WO2023164915A1 - 电化学装置和电子装置 - Google Patents

电化学装置和电子装置 Download PDF

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WO2023164915A1
WO2023164915A1 PCT/CN2022/079190 CN2022079190W WO2023164915A1 WO 2023164915 A1 WO2023164915 A1 WO 2023164915A1 CN 2022079190 W CN2022079190 W CN 2022079190W WO 2023164915 A1 WO2023164915 A1 WO 2023164915A1
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negative electrode
active material
electrode active
material layer
electrochemical device
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PCT/CN2022/079190
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English (en)
French (fr)
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王莹莹
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宁德新能源科技有限公司
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Priority to PCT/CN2022/079190 priority Critical patent/WO2023164915A1/zh
Priority to CN202280004048.2A priority patent/CN117256056A/zh
Publication of WO2023164915A1 publication Critical patent/WO2023164915A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of energy storage, in particular to an electrochemical device and an electronic device.
  • lithium-ion batteries are widely used in 3C digital, electric tools, energy storage grid, aerospace and other fields.
  • the positive and negative electrode materials are the key substances that determine the performance of the battery.
  • graphite negative electrode active materials with a low degree of orientation have small Z-direction cyclic expansion and excellent dynamic performance, which can effectively reduce the thickness expansion rate of lithium-ion batteries.
  • graphite with a low degree of orientation is often not easy to disperse, and the homogenization of the slurry is poor, which in turn leads to a high deformation rate of lithium-ion batteries, which limits its large-scale application.
  • the present application provides an electrochemical device and an electronic device including the electrochemical device.
  • the electrochemical device of the present application takes into account high volumetric energy density, excellent cycle performance and low-temperature rate performance.
  • the present application provides an electrochemical device, which includes a negative electrode, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a negative electrode additive, and the negative electrode active material includes graphite, wherein, The orientation index OI of the negative electrode active material is ⁇ 11, and the weight loss rate of the negative electrode active material layer is W T % within the temperature range of 25 ° C to 600 ° C by using thermogravimetric test, 1 ⁇ W T ⁇ 2.5. In the present application, when the W T value is within the above range, the cycle performance and rate comprehensive performance of the electrochemical device are optimal.
  • the W T value is too small, the consistency of the slurry homogenate for preparing the negative electrode active material layer is poor, so that the cohesion between the negative electrode active material layer and the current collector is low, and then the expansion of graphite in the XY direction cannot be suppressed during the cycle, resulting in The cycle expansion rate and deformation rate of the electrochemical device increase. If the W T value is too large, the graphite content of the negative electrode active material will be too low, resulting in a decrease in the ionic conductivity of the pole piece, resulting in a decrease in the discharge rate of the electrochemical device.
  • the orientation index OI of the negative electrode active material is the ratio of the peak area of the surface (004) to the peak area of the surface (110) obtained by testing the negative electrode active material by X-ray diffraction method.
  • the tap density TD g/cm 3 of the negative electrode active material is ⁇ 0.9 g/cm 3 .
  • the weight loss rate of the negative electrode active material layer is a% in the temperature range of 200°C to 360°C, and the weight loss of the negative electrode active material layer in the temperature range of 360°C to 450°C is measured by thermogravimetric testing.
  • the rate is b%, meeting at least one of the following conditions: (I) a+b ⁇ 2.5; (II) a ⁇ 1.5b; (III) a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100.
  • the negative electrode active material layer satisfies at least one of the conditions (a) or (b): (a) 0.8 ⁇ a ⁇ 2, 0.1 ⁇ b ⁇ 0.7; (b) 0.6 ⁇ TD ⁇ 0.9 .
  • the weight loss rate of the negative electrode active material layer is a% in the temperature range of 200°C to 360°C, and the weight loss of the negative electrode active material layer in the temperature range of 360°C to 450°C is measured by thermogravimetric testing.
  • the rate is b%, where a+b ⁇ 2.5. If the value of a+b is too large, the graphite content of the negative electrode active material will be too low, which in turn will reduce the ionic conductivity of the pole piece, resulting in a decrease in the discharge rate of the electrochemical device.
  • the weight loss rate of the negative electrode active material layer is a% within the temperature range of 200° C. to 360° C. by thermogravimetric test, wherein 0.8 ⁇ a ⁇ 2.2. In some embodiments, 0.8 ⁇ a ⁇ 2.0. In some embodiments, 1.1 ⁇ a ⁇ 1.9.
  • the value of a is related to the content of the negative electrode additive in the negative electrode active material layer, and the larger the value of a, the higher the content of the negative electrode additive in the negative electrode active material layer. If the value of a is too large, correspondingly, the content of the negative electrode active material graphite is too low, and the ionic conductivity of the pole piece decreases, resulting in poor discharge rate performance of the electrochemical device.
  • the a value is too small, the amount of negative electrode additive is too small, the homogenization of the slurry for preparing the negative electrode active material layer is poor, and the bonding force between the negative electrode active material layer and the current collector is weak, which in turn makes the cyclic expansion rate and deformation of the electrochemical device rate increases.
  • the weight loss rate of the negative electrode active material layer is b% in the temperature range of 360° C. to 450° C. by thermogravimetric test, wherein 0.1 ⁇ b ⁇ 0.7. In some embodiments, 0.2 ⁇ b ⁇ 0.5.
  • the larger the value of b the higher the cohesive force of the pole piece. High cohesive force can inhibit the expansion of graphite in the XY direction, thereby reducing the cycle deformation rate of the electrochemical device and improving its cycle capacity retention rate.
  • the b value is too large, the ionic conductivity of the pole piece will decrease, resulting in a decrease in the discharge rate of the electrochemical device.
  • the weight loss rate of the negative electrode active material layer is a% within the temperature range of 200°C to 360°C, and the tap density TD g/cm 3 of the negative electrode active material is ⁇ 0.9g/ cm 3 , where a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100.
  • a and TD satisfy the relational expression a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100, the homogenization consistency of the negative electrode active material layer slurry is good, and a uniformly dispersed bonding network can be formed in the negative electrode active material layer, which is conducive to improving the battery life.
  • the cycle capacity retention rate of the chemical device and the reduction of its cycle deformation rate is a% within the temperature range of 200°C to 360°C, and the tap density TD g/cm 3 of the negative electrode active material is ⁇ 0.9g/ cm 3 , where a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100.
  • the negative electrode active material layer contains substances having absorption peaks in the range of 1540 cm ⁇ 1 to 1630 cm ⁇ 1 by Fourier transform infrared testing.
  • the absorption peak at 1540cm -1 to 1630cm -1 represents the stretching vibration of the carboxyl group.
  • the negative electrode additive includes at least one of hydroxyalkyl carboxymethyl cellulose or an alkali metal salt of hydroxyalkyl carboxymethyl cellulose.
  • the hydroxyalkyl carboxymethyl cellulose includes at least one of C 2 -C 6 hydroxyalkyl carboxymethyl cellulose.
  • the alkali metal salt of hydroxyalkyl carboxymethyl cellulose includes at least one of the alkali metal salts of C 2 -C 6 hydroxyalkyl carboxymethyl cellulose.
  • the alkali metal salt of hydroxyalkyl carboxymethyl cellulose includes at least one of an alkali metal salt of hydroxyethyl carboxymethyl cellulose or an alkali metal salt of hydroxypropyl carboxymethyl cellulose kind.
  • the alkali metal is lithium, sodium, potassium, rubidium, or cesium.
  • the negative electrode additive includes hydroxypropyl carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, hydroxyethyl carboxymethyl cellulose, hydroxypropyl carboxymethyl cellulose, At least one of lithium ethyl carboxymethyl cellulose or sodium hydroxyethyl carboxymethyl cellulose.
  • This kind of graphite with low OI value (OI ⁇ 11) and low TD (TD ⁇ 0.9) is not easy to disperse, and often requires a large amount of dispersant to ensure the consistency of the homogenate.
  • Sodium carboxymethyl cellulose (CMC) is used as a dispersant in conventional negative electrode sheets.
  • CMC can disperse suspended graphite and bind graphite particles, due to its high brittleness, the viscosity in the active material layer during cold pressing The junction network is easily damaged, and the improvement of the cycle deformation rate of the electrochemical device is limited.
  • the hydroxyalkyl substitution degree of the negative electrode additive is 0.1 to 0.3. In some embodiments, the hydroxyalkyl substitution degree of the negative electrode additive is 0.16 to 0.28. In some embodiments, the degree of carboxymethyl substitution of the negative electrode additive is 0.5 to 0.9. As the substitution degree of the hydroxyalkyl group increases, the flexibility of the negative electrode additive increases and the brittleness decreases. After the pole piece containing the negative electrode additive is rolled, the bonding network damage under the action of external force is reduced, and the bonding performance is improved.
  • the highly flexible negative electrode additive can also reduce the bond brittle cracks caused by graphite expansion and contraction during the cycle, which is beneficial to improve the cycle capacity retention rate and reduce the cycle deformation rate of the electrochemical device.
  • the hydroxyalkyl substitution is too high, the bulk strength of the negative electrode additive will be reduced, which will lead to a decrease in the binding force of the corresponding pole piece.
  • the negative electrode additive includes at least one of alkali metal salts of hydroxyalkyl carboxymethyl cellulose
  • the negative electrode active material layer includes region A and region B, wherein the content of alkali metal elements in region A is the same as The ratio of the alkali metal element content in the area B is 0.8 to 1.2, wherein, the area A is the area from the center of the thickness direction of the negative electrode active material layer to the surface side of the negative electrode active material layer, and the area B is from the thickness of the negative electrode active material layer The direction starts from the center to the area on the side of the negative electrode current collector.
  • the negative electrode additive includes at least one of alkali metal salts of C 2 -C 6 hydroxyalkyl carboxymethylcellulose, wherein the content of alkali metal elements in region A is equal to the content of alkali metal elements in region B The ratio is 0.8 to 1.2. In some embodiments, the negative electrode additive includes lithium hydroxypropyl carboxymethyl cellulose, wherein the ratio of the lithium element content in region A to the lithium element content in region B is 0.8 to 1.2.
  • the negative active material layer further includes a binder.
  • the binder includes styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, water-based acrylic resin , polyvinyl formal or at least one of styrene-acrylic copolymer resin.
  • the electrochemical device satisfies at least one of the conditions (i) or (ii): (i) the binding force between the negative electrode active material layer and the negative electrode current collector is 8N/m to 15N/m m; (ii) The ionic conductivity of the negative electrode is 0.1 S/cm to 0.4 S/cm.
  • the present application provides an electronic device, which includes the electrochemical device of the second aspect.
  • high-activity materials can be prepared by using low orientation index (orientation index ⁇ 11) low tap density (tap density ⁇ 0.9) graphite and hydroxyalkyl carboxymethyl cellulose additives and optimizing the ratio content of the negative pole piece, and then make the electrochemical device containing the pole piece have high volumetric energy density, excellent cycle performance and low temperature rate performance.
  • FIG. 1 is an infrared spectrum of an anode additive in an electrochemical device according to some embodiments of the present application.
  • FIG. 2 is a thermogravimetric graph of an anode active material layer in an electrochemical device according to some embodiments of the present application.
  • the application provides an electrochemical device, which includes a negative electrode, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a negative electrode additive, and the negative electrode active material includes graphite, wherein the negative electrode active material Orientation index OI ⁇ 11, using thermogravimetric test, within the temperature range of 25°C to 600°C, the weight loss rate of the negative electrode active material layer is W T %, 1 ⁇ W T ⁇ 2.5.
  • the W T value is within the above range, the cycle performance and rate comprehensive performance of the electrochemical device are optimal.
  • the W T value is too small, the uniformity of the homogenate in the preparation of the negative electrode active material layer is poor, so that the cohesive force between the negative electrode active material layer and the current collector is low, and then during the cycle, the expansion of graphite in the XY direction cannot be suppressed, resulting in electrochemical The cyclic expansion rate and deformation rate of the device increase. If the W T value is too large, the graphite content of the negative electrode active material will be too low, resulting in a decrease in the ionic conductivity of the pole piece.
  • W T is in the range of 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or a combination of any two of these values. In some embodiments, 1.5 ⁇ W T ⁇ 2.2.
  • the OI is 5.0, 5.5, 6.0, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5 or a range consisting of any two of these values.
  • the orientation index OI of the negative electrode active material is the ratio of the peak area of the surface (004) to the peak area of the surface (110) obtained by testing the negative electrode active material by X-ray diffraction method.
  • the tap density TD g/cm 3 of the negative electrode active material is ⁇ 0.9 g/cm 3 .
  • TD is a range of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or a combination of any two of these values. In some embodiments, 0.6 ⁇ TD ⁇ 0.9.
  • the weight loss rate of the negative electrode active material layer is a% in the temperature range of 200°C to 360°C, and the weight loss of the negative electrode active material layer in the temperature range of 360°C to 450°C is measured by thermogravimetric testing.
  • the rate is b%, where a+b ⁇ 2.5. If the value of a+b is too large, the graphite content of the negative electrode active material will be too low, which in turn will reduce the ionic conductivity of the pole piece, resulting in a decrease in the discharge rate of the electrochemical device.
  • a+b is 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or a range consisting of any two of these values. In some embodiments, 1.5 ⁇ a+b ⁇ 2.2.
  • the weight loss rate of the negative electrode active material layer is a% within the temperature range of 200° C. to 360° C. by thermogravimetric test, wherein 0.8 ⁇ a ⁇ 2.2.
  • a is a range of 0.9, 1.0, 1.15, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.95, 2.0, 2.1, or a combination of any two of these values.
  • 0.8 ⁇ a ⁇ 2.0 In some embodiments, 1.1 ⁇ a ⁇ 1.9.
  • the a value is related to the content of the negative electrode additive in the negative electrode active material layer, and the larger the value of a, the higher the content of the negative electrode additive in the negative electrode active material layer.
  • the value of a is too large, correspondingly, the content of the negative electrode active material graphite is too low, and the ionic conductivity of the pole piece decreases, resulting in poor discharge rate performance of the electrochemical device.
  • the a value is too small, the amount of negative electrode additive is too small, the homogenization of the slurry for preparing the negative electrode active material layer is poor, and the bonding force between the negative electrode active material layer and the current collector is weak, which in turn makes the cyclic expansion rate and deformation of the electrochemical device rate increases.
  • the weight loss rate of the negative electrode active material layer is b% within the temperature range of 360° C. to 450° C. by thermogravimetric test, wherein 0.1 ⁇ b ⁇ 0.7.
  • b is a range of 0.15, 0.25, 0.3, 0.4, 0.55, 0.6, or a combination of any two of these values.
  • 0.2 ⁇ b ⁇ 0.5 The larger the value of b, the higher the cohesive force of the pole piece. High cohesive force can inhibit the expansion of graphite in the XY direction, thereby reducing the cycle deformation rate of the electrochemical device and improving its cycle capacity retention rate.
  • the b value is too large, the ionic conductivity of the pole piece will decrease, resulting in a decrease in the discharge rate of the electrochemical device.
  • the weight loss rate of the negative electrode active material layer is a% within the temperature range of 200°C to 360°C, and the tap density TD g/cm 3 of the negative electrode active material is ⁇ 0.9g/ cm 3 , where a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100.
  • a and TD satisfy the relational expression a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100, the homogenization consistency of the negative electrode active material layer slurry is good, and a uniformly dispersed bonding network can be formed in the negative electrode active material layer, which is conducive to improving the battery life.
  • the cycle capacity retention rate of the chemical device and the reduction of its cycle deformation rate is a% within the temperature range of 200°C to 360°C, and the tap density TD g/cm 3 of the negative electrode active material is ⁇ 0.9g/ cm 3 , where a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100.
  • the negative electrode active material layer contains substances having absorption peaks in the range of 1540 cm ⁇ 1 to 1630 cm ⁇ 1 by Fourier transform infrared testing.
  • the absorption peak at 1540cm -1 to 1630cm -1 represents the stretching vibration of the carboxyl group.
  • the negative electrode additive includes at least one of hydroxyalkyl carboxymethyl cellulose or an alkali metal salt of hydroxyalkyl carboxymethyl cellulose.
  • the hydroxyalkyl carboxymethyl cellulose includes at least one of C 2 -C 6 hydroxyalkyl carboxymethyl cellulose.
  • the alkali metal salt of hydroxyalkyl carboxymethyl cellulose includes at least one of the alkali metal salts of C 2 -C 6 hydroxyalkyl carboxymethyl cellulose.
  • the alkali metal salt of hydroxyalkyl carboxymethyl cellulose includes at least one of an alkali metal salt of hydroxyethyl carboxymethyl cellulose or an alkali metal salt of hydroxypropyl carboxymethyl cellulose kind.
  • the alkali metal is lithium, sodium, potassium, rubidium, or cesium.
  • the C 2 -C 6 hydroxyalkyl group is hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxypentyl or hydroxyhexyl.
  • the negative electrode additive includes hydroxypropyl carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, hydroxyethyl carboxymethyl cellulose, hydroxypropyl carboxymethyl cellulose, At least one of lithium ethyl carboxymethyl cellulose or sodium hydroxyethyl carboxymethyl cellulose.
  • This kind of graphite with low OI value (OI ⁇ 11) and low TD (TD ⁇ 0.9) is not easy to disperse, and often requires a large amount of dispersant to ensure the consistency of the homogenate.
  • Sodium carboxymethyl cellulose (CMC) is used as a dispersant in conventional negative electrode sheets.
  • CMC can disperse suspended graphite and bind graphite particles, due to its high brittleness, the viscosity in the active material layer during cold pressing The junction network is easily damaged, and the improvement of the cycle deformation rate of the electrochemical device is limited.
  • the hydroxyalkyl substitution degree of the negative electrode additive is 0.1 to 0.3. In some embodiments, the hydroxyalkyl substitution degree of the negative electrode additive is 0.13, 0.15, 0.17, 0.19, 0.2, 0.21, 0.23, 0.25, 0.27, 0.29 or any combination of these values. In some embodiments, the hydroxyalkyl substitution degree of the negative electrode additive is 0.16 to 0.28. As the substitution degree of the hydroxyalkyl group increases, the flexibility of the negative electrode additive increases and the brittleness decreases. After the pole piece containing the negative electrode additive is rolled, the bonding network damage under the action of external force is reduced, and the bonding performance is improved.
  • the highly flexible negative electrode additive can also reduce the bond brittle cracks caused by graphite expansion and contraction during the cycle, which is beneficial to improve the cycle capacity retention rate and reduce the cycle deformation rate of the electrochemical device.
  • the hydroxyalkyl substitution is too high, the bulk strength of the negative electrode additive will decrease, which will lead to a decrease in the binding force of the corresponding electrode sheet.
  • the hydroxypropyl substitution degree of the negative electrode additive is 0.1 to 0.3. In some embodiments, the hydroxypropyl substitution degree of the negative electrode additive is 0.16 to 0.28. In some embodiments, the hydroxyethyl substitution degree of the negative electrode additive is 0.1 to 0.3. In some embodiments, the hydroxyethyl substitution degree of the negative electrode additive is 0.16 to 0.28.
  • the degree of carboxymethyl substitution of the negative electrode additive is 0.5 to 0.9. In some embodiments, the degree of carboxymethyl substitution of the negative electrode additive is 0.55, 0.6, 0.65, 0.7, 0.75, 0.85, 0.85 or a range consisting of any two of these values.
  • the negative electrode additive includes at least one of the alkali metal salts of hydroxyalkyl carboxymethylcellulose, wherein the negative electrode active material layer includes region A and region B, wherein the alkali metal element in region A
  • the ratio of the content to the alkali metal element content in the area B is 0.8 to 1.2
  • the area A is the area from the center of the thickness direction of the negative electrode active material layer to the surface side of the negative electrode active material layer
  • the area B is from the thickness of the negative electrode active material layer The direction starts from the center to the area on the side of the negative electrode current collector.
  • the negative electrode additive includes at least one of alkali metal salts of C 2 -C 6 hydroxyalkyl carboxymethylcellulose, wherein the content of alkali metal elements in region A is equal to the content of alkali metal elements in region B The ratio is 0.8 to 1.2. In some embodiments, the negative electrode additive includes lithium hydroxypropyl carboxymethyl cellulose, wherein the ratio of the lithium element content in region A to the lithium element content in region B is 0.8 to 1.2.
  • the negative active material layer further includes a binder.
  • the binder includes styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, water-based acrylic resin , polyvinyl formal or at least one of styrene-acrylic copolymer resin.
  • the binding force between the negative electrode active material layer and the negative electrode current collector is 8N/m to 15N/m.
  • the ion conductivity of the negative electrode is 0.1 S/cm to 0.4 S/cm.
  • the negative current collector can be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, or a combination thereof.
  • the electrochemical device of the present application further includes a positive electrode, and the positive electrode includes a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer includes a positive electrode active material, a binder and a conductive agent.
  • the positive electrode current collector may use a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used.
  • the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.
  • the positive electrode active material may include lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, At least one of lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide and lithium titanate.
  • the binder may include various binder polymers such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified At least one of polyvinylidene fluoride, modified SBR rubber or polyurethane.
  • the polyolefin-based binder includes at least one of polyethylene, polypropylene, polyalkene, polyenol, or polyacrylic acid.
  • any conductive material can be used as the conductive agent as long as it does not cause chemical changes.
  • Examples of the conductive agent include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.; metal-based materials such as metal powder or metal fiber including copper, nickel, aluminum, silver, etc. ; Conductive polymers, such as polyphenylene derivatives, etc.; or their mixtures.
  • the electrochemical device of the present application also includes a separator.
  • the material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art.
  • the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application.
  • a release film may include a substrate layer and a surface treatment layer.
  • the substrate layer is non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite film can be selected.
  • At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials.
  • the inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, At least one of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl alkoxy , polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene at least one.
  • Polymer is contained in the polymer layer, and the material of polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl alkoxide, polyvinylidene fluoride, At least one of poly(vinylidene fluoride-hexafluoropropylene).
  • the electrochemical device of the present application also includes an electrolyte.
  • the electrolyte solution that can be used in the present application can be the electrolyte solution known in the prior art.
  • the electrolyte includes an organic solvent, a lithium salt, and optional additives.
  • the organic solvent of the electrolytic solution according to the present application can be any organic solvent known in the prior art that can be used as a solvent for the electrolytic solution.
  • the electrolyte used in the electrolytic solution according to the present application is not limited, and it may be any electrolyte known in the prior art.
  • the additive of the electrolytic solution according to the present application may be any additive known in the prior art as an additive to the electrolytic solution.
  • organic solvents include, but are not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC ), propylene carbonate or ethyl propionate.
  • the organic solvent includes an ether solvent, for example, at least one of 1,3-dioxane (DOL) and ethylene glycol dimethyl ether (DME).
  • the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
  • lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bistrifluoromethanesulfonylimide LiN (CF 3 SO 2 ) 2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium bisoxalate borate LiB(C 2 O 4 ) 2 (LiBOB) or Lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) (LiDFOB).
  • the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries or capacitors.
  • the electrochemical device is a lithium secondary battery.
  • lithium secondary batteries include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.
  • the present application further provides an electronic device, which includes the electrochemical device described in the first aspect of the present application.
  • electronic devices of the present application include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets , VCR, LCD TV, Portable Cleaner, Portable CD Player, Mini Disc, Transceiver, Electronic Notepad, Calculator, Memory Card, Portable Recorder, Radio, Backup Power, Motor, Automobile, Motorcycle, Assisted Bicycle, Bicycle , Lighting appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • negative electrode artificial graphite (OI value, tap density see Table 1), additive (see Table 1 for specific types) and water-based binder styrene-acrylic acid copolymer resin (styrene-acrylic resin) according to (96-98.5): (0.5-2.5): (0-2.0) mass ratio mixed with deionized water, stirred evenly, to obtain negative electrode slurry.
  • the negative electrode slurry was coated on a 6 ⁇ m copper foil, dried, cold pressed, cut into pieces, and tabs were welded to obtain a negative electrode.
  • Preparation of the positive electrode mix lithium cobalt oxide, conductive carbon, and polyvinylidene fluoride according to a mass ratio of 96:2:2, add solvent N-methyl-2-pyrrolidone (NMP) to make a slurry, and coat it on aluminum foil. Drying, cold pressing, cutting into pieces and welding tabs to obtain the positive electrode.
  • NMP solvent N-methyl-2-pyrrolidone
  • Preparation of lithium-ion battery stack the positive electrode, separator (PE porous polymer film), and negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play the role of isolation, and then wind up to obtain a bare cell; the bare cell Put it in the outer packaging foil, inject the electrolyte (the solvent is EC and DMC with a volume ratio of 1:1, 1M/L LiPF 6 solution) into the dried battery, and go through vacuum packaging, standing, chemical formation, shaping, etc. The process is to complete the preparation of lithium-ion batteries.
  • the solvent is EC and DMC with a volume ratio of 1:1, 1M/L LiPF 6 solution
  • the tap density is the mass per unit volume measured after the powder in the container is tapped under specified conditions, and the unit is g/cm 3 .
  • the test method is to fix the graduated cylinder containing a certain mass of powder on the mechanical vibration device, the vibration motor drives the mechanical vibration device to vibrate vertically up and down, and the graduated cylinder with powder vibrates rhythmically with the mechanical vibration device. As the number of times increases, the powder in the graduated cylinder is gradually vibrated. When the number of vibrations reaches the set number, the mechanical vibration device stops vibrating and the volume of the graduated cylinder is read. According to the definition of density: the mass is divided by the volume, so as to obtain the powder density after vibration. Specific process parameters: vibration frequency: 5000 times; vibration frequency: 250 ⁇ 15 times/min; ambient temperature: 15°C to 28°C.
  • Carboxymethyl substitution degree The test standard of carboxymethyl substitution degree is tested according to the method in GB/T 1904-2005 "Food Additive Sodium Carboxymethyl Cellulose".
  • Hydroxyethyl substitution degree or hydroxypropyl substitution degree refer to D2363-72, "1976 Annual Book of ASTM Standards" for testing.
  • thermogravimetric curve shows the weight loss rate W T % at the temperature between 20°C and 600°C.
  • the rate of weight loss between 200°C and 360°C is a %.
  • the weight loss rate between 360°C and 450°C is b%.
  • Adhesion test between the negative electrode active material layer and the negative electrode current collector the brand of the instrument used is Instron, and the model is 33652.
  • the negative electrode width 30mm ⁇ length (100mm to 160mm)
  • the steel plate with double-sided tape model: 3M9448A, width 20mm ⁇ length (90mm to 150mm)
  • the paper tape with the same width as the negative electrode and
  • the other side of the negative electrode is fixed with adhesive tape, adjust the limit block of the tensile machine to a suitable position, fold the paper tape upwards and slide 40mm, the slip rate is 50mm/min, and test the negative electrode at 180° (that is, stretching in the opposite direction)
  • the binding force between the active material layer and the negative electrode current collector was tested.
  • the packaging bag, pole pieces, and isolation film stand at 60°C for 4 hours before use. Then, use ceramic scissors to cut the pole piece into a small piece larger than the die size (die size, 23mm ⁇ 35mm ⁇ 2mm), put the small piece on the die for punching, and take out the filled pole piece with tweezers for later use .
  • the pole piece is then made into a single-layer symmetrical battery. Put the symmetrical battery on the electrochemical workstation to test EIS, set the frequency from 0.5Hz to 200kHz, and the disturbance voltage is 10mV; calculate the ionic resistance Rion of the pole piece through the intersection of the two straight lines of EIS. Calculate the ionic conductivity of the pole piece by the following formula:
  • Pole piece ionic conductivity d/(Rion ⁇ A), wherein, d is the thickness of the pole piece, and A is the area of the pole piece;
  • the lithium-ion battery was charged to 4.45V at a constant current of 1C, then charged at a constant voltage to a current of 0.05C, and then discharged to 3.0V at a constant current of 1C. This was the first cycle. Lithium-ion cells were cycled several times under the above conditions. The capacity retention rate of the lithium-ion battery after cycling is calculated by the following formula:
  • Capacity retention rate after cycle (discharge capacity corresponding to the number of cycles/discharge capacity of the first cycle) ⁇ 100%
  • Discharge percentage (-20°C discharge capacity/25°C discharge capacity) ⁇ 100%
  • the measured distance between the two plates is the thickness of the lithium-ion battery.
  • the cycle thickness expansion rate of the lithium-ion battery is calculated by the following formula:
  • Cycle thickness expansion rate (thickness of lithium-ion battery corresponding to the number of cycles / thickness of lithium-ion battery for the first cycle - 1) ⁇ 100%
  • Lithium-ion battery thickness test Place the lithium-ion battery between two plates, press down on the upper plate, and when the pressure is 700g, the measured distance between the two plates is the thickness of the lithium-ion battery. ;
  • Lithium-ion battery micrometer thickness test Select 3 points roughly equally divided on the surface of the battery body on the Al tab side (positive tab), use a micrometer to measure the thickness of the three points and take the average as the lithium-ion battery micrometer thickness.
  • the cycle deformation rate of lithium-ion battery is calculated by the following formula:
  • Cyclic deformation rate (cell thickness corresponding to the number of cycles/thickness of the cell micrometer corresponding to the number of cycles-1) ⁇ 100%.
  • the test standard of flexibility level refers to GB/T 1731-93 "Determination of flexibility of paint film".
  • the shaft rod 7 is used for testing, and the degree of flexibility is judged according to the degree of cracking inside the bending of the pole piece.
  • the crack width on the inner side of the pole piece bending is less than 10 ⁇ m, it is judged that the flexibility level is excellent.
  • the inner side of the pole piece bending is 10 ⁇ m ⁇ crack width ⁇ 150 ⁇ m, it is judged that the flexibility level is medium.
  • the crack width on the inner side of the pole piece bends > 150 ⁇ m it is judged that the flexibility level is poor.
  • Example 1-1 to Example 1-13 and Comparative Example 3 the additives are all lithium hydroxypropyl carboxymethyl cellulose; in Comparative Example 1 and Comparative Example 2, the additives are all lithium carboxymethyl cellulose ; Relational expression 1 is (-0.0135 ⁇ TD+0.0263) ⁇ 100.
  • embodiment 1-1 to embodiment 1-7 have studied the impact of the OI value of negative electrode active material artificial graphite on performance, and wherein when the OI value of artificial graphite is 8-9, the negative pole sheet and lithium-ion battery The overall performance is the best.
  • Examples 1-11 to Examples 1-13 studied the influence of the thermal weight loss rate W T % of the negative electrode active material layer at 600 ° C on performance, wherein as W T increases, the cycle deformation rate of lithium-ion batteries decreases , but the ionic conductivity of the pole piece decreases, which reduces the discharge rate performance of the lithium-ion battery.
  • lithium carboxymethyl cellulose is used as an additive in Comparative Example 1. Due to the high brittleness of lithium carboxymethyl cellulose, it is easy to crack after rolling, resulting in low adhesion of the pole piece, and then in the cycle process Among them, the expansion of graphite in the XY direction cannot be suppressed, so that the cycle deformation rate is as high as 6%, and the cycle capacity retention rate is only about 60%. Comparative example 2 increases the content of binding agent in the pole sheet on the basis of comparative example 1 (the size of b is related to the content of binding agent in the negative electrode active material layer, and the b value is larger, shows that binding agent in the negative electrode active material layer The higher the content of the agent), then the adhesion of the pole piece is improved.
  • Example 2-1 to Example 2-5 studied the influence of the hydroxypropyl substitution degree of the additive hydroxypropyl carboxymethylcellulose lithium on performance, wherein the hydroxypropyl substitution degree is in the range of 0.16 to 0.28 , the performance of the negative pole piece and the performance of the lithium-ion battery are excellent.
  • the adhesion force of the negative electrode sheet (that is, the adhesive force between the negative electrode active material layer and the negative electrode current collector) is >8N/m, and the ion conductivity of the negative electrode sheet is >0.2S/cm.
  • the cycle capacity retention rate of the lithium-ion battery is more than 80%, the deformation rate is less than 2%, and the discharge rate is more than 50%.
  • the effect is the best when the degree of substitution of hydroxypropyl group is 0.22, the cohesive force is 14N/m, the ionic conductivity of the pole piece is 0.23S/cm, and the cycle capacity retention rate of the lithium-ion battery is 82.2 %. From the data of Example 2-1 to Example 2-5, it can also be seen that as the hydroxypropyl substitution degree of lithium hydroxypropyl carboxymethyl cellulose increases, the adhesion force of the pole piece first increases and then decreases.
  • Examples 2-6 to Examples 2-11 studied the influence of the negative electrode active material layer on the performance of the thermal weight loss rate a% in the range of 200°C to 360°C and the thermal weight loss rate b% in the range of 360°C to 450°C .
  • the size of a is related to the content of hydroxypropyl carboxymethyl cellulose lithium in the negative electrode active material layer, and the larger a is, the higher the content of hydroxypropyl carboxymethyl cellulose lithium in the negative electrode active material layer is.
  • the size of b is related to the content of the binder in the negative electrode active material layer, and the larger the value of b is, the higher the content of the binder in the negative electrode active material layer is.
  • Example 2-10 and Example 2-11 when a is less than 1.5, correspondingly, a is less than (-0.0135 ⁇ TD+0.0263) ⁇ 100. At this time, the cyclic deformation rate of the lithium-ion battery is greater than 3%, and the capacity The retention rate is less than 80%.
  • Example 2-7 to Example 2-10 a is greater than 1.5, correspondingly, a is greater than (-0.0135 ⁇ TD+0.0263) ⁇ 100, the consistency of slurry homogenization is good, and a uniform dispersion can be formed in the negative electrode active material layer The network is bonded, so that the cycle capacity retention rate of the lithium-ion battery is >80% and the deformation rate is ⁇ 2%.
  • b is 0, that is, the content of the binder in the negative electrode active material layer is 0, so that the bonding network of the negative electrode sheet is poor, resulting in increased deformation in the XY direction due to bonding failure, and then This makes the expansion deformation rate and thickness expansion rate of the lithium-ion battery slightly larger. Therefore, when a and b satisfy a+b ⁇ 2; a ⁇ (-0.0135 ⁇ TD+0.0263) ⁇ 100, the performance of the negative electrode sheet and the performance of the lithium-ion battery are both excellent.

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Abstract

本发明提供一种电化学装置，其包括负极，负极包括负极集流体和负极活性材料层，负极活性材料层包括负极活性材料和负极添加剂，负极活性材料包含石墨，其中，负极活性材料的取向指数OI≤11，采用热重测试，在25℃至600℃的温度范围内，负极活性材料层的失重率为WT％，1≤WT≤2.5。该电化学装置兼顾高的体积能量密度、优异的循环性能和低温倍率性能。还提供一种包括电化学装置的电子装置。

Description

电化学装置和电子装置 技术领域
本申请涉及储能领域，具体涉及一种电化学装置和电子装置。
背景技术
作为一种新型储能装置，锂离子电池被广泛应用于3C数码、电动工具、储能电网、航空航天等领域。而随着科技的发展，人们对锂离子电池性能的要求变得越来越高，因此在确保安全的前提下，电池的能量密度和充放电功率等参数急需提高。在锂离子电池中，正负极材料是决定电池性能的关键物质。现有技术中，低取向度的石墨负极活性材料Z方向循环膨胀小，动力学性能优异，能够有效降低锂离子电池的厚度膨胀率。但低取向度石墨往往不容易分散，浆料匀浆一致性差，进而使得锂离子电池的变形率高，限制其大规模应用。
发明内容
针对现有技术的不足，本申请提供了一种电化学装置及包括该电化学装置的电子装置。本申请的电化学装置兼顾高的体积能量密度、优异的循环性能和低温倍率性能。
第一方面，本申请提供了一种电化学装置，其包括负极，该负极包括负极集流体和负极活性材料层，负极活性材料层包括负极活性材料和负极添加剂，负极活性材料包含石墨，其中，负极活性材料的取向指数OI≤11，采用热重测试，在25℃至600℃的温度范围内，负极活性材料层的失重率为W T％，1≤W T≤2.5。本申请中，W T值在上述范围内，电化学装置的循环性能及倍率综合性能最优。W T值过小，制备负极活性材料层的浆料匀浆一致性差，使得负极活性材料层与集流体之间的粘结力低，进而在循环过程中，无法抑制石墨XY方向的膨胀，导致电化学装置的循环膨胀率及变形率增大。W T值过大，会导致负极活性材料石墨的含量过低，使得极片离子电导率降低，导致电化学装置的放电倍率降低。
根据本申请的一些实施方式，6≤OI≤10。本申请中，负极活性材料的取向指数OI为通过X射线衍射法对负极活性材料进行测试而得到的面(004)的峰面积和面(110)的峰面积的比值。
根据本申请的一些实施方式，负极活性材料的振实密度TD g/cm 3≤0.9g/cm 3。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，在360℃至450℃的温度范围内负极活性材料层的失重率为b％，满足如下条件中的至少一者：(Ⅰ)a+b＜2.5；(Ⅱ)a≥1.5b；(Ⅲ)a≥(-0.0135×TD+0.0263)×100。
根据本申请的一些实施方式，负极活性材料层满足条件(a)或(b)中的至少一者：(a)0.8≤a≤2，0.1≤b≤0.7；(b)0.6≤TD≤0.9。
根据本申请的一些实施方式，1.1≤a≤1.9，0.2≤b≤0.5。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，在360℃至450℃的温度范围内负极活性材料层的失重率为b％，其中，a+b＜2.5。a+b的值过大，会导致负极活性材料石墨的含量过低，进而使得极片离子电导率降低，导致电化学装置的放电倍率降低。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，其中，0.8≤a≤2.2。在一些实施方式中，0.8≤a≤2.0。在一些实施方式中，1.1≤a≤1.9。本申请中，a值与负极活性材料层中负极添加剂的含量有关，a值越大，表明负极活性材料层中负极添加剂的含量越高。a值过大，相应地负极活性材料石墨的含量过低，极片离子电导率降低，导致电化学装置的放电倍率性能差。a值过小，负极添加剂量过少，制备负极活性材料层的浆料匀浆一致性差，负极活性材料层与集流体之间的粘结力薄弱，进而使得电化学装置的循环膨胀率及变形率增大。
根据本申请的一些实施方式，采用热重测试，在360℃至450℃的温度范围负极活性材料层的失重率为b％，其中，0.1≤b≤0.7。在一些实施方式中，0.2≤b≤0.5。b值越大，极片粘结力相应越高。高的粘结力可以抑制石墨XY方向的膨胀，进而降低电化学装置的循环变形率，提升其循环容量保持率。然而，b值过大会使得极片离子电导率降低，导致电化学装置的放电倍率降低。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，负极活性材料的振实密度TD g/cm 3≤0.9g/cm 3，其中，a≥(-0.0135×TD+0.0263)×100。a与TD满足关系式a≥(-0.0135×TD+0.0263)×100时，负极活性材料层浆料的匀浆一致性良好，负极活性材料层中能够形成均匀分散粘结网络，有利于提升电化学装置的循环容量保持率和降低其循环变形率。
根据本申请的一些实施方式，采用傅里叶红外测试，该负极活性材料层包含谱图在 1540cm -1至1630cm -1范围具有吸收峰的物质。本申请中，傅里叶红外测试谱图中，在1540cm -1至1630cm -1的吸收峰代表羧基的伸缩振动。
根据本申请的一些实施方式，负极添加剂包括羟烷基羧甲基纤维素或羟烷基羧甲基纤维素的碱金属盐中的至少一种。在一些实施方式中，羟烷基羧甲基纤维素包括C 2-C 6羟烷基羧甲基纤维素中的至少一种。在一些实施方式中，羟烷基羧甲基纤维素的碱金属盐包括C 2-C 6羟烷基羧甲基纤维素的碱金属盐中的至少一种。根据本申请的一些实施方式，羟烷基羧甲基纤维素的碱金属盐包括羟乙基羧甲基纤维素的碱金属盐或羟丙基羧甲基纤维素的碱金属盐中的至少一种。在一些实施方式中，碱金属为锂、钠、钾、铷或铯。
根据本申请的一些实施方式，负极添加剂包括羟丙基羧甲基纤维素、羟丙基羧甲基纤维素锂、羟丙基羧甲基纤维素钠、羟乙基羧甲基纤维素、羟乙基羧甲基纤维素锂或羟乙基羧甲基纤维素钠中的至少一种。
低OI值(OI≤11)的人造石墨各向同性强，具备Z方向膨胀低和动力学性能优异的优势。充电时，锂离子可快速嵌入低OI值石墨中，在XY方向释放一定厚度膨胀，使得Z方向的膨胀相对降低，进而能够降低电化学装置的循环膨胀率。但由于极片XY方向膨胀，极片易脱膜，变形率高，进而会降低电化学装置的循环容量保持率。此外，低OI值石墨多为二次颗粒堆积而成，在多数情况下低OI值石墨往往伴随振实密度低。此类低OI值(OI≤11)低TD(TD≤0.9)石墨不容易分散，往往需要大量分散剂才能保证匀浆一致性。常规的负极极片中采用羧甲基纤维素钠(CMC)做分散剂，虽然CMC可起到分散悬浮石墨以及粘结石墨颗粒作用，但由于其脆性大，冷压过程活性材料层中的粘结网络易破坏，对电化学装置的循环变形率改善有限。本申请通过在负极中添加柔韧性优异的羟烷基羧甲基纤维素类分散剂，能够有效降低活性材料层在辊压外力/颗粒膨胀收缩过程由于脆性而导致的粘结网络破坏，使得极片在经过辊压和长循环后仍然保持较高的粘结力和离子电导率，进而使得电化学装置具有高的体积能量密度、优异的循环性能和低温倍率性能。
根据本申请的一些实施方式，负极添加剂的羟烷基取代度为0.1至0.3。在一些实施方式中，负极添加剂的羟烷基取代度为0.16至0.28。在一些实施方式中，负极添加剂的羧甲基取代度为0.5至0.9。随着羟烷基取代度增加，负极添加剂的柔韧性增加，脆性降低，包含该负极添加剂的极片在辊压后，外力作用下的粘结网络破坏减少，粘结性能得到提升。同时，高柔韧性的负极添加剂还可以降低循环过程中石墨膨胀收缩导致的粘结脆性龟裂，进而有利于提升电化学装置的循环容量保持率和降低其循环变形率。但羟烷基取代 度过高时，负极添加剂的本体强度会降低，会导致相应极片的粘结力下降。
根据本申请的一些实施方式，负极添加剂包括羟烷基羧甲基纤维素的碱金属盐中的至少一种，负极活性材料层包括区域A和区域B，其中，区域A中碱金属元素含量与区域B中碱金属元素含量的比值为0.8至1.2，其中，区域A为从负极活性材料层的厚度方向的中心开始至负极活性材料层表面侧的区域，区域B为从负极活性材料层的厚度方向的中心开始至负极集流体侧的区域。在一些实施方式中，负极添加剂包括C 2-C 6羟烷基羧甲基纤维素的碱金属盐中的至少一种，其中，区域A中碱金属元素含量与区域B中碱金属元素含量的比值为0.8至1.2。在一些实施方式中，负极添加剂包括羟丙基羧甲基纤维素锂，其中，区域A中锂元素含量与区域B中锂元素含量的比值为0.8至1.2。
根据本申请的一些实施方式，该负极活性材料层还包括粘结剂。在一些实施方式中，粘结剂包括丁苯橡胶、聚丙烯酸、聚丙烯酸盐、聚酰亚胺、聚酰胺酰亚胺、聚偏氟乙烯、聚二氟乙烯、聚四氟乙烯、水性丙烯酸树脂、聚乙烯醇缩甲醛或苯乙烯-丙烯酸共聚树脂中的至少一种。
根据本申请的一些实施方式，电化学装置满足条件(ⅰ)或(ⅱ)中的至少一者：(ⅰ)负极活性材料层和负极集流体之间的粘结力为8N/m至15N/m；(ⅱ)负极的离子电导率为0.1S/cm至0.4S/cm。
第二方面，本申请提供了一种电子装置，其包括第二方面的电化学装置。
本申请通过搭配使用低取向指数(取向指数≤11)低振实密度(振实密度≤0.9)石墨和羟烷基羧甲基纤维素类添加剂，并进行配比优化，可制备得到高活性材料含量的负极极片，进而使得包含该极片的电化学装置兼具高的体积能量密度、优异的循环性能和低温倍率性能。
附图说明
图1为根据本申请的一些实施方式的电化学装置中负极添加剂的红外谱图。
图2为根据本申请的一些实施方式的电化学装置中负极活性材料层的热重曲线图。
具体实施方式
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明 本申请而不用于限制本申请的范围。
一、电化学装置
本申请提供了一种电化学装置，其包括负极，该负极包括负极集流体和负极活性材料层，负极活性材料层包括负极活性材料和负极添加剂，负极活性材料包含石墨，其中，负极活性材料的取向指数OI≤11，采用热重测试，在25℃至600℃的温度范围内，负极活性材料层的失重率为W T％，1≤W T≤2.5。本申请中，W T值在上述范围内，电化学装置的循环性能及倍率综合性能最优。W T值过小，制备负极活性材料层的匀浆一致性差，使得负极活性材料层与集流体之间的粘结力低，进而在循环过程中，无法抑制石墨XY方向的膨胀，导致电化学装置的循环膨胀率及变形率增大。W T值过大，会导致负极活性材料石墨的含量过低，使得极片离子电导率降低。一些实施方式中，W T为1.1、1.2、1.3、1.4、1.5、1.6、1.7、1.8、1.9、2.0、2.1、2.2、2.3、2.4或这些值中任意两者组成的范围。在一些实施方式中，1.5≤W T≤2.2。
根据本申请的一些实施方式，OI为5.0、5.5、6.0、6.5、7、7.5、8、8.5、9、9.5、10、10.5或这些值中任意两者组成的范围。在一些实施方式中，6≤OI≤10。本申请中，负极活性材料的取向指数OI为通过X射线衍射法对负极活性材料进行测试而得到的面(004)的峰面积和面(110)的峰面积的比值。
根据本申请的一些实施方式，负极活性材料的振实密度TD g/cm 3≤0.9g/cm 3。在一些实施方式中，TD为0.5、0.55、0.6、0.65、0.7、0.75、0.8、0.85、0.9或这些值中任意两者组成的范围。在一些实施方式中，0.6≤TD≤0.9。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，在360℃至450℃的温度范围内负极活性材料层的失重率为b％，其中，a+b＜2.5。a+b的值过大，会导致负极活性材料石墨的含量过低，进而使得极片离子电导率降低，导致电化学装置的放电倍率降低。在一些实施方式中，a+b为1.1、1.2、1.3、1.4、1.5、1.6、1.7、1.8、1.9、2.0、2.1、2.2、2.3、2.4或这些值中任意两者组成的范围。在一些实施方式中，1.5≤a+b≤2.2。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，其中，0.8≤a≤2.2。在一些实施方式中，a为0.9、1.0、1.15、1.2、1.3、1.4、1.5、1.6、1.7、1.8、1.95、2.0、2.1或这些值中任意两者组成的范围。在一些实施方式中，0.8≤a≤2.0。在一些实施方式中，1.1≤a≤1.9。本申请中，a值与负 极活性材料层中负极添加剂的含量有关，a值越大，表明负极活性材料层中负极添加剂的含量越高。a值过大，相应地负极活性材料石墨的含量过低，极片离子电导率降低，导致电化学装置的放电倍率性能差。a值过小，负极添加剂量过少，制备负极活性材料层的浆料匀浆一致性差，负极活性材料层与集流体之间的粘结力薄弱，进而使得电化学装置的循环膨胀率及变形率增大。
根据本申请的一些实施方式，采用热重测试，在360℃至450℃的温度范围内负极活性材料层的失重率为b％，其中，0.1≤b≤0.7。在一些实施方式中，b为0.15、0.25、0.3、0.4、0.55、0.6或这些值中任意两者组成的范围。在一些实施方式中，0.2≤b≤0.5。b值越大，极片粘结力相应越高。高的粘结力可以抑制石墨XY方向的膨胀，进而降低电化学装置的循环变形率，提升其循环容量保持率。然而，b值过大，会使得极片离子电导率降低，导致电化学装置的放电倍率降低。
根据本申请的一些实施方式，采用热重测试，在200℃至360℃的温度范围内负极活性材料层的失重率为a％，负极活性材料的振实密度TD g/cm 3≤0.9g/cm 3，其中，a≥(-0.0135×TD+0.0263)×100。a与TD满足关系式a≥(-0.0135×TD+0.0263)×100时，负极活性材料层浆料的匀浆一致性良好，负极活性材料层中能够形成均匀分散粘结网络，有利于提升电化学装置的循环容量保持率和降低其循环变形率。
根据本申请的一些实施方式，采用傅里叶红外测试，该负极活性材料层包含谱图在1540cm -1至1630cm -1范围具有吸收峰的物质。本申请中，傅里叶红外测试谱图中，在1540cm -1至1630cm -1的吸收峰代表羧基的伸缩振动。
根据本申请的一些实施方式，负极添加剂包括羟烷基羧甲基纤维素或羟烷基羧甲基纤维素的碱金属盐中的至少一种。在一些实施方式中，羟烷基羧甲基纤维素包括C 2-C 6羟烷基羧甲基纤维素中的至少一种。在一些实施方式中，羟烷基羧甲基纤维素的碱金属盐包括C 2-C 6羟烷基羧甲基纤维素的碱金属盐中的至少一种。根据本申请的一些实施方式，羟烷基羧甲基纤维素的碱金属盐包括羟乙基羧甲基纤维素的碱金属盐或羟丙基羧甲基纤维素的碱金属盐中的至少一种。在一些实施方式中，碱金属为锂、钠、钾、铷或铯。在一些实施方式中，C 2-C 6羟烷基为羟乙基、羟丙基、羟丁基、羟戊基或羟己基。
根据本申请的一些实施方式，负极添加剂包括羟丙基羧甲基纤维素、羟丙基羧甲基纤维素锂、羟丙基羧甲基纤维素钠、羟乙基羧甲基纤维素、羟乙基羧甲基纤维素锂或羟乙基羧甲基纤维素钠中的至少一种。
低OI值(OI≤11)的人造石墨各向同性强，具备Z方向膨胀低和动力学性能优异的 优势。充电时，锂离子可快速嵌入低OI值石墨中，在XY方向释放一定厚度膨胀，使得Z方向的膨胀相对降低，进而能够降低电化学装置的循环膨胀率。但由于极片XY方向膨胀，极片易脱膜，变形率高，进而会降低电化学装置的循环容量保持率。此外，低OI值石墨多为二次颗粒堆积而成，在多数情况下低OI值石墨往往伴随振实密度低。此类低OI值(OI≤11)低TD(TD≤0.9)石墨不容易分散，往往需要大量分散剂才能保证匀浆一致性。常规的负极极片中采用羧甲基纤维素钠(CMC)做分散剂，虽然CMC可起到分散悬浮石墨以及粘结石墨颗粒作用，但由于其脆性大，冷压过程活性材料层中的粘结网络易破坏，对电化学装置的循环变形率改善有限。本申请通过在负极中添加柔韧性优异的羟烷基羧甲基纤维素类分散剂，能够有效降低活性材料层在辊压外力/颗粒膨胀收缩过程由于脆性而导致的粘结网络破坏，使得极片在经过辊压和长循环后仍然保持较高的粘结力和离子电导率，进而使得电化学装置具有高的体积能量密度、优异的循环性能和低温倍率性能。
根据本申请的一些实施方式，负极添加剂的羟烷基取代度为0.1至0.3。在一些实施方式中，负极添加剂的羟烷基取代度为0.13、0.15、0.17、0.19、0.2、0.21、0.23、0.25、0.27、0.29或这些值中任意两者组成的范围。在一些实施方式中，负极添加剂的羟烷基取代度为0.16至0.28。随着羟烷基取代度增加，负极添加剂的柔韧性增加，脆性降低，包含该负极添加剂的极片在辊压后，外力作用下的粘结网络破坏减少，粘结性能得到提升。同时，高柔韧性的负极添加剂还可以降低循环过程中石墨膨胀收缩导致的粘结脆性龟裂，进而有利于提升电化学装置的循环容量保持率和降低其循环变形率。但羟烷基取代度过高时，负极添加剂的本体强度会降低，会导致相应极片的粘结力下降。
根据本申请的一些实施方式，负极添加剂的羟丙基取代度为0.1至0.3。在一些实施方式中，负极添加剂的羟丙基取代度为0.16至0.28。在一些实施方式中，负极添加剂的羟乙基取代度为0.1至0.3。在一些实施方式中，负极添加剂的羟乙基取代度为0.16至0.28。
在一些实施方式中，负极添加剂的羧甲基取代度为0.5至0.9。在一些实施方式中，负极添加剂的羧甲基取代度为0.55、0.6、0.65、0.7、0.75、0.85、0.85或这些值中任意两者组成的范围。
根据本申请的一些实施方式，负极添加剂包括羟烷基羧甲基纤维素的碱金属盐中的至少一种，其中，负极活性材料层包括区域A和区域B，其中，区域A中碱金属元素含量与区域B中碱金属元素含量的比值为0.8至1.2，区域A为从负极活性材料层的厚度方向的中心开始至负极活性材料层表面侧的区域，区域B为从负极活性材料层的厚度方向的 中心开始至负极集流体侧的区域。在一些实施方式中，负极添加剂包括C 2-C 6羟烷基羧甲基纤维素的碱金属盐中的至少一种，其中，区域A中碱金属元素含量与区域B中碱金属元素含量的比值为0.8至1.2。在一些实施方式中，负极添加剂包括羟丙基羧甲基纤维素锂，其中，区域A中锂元素含量与区域B中锂元素含量的比值为0.8至1.2。
根据本申请的一些实施方式，该负极活性材料层还包括粘结剂。在一些实施方式中，粘结剂包括丁苯橡胶、聚丙烯酸、聚丙烯酸盐、聚酰亚胺、聚酰胺酰亚胺、聚偏氟乙烯、聚二氟乙烯、聚四氟乙烯、水性丙烯酸树脂、聚乙烯醇缩甲醛或苯乙烯-丙烯酸共聚树脂中的至少一种。
根据本申请的一些实施方式，负极活性材料层和负极集流体之间的粘结力为8N/m至15N/m。根据本申请的一些实施方式，负极的离子电导率为0.1S/cm至0.4S/cm。
根据本申请的一些实施方式，负极集流体负极集流体可以为铜箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜、包覆有导电金属的聚合物基板或它们的组合。
本申请的电化学装置还包括正极，正极包括正极集流体和正极活性材料层，其中，正极活性材料层包括正极活性材料、粘结剂和导电剂。
根据本申请的一些实施方式，正极集流体可以采用金属箔片或复合集流体。例如，可以使用铝箔。复合集流体可以通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子基材上而形成。
根据本申请的一些实施方式，正极活性材料可以包括钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂和钛酸锂中的至少一种。在一些实施例中，粘结剂可以包括各种粘合剂聚合物，例如聚偏氟乙烯、聚四氟乙烯、聚烯烃类、羧甲基纤维素钠、羧甲基纤维素锂、改性聚偏氟乙烯、改性SBR橡胶或聚氨酯中的至少一种。在一些实施例中，聚烯烃类粘结剂包括聚乙烯、聚丙烯、聚烯酯、聚烯醇或聚丙烯酸中的至少一种。在一些实施例中，可以使用任何导电的材料作为导电剂，只要它不引起化学变化即可。导电剂的示例包括：碳基材料，例如天然石墨、人造石墨、炭黑、乙炔黑、科琴黑、碳纤维等；金属基材料，例如包括铜、镍、铝、银等的金属粉或金属纤维；导电聚合物，例如聚亚苯基衍生物等；或它们的混合物。
本申请的电化学装置还包括隔离膜，本申请的电化学装置中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。
聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
本申请的电化学装置还包括电解液。可用于本申请的电解液可以为现有技术中已知的电解液。
在一些实施方式中，电解液包括有机溶剂、锂盐和可选的添加剂。根据本申请的电解液的有机溶剂可为现有技术中已知的任何可作为电解液的溶剂的有机溶剂。根据本申请的电解液中使用的电解质没有限制，其可为现有技术中已知的任何电解质。根据本申请的电解液的添加剂可为现有技术中已知的任何可作为电解液添加剂的添加剂。在一些实施例中，有机溶剂包括，但不限于：碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯或丙酸乙酯。在一些实施例中，有机溶剂包括醚类溶剂，例如包括1，3-二氧五环(DOL)和乙二醇二甲醚(DME)中的至少一种。在一些实施例中，锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施例中，锂盐包括，但不限于：六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、二氟磷酸锂(LiPO 2F 2)、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)(LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(LiBOB)或二氟草酸硼酸锂LiBF 2(C 2O 4)(LiDFOB)。
在一些实施例中，本申请的电化学装置包括，但不限于：所有种类的一次电池、二次电池或电容。在一些实施例中，电化学装置是锂二次电池。在一些实施例中，锂二次电池 包括，但不限于：锂金属二次电池、锂离子二次电池、锂聚合物二次电池或锂离子聚合物二次电池。
二、电子装置
本申请进一步提供了一种电子装置，其包括本申请第一方面所述的电化学装置。
本申请的电子设备或装置没有特别限定。在一些实施例中，本申请的电子设备包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
在下述实施例及对比例中，所使用到的试剂、材料以及仪器如没有特殊的说明，均可商购获得。
实施例及对比例
负极的制备：将人造石墨(OI值、振实密度见表1)、添加剂(具体种类见表1)和水性粘结剂苯乙烯-丙烯酸共聚树脂(苯丙树脂)按照(96-98.5):(0.5-2.5):(0-2.0)质量比例与去离子水混合，搅拌均匀，得到负极浆料。将该负极浆料涂布在6μm的铜箔上，干燥，冷压，再经过裁片、焊接极耳，得到负极。
正极的制备：将钴酸锂、导电碳、聚偏氟乙烯按照质量比96:2:2混合，加入溶剂N-甲基-2-吡咯烷酮(NMP)制成浆料，涂布在铝箔上，干燥，冷压、再经过裁片、焊接极耳，得到正极。
锂离子电池的制备：将正极、隔离膜(PE多孔聚合物薄膜)、负极按顺序叠好，使隔离膜处于正极和负极之间起到隔离的作用，然后卷绕得到裸电池；将裸电池置于外包装箔中，将电解液(溶剂为体积比为1:1的EC和DMC，1M/L LiPF 6溶液)注入到干燥后的电池中，经过真空封装、静置、化成、整形等工序，即完成锂离子电池的制备。
测试方法
1、振实密度
振实密度为在规定条件下容器中的粉末经振实后所测得的单位体积的质量，单位为 g/cm 3。测试方法为将装有一定质量的粉末的刻度量筒固定在机械振动装置上，振动电机带动机械振动装置垂直上下振动，装有粉末的刻度量筒随机械振动装置而发生有节拍的振动，随着振动次数的增加，刻度量筒里的粉末逐渐振实，振动次数达到设定次数后，机械振动装置停止振动，读出刻度量筒的体积。根据密度的定义：质量除以体积，从而求出振实后的粉末密度。具体的工艺参数：振动次数：5000次；振动频率：250±15次/min；环境温度：15℃至28℃。
2、添加剂取代度
羧甲基取代度：羧甲基取代度的测试标准参照GB/T 1904-2005《食品添加剂羧甲基纤维素钠》中的方法进行测试。
羟乙基取代度或羟丙基取代度：参考D2363-72，“1976 Annual Book of ASTM Standards”进行测试。
3、负极活性材料层热重测试
从极片上刮粉，将粉末至于热重测试仪中，设置温度范围20℃至600℃，升温速率5℃/min，气体氛围为氮气。
所得到的热重曲线在温度为20℃至600℃之间的重量降低率为W T％。在200℃至360℃之间的重量降低率为a％。在360℃至450℃之间的重量降低率为b％。
4、粘结力
负极活性材料层与负极集流体粘结力测试：所用仪器的品牌为Instron，型号为33652。具体地，将负极(宽30mm×长度(100mm至160mm))用双面胶纸(型号：3M9448A，宽度20mm×长度(90mm至150mm))固定于钢板上，将与负极等宽的纸带与负极另一侧用胶纸固定，调整拉力机限位块至合适位置，将纸带向上翻折及滑移40mm，滑移速率为50mm/min，测试180°下(即反方向拉伸)负极活性材料层与负极集流体之间的粘结力。
5、离子电导率
先将包装袋、极片、隔离膜在使用前于60℃下静置4h。然后，将极片用陶瓷剪刀剪成比刀模尺寸(刀模尺寸，23mm×35mm×2mm)大些的小片，将小片放在刀模上进行冲切，充好的极片用镊子取出备用。然后将极片做成单层对称电池。将对称电池置于电化学工作站测试EIS，设置频率0.5Hz至200kHz，扰动电压为10mV；通过EIS两条直线的交点，计算出极片的离子电阻Rion。通过下式计算极片的离子电导率：
极片离子电导率＝d/(Rion×A)，其中，d为极片的厚度，A为极片的面积；
6、循环后容量保持率
在45℃下，将锂离子电池以1C恒流充电至4.45V，然后恒压充电至电流为0.05C，再以1C恒流放电至3.0V，此为首次循环。按照上述条件对锂离子电池进行多次循环。通过下式计算锂离子电池的循环后容量保持率：
循环后容量保持率＝(对应循环次数的放电容量/首次循环的放电容量)×100％
7、放电百分比
在25℃下，以0.5C恒流充电到4.45V，恒压充电至0.05C截止，然后以0.5C恒流放到3.0V截止，记录为25℃放电容量。在25℃下，以0.5C恒流充电到4.45V，恒压充电至0.05C截止，之后将电池置于-20℃恒温箱中，静置2小时，再以0.5C恒流放电到3.0V截止，记录为-20℃放电容量。通过下式计算锂离子电池的放电百分比：
放电百分比＝(-20℃放电容量/25℃放电容量)×100％
8、循环厚度膨胀率
将锂离子电池置于两平板之间，上平板下压，压力为700g时，测得的两平板之间的距离即为锂离子电池的厚度。
在45℃下，将锂离子电池以1C恒流充电至4.45V，然后恒压充电至电流为0.05C，测量锂离子电池厚度，即为锂离子电池首次满充厚度，然后按照循环流程测试进行多次循环，测试锂离子电池厚度。通过下式计算锂离子电池的循环厚度膨胀率：
循环厚度膨胀率＝(对应循环次数的锂离子电池厚度/首次循环的锂离子电池厚度-1)×100％
9、循环变形率
锂离子电池厚度测试：将锂离子电池置于两平板之间，上平板下压，压力为700g时，测得的两平板之间的距离即为锂离子电池的厚度。；
锂离子电池千分尺厚度测试：在Al极耳侧(正极极耳)的电池主体表面选取大概均等分的3个点，使用千分尺测量三个点厚度并取平均值为锂离子电池千分尺厚度。通过下式计算锂离子电池循环变形率：
循环变形率＝(对应循环次数的电芯厚度/对应循环次数的电芯千分尺厚度-1)×100％。
10、柔韧性等级
柔韧性等级的测试标准参照GB/T 1731-93《漆膜柔韧性测定法》。其中，采用轴棒7进行测试，并根据极片弯曲内侧开裂程度判定柔韧性的优异程度。当极片弯曲内侧裂缝宽度＜10μm时，则判定柔韧性等级为优。当极片弯曲内侧10μm≤裂缝宽度≤150μm时，则判定柔韧性等级为中。当极片弯曲内侧裂缝宽度＞150μm时，则判定柔韧性等级为差。
测试结果
表1-1
Figure PCTCN2022079190-appb-000001
注：实施例1-1至实施例1-13以及对比例3中，添加剂均为羟丙基羧甲基纤维素锂；对比例1和对比例2中，添加剂均为羧甲基纤维素锂；关系式1为(-0.0135×TD+0.0263)×100。
表1-2
Figure PCTCN2022079190-appb-000002
Figure PCTCN2022079190-appb-000003
表1中，实施例1-1至实施例1-7研究了负极活性材料人造石墨的OI值对性能的影响，其中人造石墨的OI值为8-9时，负极极片以及锂离子电池的综合性能最优异。
表1中，实施例1-11至实施例1-13研究了负极活性材料层在600℃时热失重率W T％对性能的影响，其中随W T增加，锂离子电池的循环变形率下降，但极片离子电导率降低，使得锂离子电池的放电倍率性能下降。
表1中，对比例1中使用羧甲基纤维素锂作为添加剂，由于羧甲基纤维素锂的脆性大，经过辊压后容易发生龟裂，导致极片粘结力低，进而在循环过程中，无法抑制石墨XY方向的膨胀，使得循环变形率高达6％，循环容量保持率仅为60％左右。对比例2在对比例1的基础上增加了极片中粘结剂的含量(b的大小与负极活性材料层中粘结剂的含量有关，b值越大，表明负极活性材料层中粘结剂的含量越高)，进而使得极片粘结力得到了提高。虽然极片粘结力的提高可以抑制石墨XY方向的膨胀，进而降低锂离子电池的循环变形率，提升其循环容量保持率，但由于粘结剂在石墨表面包覆，其含量过多时会阻碍锂离子的传输，进而使得极片离子电导率降低，导致锂离子电池的放电倍率降低。对比例3中使用常规OI值石墨，锂离子电池的变形率降低，循环容量保持率良好，但相对实施例1-1，其循环膨胀率偏大，离子电导率低，放电百分比降低，不具备实施例1-1中低OI值石墨所带来的性能优势。
表2-1
Figure PCTCN2022079190-appb-000004
注：实施例2-1至实施例2-21中负极活性材料人造石墨的OI值均为8，TD均为0.8；关系式1为(-0.0135×TD+0.0263)×100。
表2-2
Figure PCTCN2022079190-appb-000005
Figure PCTCN2022079190-appb-000006
表2中，实施例2-1至实施例2-5研究了添加剂羟丙基羧甲基纤维素锂的羟丙基取代度对性能的影响，其中羟丙基取代度在0.16至0.28范围内时，负极极片的性能和锂离子电池的性能均较优异。负极极片粘结力(即负极活性材料层和负极集流体之间的粘结力)＞8N/m，负极极片的离子电导率＞0.2S/cm。锂离子电池的循环容量保持率＞80％且变形率＜2％，放电倍率＞50％。其中实施例2-3中羟丙基取代度为0.22时的效果最优，粘结力为14N/m，极片的离子电导率为0.23S/cm，锂离子电池的循环容量保持率为82.2％。通过实施例2-1至实施例2-5的数据还可以看到随着羟丙基羧甲基纤维素锂的羟丙基取代度增加，极片粘结力先增加后下降。这是因为随着羟丙基取代度增加，羟丙基羧甲基纤维素锂的柔韧性增加，脆性降低，使得极片在辊压后，外力作用下的粘结网络破坏减少，进而粘结性能得到提升，同时还可以降低循环过程中石墨膨胀收缩导致的粘结脆性龟裂。但随着羟丙基取代度的进一步增加，羟丙基羧甲基纤维素锂的本体强度会降低，进而会导致相应极片的粘结力下降。
表2中，实施例2-6至实施例2-11研究了负极活性材料层在200℃至360℃范围内热失重率a％和在360℃至450℃范围内热失重率b％对性能的影响。a的大小与负极活性材料层中羟丙基羧甲基纤维素锂的含量有关，a越大，表明负极活性材料层中羟丙基羧甲基纤维素锂的含量越高。b的大小与负极活性材料层中粘结剂的含量有关，b值越大，表明 负极活性材料层中粘结剂的含量越高。实施例2-10和实施例2-11中，a小于1.5时，相对应地，a小于(-0.0135×TD+0.0263)×100，此时，锂离子电池的循环变形率大于3％，容量保持率小于80％。这是因为而低振实密度(振实密度小于0.9g/cm 3)的人造石墨不容易分散，羟丙基羧甲基纤维素锂的含量过低时，浆料匀浆一致性差，负极活性材料层中添加剂和粘结剂分散不均匀，无法形成均匀有效粘结网络，进而不能抑制石墨膨胀滑移错位。实施例2-7至实施例2-10中，a大于1.5，相应地，a大于(-0.0135×TD+0.0263)×100，浆料匀浆一致性良好，负极活性材料层中能够形成均匀分散粘结网络，进而使得锂离子电池的循环容量保持率＞80％且变形率＜2％。实施例2-6中，b为0，即负极活性材料层中粘结剂的含量为0，使得负极极片的粘结网络差，导致由于粘结失效而引起的XY方向变形增大，进而使得锂离子电池的膨胀变形率及厚度膨胀率略大。因此，当a和b满足a+b＜2；a≥(-0.0135×TD+0.0263)×100时，负极极片的性能和锂离子电池的性能均较优异。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的精神、原理及范的情况下对实施例进行改变，替代和修改。

Claims (15)

  1. 一种电化学装置，包括负极，所述负极包括负极集流体和负极活性材料层，所述负极活性材料层包括负极活性材料和负极添加剂，所述负极活性材料包含石墨，其中，
    所述负极活性材料的取向指数OI≤11，采用热重测试，在25℃至600℃的温度范围内，所述负极活性材料层的失重率为W T％，1≤W T≤2.5。
  2. 根据权利要求1所述的电化学装置，其中，所述负极活性材料的振实密度TD g/cm 3≤0.9g/cm 3。
  3. 根据权利要求1或2所述的电化学装置，其中，采用热重测试，在200℃至360℃的温度范围内所述负极活性材料层的失重率为a％，在温度为360℃至450℃的温度范围内所述负极活性材料层的失重率为b％，满足如下条件中的至少一者：
    (Ⅰ)a+b＜2.5；
    (Ⅱ)a≥1.5b；
    (Ⅲ)a≥(-0.0135×TD+0.0263)×100。
  4. 根据权利要求3所述的电化学装置，其中，所述负极活性材料层满足条件(a)或(b)中的至少一者：
    (a)0.8≤a≤2.2，0.1≤b≤0.7；
    (b)0.6≤TD≤0.9。
  5. 根据权利要求3所述的电化学装置，其中，1.1≤a≤1.9，0.2≤b≤0.5。
  6. 根据权利要求1所述的电化学装置，其中，采用傅里叶红外测试，所述负极活性材料层包含谱图在1540cm -1至1630cm -1范围具有吸收峰的物质。
  7. 根据权利要求1所述的电化学装置，其中，所述负极添加剂包括羟烷基羧甲基纤维素或羟烷基羧甲基纤维素的碱金属盐中的至少一种。
  8. 根据权利要求1所述的电化学装置，其中，所述负极添加剂包括羟丙基羧甲基纤维素、羟丙基羧甲基纤维素锂、羟丙基羧甲基纤维素钠、羟乙基羧甲基纤维素、羟乙基羧甲基纤维素锂或羟乙基羧甲基纤维素钠中的至少一种。
  9. 根据权利要求7所述的电化学装置，其中，所述负极添加剂的羟烷基取代度为0.1至0.3，羧甲基取代度为0.5至0.9。
  10. 根据权利要求7所述的电化学装置，其中，所述负极添加剂的羟烷基取代度为0.16至0.28。
  11. 根据权利要求1所述的电化学装置，其中，所述负极添加剂包括羟烷基羧甲基纤 维素的碱金属盐中的至少一种，
    所述负极活性材料层包括区域A和区域B，其中，区域A中碱金属元素含量与区域B中碱金属元素含量的比值为0.8至1.2，
    所述区域A为从负极活性材料层的厚度方向的中心开始至负极活性材料层表面侧的区域，区域B为从负极活性材料层的厚度方向的中心开始至负极集流体侧的区域。
  12. 根据权利要求11所述的电化学装置，其中，所述添加剂包括羟丙基羧甲基纤维素锂，所述区域A中锂元素含量与区域B中锂元素含量的比值为0.8至1.2。
  13. 根据权利要求1所述的电化学装置，其中，所述负极活性材料层还包括粘结剂，所述粘结剂包括丁苯橡胶、聚丙烯酸、聚丙烯酸盐、聚酰亚胺、聚酰胺酰亚胺、聚偏氟乙烯、聚二氟乙烯、聚四氟乙烯、水性丙烯酸树脂、聚乙烯醇缩甲醛或苯乙烯-丙烯酸共聚树脂中的至少一种。
  14. 根据权利要求1所述的电化学装置，其中，所述电化学装置满足条件(ⅰ)或(ⅱ)中的至少一者：
    (ⅰ)所述负极活性材料层和所述负极集流体之间的粘结力为8N/m至15N/m；
    (ⅱ)所述负极的离子电导率为0.1S/cm至0.4S/cm。
  15. 一种电子装置，包括权利要求1至14中任一项所述的电化学装置。
PCT/CN2022/079190 2022-03-04 2022-03-04 电化学装置和电子装置 WO2023164915A1 (zh)

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