Lithium ion battery and preparation method and application thereof

Abstract

The application provides a lithium ion battery and a preparation method and application thereof, the lithium ion battery comprises a pole piece and a diaphragm, the pole piece comprises two end compaction zones and a middle compaction zone, and the diaphragm comprises two end coating zones and a middle uncoated zone; the two end compaction zones of the pole piece and the two end coating zones of the diaphragm are mutually embedded, the middle compaction zone of the pole piece and the middle uncoated zone of the diaphragm are mutually embedded; and the compaction density of the two end compaction zones is greater than that of the middle compaction zone. The pole piece and the diaphragm of the lithium ion battery are mutually embedded, the middle part of the pole piece is easy to soak, and the soaking property is improved due to the matching of the two sides and the coating zones of the diaphragm, so that the problems of uneven soaking of the pole piece and poor soaking property can be solved, the high-temperature standing time of the battery is shortened on the basis of ensuring the soaking effect, the energy consumption is saved, the battery production efficiency is improved, and the electrochemical performance of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a lithium-ion battery, its preparation method and application. Background Technology

[0002] In recent years, lithium-ion electric vehicles have experienced rapid development. As a crucial component of electric vehicles, lithium-ion batteries face increasingly stringent requirements for energy density and overall performance. To improve the energy density of lithium-ion batteries, methods such as employing high-voltage solid electrode systems and increasing cell height and thickness are effective solutions. However, while these methods enhance battery energy density, they also introduce other problems, such as reduced electrolyte wetting efficiency and increased wetting difficulty. Sufficient electrolyte wetting allows for a better interface during the pre-charge stage, improving cell cycle and storage performance. Insufficient electrolyte wetting, on the other hand, can lead to black spots on the electrode surface after battery formation, deteriorating battery performance and potentially causing lithium plating and thermal runaway during use, endangering the safety of users and their property.

[0003] Currently, traditional methods for improving electrolyte wetting efficiency include: one method is to use a high-pressure injection machine and employ a cyclical process of vacuuming and devastating to ensure that the electrolyte fills as much of the cell's internal pores as possible, such as between electrodes, between electrodes and separators, and between the core and the casing wall; another method is the lithium battery wetting process and lithium battery wetting formation method disclosed in existing technology CN109818081A, which involves installing the electrode core inside a casing with an opening at one end to create a semi-finished battery; and the method also involves adjusting the temperature... Electrolyte is injected into the semi-finished battery T1. After the electrolyte is injected, the battery is transferred to the vacuum chamber inside the glove box and evacuated until the vacuum degree inside the vacuum chamber reaches P. The pressure holding time is t. The semi-finished battery after completing the electrolyte injection and wetting step is sealed to make a finished battery. The finished battery is first placed upside down for wetting, and then placed upright for wetting. The above method is costly and it is difficult to make the electrode uniformly wetted. The degree of wetting of the electrode is different, and there may even be some unwetted areas.

[0004] Another method is to let the cell stand at room temperature or high temperature before formation, allowing the electrolyte to fully wet the electrode sheet through a certain period of standing. Alternatively, the ambient temperature can be increased to accelerate the wetting of the electrode sheet by high-temperature wetting, thus shortening the wetting time. However, both of these methods have high energy consumption and low production capacity, which increases manufacturing costs to varying degrees. Furthermore, as the energy density of lithium batteries increases, the amount of active material coated on the electrode sheet continues to increase, and the compaction density increases. In particular, the height and thickness of the cell continue to increase. After wetting using the above methods, the electrode sheet is not uniformly wetted, and there are often unwetted areas in the middle. After formation, severe lithium plating will occur at the interface of the unwetted areas.

[0005] Based on the above research, there is a need to provide a lithium-ion battery in which the electrodes are easily wetted, do not require long-term or high-temperature wetting, have low energy consumption, and high production efficiency. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-ion battery, its preparation method and application. The lithium-ion battery has an interlocking electrode and a separator. The electrode has a low compaction density in the middle and the separator is not coated in the middle. That is, the electrode cross-section is convex in the middle and the separator cross-section is concave in the middle. Thus, the interlocking of the electrode and the separator makes the electrode easy to wet, solving the problem of uneven electrode wetting and difficulty in wetting the middle part.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising an electrode and a separator, the electrode comprising a compacted region at both ends and a compacted region in the middle, and the separator comprising a coated region at both ends and an uncoated region in the middle.

[0009] The compacted areas at both ends of the electrode sheet are interlocked with the coated areas at both ends of the diaphragm, and the compacted area in the middle of the electrode sheet is interlocked with the uncoated area in the middle of the diaphragm.

[0010] The compaction density of the two end compaction zones is greater than that of the middle compaction zone.

[0011] The electrode of this invention has a high-compaction zone at both ends with a larger compaction density and a low-compaction zone in the middle with a smaller compaction density. That is, the thickness at both ends of the electrode is less than the thickness in the middle, making the side cross-section of the electrode convex. The separator of this invention has a coating at both ends and an uncoated area in the middle. That is, the thickness at both ends of the separator is greater than the thickness in the middle, making the side cross-section of the separator concave. In contrast to the electrode, they can be interlocked. Therefore, the electrode of this invention has a low compaction density in the middle, which is easy to wet, and the high compaction density on both sides matches the coating area of ​​the separator, thus improving wettability. This solves the problems of uneven electrode wettability and poor wettability. While ensuring the wettability effect, it shortens the battery high-temperature resting time, saves energy, improves battery production efficiency, enhances the lithium-ion transport path, and ensures good battery interface and electrochemical performance.

[0012] The diaphragm and electrode contact surfaces of the present invention are interlocked, with a smooth interface and no gaps.

[0013] The electrode of the present invention includes a compacted area at both ends and a compacted area in the middle on only one side, or both sides include a compacted area at both ends and a compacted area in the middle. The diaphragm includes a coated area at both ends and an uncoated area in the middle on only one side, or both sides have a coated area at both ends and an uncoated area in the middle.

[0014] Preferably, the width of the electrode is 150-350mm, for example, it can be 150mm, 175mm, 200mm, 225mm, 250mm, 275mm, 300mm, 325mm or 350mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] The width direction described in this invention is perpendicular to the electrode extension direction.

[0016] When the width of the electrode in this invention is within a reasonable range, the electrolyte wetting effect is optimal, while also ensuring the overall electrochemical performance of the battery. If the electrode width is too large, the electrode wettability will decrease. If the electrode width is too small, the combination of irregular electrode and irregular separator will increase the battery cost and also cause a decrease in battery performance such as energy density.

[0017] Preferably, the width of the central compaction zone is 0-20% of the electrode width, but not including 0%. For example, it can be 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, or 20%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 8-20%.

[0018] In order to further improve the uniformity of electrode wetting and enhance the matching effect of irregular electrode and irregularly shaped separator, this invention ensures that the overall compaction density of the electrode can be guaranteed within a reasonable width of the low compaction zone in the middle. If the width of the central compaction zone is too small, the wettability of the middle part of the electrode cannot be guaranteed; if the width is too large, the overall wettability of the electrode cannot be guaranteed.

[0019] Preferably, the compaction density ratio between the compaction zones at both ends and the compaction zone in the middle is (1-1.1):1, but does not include 1:1. For example, it can be 1.01:1, 1.03:1, 1.05:1, 1.07:1, 1.09:1 or 1.1:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] The ratio of compaction density of the high compaction zone at both ends to the low compaction zone in the middle is within a reasonable range, which can ensure wettability on the one hand and uniform distribution of current density on the other. If the difference in compaction density is too large, it will lead to uneven distribution of current density on the electrode surface during charging and discharging, inconsistent local reaction degree, resulting in lithium plating on the electrode and deterioration of electrical performance.

[0021] Preferably, the electrode is a positive electrode, and the areal density of the positive electrode is greater than 200 g / m³. 2 For example, it could be 200g / m 2 220g / m 2 240g / m 2260g / m 2 280g / m 2 Or 300g / m 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0022] Preferably, the compaction density of the central compaction zone of the positive electrode sheet is 2.2-2.35 g / mm². 3 For example, it could be 2.2 g / mm 3 2.22g / mm 3 2.24g / mm 3 2.26g / mm 3 2.28g / mm 3 2.30g / mm 3 2.32g / mm 3 2.34g / mm 3 Or 2.35g / mm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0023] Preferably, the compaction density of the compacted regions at both ends of the positive electrode sheet is 2.3-2.5 g / mm². 3 For example, it could be 2.3 g / mm 3 2.32g / mm 3 2.34g / mm 3 2.36g / mm 3 2.38g / mm 3 2.40g / mm 3 2.42g / mm 3 2.44g / mm 3 2.46g / mm 3 2.48g / mm 3 Or 2.5g / mm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0024] Preferably, the electrode is a negative electrode, and the areal density of the negative electrode is greater than 97 g / m³. 2 For example, it could be 97g / m 2 100g / m 2 120g / m 2 140g / m 2 160g / m 2 Or 180g / m 2 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0025] Preferably, the compaction density of the central compaction zone of the negative electrode sheet is 1.3-1.5 g / mm². 3 For example, it could be 1.3 g / mm 3 1.35g / mm 3 1.4g / mm 3 1.45g / mm 3 Or 1.5g / mm 3 The compaction density of the compacted zones at both ends is 1.5-1.7 g / mm². 3 For example, it could be 1.5g / mm 3 1.55g / mm 3 1.6g / mm 3 1.65g / mm 3 Or 1.7g / mm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0026] The electrode in this invention is a positive electrode and / or a negative electrode. When both the positive and negative electrodes of the battery have high compaction regions at both ends and a low compaction region in the middle, the separator includes coated regions at both ends and an uncoated region in the middle on both sides to match the irregularly shaped electrodes on both sides. If only the positive or negative electrode in the battery has high compaction regions at both ends and a low compaction region in the middle, the separator includes coated regions at both ends and an uncoated region in the middle on one side, and the other side is entirely coated or uncoated to ensure the flatness of the interface between the separator and the electrode.

[0027] Preferably, the coatings on both sides of the diaphragm comprise ceramic and polymer materials.

[0028] Preferably, the mass ratio of the ceramic material to the polymer material is 1:(0.01-0.2), for example, it can be 1:0.01, 1:0.05, 1:0.1, 1:0.15 or 1:0.2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the ceramic material has a hollow tubular morphology and includes any one or a combination of at least two of SiO2 (silicon dioxide), Al2O3 (alumina) or TiO2 (titanium dioxide). Typical but non-limiting combinations include the combination of SiO2 and Al2O3, or the combination of Al2O3 and TiO2.

[0030] Preferably, the polymer material comprises any one or a combination of at least two of polyacrylate, polyvinylidene fluoride, polyimide, or polyurethane. Typical but non-limiting combinations include a combination of polyacrylate and polyvinylidene fluoride, a combination of polyvinylidene fluoride and polyimide, or a combination of polyurethane and polyimide.

[0031] In a second aspect, the present invention provides a method for preparing a lithium-ion battery as described in the first aspect, the method comprising the following steps:

[0032] The electrode sheets are rolled using irregularly shaped rollers, and then the electrode sheets and separators are interlocked, wound, assembled, and injected with electrolyte to obtain the lithium-ion battery.

[0033] The radius of the shaped roller at the middle is smaller than the radii at both ends.

[0034] The electrode sheet of the present invention is obtained by rolling with a shaped roller with a small radius in the middle. That is, the preparation process of the present invention does not require additional steps compared with the preparation of conventional lithium-ion batteries. It only requires replacing the roller used for rolling the electrode sheet with a shaped roller. Furthermore, the radius of the shaped roller in the middle of the present invention can be adjusted according to the requirements of different compaction densities. The present invention does not specifically limit the diameter of the shaped roller.

[0035] Preferably, the preparation method further includes a settling and formation step after liquid injection.

[0036] Thirdly, the present invention provides an electronic device comprising a lithium-ion battery as described in the first aspect.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The battery of this invention employs an interlocking irregular structure for its electrodes and separator. The upper and lower ends of the electrode are high-compacted regions, while the middle section is a low-compacted region with lower compaction density. The separator is coated at both ends, with an uncoated area in the middle. This design makes the less wettable areas in the middle of the electrode easier to wet due to the lower compaction density. The high-compacted regions at both ends of the electrode, combined with the coated areas of the separator, enhance wettability. Therefore, the overall wettability of the electrode of this invention is good, and the interface between the separator and the electrode is smooth. This solves the problem of uneven wetting and poor wettability caused by increased electrode compaction density or thickness. While ensuring the wetting effect, it shortens the battery's high-temperature settling time, saves energy, improves battery production efficiency, shortens the lithium-ion transport path, and ensures good interface and electrochemical performance of the battery. Attached Figure Description

[0039] Figure 1 This is a side view showing the assembled and disassembled positive electrode, separator, and negative electrode as described in Embodiment 1 of the present invention;

[0040] Figure 2 This is a side view showing the disassembled assembly of the positive electrode and separator as described in Embodiment 1 of the present invention.

[0041] Figure 3 This is a schematic diagram of the positive electrode sheet described in Embodiment 1 of the present invention;

[0042] Figure 4 This is a schematic diagram of the irregularly shaped roller described in Embodiment 1 of the present invention;

[0043] Figure 5 This is an interface diagram of the positive electrode sheet of the lithium-ion battery described in Embodiment 1 of the present invention after it has been left to stand.

[0044] Figure 6 This is an interface diagram of the positive electrode sheet of the lithium-ion battery after it has been fully charged according to Embodiment 1 of the present invention;

[0045] Figure 7 This is an interface diagram of the positive electrode sheet of the lithium-ion battery described in Comparative Example 1 of the present invention after it has been left to stand.

[0046] Figure 8 This is an interface diagram of the positive electrode sheet of the lithium-ion battery described in Comparative Example 1 of the present invention after it has been fully charged.

[0047] Among them, 1-positive electrode sheet, 11-positive electrode end compaction zone, 12-positive electrode middle compaction zone, 2-diaphragm, 21-end coated zone, 22-middle uncoated zone, 3-negative electrode sheet, 4-shaped roller, 41-end zone, 42-middle zone. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0049] In the following examples and comparative examples, the active material of the positive electrode is lithium iron phosphate, the active material of the negative electrode is graphite, the electrolyte is lithium hexafluorophosphate electrolyte, and the base film of the separator is polypropylene. The above description is only for the purpose of more completely illustrating the technical solution of the present invention and should not be regarded as a specific limitation of the present invention.

[0050] Example 1

[0051] This embodiment provides a lithium-ion battery, which includes a positive electrode 1, a separator 2, and a negative electrode 3 stacked sequentially. The positive electrode 1 and the negative electrode 3 are respectively interlocked with the separator 2. A side view of the interlocked assembly is shown below. Figure 1 As shown;

[0052] The side view of the assembly and disassembly of the positive electrode 1 and the separator 2 is shown below. Figure 2 As shown, the structural schematic diagram of the positive electrode 1 is as follows: Figure 3As shown, the positive electrode 1 includes a positive electrode end compaction area 11 and a positive electrode middle compaction area 12 on one side, and the separator 2 includes a positive electrode end coating area 21 and a middle uncoated area 22 on one side. The positive electrode end compaction area 11 is interlocked with the positive electrode end coating area 21 on one side of the separator 2, and the positive electrode middle compaction area 12 is interlocked with the middle uncoated area 22 on one side of the separator 2. The negative electrode 3 is interlocked with the positive electrode 1 on the other side of the separator 2 in the same manner.

[0053] The width of the positive electrode 1 is 250 mm, and the width direction is perpendicular to the extension direction of the electrode. The width of the compacted region 12 in the middle of the positive electrode is 15% of the width of the positive electrode 1. The areal density of the positive electrode 1 is 280 g / m³. 2 The compaction density of the central compaction zone 12 of the positive electrode is 2.28 g / mm². 3 The compaction density of the compaction zone 11 at both ends of the positive electrode is 2.4 g / mm². 3 The ratio of the compaction density of the compaction zone 11 at both ends of the positive electrode to the compaction zone 12 in the middle of the positive electrode is 1.05:1;

[0054] The width of the negative electrode 3 is 250 mm, and the width direction is perpendicular to the electrode extension direction. The width of the central compaction zone of the negative electrode 3 is 15% of the width of the negative electrode 3. The areal density of the negative electrode 3 is 100 g / m³. 2 The compaction density of the central compaction zone of the negative electrode 3 is 1.46 g / mm². 3 The compaction density of the compacted areas at both ends of the negative electrode 3 is 1.6 g / mm². 3 The ratio of compaction density between the compaction zones at both ends of the negative electrode and the compaction zone in the middle of the negative electrode is 1.1:1.

[0055] The coating of the two end coating areas 21 of the diaphragm 2 consists of SiO2 and polyacrylate in a mass ratio of 1:0.04.

[0056] The method for preparing the lithium-ion battery includes the following steps:

[0057] The positive electrode 1 and the negative electrode 3 are rolled using a shaped roller 4, and then the positive electrode 1 and the negative electrode 3 are respectively interlocked with the separator 2, wound, assembled, injected with electrolyte, left to stand, and formed to obtain the lithium-ion battery; the structural schematic diagram of the shaped roller 4 is shown below. Figure 4 As shown, the radius of the middle region 42 is smaller than the radius of the two end regions 41;

[0058] The interface diagram of the positive electrode 1 of the lithium-ion battery after being left to stand in this embodiment is as follows: Figure 5 As shown, the interface diagram of the positive electrode 1 after the lithium-ion battery is fully charged is as follows. Figure 6 As shown.

[0059] Example 2

[0060] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet, a separator, and a negative electrode sheet stacked sequentially. The positive electrode sheet and the negative electrode sheet are respectively interlocked with the separator. One side of the positive electrode sheet includes a positive electrode end compaction area and a positive electrode middle compaction area. One side of the separator includes a positive electrode end coating area and a middle uncoated area. The positive electrode end compaction area is interlocked with the positive electrode end coating area and the positive electrode middle compaction area is interlocked with the middle uncoated area of ​​the separator. At the same time, the negative electrode sheet is interlocked with the positive electrode sheet on the other side of the separator in the same manner.

[0061] The positive electrode sheet has a width of 150 mm, and the width direction is perpendicular to the electrode sheet's extension direction. The width of the compacted region in the middle of the positive electrode sheet is 8% of the width of the positive electrode sheet. The areal density of the positive electrode sheet is 200 g / m³. 2 The compaction density of the compacted zone in the middle of the positive electrode is 2.2 g / mm². 3 The compaction density of the compacted zones at both ends of the positive electrode is 2.42 g / mm². 3 The ratio of the compaction density of the compaction zone at both ends of the positive electrode to that of the compaction zone in the middle of the positive electrode is 1.1:1;

[0062] The negative electrode sheet has a width of 150 mm, and the width direction is perpendicular to the electrode sheet's extension direction. The width of the central compacted zone of the negative electrode sheet is 8% of the negative electrode sheet's width. The areal density of the negative electrode sheet is 100 g / m³. 2 The compaction density of the central compaction zone of the negative electrode sheet is 1.5 g / mm². 3 The compaction density of the compacted areas at both ends of the negative electrode is 1.6 g / mm². 3 The ratio of compaction density between the compaction zones at both ends of the negative electrode and the compaction zone in the middle of the negative electrode is 1.07:1.

[0063] The coating of the diaphragm's coating area comprises Al2O3 and polyacrylate in a mass ratio of 1:0.01;

[0064] The method for preparing the lithium-ion battery includes the following steps:

[0065] The positive and negative electrode sheets are rolled using irregularly shaped rollers, and then the positive and negative electrode sheets are respectively interlocked with the separator, wound, assembled, injected with liquid, left to stand and formed to obtain the lithium-ion battery; the radius of the middle part of the irregularly shaped roller is smaller than the radius of the two ends.

[0066] Example 3

[0067] This embodiment provides a lithium-ion battery, which includes a positive electrode sheet, a separator, and a negative electrode sheet stacked sequentially. The positive electrode sheet and the negative electrode sheet are respectively interlocked with the separator. One side of the positive electrode sheet includes a positive electrode end compaction area and a positive electrode middle compaction area. One side of the separator includes a positive electrode end coating area and a middle uncoated area. The positive electrode end compaction area is interlocked with the positive electrode end coating area and the positive electrode middle compaction area is interlocked with the middle uncoated area of ​​the separator. At the same time, the negative electrode sheet is interlocked with the positive electrode sheet on the other side of the separator in the same manner.

[0068] The positive electrode sheet has a width of 350 mm, and the width direction is perpendicular to the electrode sheet's extension direction. The width of the compacted region in the middle of the positive electrode sheet is 20% of the width of the positive electrode sheet. The areal density of the positive electrode sheet is 300 g / m³. 2 The compaction density of the compacted zone in the middle of the positive electrode is 2.35 g / mm². 3 The compaction density of the compacted zones at both ends of the positive electrode is 2.38 g / mm². 3 The ratio of the compaction density of the compaction zone at both ends of the positive electrode to the compaction zone in the middle of the positive electrode is 1.01:1;

[0069] The negative electrode sheet has a width of 350 mm, and the width direction is perpendicular to the electrode sheet's extension direction. The width of the central compacted zone of the negative electrode sheet is 20% of the negative electrode sheet's width. The areal density of the negative electrode sheet is 97 g / m³. 2 The compaction density of the central compaction zone of the negative electrode sheet is 1.5 g / mm². 3 The compaction density of the compacted areas at both ends of the negative electrode is 1.52 g / mm². 3 The ratio of compaction density between the compaction zones at both ends of the negative electrode and the compaction zone in the middle of the negative electrode is 1.01:1.

[0070] The coating of the diaphragm's coating area comprises TiO2 and polyacrylate in a mass ratio of 1:0.2;

[0071] The method for preparing the lithium-ion battery includes the following steps:

[0072] The positive and negative electrode sheets are rolled using irregularly shaped rollers, and then the positive and negative electrode sheets are respectively interlocked with the separator, wound, assembled, injected with liquid, left to stand and formed to obtain the lithium-ion battery; the radius of the middle part of the irregularly shaped roller is smaller than the radius of the two ends.

[0073] Example 4

[0074] This embodiment provides a lithium-ion battery, which is the same as that in Embodiment 1 except that the width of the positive electrode and the negative electrode is 140mm.

[0075] Example 5

[0076] This embodiment provides a lithium-ion battery, which is the same as that in Embodiment 1 except that the width of the positive electrode and the negative electrode is 370mm.

[0077] Example 6

[0078] This embodiment provides a lithium-ion battery, which is the same as that in Embodiment 1 except that the width of the compacted area in the middle of the positive electrode is 6% of the width of the positive electrode sheet.

[0079] Example 7

[0080] This embodiment provides a lithium-ion battery, which is the same as that in Embodiment 1 except that the width of the compacted area in the middle of the positive electrode is 22% of the width of the positive electrode sheet.

[0081] Example 8

[0082] This embodiment provides a lithium-ion battery, wherein the compaction density of the central compacted region of the positive electrode is 2.09 g / mm². 3 The ratio of the compaction density of the compaction zone at both ends of the positive electrode to the compaction zone in the middle of the positive electrode is 1.15:1. Apart from the corresponding change in the diaphragm, everything else is the same as in Example 1.

[0083] Example 9

[0084] This embodiment provides a lithium-ion battery, wherein the compaction density of the central compacted region of the positive electrode is 2.0 g / mm². 3 The ratio of the compaction density of the compaction zone at both ends of the positive electrode to the compaction zone in the middle of the positive electrode is 1.2:1. Apart from the corresponding change in the diaphragm, everything else is the same as in Example 1.

[0085] Example 10

[0086] This embodiment provides a lithium-ion battery, wherein the compaction density of the compacted regions at both ends of the positive electrode is 2.62 g / mm². 3 The ratio of the compaction density of the compaction zone at both ends of the positive electrode to the compaction zone in the middle of the positive electrode is 1.15:1. Apart from the corresponding change in the diaphragm, everything else is the same as in Example 1.

[0087] Example 11

[0088] This embodiment provides a lithium-ion battery, wherein the compaction density of the compacted regions at both ends of the positive electrode is 2.74 g / mm². 3 The ratio of the compaction density of the compaction zone at both ends of the positive electrode to the compaction zone in the middle of the positive electrode is 1.2:1. Apart from the corresponding change in the diaphragm, everything else is the same as in Example 1.

[0089] Comparative Example 1

[0090] This comparative example provides a lithium-ion battery, wherein the lithium-ion battery has a compaction density of 2.4 g / mm² except for the positive electrode sheet. 3 The compaction density of the negative electrode sheets is 1.6 g / mm². 3 Except for the coated areas on both sides of the diaphragm, everything else is the same as in Example 1.

[0091] The interface diagram of the positive electrode of the lithium-ion battery described in this comparative example after being left to stand is shown in the figure below. Figure 7 As shown, the interface diagram of the positive electrode plate of the lithium-ion battery after it has been fully charged is as follows. Figure 8 As shown.

[0092] Comparative Example 2

[0093] This comparative example provides a lithium-ion battery, which is the same as that in Example 1 except that both sides of the separator are coated areas.

[0094] The lithium-ion batteries provided in the above embodiments and comparative examples were left to stand at 45°C for 24 hours after electrolyte injection, followed by formation. The presence of lithium plating on the positive electrode surface was then observed. Simultaneously, the initial discharge capacity and capacity retention after 100 cycles were tested under 1C charge-discharge conditions. The test results are shown in the table below:

[0095] Table 1

[0096]

[0097]

[0098] The following points can be observed from Table 1:

[0099] (1) As can be seen from Example 1, Comparative Example 1 and Comparative Example 2, the combination of the electrode and separator with the specific structure of the present invention can solve the problems of poor wettability and uneven wettability of the electrode. The resulting lithium-ion battery has good wettability and will not be lithium-deposited. The interface between the interlocking electrode and separator shortens the lithium-ion transport path and ensures good interface and electrochemical performance of the battery. As can be seen from Example 1 and Examples 4-5, the present invention has a good wettability for electrode with a width of 150-350mm and can obtain a battery with excellent comprehensive performance. If the electrode width is too large, the electrode wettability will decrease. If the electrode width is too small, the combination of irregular electrode and irregular separator will increase the battery cost and decrease the overall performance of the battery.

[0100] (2) As can be seen from Examples 1 and 6-7, the width of the central compaction zone also affects the wettability. If the width of the central compaction zone is too small, the wettability of the center of the electrode cannot be guaranteed. If the width is too large, the overall wettability and comprehensive electrochemical performance of the electrode cannot be guaranteed. As can be seen from Examples 1 and 8-11, if the central compaction zone is too small and the compaction zones at both ends are too large, the ratio of the compaction density of the center and the two ends will not be within a reasonable range. This will lead to uneven distribution of current density on the electrode surface and inconsistent local reaction degree during charging and discharging, thereby deteriorating the battery's electrical performance.

[0101] In summary, this invention provides a lithium-ion battery, its preparation method, and its application. The electrode and separator of the lithium-ion battery are interlocked, the compaction density in the middle of the electrode is low, and the middle of the separator is not coated. That is, the cross-section of the electrode is convex in the middle, and the cross-section of the separator is concave in the middle. Thus, the interlocking of the electrode and the separator makes the electrode easy to wet, solving the problems of uneven electrode wetting and difficulty in wetting the middle part.

[0102] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes an electrode and a separator. The electrode includes a compacted area at both ends and a compacted area in the middle. The separator includes coated areas at both ends and an uncoated area in the middle. The compacted areas at both ends of the electrode sheet are interlocked with the coated areas at both ends of the diaphragm, and the compacted area in the middle of the electrode sheet is interlocked with the uncoated area in the middle of the diaphragm. The compaction density of the compaction zones at both ends is greater than that of the compaction zone in the middle. The width of the electrode is 150-350mm, and the width direction is perpendicular to the extension direction of the electrode. The width of the central compaction zone is 8-20% of the electrode width; The compaction density ratio between the two compaction zones and the middle compaction zone is (1.05-1.1):1; When the electrode is a positive electrode, the compaction density of the compacted areas at both ends of the positive electrode is 2.3-2.5 g / mm². 3 .

2. The lithium-ion battery according to claim 1, characterized in that, The areal density of the positive electrode is greater than 200 g / m³. 2 .

3. The lithium-ion battery according to claim 1, characterized in that, The compaction density of the central compacted zone of the positive electrode is 2.2-2.35 g / mm². 3 .

4. The lithium-ion battery according to claim 1, characterized in that, When the electrode is a negative electrode, the areal density of the negative electrode is greater than 97 g / m³. 2 .

5. The lithium-ion battery according to claim 4, characterized in that, The compaction density of the central compaction zone of the negative electrode is 1.3-1.5 g / mm². 3 The compaction density of the compacted zones at both ends is 1.5-1.7 g / mm². 3 .

6. The lithium-ion battery according to claim 1, characterized in that, The coatings at both ends of the diaphragm include ceramic and polymer materials.

7. The lithium-ion battery according to claim 6, characterized in that, The mass ratio of the ceramic material to the polymer material is 1:(0.01-0.2).

8. The lithium-ion battery according to claim 6, characterized in that, The ceramic material has a hollow tubular morphology and includes any one or a combination of at least two of silicon dioxide, alumina, or titanium dioxide.

9. The lithium-ion battery according to claim 6, characterized in that, The polymer material includes any one or a combination of at least two of polyacrylate, polyvinylidene fluoride, polyimide, or polyurethane.

10. A method for preparing a lithium-ion battery as described in any one of claims 1-9, characterized in that, The preparation method includes the following steps: The electrode sheets are rolled using irregularly shaped rollers, and then the electrode sheets and separators are interlocked, wound, assembled, and injected with electrolyte to obtain the lithium-ion battery. The radius of the shaped roller at the middle is smaller than the radii at both ends.

11. The preparation method according to claim 10, characterized in that, The preparation method also includes a settling and formation step after liquid injection.

12. An electronic device, characterized in that, The electronic device includes a lithium-ion battery as described in any one of claims 1-9.

Images