Lithium battery pole group and soft package polymer lithium ion battery

Abstract

The utility model relates to a lithium battery pole group which comprises a positive plate, a diaphragm and a negative plate, the negative plate is aligned with the central line of the positive plate along the width direction of the positive plate, the surface density of the positive plate is 10 mg / cm < 2 >-50 mg / cm < 2 >, the compaction density is 2.0 g / cm < 3 >-4.5 g / cm < 3 >, the surface density of the negative plate is 5 mg / cm < 2 >-30 mg / cm < 2 >, the compaction density is 1.3 g / cm < 3 >-1.8 g / cm < 3 >, the width of the negative plate is greater than that of the positive plate, and when C is greater than or equal to 1 and less than 2, delta Wss is greater than or equal to 0.3 mm and less than or equal to 1.0 mm; when C is greater than or equal to 2 and less than 4, delta Wss is greater than or equal to 0.7 mm and less than or equal to 1.3 mm; when C is greater than or equal to 4 and less than 5, delta Wss is greater than or equal to 1.0 mm and less than or equal to 1.5 mm; wherein C is the cyclic charging rate, and delta Wss is the width exceeding the single side of the negative plate. According to the utility model, the problem of overhang lithium precipitation of the negative electrode under the condition of high-rate charging is solved.

Description

Technical Field

[0001] This utility model belongs to the field of lithium battery technology, and particularly relates to a lithium battery electrode assembly and a soft-pack polymer lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices due to their high energy density and long cycle life. During charging, lithium-ion batteries exhibit lithium plating, where lithium ions combine with electrons instead of being embedded in graphite, reducing to metallic lithium on the negative electrode surface. This phenomenon is particularly pronounced under high-rate charging conditions, where the significant difference in current density between the edge and center regions of the negative electrode exacerbates lithium plating along the width of the negative electrode.

[0003] In battery structure design, the width of the negative electrode is usually made to be greater than the width of the positive electrode. The part of the negative electrode that exceeds the width of the positive electrode is called the overhang. This is to prevent lithium ions that escape from the edge of the positive electrode from not being fully embedded in the graphite of the negative electrode and instead depositing on the edge of the electrode to form metallic lithium.

[0004] During the charging and discharging process of lithium-ion batteries, the overhang region exhibits a certain edge effect. During low-rate charging and discharging, lithium ions in the overhang can diffuse back to the positive electrode; during high-rate charging and discharging, the positive electrode is induced to undergo excessive delithiation, resulting in an excessively high local concentration of lithium ions in the overhang, a decrease in the overpotential of the negative electrode, and the excess lithium ions cannot diffuse back to the positive electrode. In the next charging and discharging cycle, the negative electrode overhang will be insufficient, leading to lithium plating.

[0005] Currently, there are two main categories of methods to address the problem of lithium plating overhang during cycling. One category involves designing special battery structures. For example, CN 218414694U mentions a battery structure to improve lithium plating at the cell edges, which uses a double-layer coating on the bottom and surface, with insulating layers at both ends of the surface width. CN218602471U provides an electrode core that uses a first and second coating adjustment zone to adjust the amount of coating on the four sides of the electrode core, thus solving the problem of lithium plating at the edges of stacked batteries. The other category focuses on materials. For example, CN118398769A uses a functional layer containing inorganic particles and conductive agents at the edge of the current collector of the positive electrode to solve the problem of lithium deposition at the edge of the negative electrode; CN110148708B uses a double-layer coating design for the negative electrode with a silicon-containing coating on the top layer and a silicon-free pure graphite layer on the bottom layer to avoid lithium deposition on the surface of the negative electrode under high-rate fast charging; CN117613515A uses an intermittent coating separator structure, with different dynamics in the middle and edge regions of the base film and the single or double coating structure on the base film, which improves the phenomenon of lithium or sodium deposition at the edge of the negative electrode.

[0006] Existing technical solutions either involve the introduction of new materials or special structures such as double-layer coating, edge coating, and groove design, which have a high dependence on materials and poor versatility between different chemical systems, thus increasing manufacturing costs. At the same time, they do not differentiate between application scenarios for different charging rates of lithium-ion batteries, and do not carry out differentiated overhang design for high-rate, especially 2C-5C fast-charging batteries. A design with low charging rate and high overhang will reduce the effective area of ​​the positive electrode and reduce the volumetric energy density of the battery. Utility Model Content

[0007] The purpose of this invention is to overcome the shortcomings of the above-mentioned technologies and provide a lithium battery electrode assembly and a soft-pack polymer lithium-ion battery, which can improve the volumetric energy density of the battery and solve the problem of lithium deposition on the negative electrode under high-rate charging conditions of 2C-5C.

[0008] To achieve the above objectives, this utility model adopts the following technical solution: a lithium battery electrode assembly, comprising a positive electrode, a separator, and a negative electrode, wherein the negative electrode is aligned with the center line of the positive electrode along the width direction of the positive electrode, and the areal density of the positive electrode is 10 mg / cm³. 2 -50 mg / cm 2 The compacted density is 2.0 g / cm³. 3 -4.5g / cm 3 The areal density of the negative electrode is 5 mg / cm³. 2 -30mg / cm 2 The compacted density is 1.3 g / cm³. 3 -1.8g / cm 3 The width of the negative electrode is greater than the width of the positive electrode.

[0009] When 1≤C<2, 0.6mm≤Wa-Wc≤2.0mm, 0.3mm≤ΔWss≤1.0mm;

[0010] When 2≤C<4, 1.4mm≤Wa-Wc≤2.6mm, 0.7mm≤ΔWss≤1.3mm;

[0011] When 4≤C<5, 2.0mm≤Wa-Wc≤3.0mm, 1.0mm≤ΔWss≤1.5mm;

[0012] Where C is the cycle charge rate, Wa is the width of the negative electrode, Wc is the width of the positive electrode, and ΔWss is the width of the negative electrode extending beyond one side.

[0013] Furthermore, the pole group is made into a wound pole group when 1≤C<4.

[0014] Furthermore, when 4 ≤ C < 5, the electrode group is made into a stacked electrode group.

[0015] Furthermore, the thickness of the diaphragm is 5-25 μm.

[0016] Furthermore, the diaphragm is aligned with the centerline along the length of the electrode assembly.

[0017] A type of wound or stacked soft-pack polymer lithium-ion battery is made of wound or stacked electrode assembly capable of 1C-5C charging cycles.

[0018] Beneficial effects: Compared with the prior art, this utility model improves the volumetric energy density of the battery without introducing new materials or structures, solves the problem of lithium deposition on the negative electrode under different charging rates, especially under high charging rates, improves the cycle life of the battery, is simple to operate, highly versatile, and easy to implement; the electrode assembly and lithium-ion battery provided by this utility model are differentiated according to different cycle charging rates of lithium-ion batteries, reducing the area of ​​overhang in the inactive part while ensuring safety and cycle performance, thereby improving the battery energy density and enhancing the range. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the planar structure of the positive and negative electrode plates in a wound electrode assembly;

[0020] Figure 2 This is a schematic diagram of the planar structure of a wound pole assembly;

[0021] Figure 3 This is a comparison chart of lithium-ion battery cycling between Example 1 and Comparative Example 1;

[0022] Figure 4 This is a cycle diagram of a lithium-ion battery from Example 2;

[0023] Figure 5 This is a comparison chart of lithium-ion battery cycling between Example 3 and Comparative Example 2;

[0024] Figure 6 This is a cycle diagram of the lithium-ion battery in Example 4.

[0025] In the diagram: 1-positive electrode; 2-negative electrode; 11-positive tab; 21-negative tab; 3-diaphragm. Detailed Implementation

[0026] To better understand the above-mentioned objectives, features, and advantages of this utility model, the present utility model will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of this utility model; the described embodiments are merely some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this utility model pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the utility model.

[0027] As shown in the attached figures, this embodiment provides a lithium battery electrode assembly, comprising a positive electrode, a separator, and a negative electrode. Along the width direction of the positive electrode, the negative electrode is aligned with the center line of the positive electrode. The areal density of the positive electrode is 10 mg / cm³. 2 -50mg / cm 2 The compacted density is 2.0 g / cm³. 3 -4.5g / cm 3 The areal density of the negative electrode is 5 mg / cm³. 2 -30mg / cm 2 The compacted density is 1.3 g / cm³. 3 -1.8g / cm 3 The width of the negative electrode is greater than the width of the positive electrode.

[0028] When 1≤C<2, 0.6mm≤Wa-Wc≤2.0mm, 0.3mm≤ΔWss≤1.0mm;

[0029] When 2≤C<4, 1.4mm≤Wa-Wc≤2.6mm, 0.7mm≤ΔWss≤1.3mm;

[0030] When 4≤C<5, 2.0mm≤Wa-Wc≤3.0mm, 1.0mm≤ΔWss≤1.5mm;

[0031] Where C is the cycle charge rate, Wa is the width of the negative electrode, Wc is the width of the positive electrode, and ΔWss is the width of the negative electrode extending beyond one side.

[0032] In a preferred embodiment, the thickness of the diaphragm is 5-25 μm.

[0033] In a preferred embodiment, the diaphragm is aligned with the centerline along the length of the electrode assembly.

[0034] A lithium-ion battery comprising a pouch polymer lithium-ion battery made of an electrode assembly for charging cycles at 1C-5C rates.

[0035] The cycle charge rate C of the polymer lithium-ion battery and the widths of the positive electrode Wc, negative electrode Wa, and the width ΔWss of the negative electrode exceeding the width of the positive electrode on one side by the electrode assembly are related as follows:

[0036] When 1≤C<2, 1.0mm≤Wa-Wc≤1.3mm, 0.3mm≤ΔWss≤1.0mm;

[0037] When 2≤C<4, 1.5mm≤Wa-Wc≤2.0mm, 0.7mm≤ΔWss≤1.3mm;

[0038] When 4≤C<5, 2.2mm≤Wa-Wc≤2.5mm, 1.0mm≤ΔWss≤1.5mm;

[0039] A type of wound or stacked soft-pack polymer lithium-ion battery, made of wound or stacked electrode groups capable of 1C-5C charging cycles.

[0040] Preparation method

[0041] The positive / negative electrode sheets, wound electrode assemblies, and lithium-ion batteries described in this invention can be prepared according to conventional methods in the art. Specifically, a conductive agent, binder, active material, solvent, and dispersant are added and stirred to form an active material slurry. The active material slurry is coated onto the surface of a current collector, and then dried, rolled, and sheared to obtain electrode sheets. Pre-reserved positions on the current collector are used for welding tabs. The electrode sheets and separator prepared according to the above steps are wound or stacked to obtain wound electrode assemblies or stacked electrode assemblies, respectively. The electrode assemblies are placed in an aluminum-plastic shell, sealed from the top side, and then injected with electrolyte. After forming in a fixture, hot pressing, capacity testing, direct sealing, and sorting, lithium-ion batteries are obtained.

[0042] The effects of this invention are further illustrated below with a comparison of the embodiments and comparative examples. Example

[0043] This embodiment provides a lithium battery electrode assembly, wherein the positive electrode sheet density is 39.0 mg / cm³. 2 The compacted density is 4.2 g / cm³. 3 Width Wc = 89.0 mm; the surface density of the negative electrode is 21.4 mg / cm³. 2 The compacted density is 1.78 g / cm³. 3The electrode assembly has a width Wa = 90.0 mm, Wa - Wc = 1.0 mm, and ΔWss = 0.5 mm; the separator thickness is 8 μm. The positive and negative electrode sheets, along with the separator, are aligned and wound along the center of the electrode assembly length to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic shell, sealed from the top side, and then injected with electrolyte. It is then formed using a fixture, hot-pressed, capacity-graded, and directly sealed. Finally, it is sorted to obtain a lithium-ion battery. This lithium-ion battery is used in a 1.2C charging cycle and meets the following conditions: when 1 ≤ C < 2, 1.0 mm ≤ Wa - Wc ≤ 1.3 mm, and 0.3 mm ≤ ΔWss ≤ 1.0 mm. Example

[0044] This embodiment provides a lithium battery electrode assembly. The positive electrode sheet density is 28.0 mg / cm³. 2 The compacted density is 4.1 g / cm³. 3 The width Wc = 66.5 mm; the surface density of the negative electrode sheet is 15.0 mg / cm³. 2 The compacted density is 1.70 g / cm³. 3 The electrode assembly has a width Wa = 68.0 mm, Wa - Wc = 1.5 mm, and ΔWss = 0.75 mm; the separator thickness is 8 μm. The positive and negative electrode sheets, along with the separator, are aligned and wound along the center of the electrode assembly length to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic shell, sealed from the top side, and then injected with electrolyte. It is then formed using a fixture, hot-pressed, capacity-graded, and directly sealed, finally sorted to obtain a lithium-ion battery. This lithium-ion battery is used in a 2C rate charging cycle, satisfying the following conditions: when 2 ≤ C < 4, 1.5 mm ≤ Wa - Wc ≤ 2 mm, and 0.7 mm ≤ ΔWss ≤ 1.3 mm. Example

[0045] This embodiment provides a lithium battery electrode assembly. The positive electrode sheet density is 26.0 mg / cm³. 2 The compacted density is 4.1 g / cm³. 3 The width Wc = 75 mm; the surface density of the negative electrode sheet is 14.4 mg / cm³. 2 The compacted density is 1.65 g / cm³. 3 The electrode assembly has a width Wa = 76.5 mm, Wa-Wc = 1.5 mm, and ΔWss = 0.75 mm; the separator thickness is 10 μm. The positive and negative electrode sheets, along with the separator, are aligned and wound along the center of the electrode assembly length to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic shell, sealed from the top side, and then injected with electrolyte. It is then formed using a fixture, hot-pressed, capacity-graded, and directly sealed, finally sorted to obtain a lithium-ion battery. This lithium-ion battery is used in a 3C charging cycle and meets the following conditions: when 2 ≤ C < 4, 1.5 mm ≤ Wa-Wc ≤ 2 mm, and 0.7 mm ≤ ΔWss ≤ 1.3 mm. Example

[0046] This embodiment provides a lithium battery electrode assembly. The positive electrode sheet density is 22.4 mg / cm³. 2 The compacted density is 4.05 g / cm³. 3 The width Wc = 75.3 mm; the surface density of the negative electrode is 11.95 mg / cm³. 2 The compacted density is 1.55 g / cm³. 3 The width Wa = 77.5 mm, Wa-Wc = 2.2 mm, ΔWss = 1.1 mm; the separator thickness is 12 μm. The positive and negative electrode sheets, along with the separator, are aligned along the center of the electrode assembly length and stacked to obtain a stacked electrode assembly. The electrode assembly is placed in an aluminum-plastic shell, top-side sealed, and then injected with electrolyte. It is then formed using a fixture, hot-pressed, capacity-graded, and directly sealed, finally sorted to obtain a lithium-ion battery. This lithium-ion battery is used in a 5C charging cycle, satisfying the following conditions: when 4 ≤ C ≤ 5, 2.2 mm ≤ Wa-Wc ≤ 2.5 mm, 1.0 mm ≤ ΔWss ≤ 1.5 mm. Example

[0047] This embodiment provides a lithium battery electrode assembly. The positive electrode sheet density is 10 mg / cm³. 2 The compacted density is 2.0 g / cm³. 3 ,width W c =75.3mm; the anode sheet density is 5 mg / cm³. 2 The compacted density is 1.3 g / cm³. 3 Width W a =77.5mm, W a - W c =2.2mm, Δ W ss =1.1mm; the separator thickness is 12μm; the above positive and negative electrode sheets are aligned with the separator along the center of the electrode assembly length to obtain a stacked electrode assembly. The electrode assembly is placed in an aluminum-plastic shell, sealed on the top side, and then injected with electrolyte. It then undergoes formation, hot pressing, capacity testing, and direct sealing, and finally sorting to obtain a lithium-ion battery. This lithium-ion battery is used in a 5C rate charging cycle, satisfying the condition: when 4≤C≤5, 2.2mm≤ W a - W c ≤2.5mm, 1.0mm≤Δ W ss ≤1.5mm. Example

[0048] This embodiment provides a lithium battery electrode assembly. The positive electrode sheet density is 50 mg / cm³. 2 The compacted density is 4.5 g / cm³. 3 ,width W c =89.0mm; the anode sheet density is 30 mg / cm³. 2 The compacted density is 1.8 g / cm³. 3 Width W a =90.0mm, W a - W c =1.0mm, Δ W ss =0.5mm; the separator thickness is 8μm; the above positive and negative electrode sheets are aligned with the separator along the center of the electrode assembly length and wound to obtain a wound electrode assembly. The electrode assembly is placed in an aluminum-plastic shell, sealed on the top side, and then injected with electrolyte. It is then formed using a fixture, hot-pressed, capacity-graded, and directly sealed, and finally sorted to obtain a lithium-ion battery. This lithium-ion battery is used in a 1.2C rate charging cycle, satisfying the condition: when 1≤C<2, 1.0mm≤ W a - W c ≤1.3mm, 0.3mm≤Δ W ss ≤1.0mm.

[0049] Comparative Example 1

[0050] The wound electrode assembly and lithium-ion battery were fabricated according to Example 1. The difference lies in the width Wc of the positive electrode sheet, which is 88.5 mm, Wa-Wc = 1.5 mm, and ΔWss = 0.75 mm.

[0051] Comparative Example 2

[0052] The wound electrode assembly and lithium-ion battery were fabricated according to Example 3. The difference lies in the positive electrode width Wc = 75.2 mm, Wa - Wc = 1.3 mm, and ΔWss = 0.65 mm.

[0053] See appendix for details Figure 3-6 These are the cycle test results for each embodiment and comparative example. The volumetric energy density and cycle performance of the lithium-ion batteries in the above embodiments and comparative examples were tested. The test methods are as follows:

[0054] Volumetric energy density test

[0055] The thickness (mm) of the lithium-ion battery was measured using a 500gf platen thickness gauge (PPG), and the length and width (mm) were measured using 100gf calipers. The battery's discharge energy (Wh) was measured at 25±3℃ using a charge / discharge cycle of 0.2C constant current charging, 0.05C constant voltage cutoff, and 0.2C discharging. The volumetric energy density VED (Wh / L) of the battery was calculated using the following formula:

[0056]

[0057] Cyclic performance test

[0058] The Arbin charge-discharge equipment was used for cycle performance testing. The lithium-ion batteries in the examples and comparative examples were charged according to the corresponding charging rate at 25±3℃. The cycle test was carried out in the form of 0.05C constant voltage cutoff and 0.5C discharge. Before the test, the thickness of the battery at 30% SOC was measured using a 500gf platen thickness gauge (PPG). During the cycle, the thickness of the battery at full charge was measured every 100 cycles.

[0059] Capacity retention rate (%) = Current cycle discharge capacity (mAh) / Initial discharge capacity (mAh) × 100%;

[0060] Thickness expansion rate (%) = Fully charged thickness during cycling (mm) / Initial 30% SOC battery thickness (mm) × 100%;

[0061] After 800 cycles, the battery was disassembled to observe the lithium plating on the negative electrode surface. The severity of lithium plating on the negative electrode surface was indicated by 1, 2, 3, and 4, where 1 indicates no lithium plating, meaning there is no gray-black dead area or silver lithium metal on the negative electrode surface; 2 indicates gray-black dotted or linear lithium plating on the overhang of the negative electrode sheet; 3 indicates that, based on 2, the lithium plating area extends from the overhang towards the center of the width of the negative electrode sheet, appearing gray-black; and 4 indicates that, based on 3, the lithium plating area has extended to the center of the width of the negative electrode sheet, with silver lithium metal deposited on the overhang.

[0062] The test results are shown in Table 1.

[0063] Table 1

[0064] The comparative conclusions can be seen from Table 1.

[0065] I. Comparative Example 1 and Comparative Example 1:

[0066] Example 1: Lithium-ion battery undergoing 1.2C charging cycle ( W a - W c =1.0mm, Δ W ss=0.5mm;) compared to the lithium-ion battery with high overhang design in Comparative Example 1 ( W a - W c =1.5mm, Δ W ss Compared to the 0.75mm, the capacity retention rate and thickness expansion rate after 800 cycles were comparable. No obvious lithium plating was found on the surface of the negative electrode after disassembly after cycling. The volumetric energy density of Example 1 was 0.64% (5Wh / L) higher than that of Comparative Example 1. This indicates that although widening the single-sided overhang can reduce the risk of lithium plating during cycling under the specified charging rate, it will cause a loss of volumetric energy density.

[0067] II. Comparative Example 3 and Comparative Example 2:

[0068] Based on the lithium-ion battery provided by this utility model, further tightening the single-sided overhang can improve the volumetric energy density, but it also increases the risk of lithium deposition on the negative electrode overhang during cycling. This is further confirmed by the cycling test results and the lithium deposition on the negative electrode surface after battery disassembly.

[0069] III. Results of Examples 2 and 4: The wound electrode assembly and lithium-ion battery provided by this utility model are also applicable to 2C and 4C charging rate cycles.

[0070] Based on embodiments 1-3 or 6, the wound electrode assembly and lithium-ion battery provided by this utility model have certain applicability to application scenarios with different charging rate cycles.

[0071] The above detailed description of a lithium battery electrode assembly and a soft-pack polymer lithium-ion battery with reference to the embodiments is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes and modifications without departing from the overall concept of this utility model should be within the protection scope of this utility model.

Claims

1. A lithium battery pole pack, characterized by: A polar group comprising a positive electrode sheet, a separator, and a negative electrode sheet, along the positive electrode sheet width direction, the negative electrode sheet is aligned with the positive electrode sheet center line, the positive electrode sheet area density is 10 mg / cm 2 - 50 mg / cm 2 , the compaction density is 2.0 g / cm 3 - 4.5 g / cm 3 , the negative electrode sheet area density is 5 mg / cm 2 - 30 mg / cm 2 , the compaction density is 1.3 g / cm 3 - 1.8 g / cm 3 , the negative electrode sheet width is greater than the positive electrode sheet width, when 1≤C<2, 0.6mm≤Wa-Wc≤2.0mm, 0.3mm≤ΔWss≤1.0mm; when 2≤C<4, 1.4mm≤Wa-Wc≤2.6mm, 0.7mm≤ΔWss≤1.3mm; when 4≤C<5, 2.0mm≤Wa-Wc≤3.0mm, 1.0mm≤ΔWss≤1.5mm; wherein C is the cycle charge rate, Wa is the width of the negative electrode sheet, Wc is the width of the positive electrode sheet, and ΔWss is the width of the negative electrode sheet overhanging on one side.

2. The lithium battery pole pack of claim 1, wherein: The electrode group is a wound electrode group when 1≤C<4.

3. The lithium battery pole pack of claim 1, wherein: The electrode group is a stacked electrode group when 4≤C<5.

4. The lithium battery pole pack of claim 1, wherein: The separator has a thickness of 5-25μm.

5. The lithium battery pole pack of claim 1 or 4, wherein: The separator is aligned along the center line of the length direction of the electrode group.

6. A pouch polymer lithium ion battery characterized by: A wound or stacked soft pack polymer lithium ion battery made of the wound electrode group or the stacked electrode group for 1C-5C rate charge cycle according to any one of claims 1-5.

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