battery
By controlling the expansion ratio and optimizing the electrode capacity ratio during the charging process of lithium-ion batteries, the problem of high deformation rate during charging and discharging of lithium-ion batteries has been solved, thereby improving the cycle performance and space utilization of the batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHUHAI COSMX BATTERY CO LTD
- Filing Date
- 2023-02-28
- Publication Date
- 2026-05-12
AI Technical Summary
Existing lithium-ion batteries have a high deformation rate due to expansion and contraction during charging and discharging, which affects the space utilization of electronic products, especially in consumer and wearable devices where extra space needs to be reserved.
By controlling the expansion ratio during the charging process of lithium-ion batteries, ensuring that the expansion ratio of the battery in the later stage of charging is within the range of 1.1-1.5 compared to the early stage of charging, the areal capacity ratio of the negative electrode and the positive electrode is optimized, and the porosity and compaction density of the negative and positive electrode coatings are adjusted.
It significantly reduces the deformation rate of lithium-ion batteries after multiple cycles, improves the cycle performance and energy density of the batteries, and reduces battery deformation during charging and discharging.
Smart Images
Figure CN116314584B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of batteries, and more specifically to batteries. Background Technology
[0002] Currently widely used lithium-ion batteries are mainly composed of graphite anodes. During charging and discharging, these batteries undergo reversible expansion and contraction. Therefore, electronic products used in consumer and wearable applications require sufficient space to accommodate the batteries. This necessitates reducing the battery's expansion rate to improve the space utilization of electronic products.
[0003] Therefore, it is very important to discover a battery with a low expansion rate. Summary of the Invention
[0004] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a battery. The battery of this invention improves cycle performance and reduces the deformation rate after multiple cycles by controlling the ratio of the battery's expansion rate in the early stage of charging to that in the later stage of charging within the range of 1.1-1.5.
[0005] The expansion of lithium-ion batteries mainly originates from the volumetric strain caused by lithium intercalation in the negative electrode material during charging. The inventors of this invention have discovered a certain pattern in lithium-ion battery expansion: larger expansion in the early stages of charging, smaller expansion in the middle stages, and larger expansion in the later stages. Therefore, the expansion in the early and late stages of charging are the main factors affecting battery deformation rate. When the ratio of the battery's expansion rate in the later stages of charging to that in the early stages is within the range of 1.1-1.5, the battery deformation rate after multiple cycles is significantly reduced. This may be because: when the ratio is small (e.g., less than 1.1), the expansion rate in the early stages of charging accounts for a larger proportion, indicating lower utilization of the negative electrode active material, larger remaining capacity, and faster capacity decay in the later stages of cycling; when the ratio is large (e.g., greater than 1.5), the expansion rate in the later stages of charging accounts for a larger proportion, indicating higher utilization of the negative electrode active material, which easily leads to greater expansion.
[0006] The present invention provides a battery whose charging expansion curve includes a first stage, a second stage and a third stage, wherein the inflection point from the first stage to the second stage is A1 and the inflection point from the second stage to the third stage is A2; the expansion rate of the battery in the first stage is Δa and the expansion rate of the battery in the third stage is Δb, wherein Δa and Δb satisfy 1.1≤Δb / Δa≤1.5.
[0007] By using the above technical solution, the present invention has at least the following advantages compared with the prior art: The battery of the present invention controls the ratio of the expansion rate under different charging stages, that is, the ratio of the expansion rate of the battery in the later stage of charging to the expansion rate of the battery in the early stage of charging is in the range of 1.1-1.5, thereby improving the cycle performance of the battery while maintaining a high energy density and reducing the deformation rate of the battery after multiple cycles.
[0008] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description
[0009] Figure 1 The figure shows the charging expansion curve of the battery in an example of the present invention.
[0010] Figure 2 The figure shown is a schematic cross-sectional view of the negative electrode sheet in an example of the present invention.
[0011] Figure 3 The figure shown is a schematic cross-sectional view of the positive electrode sheet in an example of the present invention. Detailed Implementation
[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.
[0013] The first aspect of the present invention provides a battery whose charging expansion curve may include a first stage, a second stage, and a third stage. The inflection point from the first stage to the second stage may be A1, and the inflection point from the second stage to the third stage may be A2. The expansion rate of the battery in the first stage is Δa, and the expansion rate of the battery in the third stage is Δb. Δa and Δb satisfy 1.1 ≤ Δb / Δa ≤ 1.5, for example, Δb / Δa equals 1.1, 1.11, 1.12, 1.13, etc. 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.4, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, or 1.5.
[0014] In the present invention, the "charging expansion curve of the battery" refers to the curve of the expansion rate of the battery varying with the SOC during the charging process of the battery. As Figure 1 shown is the charging expansion curve of the battery in an example of the present invention. From Figure 1 it can be seen that the charging expansion curve can be divided into three stages: 0 ≤ SOC ≤ 28% is the first stage, 28% < SOC < 57.6% is the second stage, and 57.6% ≤ SOC ≤ 100% is the third stage. Among them, the inflection point A1 from the first stage to the second stage is approximately when SOC is equal to 28%, and the inflection point A2 from the second stage to the third stage is approximately when SOC is equal to 57.6%; the expansion rate Δa of the battery in the first stage is 1.19%, and the expansion rate of the battery in the third stage is Δb of 1.74%. Among them, Δa = the expansion rate of the battery at 28% SOC - the expansion rate of the battery at 0 SOC; Δb = the expansion rate of the battery at 100% SOC - the expansion rate of the battery at 57.6% SOC.
[0015] In the present invention, the term "SOC" has its conventional meaning in the art. The term "SOC" refers to the state of charge of the battery, usually expressed as a percentage. For example: when SOC is 0, it means the battery is completely discharged; when SOC is 100%, it means the battery is fully charged.
[0016] In the present invention, the expansion rate of the battery can be measured by an in-situ dilatometer, that is, during the charging process of the battery, the expansion data of the battery from 0 SOC to 100% SOC is monitored in real time, and then the charging expansion curve of the battery as shown in Figure 1 can be obtained.
[0017] It can be understood that due to the differences between different batteries, the charging expansion curves between different batteries also have differences. The "inflection point" has its conventional meaning in the art. In the present invention, the term "inflection point" refers to the point on the charging expansion curve where the slope change exceeds 30%.
[0018] The main reason for the expansion of lithium-ion batteries is the volume strain caused by the intercalation of lithium in the negative electrode material during the charging process. The inventors of the present invention have found through a large number of studies that the expansion of lithium-ion batteries has certain rules: the expansion curve of the battery during the charging process can be divided into three stages. Among them, the first stage corresponds to the early stage of charging, the second stage corresponds to the middle stage of charging, and the third stage corresponds to the late stage of charging; in the first stage (early stage of charging) and the third stage (late stage of charging), the expansion rate of the battery is relatively large, while in the second stage (middle stage of charging), the expansion rate of the battery is relatively small. As Figure 1 shown is the charging expansion curve of the battery in an example of the present invention. From Figure 1It can be seen that the expansion rate is relatively large in the first stage (early charging stage, SOC is about 0-28%) and the third stage (late charging stage, SOC is about 57.6%-100%), at about 1.19% and 1.74% respectively; while the expansion rate is relatively small in the second stage (mid-charging stage, SOC is about 28%-57.6%), at about 0.5%. Therefore, the expansion rates in the first stage (early charging) and the third stage (late charging) are the main factors affecting battery deformation. By controlling the ratio of the expansion rate in the third stage (late charging) to that in the first stage (early charging) within the range of 1.1-1.5, the deformation rate of the lithium-ion battery after multiple cycles can be significantly reduced. The reason may be that when Δb / Δa is small (less than 1.1, for example, equal to 1), the expansion rate of the battery in the first stage (early charging, SOC approximately 0-28%) is relatively large, indicating that the utilization rate of the negative electrode active material is low, the remaining capacity of the negative electrode is large, and the capacity decay is faster in the later stage of the cycle. When Δb / Δa is large (greater than 1.5, for example, equal to 1.6), the expansion rate of the battery in the third stage (late charging, SOC approximately 57.6%-100%) is relatively large, indicating that the utilization rate of the negative electrode active material is high, which easily leads to greater expansion. In addition, the delithiation cutoff potential of the negative electrode material is higher, which may cause more side reactions and lead to the failure of the negative electrode active material. By controlling Δb / Δa within the range of 1.1-1.5, the ratio between the positive and negative electrodes can be effectively balanced, resulting in a smaller deformation rate and better cycle performance while meeting battery performance requirements.
[0019] In one instance, 1.15 ≤ Δb / Δa ≤ 1.35.
[0020] In this invention, the range of values for Δa and Δb is not specifically limited. As long as 1.1≤Δb / Δa≤1.5, a good technical effect can be achieved.
[0021] In this invention, 0.70≤Δa≤1.60, for example 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50 or 1.60.
[0022] In one instance, 0.80 ≤ Δa ≤ 1.50.
[0023] In one instance, 1.05 ≤ Δa ≤ 1.10.
[0024] In the present invention, 0.77 ≤ Δb ≤ 2.40, such as 0.77, 0.80, 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30 or 2.40.
[0025] In one example, 0.90 ≤ Δb ≤ 2.10.
[0026] In one example, 1.10 ≤ Δb ≤ 1.70.
[0027] The A1 can be located at 0 < SOC ≤ 30% (such as SOC being 1%, 5%, 10%, 15%, 20%, 25% or 30%), and the A2 can be located at 50% ≤ SOC ≤ 100% (such as SOC being 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%).
[0028] The battery may further include a negative electrode sheet, which may include a negative electrode current collector and a negative electrode coating on at least one surface of the negative electrode current collector. As Figure 2 Shown is a schematic cross-sectional view of the negative electrode sheet in one example of the present invention, where Figure 2 (a) is the case where the negative electrode coating is coated on one side, Figure 2 (b) is the case where the negative electrode coating is coated on both sides. In Figure 2 (a), the negative electrode sheet includes a negative electrode current collector 1 and a negative electrode coating 2 on one surface of the negative electrode current collector 1; in Figure 2 (b), the negative electrode sheet includes a negative electrode current collector 1 and negative electrode coatings 2 on both surfaces of the negative electrode current collector 1.
[0029] The battery may further include a positive electrode sheet, which may include a positive electrode current collector and a positive electrode coating on at least one surface of the positive electrode current collector. As Figure 3 Shown is a schematic cross-sectional view of the positive electrode sheet in one example of the present invention, where Figure 3 (a) is the case where the positive electrode coating is coated on one side, Figure 3 (b) is the case where the positive electrode coating is coated on both sides. In Figure 3 (a), the positive electrode sheet includes a positive electrode current collector 3 and a positive electrode coating 4 on one surface of the positive electrode current collector 3; in Figure 3 (b), the positive electrode sheet includes a positive electrode current collector 3 and positive electrode coatings 4 on both surfaces of the positive electrode current collector 3.
[0030] The inventors of the present invention found that in order to control Δb / Δa within the range of 1.1 - 1.5, the ratio of the areal capacity of the negative electrode sheet to the areal capacity of the positive electrode sheet can be defined.
[0031] The ratio of the areal capacity of the negative electrode to the areal capacity of the positive electrode can be (1.01-1.2):1, for example, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.1:1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, 1.15:1, 1.16:1, 1.17:1, 1.18:1, 1.19:1 or 1.2:1.
[0032] In one example, the ratio of the areal capacity of the negative electrode to the areal capacity of the positive electrode is (1.03-1.08):1.
[0033] The areal capacity of the negative electrode can be 1.6 mAh / cm³. 2 -4.4mAh / cm 2 For example, 1.6mAh / cm 2 2mAh / cm 2 2.5mAh / cm 2 3mAh / cm 2 3.5mAh / cm 2 4mAh / cm 2 Or 4.4mAh / cm 2 .
[0034] In one example, the areal capacity of the negative electrode is 1.9 mAh / cm². 2 -2.3mAh / cm 2 .
[0035] The areal capacity of the positive electrode can be 1.5 mAh / cm². 2 -4.0mAh / cm 2 For example, 1.5mAh / cm 2 2mAh / cm 2 2.5mAh / cm 2 3mAh / cm 2 3.5mAh / cm 2 Or 4.0mAh / cm 2 .
[0036] In one example, the areal capacity of the positive electrode is 1.8 mAh / cm². 2 -2.2mAh / cm 2 .
[0037] In this invention, the "area capacity of the positive electrode" and the "area capacity of the negative electrode" can be measured by the following method, specifically as follows: taking an area of 25 cm²... 2The positive electrode plate has an area of 25 cm². 2 The negative electrode was assembled with a lithium sheet to form a half-cell. The areal capacity of the positive electrode and the areal capacity of the negative electrode were measured by charging and discharging at 0.05C.
[0038] The areal density of the positive electrode can be 0.01 mg / cm³. 2 -30mg / cm 2 For example, 0.01 mg / cm³ 2 0.05 mg / cm 2 0.1 mg / cm 2 0.5 mg / cm 2 1mg / cm 2 5mg / cm 2 10mg / cm 2 15mg / cm 2 20mg / cm 2 25mg / cm 2 Or 30mg / cm 2 .
[0039] In one example, the areal density of the positive electrode is 11.5 mg / cm³. 2 -13.5mg / cm 2 .
[0040] The areal density of the negative electrode can be 0.01 mg / cm³. 2 -15mg / cm 2 For example, 0.01 mg / cm³ 2 0.05 mg / cm 2 0.1 mg / cm 2 0.5 mg / cm 2 1mg / cm 2 5mg / cm 2 10mg / cm 2 Or 15mg / cm 2 .
[0041] In one example, the areal density of the negative electrode is 4.5 mg / cm³. 2 -6mg / cm 2 .
[0042] The compaction density of the negative electrode coating can be 1.0 g / cm³. 3 -2.0g / cm 3 For example, 1g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 or 2g / cm 3 .
[0043] The compaction density of the positive electrode coating is 3.2 g / cm³. 3 -4.8g / cm 3 For example, 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 3.9g / cm 3 4g / cm 3 4.1g / cm 3 4.2g / cm 3 4.3g / cm 3 4.4 g / cm 3 4.5g / cm 3 4.6g / cm 3 4.7g / cm 3 Or 4.8g / cm 3 .
[0044] The inventors of this invention have discovered that when the porosity of the negative electrode coating and the porosity of the positive electrode coating are both within a certain range, the cycle performance of the battery is better.
[0045] The porosity of the negative electrode coating can be 20%-45%, for example 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%.
[0046] The porosity of the positive electrode coating can be 20%-45%, for example 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%.
[0047] The negative electrode coating may include a negative electrode active material, a first binder, and a first conductive agent.
[0048] The negative electrode active material can be selected from negative electrode active materials commonly used in the art, such as at least one of graphite, hard carbon, soft carbon, silicon, silicon-oxygen materials, silicon-carbon materials and metal oxides.
[0049] Based on the total weight of the negative electrode coating, the content of the negative electrode active material can be 80-99% by weight (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% by weight), the content of the first binder can be 0.5-10% by weight (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5% by weight), and the content of the first conductive agent can be 0.5-10% by weight (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5% by weight).
[0050] In one example, based on the total weight of the negative electrode coating, the content of the negative electrode active material is 95-97% by weight, the content of the first binder is 1.5-2.5% by weight, and the content of the first conductive agent is 1.5-2.5% by weight.
[0051] The positive electrode coating may include a positive electrode active material, a second binder, and a second conductive agent.
[0052] The positive electrode active material can be selected from the positive electrode active materials commonly used in the art, such as lithium cobalt oxide, nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials, nickel cobalt manganese aluminum quaternary materials, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel manganese oxide binary materials, lithium-rich manganese-based materials, and lithium manganese iron phosphate.
[0053] Based on the total weight of the positive electrode coating, the content of the positive electrode active material can be 80-99% by weight (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% by weight), the content of the second binder can be 0.5-10% by weight (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5% by weight), and the content of the second conductive agent can be 0.5-10% by weight (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5% by weight).
[0054] In one example, based on the total weight of the positive electrode coating, the content of the positive electrode active material is 95-98% by weight, the content of the second binder is 1-2.5% by weight, and the content of the second conductive agent is 1-2.5% by weight.
[0055] The first adhesive and the second adhesive may be selected from adhesives conventionally used in the art, such as at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, polyurethane, fluorinated rubber, polyvinyl alcohol or sodium polyacrylate.
[0056] The first conductive agent and the second conductive agent may be selected from conductive agents commonly used in the art, such as at least one selected from conductive carbon black, acetylene black, conductive graphite, carbon nanotubes and carbon fibers.
[0057] The thickness of the negative electrode current collector can be 4μm-6μm, for example, 4μm, 5μm or 6μm.
[0058] The thickness of the positive electrode current collector can be 9μm-11μm, for example, 9μm, 10μm or 11μm.
[0059] The thickness of the negative electrode coating can be 25μm-120μm, for example, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm or 120μm.
[0060] In one example, the thickness of the negative electrode coating is 25 μm-33 μm.
[0061] The thickness of the positive electrode coating can be 20μm-100μm, for example, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm.
[0062] In one example, the thickness of the positive electrode coating is 25 μm-33 μm.
[0063] In this invention, the thickness of the negative electrode coating refers to the thickness of the negative electrode coating on one side; the thickness of the positive electrode coating refers to the thickness of the positive electrode coating on one side.
[0064] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.
[0065] The battery of the present invention can significantly improve battery expansion and enhance cycle performance by controlling the ratio of the battery expansion rate in the later stage of charging to the battery expansion rate in the early stage of charging within the range of 1.1-1.5.
[0066] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
[0067] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.
[0068] The following examples illustrate the battery of the present invention.
[0069] Example 1
[0070] Prepare the battery according to the following steps:
[0071] (1) Preparation of negative electrode:
[0072] Graphite, conductive carbon black, and styrene-butadiene latex were added to a mixing tank in a mass ratio of 96.5:1.5:2, followed by deionized water. The mixture, containing 45 wt% solids, was passed through a 200-mesh sieve to obtain a negative electrode slurry. This slurry was then coated onto both sides of a copper foil (5 μm thick) using a transfer coating machine. After drying at 120°C and rolling, a negative electrode sheet was obtained. The negative electrode coating had a thickness of 30.6 μm, a porosity of 27.7%, and a compaction density of 1.75 g / cm³. 3 The areal density of the negative electrode is 5.35 mg / cm³. 2 The areal capacity of the negative electrode is 2.144 mAh / cm². 2 ;
[0073] (2) Preparation of positive electrode sheet:
[0074] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 97.6:1.4:1. N-methylpyrrolidone (75 wt% solids) was then added. The mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry. This slurry was coated onto both sides of an aluminum foil (10 μm thick) using a coating machine. After drying at 120°C and rolling, a positive electrode sheet was obtained. The positive electrode coating had a thickness of 29.8 μm, a porosity of 23.4%, and a compaction density of 4.15 g / cm³. 3 The areal density of the positive electrode is 12.38 mg / cm³. 2 The areal capacity of the positive electrode is 2.042 mAh / cm². 2 ;
[0075] (3) Battery fabrication:
[0076] The negative electrode obtained in step (1) and the positive electrode obtained in step (2) are wound together with the separator to form a core (width is 62mm), packaged with aluminum-plastic film, baked to remove moisture, injected with electrolyte, and hot-pressed to form a battery.
[0077] Example 2
[0078] Prepare the battery according to the following steps:
[0079] (1) Preparation of negative electrode:
[0080] Graphite, conductive carbon black, and styrene-butadiene latex were added to a mixing tank in a mass ratio of 96.5:1.5:2, followed by deionized water. The mixture, containing 45 wt% solids, was passed through a 200-mesh sieve to obtain a negative electrode slurry. This slurry was then coated onto both sides of a copper foil (5 μm thick) using a transfer coating machine. After drying at 120°C and rolling, a negative electrode sheet was obtained. The negative electrode coating had a thickness of 28.3 μm, a porosity of 27.5%, and a compaction density of 1.75 g / cm³. 3 The areal density of the negative electrode is 4.95 mg / cm³. 2 The surface capacity of the negative electrode is 1.984 mAh / cm². 2 ;
[0081] (2) Preparation of positive electrode sheet:
[0082] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 97.6:1.4:1. N-methylpyrrolidone (75 wt% solids) was then added. The mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry. This slurry was coated onto both sides of an aluminum foil (10 μm thick) using a coating machine. After drying at 120°C and rolling, a positive electrode sheet was obtained. The positive electrode coating had a thickness of 26.8 μm, a porosity of 23.5%, and a compaction density of 4.15 g / cm³. 3 The areal density of the positive electrode is 11.14 mg / cm³. 2 The surface capacity of the positive electrode is 1.837 mAh / cm². 2 ;
[0083] (3) Battery fabrication:
[0084] The negative electrode obtained in step (1) and the positive electrode obtained in step (2) are wound together with the separator to form a core (width is 62mm), packaged with aluminum-plastic film, baked to remove moisture, injected with electrolyte, and hot-pressed to form a battery.
[0085] Example 3
[0086] Prepare the battery according to the following steps:
[0087] (1) Preparation of negative electrode:
[0088] Graphite, conductive carbon black, and styrene-butadiene latex were added to a mixing tank in a mass ratio of 96.5:1.5:2, followed by deionized water. The mixture, containing 45 wt% solids, was passed through a 200-mesh sieve to obtain a negative electrode slurry. This slurry was then coated onto both sides of a copper foil (5 μm thick) using a transfer coating machine. After drying at 120°C and rolling, a negative electrode sheet was obtained. The negative electrode coating had a thickness of 32.3 μm, a porosity of 27.8%, and a compaction density of 1.75 g / cm³. 3 The areal density of the negative electrode is 5.66 mg / cm³. 2 The negative electrode has an area capacity of 2.266 mAh / cm². 2 ;
[0089] (2) Preparation of positive electrode sheet:
[0090] Lithium cobalt oxide, acetylene black, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 97.6:1.4:1. N-methylpyrrolidone (75 wt% solids) was then added. The mixture was passed through a 200-mesh sieve to obtain a positive electrode slurry. This slurry was coated onto both sides of an aluminum foil (10 μm thick) using a coating machine. After drying at 120°C and rolling, a positive electrode sheet was obtained. The positive electrode coating had a thickness of 32.1 μm, a porosity of 23.2%, and a compaction density of 4.15 g / cm³. 3 The areal density of the positive electrode is 13.34 mg / cm³. 2 The surface capacity of the positive electrode is 2.200 mAh / cm². 2 ;
[0091] (3) Battery fabrication:
[0092] The negative electrode obtained in step (1) and the positive electrode obtained in step (2) are wound together with the separator to form a core (width is 62mm), packaged with aluminum-plastic film, baked to remove moisture, injected with electrolyte, and hot-pressed to form a battery.
[0093] Example 4
[0094] This set of examples is used to verify the impact of changes in the ratio of negative electrode surface capacity to positive electrode surface capacity.
[0095] This set of embodiments is based on Embodiment 1, except that the ratio of the negative electrode capacity to the positive electrode capacity is changed. Specifically:
[0096] In Example 4a, the thickness of the positive electrode coating was 26.1 μm, the porosity of the positive electrode coating was 23.3%, and the areal density of the positive electrode sheet was 10.83 mg / cm³.2 The surface capacity of the positive electrode is 1.787 mAh / cm². 2 ;
[0097] In Example 4b, the thickness of the positive electrode coating was 30.7 μm, the porosity of the positive electrode coating was 23.2%, and the areal density of the positive electrode sheet was 12.74 mg / cm³. 2 The areal capacity of the positive electrode is 2.102 mAh / cm². 2 ;
[0098] In Example 4c, the thickness of the positive electrode coating was 30.6 μm, the porosity of the positive electrode coating was 23.7%, and the areal density of the positive electrode sheet was 12.68 mg / cm³. 2 The surface capacity of the positive electrode is 2.092 mAh / cm². 2 ;
[0099] In Example 4d, the thickness of the positive electrode coating was 31.0 μm, the porosity of the positive electrode coating was 23.1%, and the areal density of the positive electrode sheet was 12.87 mg / cm³. 2 The areal capacity of the positive electrode is 2.123 mAh / cm². 2 .
[0100] Comparative Example 1
[0101] The procedure was carried out in accordance with Example 1, except that the ratio of negative electrode surface capacity to positive electrode surface capacity was changed. Specifically, the thickness of the positive electrode coating was 25.1 μm, the porosity of the positive electrode coating was 23.6%, and the areal density of the positive electrode sheet was 10.40 mg / cm³. 2 The areal capacity of the positive electrode is 1.715 mAh / cm². 2 .
[0102] Comparative Example 2
[0103] The procedure was carried out in accordance with Example 1, except that the ratio of negative electrode surface capacity to positive electrode surface capacity was changed. Specifically, the thickness of the positive electrode coating was 31.2 μm, the porosity of the positive electrode coating was 23.3%, and the areal density of the positive electrode sheet was 12.93 mg / cm³. 2 The surface capacity of the positive electrode is 2.133 mAh / cm². 2 .
[0104] Test case
[0105] (1) Battery expansion rate
[0106] Using an in-situ dilatometer, the batteries prepared in the examples and comparative examples were charged. Specifically, the batteries were discharged to the lower limit voltage of 3.0V, left to stand for 2 hours, and then charged to 4.5V at a constant current of 0.05C at 25°C. The expansion data of the batteries from 0SOC to 100%SOC was monitored in real time during the charging process using an in-situ dilatometer, and the results are recorded in Table 1.
[0107] Table 1
[0108]
[0109]
[0110] (2) Capacity retention test
[0111] Battery capacity was tested and energy density was calculated at 0.2C / 0.2C charge / discharge at 25℃. Cycling performance at 1C / 1C at 25℃ was also tested. The capacity retention rate after 500 cycles is recorded in Table 2.
[0112] (3) Expansion rate test
[0113] Using an in-situ dilatometer, the results were recorded in Table 2 after 500 cycles at 25°C and 1C / 1C conditions.
[0114] Table 2
[0115] Capacity retention rate (%) after 500 cycles at 25°C Expansion rate (%) after 500 cycles at 25℃ Example 1 92.2 9.0 Example 2 91.5 9.2 Example 3 91.7 10.0 Example 4a 90.1 9.8 Example 4b 91.0 10.5 Example 4c 89.9 11.2 Example 4d 89.2 11.9 Comparative Example 1 87.1 12.3 Comparative Example 2 88.2 13.0
[0116] As can be seen from Table 2, compared with the comparative example, the battery of the present invention has a significantly improved capacity retention rate after 500 cycles at 25°C and a significantly reduced expansion rate after 500 cycles at 25°C, which significantly improves the cycle performance and deformation rate after cycling.
[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A battery, characterized in that, The charging expansion curve of the battery includes a first stage, a second stage, and a third stage. The inflection point from the first stage to the second stage is A1, and the inflection point from the second stage to the third stage is A2. The expansion rate of the battery in the first stage is Δa, and the expansion rate of the battery in the third stage is Δb, and 1.1 ≤ Δb / Δa ≤ 1.5 is satisfied for Δa and Δb. A1 is located at 0 < SOC ≤ 30%, and A2 is located at 50% ≤ SOC ≤ 100%. The slope change of the inflection point on the charging expansion curve exceeds 30%. The battery further includes a negative electrode sheet and a positive electrode sheet, and the ratio of the areal capacity of the negative electrode sheet to the areal capacity of the positive electrode sheet is (1.01 - 1.2):
1.
2. The battery according to claim 1, wherein, 1.15 ≤ Δb / Δa ≤ 1.35; and / or, 0.70 ≤ Δa ≤ 1.60; and / or, 0.77 ≤ Δb ≤ 2.
40.
3. The battery according to claim 1 or 2, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode coating on at least one surface of the negative electrode current collector; the positive electrode sheet includes a positive electrode current collector and a positive electrode coating on at least one surface of the positive electrode current collector.
4. The battery according to claim 1, wherein, The ratio of the areal capacity of the negative electrode sheet to the areal capacity of the positive electrode sheet is (1.03 - 1.08):
1.
5. The battery according to claim 1, wherein, The areal capacity of the negative electrode is 1.6 mAh / cm². 2 -4.4mAh / cm 2 ; And / or, the areal capacity of the positive electrode is 1.5 mAh / cm². 2 -4.0mAh / cm 2 .
6. The battery according to claim 5, wherein, The areal capacity of the negative electrode is 1.9 mAh / cm². 2 -2.3mAh / cm 2 The areal capacity of the positive electrode is 1.8 mAh / cm². 2 -2.2mAh / cm 2 .
7. The battery according to claim 3, wherein, The compaction density of the negative electrode coating is 1.0 g / cm³. 3 -2.0g / cm 3 ; And / or, the compaction density of the positive electrode coating is 3.2 g / cm³. 3 -4.8g / cm 3 ; and / or, the porosity of the negative electrode coating is 20% - 45%; and / or, the porosity of the positive electrode coating is 20% - 45%.
8. The battery according to claim 3, wherein, The thickness of the negative electrode coating is 25μm - 120μm; and / or, the thickness of the positive electrode coating is 20μm - 100μm.
9. The battery according to claim 8, wherein, The thickness of the negative electrode coating is 25μm - 33μm, and the thickness of the positive electrode coating is 25μm - 33μm.
10. The battery according to claim 3, wherein, The negative electrode coating includes a negative electrode active material, a first binder, and a first conductive agent; and / or, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, silicon, silicon oxide material, silicon carbon material, and metal oxide; and / or, based on the total weight of the negative electrode coating, the content of the negative electrode active material is 80 - 99 wt%, the content of the first binder is 0.5 - 10 wt%, and the content of the first conductive agent is 0.5 - 10 wt%; and / or, the thickness of the negative electrode current collector is 4μm - 6μm.
11. The battery according to claim 3, wherein, The positive electrode coating includes a positive electrode active material, a second binder, and a second conductive agent; and / or, the positive electrode active material includes at least one of lithium cobalt oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, nickel cobalt manganese aluminum quaternary material, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium nickelate, lithium manganate, nickel manganese lithium binary material, lithium-rich manganese-based, and lithium manganese iron phosphate; and / or, based on the total weight of the positive electrode coating, the content of the positive electrode active material is 80 - 99 wt%, the content of the second binder is 0.5 - 10 wt%, and the content of the second conductive agent is 0.5 - 10 wt%; and / or, the thickness of the positive electrode current collector is 9μm - 11μm.