body may be arranged in the order of a separation film, a positive electrode plate, a separation film, and a negative electrode plate, when the laminated body is wound into a cell, the separation film in each layer is located at the innermost layer, the negative electrode plate is located at the outermost layer, and at this time, the "specified circle is provided with a reserved space" means that a reserved space is provided between the separation film at the innermost layer of the specified circle and the negative electrode plate at the previous circle of the specified circle.

The distance between two points of the innermost layer and the outermost layer of the bending section of the battery cell, where the curvature is maximum, can be understood as the distance between two points of the innermost layer of the battery cell, the inner side isolating membrane of the laminated body of the battery cell, the outer side positive pole piece of the laminated body of the outermost layer, and the curvature of the outermost layer, which are the maximum.

In the application, the reserved space is arranged so that a connecting line of two points at the maximum curvature position of the innermost layer and the outermost layer of the bending section of the winding battery core passes through the reserved space; two points at the maximum curvature positions of the innermost layer and the outermost layer of the bending section of the winding battery cell can be two points of a laminated body of the innermost layer and the outermost layer on the section of the battery cell, which are positioned on a central line 5 in the thickness direction of the battery cell; at this time, the headspace 3 may be disposed in the winding corner 4.

In the present application, the thickness of the laminate is understood to be the sum of the thicknesses of the positive electrode sheet, the negative electrode sheet, and the two layers of separators, and when the laminate is wound into a cell, it is considered that the thickness of the laminate in the straight section does not change before and after winding.

The inventor finds in research that the purpose of effectively inhibiting lithium precipitation and deformation of the pole piece cannot be achieved by excessively large or excessively small reserved space 3, and is not limited to any theory, and the inventor can think that when g is less than or equal to m ₁ N, which is not enough to play a role in relieving volume expansion so as to inhibit wrinkles and deformation; when g is more than or equal to 1.87m ₁ N, the reserved gap in the battery cell is too large, so that the battery cell is deformed, and a Solid Electrolyte Interface (SEI) is deteriorated, thereby influencing the lithium intercalation degree of a negative electrode and the diffusion rate of lithium ionsAnd thus causes a lithium precipitation phenomenon.

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 have found in their studies that when g and a satisfy the above proportional relationship, a better effect of suppressing deformation and lithium deposition can be obtained.

In the present application, the total number of windings N is generally an integer; "at least one designated circle in the range of N/4 to 3N/4", the "designated circle" being an integer number of circles, the designated circle being in the range of N/4 to 3N/4; when N/4 and 3N/4 are not integers, rounding is performed, and the rounded value should be in the range of N/4 to 3N/4.

In some embodiments of the first aspect of the present application, the number of the designated turns is 2 or 3, and the interval between two adjacent headspace turns is 2-5 turns of the laminate; preferably, the interval between two adjacent reserved spaces is 2-3 circles of laminated bodies; more preferably, the interval between two adjacent headspace is 2 turns of the laminate. The inventor unexpectedly found in research that the effect of preventing cell deformation and lithium precipitation is better when the number of the specified circles is 2 or 3 and the interval between two adjacent reserved spaces is 2-5 circles of the laminate.

Without being limited to any theory, the inventor also finds that, in the lithium ion battery, the battery core has different volume expansion in the lithium intercalation process, for example, the gram capacity of the silicon-based negative electrode material is as high as 1500-4200 mAh/g, which is much higher than that of the carbon-based negative electrode material in the prior art, so that the silicon-based negative electrode material is considered as the next generation lithium ion battery negative electrode material with the most application prospect; however, the silicon-based negative electrode material has about 300% volume expansion in the process of lithium intercalation and deintercalation, and the existing technology for preventing the negative electrode material from deforming and inhibiting lithium evolution can hardly be applied to the negative electrode material with high gram capacity and high expansion rate; however, by adopting the method of the application and arranging the reserved space, the unit volume capacity a (mAh/cm) of the negative pole piece is further increased ³ ) With bent sections of cellsThe distance g between two points of the innermost layer and the outermost layer with the maximum curvature satisfies 0.55m ₁ N<1000g/a<1.90m ₁ During N, the probability of deformation of the battery cell can be effectively reduced, and the problem of lithium precipitation of the battery cell is improved.

The battery core comprises a positive pole piece, a negative pole piece and an isolating membrane, wherein the negative pole piece comprises a negative current collector and a negative coating, the negative coating is formed by coating a negative material on the negative current collector, the negative coating contains a negative active material, and in some embodiments of the first aspect of the application, the negative active material on the negative pole piece contains a silicon-based material.

The silicon-based materials employed herein are those known in the art; may be prepared according to the prior art or commercially available, in some embodiments of the first aspect of the present application, the silicon-based material comprises at least one of nano-silicon particles, silicon oxide (SiOx, where 0.5 ≦ x <1.6), silicon-carbon composite, or silicon alloy; the particle size of the silicon-based material may be of a size conventional in the art, and in some embodiments of the first aspect of the present application, the SiOx, silicon carbon composite, or silicon alloy in the silicon-based material has an average particle size of 500nm to 30 μm; the average particle diameter of the nano silicon particles is less than 100 nm. In other embodiments of the first aspect of the present application, the silicon-based material may further include lithium, magnesium, and the like.

In the present application, the materials and preparation of the positive electrode sheet and the separator are not particularly limited, and may be prepared by any method known to those skilled in the art or commercially available, for example, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating layer formed by coating a positive electrode material on the positive electrode current collector, the positive electrode coating layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickelate, or lithium nickel cobaltate; the material of the isolating membrane is selected from at least one of polyethylene, polypropylene and polyvinylidene fluoride.

winding the laminated body;

The electrolyte and the packaging film adopted in the application are all materials known in the field; for example, the electrolyte can be prepared by the following method: in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was added to a solvent solution of Propylene Carbonate (PC), Ethylene Carbonate (EC), and diethyl carbonate (DEC) mixed in a weight ratio of 1:1:1 ₆ ) Mixing uniformly, wherein LiPF ₆ The concentration of (A) is about 1.15mol/L, 12 wt% of fluoroethylene carbonate (FEC) is added and the mixture is mixed evenly to obtain the electrolyte.

The packaging film can adopt an aluminum plastic film; the present application is not limited thereto.

The present application will be specifically described below with reference to examples, but the present application is not limited to these examples.

And (3) detecting the capacity of the negative pole piece:

the negative electrode sheet (single-sided area) obtained in the example was measured for thickness (t each) of the single-sided sheet and the corresponding copper foil using a ten-thousandth micrometer ₁ And t ₂ ) And after drying at 85 ℃ for 12 hours in a vacuum drying oven, cutting into round pieces with the diameter of 1.4cm by using a punching machine in a drying environment, selecting a ceglard composite membrane as an isolating membrane and adding electrolyte into the round pieces to assemble the button cell in a glove box by using a metal lithium piece as a counter electrode. Performing charge and discharge test on the battery by using blue electricity (LAND) series battery testAnd (4) performance. Where the resulting capacity is C1(mAh), the unit volume capacity a is C1/area coated (t) ₁ -t ₂ )。

Lithium separation test:

the test temperature was 25C, and the full cells prepared in each example and comparative example 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. And then carrying out 0.7C charging/0.5C discharging cycle test, taking off the battery cell after 10 cycles, and carrying out disassembly and observation on the lithium separation phenomenon.

Judging according to the state of fully charged and disassembled pole pieces, wherein the pole pieces are not separated from lithium when being golden yellow, the pole pieces are separated from lithium when being gray, and judging the lithium separation degree according to the ratio of the area of fully charged pole pieces separated from lithium (gray) to the area of the whole pole pieces:

slight lithium precipitation of < 3%

3 to 5 percent of lithium is separated out

Severe precipitation > 5%

The results are shown in Table 1.

Examples of preparation of full cell

In the following examples and comparative examples, a positive electrode sheet was prepared by the following method:

active material LiCoO ₂ The conductive carbon black and the adhesive polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 96.7: 1.7: 1.6 fully stirring and uniformly mixing in an N-methyl pyrrolidone solvent system, coating the slurry with the solid content of 30 vol% on an Al foil, drying and cold-pressing to obtain the anode piece.

In the following examples and comparative examples, a PE porous polymer film was used as a separator.

Example 1

Preparing a negative pole piece: graphite and the silicon oxide material (SiOx, wherein x is more than or equal to 0.5 ≦ x) in the embodiment<1.6) are mixed according to a certain proportion to obtain the product with the unit volume capacity of 619.8mAh/cm ³ The mixed powder of (4), mixing the mixed powder, acetylene black as a conductive agent, and polyacrylic acid (PAA) according to a weight ratio of 95: 1.2: 3.8 fully stirring and uniformly mixing in a deionized water solvent system, wherein the solid content of the slurry is 30 vol%, and then carrying out negative pole treatmentCoating the material on a Cu foil, drying and cold-pressing to obtain a negative pole piece; wherein the coating weight per unit area was 9.74mg/cm ² The coating thickness was 0.115 mm.

Preparing a full battery:

a positive pole piece, a negative pole piece and a separation film with a thickness m ₁ Winding 13 turns of the laminate of 0.260mm to obtain a cell; wherein, at two kinks of 5 th circle, through inserting the spacer, set up the headspace, make the thickness g of every kinks section central line department of electric core 3.41mm 1.01m ₁ N。

And (3) placing the battery core in a packaging film, injecting the prepared electrolyte, packaging, and performing technological processes such as formation, degassing, edge cutting and the like to obtain the full battery.

Example 2

The laminate was wound for 25 turns, and a spacer was inserted in the 17 th turn so that g was 6.63mm to 1.02m ₁ N, the rest is the same as example 1.

Example 3

The laminate was wound for 25 turns, and spacers were inserted into the 10 th turn and the 12 th turn, respectively, so that g became 12.09mm and 1.86m ₁ N, the rest is the same as example 1.

Example 4

The volume capacity per unit volume of the mixed powder in example 1 was 957.8mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 7.27mg/cm ² (ii) a The coating thickness became 0.091 mm; will have a thickness m ₁ The laminate having a thickness of 0.27mm was wound into 5 turns, and a spacer was inserted into the 2 nd turn so that g was 2.84mm and 1.05m ₁ N, the rest is the same as example 1.

Example 5

In addition to the 11 turns of the laminate, spacers were inserted into the bends of the 3 rd and 5 th turns so that two spaces were formed in each bend and g was 1.72m ₁ The same as example 4 except that the thickness of N is 4.64 mm.

Example 6

In addition to the laminate being wound for 10 turns, spacers are inserted into the bends of the 4 th turn and the 6 th turn so that each bend isForm two reserved spaces, and g is 1.75m ₁ The same as example 4 except that the thickness of N is 4.72 mm.

Example 7

The volume capacity per unit volume of the mixed powder in example 1 was adjusted to 1151.3mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 5.324mg/cm ² (ii) a The coating thickness became 0.070 mm; will have a thickness m ₁ The laminate of 0.212mm was wound for 30 turns, and a spacer was inserted in the 15 th turn so that g was 1.56m ₁ N is 9.92mm, and the rest is the same as in example 1.

Example 8

Except for the bending sections of the 9 th turn, the 14 th turn and the 19 th turn, a spacer is inserted, so that three reserved spaces are formed in each bending section, and g is 1.58m ₁ The same as in example 7 was repeated except that the thickness was 10.05 mm.

Example 9

The same as example 8 was repeated, except that spacers were inserted into the bends of the 9 th turn, the 15 th turn and the 21 st turn so that three spaces were formed in each bend.

Example 10

The same as example 8 was repeated except that spacers were inserted into the bent sections of the 9 th, 12 th, 15 th and 18 th turns so that four prepared spaces were formed in each bent section.

Example 11

The volume capacity per unit volume of the mixed powder in example 1 was adjusted to 1336.7mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 5.194mg/cm ² (ii) a The coating thickness became 0.0698 mm; will have a thickness m ₁ Winding the laminate of 0.202mm for 20 turns, inserting a spacer in the 6 th, 8 th and 10 th turns, and making g 1.47m ₁ N is 5.94mm, and the rest is the same as in example 1.

Example 12

The design volume capacity of the mixed powder in example 1 was adjusted to 1671.8mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 4.181mg/cm ² (ii) a The coating thickness became 0.0575 mm; will have a thickness m ₁ The laminate of 0.192mm was wound for 20 turns, and spacers were inserted in the 12 th and 15 th turns so that g was 1.49m ₁ N is 5.72mm, and the rest is the same as example 1.

Example 13

The design volume capacity of the mixed powder in example 1 was adjusted to 2422.2mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 2.642mg/cm ² (ii) a The coating thickness became 0.04 mm; will have a thickness m ₁ The laminate of 0.180mm was wound for 15 turns, and a spacer was inserted into the 4 th turn to set g to 1.64m ₁ N is 4.43mm, and the rest is the same as in example 1.

Example 14

The design volume capacity of the mixed powder in example 1 was adjusted to 2839.0mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was changed to 2.434mg/cm ² (ii) a The coating thickness became 0.038 mm; will have a thickness m ₁ The laminate of 0.166mm was wound into 10 turns, and spacers were inserted into the 3 rd and 5 th turns to set g to 1.66m ₁ N2.76 mm, the rest being the same as in example 1.

Example 15

By inserting spacers in the 4 th and 6 th turns, g is 1.86m ₁ The same as in example 14 except that N was 3.09 mm.

Comparative example 1

Winding the laminate so that g is m ₁ N, the rest was the same as in example 2.

Comparative example 2

By inserting a spacer, g is 1.87m ₁ N, the rest is the same as example 2.

Comparative example 3

Winding the laminate so that g is 0.95m ₁ N, the rest is the same as example 6.

Comparative example 4

By inserting a spacer, g is 1.88m ₁ N, the rest is the same as example 6.

Comparative example 5

The laminate was wound 20 times at 5 th, 7 th, 9 th, and 11 thThe spacer is inserted into the ring so that g is 1.89m ₁ N, the rest is the same as example 6.

Comparative example 6

Winding the laminate so that g is 0.85m ₁ N, the rest was the same as in example 7.

Comparative example 7

Winding the laminate so that g is 0.80m ₁ N, the rest is the same as example 11.

Comparative example 8

Winding the laminate to make g 0.79m ₁ N, the rest is the same as example 12.

Comparative example 9

Winding the laminate so that g is 0.73m ₁ N, the rest is the same as example 13.

Comparative example 10

Winding the laminate so that g is 0.95m ₁ N, the rest was the same as in example 14.

Comparative example 11

By inserting a spacer in the 5 th turn, g is made 1.88m ₁ N, the rest is the same as example 14.

Comparative example 12

The volume capacity of the mixed powder of example 14 was adjusted to 3000.0mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 2.279mg/cm ² (ii) a The coating thickness became 0.0364 mm; thickness m of the laminate ₁ Becomes 0.162 mm; the rest was the same as in example 14.

Comparative example 13

The volume capacity per unit volume of the mixed powder in example 15 was adjusted to 3000.0mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 2.279mg/cm ² (ii) a The coating thickness became 0.0364 mm; thickness m of the laminate ₁ Becomes 0.162 mm; the rest is the same as in example 15.

Comparative example 14

The design volume capacity of the mixed powder in example 1 was adjusted to 3600mAh/cm ³ (ii) a The coating weight per unit area of the negative electrode was 2.253mg/cm ² (ii) a The coating thickness became 0.0356; will have a thickness m ₁ The laminate of 0.163mm was wound for 15 turns, and spacers were inserted into the 4 th, 6 th and 8 th turns to make g 2m ₁ N is 4.89mm, and the rest is the same as example 1.

TABLE 1

"-" indicates that no reserved space is provided.

Comparing examples 1-3 with comparative examples 1-2, comparing examples 14 and 15 with comparative examples 10 and 11, the same negative pole piece unit volume capacity is illustrated, and when m is different, namely the size of the reserved space is controlled, lithium precipitation of the battery cell is different ₁ N<g<1.87m ₁ And when N is used, the phenomenon of lithium precipitation does not occur in the battery core. This shows that although the pole piece has repeated expansion and contraction processes in the lithium desorption process, and the volume expansion of the pole piece is larger when the negative active material contains the silicon-based material, if a corresponding space is reserved inside the battery cell to relieve the expansion and contraction, and the pole piece is restrained from generating wrinkle deformation, the CB value (cell balance, (negative reversible capacity × negative active material ratio)/(positive reversible capacity × positive active material ratio)) can be restrained from decreasing, and thus the lithium precipitation phenomenon is improved. As seen from comparative examples 2, 4, 5 and 11, when g.gtoreq.1.87 m ₁ During N, lithium separation or serious lithium separation occurs in the battery cell, and is not limited to any theory, which may be caused by the phenomenon that the battery cell deforms due to the fact that the g value is too large and the reserved gap in the battery cell becomes large, the Solid Electrolyte Interface (SEI) becomes poor, the lithium intercalation degree of a negative electrode and the Li + diffusion rate are influenced, and lithium separation is caused. As can be seen from comparative examples 1, 3, 6 to 10, when g.ltoreq.m ₁ When N is reached, the phenomenon of lithium precipitation in the battery cell begins to occurWithout being limited to any theory, the reserved space may not play a role in relieving volume expansion, so that the pole piece deforms after circulation to generate a severe lithium precipitation phenomenon.

The comparison between examples 11 to 13 and comparative examples 7 to 9 shows that with the increase of the unit volume capacity of the negative pole piece, if the g value is gradually increased and the reserved space at the winding corner is increased, the lithium precipitation phenomenon does not occur in the battery cell, and if the g value is further reduced, the lithium precipitation phenomenon occurs in the battery cell seriously. The increase of the unit volume capacity of the negative pole piece increases the content of active material silicon in the negative pole, so the volume expansion degree caused by the increase of the unit volume capacity of the negative pole piece is also obviously improved, and the volume expansion can be effectively relieved only by increasing the reserved space in a certain range, so that the lithium precipitation caused by the deformation of the pole piece is inhibited, if the corresponding reserved space is not available, the effect of relieving the volume expansion to inhibit the deformation is difficult to play, and the lithium precipitation of the battery cell is serious.

Compared with the comparative examples 12 and 13, in the examples 14 and 15, when the g values are the same, the pole piece after circulation has different phenomena along with the increase of the unit volume capacity of the negative pole piece, and when the unit volume capacity of the negative pole piece is less than 3000mAh/cm ³ In the process, the phenomenon of lithium precipitation does not occur on the pole piece of the battery cell; when the unit volume capacity of the negative pole piece is higher than 3000mAh/cm ³ In the process, the battery pole piece has a serious lithium precipitation phenomenon; from comparative example 14, it can be seen that too large a capacity per unit volume, and further increase of g value, still leads to severe lithium precipitation; without being limited to any theory, this may be because the setting of the g value should match the unit volume capacity of the corresponding negative electrode sheet, and the unit volume capacity is too large, which may cause too large volume expansion, and even if a large reserved space is provided, the deformation of the electrode sheet cannot be effectively inhibited, so that the lithium deposition phenomenon cannot be effectively improved.

In summary, the size of the reserved space has a great influence on the lithium separation of the battery cell. Different silicon contents can provide different unit volume capacities of the negative pole piece, but volume expansion of different degrees can be caused, so that different unit volume capacities can be matched with different g values, and when a bending section of the battery core is provided with a reserved space to meet the requirement of m ₁ N<g<1.87m ₁ When N is used, the volume expansion can be effectively relieved, and the deformation probability of the pole piece is reduced, so that the phenomenon of lithium precipitation of the battery cell is improved; the improvement is at least suitable for the cathode unit volume capacity of 619mAh/cm ³ ～3000mAh/cm ³ The negative electrode material of (1).

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

The battery cell of the lithium ion battery comprises a straight section and a bent section, and is formed by winding a laminated body comprising a positive pole piece, a negative pole piece and a separation film;

wherein the total number of winding turns of the cell is N, and the thickness of the laminated body in the straight section of the cell is m ₁ A reserved space is arranged on the inner side of at least one designated circle of the bending section of the battery cell, so that the distance g between two points at the maximum curvature position of the innermost layer and the outermost layer of the bending section of the battery cell meets 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 pole piece is a mAh/cm ³ And 619 (i) and<a<3000。
the cell of claim 1, wherein a and g satisfy: 0.55m ₁ N<1000g/a<1.90m ₁ N。
The cell of claim 1, wherein the number of the designated turns is 2 or 3, and the interval between two adjacent headspace turns is 2-5 turns of the laminate.
The cell of claim 1, wherein N is 5. ltoreq.N.ltoreq.30.
The electrical core of any of claims 1-4, wherein the negative electrode active material on the negative electrode tab comprises a silicon-based material.
The cell of claim 5, wherein the silicon-based material comprises nano-silicon particles, SiO _x At least one of silicon-carbon composite material or silicon alloy, wherein x is more than or equal to 0.5<1.6。
The electrical core of claim 6, wherein the SiOx, the silicon-carbon composite, or the silicon alloy in the silicon-based material has an average particle size of 500nm to 30 μ ι η; the average particle diameter of the nano silicon particles is less than 100 nm.
The battery cell of claim 5, wherein the silicon-based material further comprises lithium and/or magnesium.
The method of making the electrical core of any of claims 1-8, comprising:

winding the laminated body;

after the front circle of the appointed circle is wound, inserting a spacer at a bending section needing to be provided with a reserved space, and winding the appointed circle;

after the winding is completed, the spacer is taken out to form a reserved space.
A lithium ion battery comprising the cell of any of claims 1-8, further comprising an electrolyte and a packaging film, the cell being immersed in the electrolyte and encapsulated within the packaging film.
An electronic device comprising the lithium ion battery of claim 10.