WO2020078307A1 - 负极极片及二次电池 - Google Patents

负极极片及二次电池 Download PDF

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Publication number
WO2020078307A1
WO2020078307A1 PCT/CN2019/110992 CN2019110992W WO2020078307A1 WO 2020078307 A1 WO2020078307 A1 WO 2020078307A1 CN 2019110992 W CN2019110992 W CN 2019110992W WO 2020078307 A1 WO2020078307 A1 WO 2020078307A1
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Prior art keywords
negative electrode
current collector
negative
satisfies
battery
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PCT/CN2019/110992
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English (en)
French (fr)
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康蒙
申玉良
王家政
何立兵
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宁德时代新能源科技股份有限公司
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Priority to EP19873783.5A priority Critical patent/EP3813155A4/en
Priority to US16/973,903 priority patent/US11114659B2/en
Publication of WO2020078307A1 publication Critical patent/WO2020078307A1/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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 invention relates to the field of batteries, in particular to a negative pole piece and a secondary battery.
  • Rechargeable batteries have outstanding characteristics such as light weight, high energy density, no pollution, no memory effect, and long service life, so they are widely used in mobile phones, computers, household appliances, power tools and other fields.
  • the rechargeable battery completes the charging and discharging process by inserting and extracting ions between the positive and negative active materials.
  • the design of the negative pole piece will directly affect the performance of the battery. How to design a negative pole piece reasonably so as to obtain a battery that takes into account both kinetic performance and other electrochemical performance is a common problem in the industry.
  • the object of the present invention is to provide a negative pole piece and a secondary battery, which can provide the negative pole piece with excellent dynamic performance characteristics, while ensuring that the secondary battery does not sacrifice energy density It has good kinetic performance and cycle performance.
  • the present invention provides a negative electrode tab including a negative electrode current collector and a negative electrode diaphragm provided on at least one surface of the negative electrode current collector and including a negative electrode active material.
  • the negative pole piece also satisfies: 0.3 ⁇ a ⁇ (1.1 / b + 0.02 ⁇ c) ⁇ 6.0.
  • a represents the specific surface area of the negative electrode membrane, the unit is m 2 / g;
  • b represents the compacted density of the negative electrode membrane, the unit is g / cm 3 ;
  • c represents the adhesion between the negative electrode membrane and the negative electrode current collector ,
  • the unit is N / m.
  • the invention provides a secondary battery including the negative electrode tab according to the first aspect of the invention.
  • the present invention includes at least the following beneficial effects:
  • the present invention adjusts the compaction density of the negative electrode diaphragm, the specific surface area of the negative electrode diaphragm, and the adhesion between the negative electrode diaphragm and the negative electrode current collector by reasonable adjustment
  • the relationship between the three can make the negative pole piece have excellent dynamic performance, and at the same time ensure that the secondary battery has good dynamic performance and cycle performance without sacrificing energy density.
  • a negative electrode sheet which includes a negative electrode current collector and a negative electrode membrane provided on at least one surface of the negative electrode current collector and including a negative electrode active material.
  • the negative pole piece also satisfies: 0.3 ⁇ a ⁇ (1.1 / b + 0.02 ⁇ c) ⁇ 6.0.
  • a represents the specific surface area of the negative electrode membrane, the unit is m 2 / g;
  • b represents the compacted density of the negative electrode membrane, the unit is g / cm 3 ;
  • c represents the adhesion between the negative electrode membrane and the negative electrode current collector ,
  • the unit is N / m.
  • the active ions (such as lithium ions, sodium ions, etc.) that are extracted from the positive electrode active material enter the electrolyte and are accompanied by The electrolyte is conducted from the surface of the positive electrode porous electrode to the inside of the negative electrode porous electrode channel to conduct liquid phase conduction of active ions inside the negative electrode porous electrode channel; (2) electrons are conducted to the surface of the negative electrode active material body through the negative electrode current collector; (3) active ions The SEI film layer passing through the surface of the negative electrode enters the surface of the negative electrode active material to obtain electrons to complete charge exchange; (4) Active ions are solid-phase conducted from the surface of the negative electrode active material to the inside of the negative electrode active material body phase.
  • the active ions such as lithium ions, sodium ions, etc.
  • the conduction of active ions from the surface of the positive electrode porous electrode to the inside of the negative electrode porous electrode channel requires the electrolyte to fully infiltrate the pores of the negative electrode porous electrode.
  • the more unfavorable for the electrolyte to enter the greater the liquid phase conduction resistance of the active ions in the pores of the negative electrode porous electrode, thus affecting the liquid phase potential of the negative electrode during the rapid charging of the battery.
  • the electrolyte needs to have as much contact area as possible with the surface of the negative electrode active material, so that active ions can have more channels for embedding.
  • the bonding force between the negative electrode diaphragm and the negative electrode current collector can be used to reflect the electron conduction ability of the negative pole electrode.
  • the greater the bonding force between the negative electrode diaphragm and the negative electrode current collector, the negative electrode The better the electron conduction performance, the easier the charge exchange reaction between active ions and electrons on the surface of the negative electrode active material, that is, the lower the charge exchange resistance between active ions and electrons.
  • the optimization of the above parameters alone has great limitations on achieving the performance of long battery life, high energy density and fast charging at the same time, because different parameters of the negative pole piece have different effects on battery cycle life, energy density and fast charging
  • the degree of influence of abilities is different.
  • the inventor has found through extensive research that when the specific surface area a of the negative electrode membrane, the compact density b of the negative electrode membrane, and the bonding force c between the negative electrode membrane and the negative electrode current collector satisfy 0.3 ⁇ a ⁇ (1.1 / b + 0.02 ⁇ c) When ⁇ 6.0, it can ensure that the secondary battery has good dynamic performance and cycle performance without sacrificing energy density.
  • the lower limit of a ⁇ (1.1 / b + 0.02 ⁇ c) may be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, a ⁇ (1.1 / b + 0.02
  • the upper limit value of ⁇ c) may be 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0.
  • the negative pole piece satisfies: 0.6 ⁇ a ⁇ (1.1 / b + 0.02 ⁇ c) ⁇ 3.5.
  • the negative electrode diaphragm can provide enough lithium insertion channels, between the negative electrode diaphragm and the negative electrode current collector
  • the bonding force of the electrode can ensure the excellent electron conduction performance of the negative pole piece. Therefore, the liquid phase conduction resistance of the active ion in the pore of the negative electrode porous electrode is small, and the charge exchange resistance of the active ion and the electron on the surface of the negative electrode active material is small.
  • the negative pole piece has good kinetic performance, and thus can ensure that the battery has good kinetic performance and cycle performance without sacrificing energy density.
  • a ⁇ (1.1 / b + 0.02 ⁇ c) is less than 0.3, it may be because the compaction density of the negative electrode diaphragm is large, resulting in small and few pores of the porous electrode of the negative electrode, the electrolyte cannot fully infiltrate the negative electrode diaphragm, and active ions are in the negative electrode
  • the liquid phase conduction resistance inside the porous electrode channel is large; or because the specific surface area of the negative electrode membrane is small, the electrolyte cannot fully contact the negative electrode active material, resulting in that the negative electrode membrane can provide fewer lithium insertion channels; or because the negative electrode membrane
  • the binding force with the negative electrode current collector is small and cannot guarantee the good electron conduction performance of the negative electrode plate.
  • the charge exchange resistance of the active ion and the electron on the surface of the negative electrode active material is large; or because of the superimposition effect of the above unfavorable factors, the final As a result, the liquid phase conduction resistance of the active ions in the pores of the negative electrode porous electrode is large, and the charge exchange resistance of the active ions and electrons on the surface of the negative electrode active material is also large. At this time, the dynamic performance of the negative electrode plate is very poor, which is affected by The battery's dynamic performance and cycle performance are also poor.
  • a ⁇ (1.1 / b + 0.02 ⁇ c) is greater than 6.0, it may be because the compaction density of the negative electrode diaphragm is small, resulting in large and large pores of the porous electrode of the negative electrode, so that the negative electrode diaphragm is too loose; or because of the negative electrode diaphragm The specific surface area is large; or because of the strong adhesion between the negative electrode membrane and the negative electrode current collector; or because of the additive effect of the above-mentioned unfavorable factors.
  • the liquid phase conduction resistance of the active ions in the pores of the negative electrode porous electrode is small at this time, the energy density of the battery will also be smaller due to the looseness of the negative electrode membrane;
  • the contact area with the negative electrode active material is large, although the negative electrode membrane can provide sufficient lithium insertion channels, the probability of side reactions occurring between the electrolyte and the negative electrode active material will be higher, especially if the side reactions increase during the rapid charging of the battery.
  • the cycle performance of the battery will also be poor, especially the high temperature cycle performance of the battery is very poor; again, because of the strong adhesion between the negative electrode membrane and the negative electrode current collector, there is a binder content in the negative electrode membrane More or the spreading area of the binder on the surface of the negative electrode active material and the negative electrode current collector is larger, which is not conducive to the electron conduction of the negative electrode plate, and the charge exchange resistance of the active ion and the electron on the surface of the negative electrode active material is more The dynamic performance of the negative pole piece is also poor, and the dynamic performance of the battery is also poor due to its influence.
  • the specific surface area a of the negative electrode membrane satisfies 0.3 m 2 /g ⁇ a ⁇ 6.0 m 2 / g; more preferably, the specific surface area a of the negative electrode membrane satisfies 0.8m 2 /g ⁇ a ⁇ 3.5m 2 / g.
  • the larger the specific surface area of the negative electrode diaphragm the more chances that the electrolyte contacts the surface of the negative electrode active material, the more active ion insertion channels, the easier the active ion insertion process, and the battery can have better dynamic performance.
  • the compact density b of the negative electrode membrane satisfies 0.8 g / cm 3 ⁇ b ⁇ 2.0 g / cm 3 ; more preferably, the compact density of the negative electrode membrane b satisfies 1.0g / cm 3 ⁇ b ⁇ 1.6g / cm 3 .
  • the compaction density of the negative electrode diaphragm when the compaction density of the negative electrode diaphragm is small, the energy density of the battery is low, and it also affects the adhesion between the negative electrode diaphragm and the negative electrode current collector and the adhesion between the negative electrode active material particles. During the assembly process, the risk of the negative electrode diaphragm falling off becomes higher, which may affect the improvement effect on the battery dynamic performance and cycle performance, and may even cause a safety accident. Therefore, when the compaction density of the negative electrode diaphragm falls within the above-mentioned preferred range, the battery kinetic performance can be better improved, and at the same time, the electrolyte retention capacity of the negative electrode diaphragm is better, and the active ion liquid phase conduction resistance increases slowly. The cycle performance of the battery can be further improved.
  • the binding force between the negative electrode membrane and the negative electrode current collector is too strong, there is too much binder content in the negative electrode membrane or the spreading area of the binder on the surface of the negative electrode active material and the negative electrode current collector is too large Possibly, this is not conducive to the electron conduction of the negative pole piece, and the dynamic performance of the battery is also worse; at the same time, the improvement effect on the energy density of the battery may also be affected by the increase of the binder content in the negative membrane.
  • the bonding force c between the negative electrode diaphragm and the negative electrode current collector satisfies 1N / m ⁇ c ⁇ 20N / m; more preferably, the difference between the negative electrode diaphragm and the negative electrode current collector
  • the adhesive force c satisfies 2N / m ⁇ c ⁇ 10N / m.
  • the coating weight per unit area of the negative electrode is constant, the magnitude of the binding force between the negative electrode membrane and the negative electrode current collector and the content of the binder in the negative electrode membrane, the type of binder, and the negative electrode membrane pressure Factors such as the actual density are related, and those skilled in the art can select a known method to adjust the bonding force between the negative electrode membrane and the negative electrode current collector according to the actual situation.
  • the porosity of the negative electrode membrane also affects the performance of the battery.
  • the porosity of the negative electrode membrane increases, it is not conducive to the improvement of battery energy density.
  • the porosity P of the negative electrode membrane satisfies 20% ⁇ P ⁇ 55%; more preferably, the porosity P of the negative electrode membrane satisfies 25% ⁇ P ⁇ 40%.
  • the type of the negative electrode active material is not specifically limited, and can be selected according to actual needs.
  • the negative electrode active material may be selected from one or more of carbon materials, silicon-based materials, tin-based materials, and lithium titanate.
  • the carbon material may be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres; the graphite may be selected from one or more of artificial graphite and natural graphite ;
  • the silicon-based material may be selected from one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon alloys; the tin-based material may be selected from elemental tin, tin-oxygen compounds, tin alloys One or more. More preferably, the negative electrode active material is selected from one or more of carbon materials and silicon-based materials.
  • the negative electrode diaphragm may be provided on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector.
  • the negative electrode diaphragm may further include a conductive agent and a binder, wherein the types and contents of the conductive agent and the binder are not specifically limited, and can be selected according to actual needs.
  • the type of the negative electrode current collector is also not specifically limited, and can be selected according to actual needs, and copper foil is preferably used.
  • each negative electrode diaphragm given by the present invention also refer to the parameters of the single-sided negative electrode diaphragm.
  • the secondary battery of the second aspect of the present invention further includes a positive electrode tab, an electrolyte, and a separator.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode membrane provided on at least one surface of the positive electrode current collector and including a positive electrode active material, wherein the type and specific composition of the positive electrode electrode sheet They are not subject to specific restrictions and can be selected according to actual needs.
  • the positive electrode diaphragm may be provided on one surface of the positive electrode current collector or on both surfaces of the positive electrode current collector.
  • the positive electrode diaphragm may further include a conductive agent and a binder, wherein the types and contents of the conductive agent and the binder are not specifically limited, and can be selected according to actual needs.
  • the type of the positive electrode current collector is also not specifically limited, and can be selected according to actual needs, and aluminum foil is preferably used.
  • active ions are first extracted from the positive electrode and then inserted into the negative electrode during charging, and the matching of the ease of active ion extraction and insertion during this process is very important. If the kinetic performance of the positive electrode is much higher than that of the negative electrode, the active ions can be quickly extracted from the positive electrode, but the negative electrode lacks the ability to quickly insert. At this time, if a large rate of charge is used, the active ions are easily precipitated on the surface of the negative electrode.
  • the negative electrode has the ability to quickly insert active ions, but the rate of active ion extraction from the positive electrode is very slow, if a large rate of charge is used at this time
  • the active ions will not be directly reduced and precipitated on the surface of the negative electrode, the charging time required when the battery is fully charged is longer, and the battery does not actually have good dynamic performance. Therefore, the matching of positive and negative kinetic performance is also very critical to the improvement of battery kinetic performance.
  • P is the porosity of the negative electrode membrane
  • R is the resistance per unit area of the positive electrode sheet, the unit is ⁇ / cm 2 .
  • the lower limit of P / (2-R ⁇ 0.9) may be 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, and the upper limit of P / (2-R ⁇ 0.9) Values can be 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30.
  • the secondary battery satisfies 0.11 ⁇ P / (2-R ⁇ 0.9) ⁇ 0.25.
  • the positive electrode sheet resistance R per unit area satisfies 0.02 ⁇ / cm 2 ⁇ R ⁇ 1.20 ⁇ / cm 2 ; more preferably, the unit area of the positive electrode sheet resistance R satisfies 0.08 ⁇ / cm 2 ⁇ R ⁇ 0.60 ⁇ / cm 2 .
  • the smaller the resistance per unit area of the positive pole piece the stronger the electron conductivity between the positive electrode active material particles and the particles, and between the positive electrode membrane and the positive electrode current collector, the better the dynamic performance of the positive pole piece, the battery needs to be fully charged The shorter the time, the better the battery's dynamic performance.
  • the resistance per unit area of the positive pole piece should not be too small.
  • the positive electrode kinetic performance is too good when charging.
  • the potential of the negative electrode electrode easily reaches below 0V, resulting in lithium precipitation, which may affect the improvement of the battery dynamic performance. effect.
  • the positive electrode active material may be preferably selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum One or more of oxide and lithium-containing phosphates with olivine structure.
  • the positive electrode active material may be specifically selected from LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , one of LiFePO 4 (LFP), LiMnPO 4 or Several.
  • the separator is provided between the positive electrode tab and the negative electrode tab to play a role of isolation.
  • the type of the separator is not specifically limited, and may be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, and their multilayer composite membranes, but not limited to These ones.
  • the electrolytic solution includes an electrolyte salt and an organic solvent.
  • the specific types of the electrolyte salt and the organic solvent are not specifically limited, and can be selected according to actual needs.
  • the electrolyte may further include additives, and the types of the additives are not particularly limited, and may be negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain performance of the battery, such as improving battery overcharge Performance additives, additives to improve the high temperature performance of batteries, additives to improve the low temperature performance of batteries, etc.
  • the positive electrode active material see Table 1 for details
  • the conductive agent Super P the binder polyvinylidene fluoride (PVDF) at a certain mass ratio
  • NMP solvent N-methylpyrrolidone
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1: 1: 1 to obtain an organic solvent, and then the fully dried lithium salt LiPF 6 is dissolved in the mixture After the organic solvent is prepared, a concentration of 1mol / L electrolyte is prepared.
  • Polyethylene film is used as isolation film.
  • the above positive pole pieces, separators and negative pole pieces are stacked in order, so that the separation membrane is placed between the positive and negative pole pieces to play the role of isolation, and then wound to obtain the bare battery core;
  • the electrolyte is injected after drying, and the battery is obtained through the steps of vacuum sealing, standing, forming, and shaping.
  • Examples 2-27 and Comparative Examples 1-6 were prepared in a similar manner to Example 1, and the specific differences are shown in Table 1.
  • the parameters and battery performance parameters involved in the pole piece of the present invention can be tested as follows, or according to other well-known methods in the art, and the obtained test results are within the error range:
  • the specific surface area test of the negative electrode diaphragm can refer to the national standard GB / T 19587-2004 gas adsorption BET method to determine the specific surface area of solid materials.
  • the compacted density of the negative electrode diaphragm mass per unit area of the negative electrode diaphragm / thickness of the negative electrode diaphragm.
  • the mass per unit area of the negative electrode diaphragm can be weighed by a standard balance, and the thickness of the negative electrode diaphragm can be measured by a micrometer.
  • the adhesion test between the negative electrode diaphragm and the negative electrode current collector can refer to the national standard GB / T2790-1995 adhesive 180 ° peel strength test method.
  • a 180 ° peeling force test can be performed using a high-speed rail tension machine at a peeling speed of 50 mm / min. The average value of the peeling force collected when the negative electrode membrane with a length of 60 mm is completely peeled from the negative electrode current collector is taken as The binding force between the negative current collectors.
  • the four-terminal AC method of HIOKI internal resistance instrument was used for testing.
  • the diameter of the test terminal is 14mm
  • the test pressure is 25MPa
  • the sampling time is 15s.
  • the voltage can be measured.
  • the resistance per unit area of the positive pole piece voltage / current / test terminal area.
  • the batteries prepared in the examples and comparative examples were fully charged at xC and fully discharged at 1C for 10 times, then the batteries were fully charged at xC, and then the negative electrode pieces were disassembled and the negative electrode was observed Lithium deposition on the surface of the tablet. If lithium is not deposited on the surface of the negative electrode, the charging rate xC will be tested again in increments of 0.1C until the lithium is deposited on the surface of the negative electrode to stop the test. At this time, the charging rate xC minus 0.1C is the maximum charging rate of the battery .
  • the batteries prepared in the examples and comparative examples were charged with constant current to the cut-off voltage at the above maximum charge rate, and then charged with constant voltage to 0.05C at this voltage, recording the current and constant voltage charging total time.
  • the battery dynamic performance is considered excellent; if the total time is greater than or equal to 40min and less than or equal to 50min, the battery dynamic performance is considered good; if the total time is greater than 50min, the battery dynamic performance is considered poor.
  • the batteries prepared in the Examples and Comparative Examples were fully charged at 1C rate and fully discharged at 1C rate, and the actual discharge energy at this time was recorded; at 25 ° C, the battery was weighed using an electronic balance; The ratio of the actual discharge energy of the battery 1C to the weight of the battery is the actual energy density of the battery.
  • the actual energy density of the battery when the actual energy density is less than 80% of the target energy density, the actual energy density of the battery is considered to be very low; when the actual energy density is greater than or equal to 80% of the target energy density and less than 95% of the target energy density, the actual energy density of the battery is considered low When the actual energy density is greater than or equal to 95% of the target energy density and less than 105% of the target energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is greater than or equal to 105% of the target energy density and less than 120% of the target energy density, It is considered that the actual energy density of the battery is high; when the actual energy density is more than 120% of the target energy density, the actual energy density of the battery is considered to be very high.
  • the negative pole pieces of the batteries of Examples 1-27 all satisfy 0.3 ⁇ a ⁇ (1.1 / b + 0.02 ⁇ c) ⁇ 6.0, and the pore structure of the negative electrode porous electrode is developed but not loose,
  • the negative electrode membrane can provide enough lithium intercalation channels, and the adhesion between the negative electrode membrane and the negative electrode current collector can ensure the excellent electron conduction performance of the negative electrode sheet. Therefore, the liquid phase conduction resistance of lithium ions inside the pores of the negative electrode porous electrode Small, lithium ion and electron charge exchange resistance on the surface of the negative electrode active material is small, so the negative pole piece has good dynamic performance and high volume energy density characteristics, which can make the battery without sacrificing energy density Good kinetic performance and cycle performance.
  • the battery meets 0.10 ⁇ P / (2-R ⁇ 0.9) ⁇ 0.30. Cycling performance can be further improved, because the difficulty of lithium ion extraction and insertion during battery charging is more matched. It can be seen from the test results in Table 2 that the overall performance of Examples 1-18 is better than that of Examples 19-20.
  • a specific surface area of the negative film is preferably 0.3m 2 /g ⁇ 6.0m 2 / g, preferably within the above range, while better kinetics improve battery performance advantage to ensure long battery life cycle.
  • the compact density b of the negative electrode diaphragm is preferably 0.8 g / cm 3 to 2.0 g / cm 3.
  • the battery dynamic performance can be better improved while ensuring the advantages of high energy density of the battery, while the negative electrode
  • the ability of the sheet to retain the electrolyte is also better, the interface charge transfer impedance between the negative electrode active material and the electrolyte is also lower, and the battery cycle performance can be further improved.
  • the binding force c between the negative electrode membrane and the negative electrode current collector is preferably 1 N / m to 20 N / m.
  • the negative electrode sheet can have good electron conductivity, and lithium ions and electrons are on the surface of the negative electrode active material. The speed of charge exchange is faster, and thus lithium ions can be more easily inserted into the negative electrode active material bulk phase.
  • the battery can still have good kinetic performance and cycle performance without sacrificing energy density.

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Abstract

本发明提供了一种负极极片及二次电池，所述负极极片包括负极集流体以及设置在负极集流体至少一个表面上且包括负极活性物质的负极膜片。所述负极极片还满足：0.3≤a×(1.1/b+0.02×c)≤6.0。其中，a表示负极膜片的比表面积，单位为m 2/g；b表示负极膜片的压实密度，单位为g/cm 3；c表示负极膜片与负极集流体之间的粘结力，单位为N/m。本发明通过合理调节负极膜片的压实密度、负极膜片的比表面积以及负极膜片与负极集流体之间的粘结力三者之间的关系，可以使负极极片具有动力学性能优异的特点，同时保证二次电池在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。

Description

负极极片及二次电池 技术领域
本发明涉及电池领域，尤其涉及一种负极极片及二次电池。
背景技术
可充电电池具有重量轻、能量密度高、无污染、无记忆效应、使用寿命长等突出特点，因而被广泛应用于手机、电脑、家用电器、电动工具等领域。可充电电池是通过离子在正负极活性物质之间嵌入和脱出完成充电和放电过程，其中负极极片设计将直接影响电池的性能。如何通过合理设计负极极片，从而得到兼顾动力学性能以及其他电化学性能的电池是目前行业内普遍面临的问题。
发明内容
鉴于背景技术中存在的问题，本发明的目的在于提供一种负极极片及二次电池，其能使负极极片具有动力学性能优异的特点，同时保证二次电池在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。
为了达到上述目的，在本发明的第一方面，本发明提供了一种负极极片，其包括负极集流体以及设置在负极集流体至少一个表面上且包括负极活性物质的负极膜片。所述负极极片还满足：0.3≤a×(1.1/b+0.02×c)≤6.0。其中，a表示负极膜片的比表面积，单位为m 2/g；b表示负极膜片的压实密度，单位为g/cm 3；c表示负极膜片与负极集流体之间的粘结力，单位为N/m。
在本发明的第二方面，本发明提供了一种二次电池，其包括本发明第一方面所述的负极极片。
相对于现有技术，本发明至少包括如下所述的有益效果：本发明通过合理调节负极膜片的压实密度、负极膜片的比表面积以及负极膜片与负极集流体之间的粘结力三者之间的关系，可以使负极极片具有动力学性能优异的特点，同时保证二次电池在不牺牲能量密度的前提下具有良好的动力学性能和 循环性能。
具体实施方式
下面详细说明根据本发明的负极极片及二次电池。
首先说明根据本发明第一方面的负极极片，其包括负极集流体以及设置在负极集流体至少一个表面上且包括负极活性物质的负极膜片。所述负极极片还满足：0.3≤a×(1.1/b+0.02×c)≤6.0。其中，a表示负极膜片的比表面积，单位为m 2/g；b表示负极膜片的压实密度，单位为g/cm 3；c表示负极膜片与负极集流体之间的粘结力，单位为N/m。
在电池充电过程中，对于负极极片来说，需要经过如下4个电化学过程：(1)从正极活性物质中脱出的活性离子(例如锂离子、钠离子等)进入电解液中，并伴随电解液从正极多孔电极表面传导至负极多孔电极孔道内部，进行活性离子在负极多孔电极孔道内部的液相传导；(2)电子通过负极集流体传导至负极活性物质体表面；(3)活性离子穿过负极表面的SEI膜层进入到负极活性物质表面，得到电子完成电荷交换；(4)活性离子从负极活性物质表面固相传导至负极活性物质体相内部。
在上述电化学过程中，影响离子传导和电子传导的因素将直接影响负极极片的动力学性能，进而影响电池的动力学性能以及循环性能。
首先，活性离子从正极多孔电极表面传导至负极多孔电极孔道内部需要电解液充分浸润负极多孔电极的孔隙，理论上，负极膜片的压实密度越大，负极多孔电极的孔隙越少且越小，越不利于电解液进入，活性离子在负极多孔电极孔道内部的液相传导阻力越大，从而影响了电池快速充电过程中负极的液相电势。
其次，电解液需要与负极活性物质表面有尽可能多的接触面积，这样才能使得活性离子有更多的嵌入通道，理论上，负极膜片的比表面积越大，电解液与负极活性物质表面接触的机会就越多，活性离子的嵌入通道就越多，活性离子的嵌入过程就越容易，同时活性离子与电子的电荷交换阻抗也越小。
再次，只有当电子经过负极集流体到达负极活性物质表面时，活性离子 与电子才能进行电荷交换并嵌入负极活性物质体相内部，因此负极极片的电子传导能力也会影响活性离子的嵌入速度，进而影响负极极片的动力学性能。理论上，负极膜片与负极集流体之间的粘结力大小可用来反映负极极片的电子传导能力，通常，负极膜片与负极集流体之间的粘结力越大，负极极片的电子传导性能越好，活性离子与电子在负极活性物质表面的电荷交换反应越容易，即活性离子与电子的电荷交换阻抗越小。
但是仅靠上述参数自身优化，对同时实现电池长循环寿命、高能量密度以及快速充电等性能存在很大的局限性，这是因为负极极片的不同参数对电池循环寿命、能量密度以及快速充电能力的影响程度是不一样的。发明人通过大量研究发现，当负极膜片的比表面积a、负极膜片的压实密度b、负极膜片与负极集流体之间的粘结力c满足0.3≤a×(1.1/b+0.02×c)≤6.0时，可以保证二次电池在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。
在本发明的一些实施方式中，a×(1.1/b+0.02×c)的下限值可以为0.3、0.4、0.5、0.6、0.7、0.8、0.9、1.0，a×(1.1/b+0.02×c)的上限值可以为0.8、0.9、1.0、1.2、1.4、1.6、1.8、2.0、2.2、2.4、2.6、2.8、3.0、3.5、4.0、4.5、5.0、5.5、6.0。优选地，所述负极极片满足：0.6≤a×(1.1/b+0.02×c)≤3.5。
当0.3≤a×(1.1/b+0.02×c)≤6.0时，负极多孔电极的孔道结构发达但不疏松，负极膜片可提供足够多的嵌锂通道，负极膜片与负极集流体之间的粘结力可保证负极极片优异的电子传导性能，因此活性离子在负极多孔电极孔道内部的液相传导阻力较小、活性离子与电子在负极活性物质表面的电荷交换阻抗较小，此时负极极片具有良好的动力学性能，进而能保证电池在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。
若a×(1.1/b+0.02×c)小于0.3，可能因为负极膜片的压实密度较大，导致负极多孔电极的孔道小且少，电解液不能充分浸润负极膜片，活性离子在负极多孔电极孔道内部的液相传导阻力较大；或因为负极膜片的比表面积较小，电解液不能充分接触负极活性物质，导致负极膜片可提供的嵌锂通道较少；或因为负极膜片与负极集流体之间的粘结力较小而不能保证负极极片良好的电子传导性能，活性离子与电子在负极活性物质表面的电荷交换阻抗较大；或因为上述不利因素的叠加效应，最终导致活性离子在负极多孔电极孔道内部的液相传导阻抗较大、活性离子与电子在负极活性物质表面的电荷交 换阻抗也较大，此时负极极片的动力学性能很差，受其影响，电池的动力学性能和循环性能也都较差。
若a×(1.1/b+0.02×c)大于6.0，可能因为负极膜片的压实密度较小，导致负极多孔电极的孔道大且多，以致负极膜片过于疏松；或因为负极膜片的比表面积较大；或因为负极膜片与负极集流体之间的粘结作用较强；或因为上述不利因素的叠加效应。虽然此时活性离子在负极多孔电极孔道内部的液相传导阻抗较小，但是因负极膜片过于疏松，电池的能量密度也会较小；其次，因负极膜片的比表面积较大，电解液与负极活性物质的接触面积较大，尽管负极膜片可提供足够的嵌锂通道，电解液与负极活性物质接触发生副反应的概率也会越高，尤其是电池快速充电过程中副反应增加严重，电池的循环性能也会表现较差，尤其是电池的高温循环性能表现很差；再次，因负极膜片与负极集流体之间的粘结作用较强，存在负极膜片中粘结剂含量较多或粘结剂在负极活性物质表面和负极集流体上的铺展面积较大的可能，这样反而不利于负极极片的电子传导，活性离子与电子在负极活性物质表面的电荷交换阻抗反而较大，负极极片的动力学性能表现也会较差，受其影响，电池的动力学性能也表现较差。
在本发明的负极极片中，优选地，所述负极膜片的比表面积a满足0.3m 2/g≤a≤6.0m 2/g；更优选地，所述负极膜片的比表面积a满足0.8m 2/g≤a≤3.5m 2/g。负极膜片的比表面积越大，电解液与负极活性物质表面接触的机会越多，活性离子嵌入通道越多，活性离子嵌入过程越容易，电池可具有更好的动力学性能。但是同时，电解液与负极活性物质接触发生副反应的概率也越高，可能影响对电池循环性能的改善效果。因此，负极膜片的比表面积落入上述优选范围内时，可以在更好地提升电池动力学性能的同时保证电池长循环寿命优势。
在本发明的负极极片中，优选地，所述负极膜片的压实密度b满足0.8g/cm 3≤b≤2.0g/cm 3；更优选地，所述负极膜片的压实密度b满足1.0g/cm 3≤b≤1.6g/cm 3。负极膜片的压实密度越小，负极多孔电极的孔隙越多且越大，电解液进入负极多孔电极孔道内部变得越容易，活性离子从负极多孔电极表面传导至负极多孔电极孔道内部阻力越小，电池可具有更好的动力学性能。但是，负极膜片的压实密度较小时，电池的能量密度较低，同时还 会影响负极膜片与负极集流体之间的粘结作用以及负极活性物质颗粒彼此之间的粘结作用，电池装配过程中，负极膜片脱落的风险变高，可能影响对电池动力学性能和循环性能的改善效果，甚至可能引发安全事故。因此，负极膜片的压实密度落入上述优选范围内时，可以更好地提升电池动力学性能，同时负极膜片的电解液保有能力也更好，活性离子液相传导阻抗增长较缓，电池的循环性能也能得到进一步改善。
在本发明的负极极片中，负极膜片与负极集流体之间的粘结力越大，电子经过负极集流体到达负极膜片的传导能力越好，活性离子和电子在负极活性物质表面进行电荷交换的速度也会越快，电池可具有更好的动力学性能。但是，负极膜片与负极集流体之间的粘结力过强时，存在负极膜片中粘结剂含量过多或粘结剂在负极活性物质表面和负极集流体上的铺展面积过大的可能，这样反而不利于负极极片的电子传导，电池的动力学性能也表现更差；同时对电池能量密度的改善效果也可能会因负极膜片中粘结剂含量增加而受到影响。优选地，所述负极膜片与所述负极集流体之间的粘结力c满足1N/m≤c≤20N/m；更优选地，所述负极膜片与所述负极集流体之间的粘结力c满足2N/m≤c≤10N/m。
需要说明的是，在负极单位面积涂布重量一定的情况下，负极膜片与负极集流体之间的粘结力大小与负极膜片中粘结剂含量、粘结剂种类、负极膜片压实密度等因素有关，本领域技术人员可以根据实际情况选择公知的方法来调节负极膜片与负极集流体之间的粘结力大小。
在本发明的负极极片中，负极膜片的孔隙率大小也会影响电池的性能。负极膜片的孔隙率越大，电解液对负极膜片的浸润性越好，活性离子从负极多孔电极表面传导至负极多孔电极孔道内部的阻力越小，电池可具有更好的动力学性能。但是，负极膜片的孔隙率增加时，不利于电池能量密度的改善。优选地，所述负极膜片的孔隙率P满足20％≤P≤55％；更优选地，所述负极膜片的孔隙率P满足25％≤P≤40％。负极膜片的孔隙率落入上述优选范围内时，可以保证电池具有较高能量密度的同时，动力学性能也得到进一步提升。
在本发明的负极极片中，所述负极活性物质的种类并不受到具体的限制，可以根据实际需求进行选择。优选地，所述负极活性物质可选自碳材料、硅基材料、锡基材料、钛酸锂中的一种或几种。其中，所述碳材料可选自石 墨、软碳、硬碳、碳纤维、中间相碳微球中的一种或几种；所述石墨可选自人造石墨、天然石墨中的一种或几种；所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅合金中的一种或几种；所述锡基材料可选自单质锡、锡氧化合物、锡合金中的一种或几种。更优选地，所述负极活性物质选自碳材料、硅基材料中的一种或几种。
在本发明的负极极片中，所述负极膜片可设置在负极集流体的其中一个表面上也可以设置在负极集流体的两个表面上。所述负极膜片还可包括导电剂和粘结剂，其中导电剂以及粘结剂的种类和含量不受具体的限制，可根据实际需求进行选择。所述负极集流体的种类也不受具体的限制，可根据实际需求进行选择，优选可使用铜箔。
需要说明的是，当负极膜片设置在负极集流体两个表面上时，只要其中任意一个表面上的负极膜片满足本发明，即认为该负极极片落入本发明的保护范围内。同时本发明所给的各负极膜片参数也均指单面负极膜片的参数。
其次说明根据本发明第二方面的二次电池，其包括本发明第一方面所述的负极极片。
本发明第二方面的二次电池还包括正极极片、电解液以及隔离膜。
在本发明的二次电池中，所述正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包括正极活性物质的正极膜片，其中，所述正极极片的种类及具体组成均不受到具体的限制，可根据实际需求进行选择。所述正极膜片可设置在正极集流体的其中一个表面上也可以设置在正极集流体的两个表面上。所述正极膜片还可包括导电剂以及粘结剂，其中导电剂以及粘结剂的种类和含量不受具体的限制，可根据实际需求进行选择。所述正极集流体的种类也不受具体的限制，可根据实际需求进行选择，优选可使用铝箔。
在本发明的二次电池中，充电时活性离子首先从正极脱出、再嵌入到负极，该过程中活性离子脱出和嵌入难易程度的匹配十分重要。若正极的动力学性能远高于负极的动力学性能，则活性离子能快速从正极脱出，但负极欠缺快速嵌入的能力，此时若使用大倍率充电，活性离子很容易在负极表面析出，进而影响该电池的循环性能；若正极的动力学性能远低于负极的动力学 性能，即负极具备快速嵌入活性离子的能力，但活性离子从正极脱出的速度很慢，此时若使用大倍率充电，活性离子虽然不会在负极表面直接还原析出，但电池满充时所需要的充电时间更长，电池实际上也并不具备良好的动力学性能。因此，正、负极动力学性能的匹配对电池动力学性能的提升也非常关键。
发明人研究发现，正、负极动力学性能分别与负极膜片的孔隙率和正极极片单位面积的电阻相关性较大，且发明人经过大量研究发现，当二次电池满足0.10≤P/(2-R×0.9)≤0.30时，电池的动力学性能和循环性能还能得到进一步提升。其中，P为负极膜片的孔隙率；R为正极极片单位面积的电阻，单位为Ω/cm 2。
在本发明的一些实施方式中，P/(2-R×0.9)的下限值可以为0.10、0.11、0.12、0.13、0.14、0.15、0.16，P/(2-R×0.9)的上限值可以为0.14、0.15、0.16、0.17、0.18、0.19、0.20、0.21、0.22、0.23、0.24、0.25、0.26、0.27、0.28、0.29、0.30。优选地，二次电池满足0.11≤P/(2-R×0.9)≤0.25。
在本发明的二次电池中，为了进一步提升电池的动力学性能，优选地，所述正极极片单位面积的电阻R满足0.02Ω/cm 2≤R≤1.20Ω/cm 2；更优选地，所述正极极片单位面积的电阻R满足0.08Ω/cm 2≤R≤0.60Ω/cm 2。正极极片单位面积的电阻越小，正极活性物质颗粒与颗粒之间以及正极膜片与正极集流体之间的电子传导能力越强，正极极片的动力学性能越好，电池满充所需要的时间越短，电池的动力学性能越好。但是，正极极片单位面积的电阻也不宜过小，充电时受正极动力学性能太好的影响，负极电极电位极易达到0V以下，从而出现析锂，最终可能影响对电池动力学性能的改善效果。
在本发明的二次电池中，所述正极活性物质可优选选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、橄榄石结构的含锂磷酸盐中的一种或几种。优选地，正极活性物质可具体选自LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4(LFP)、LiMnPO 4中的一种或几种。
在本发明的二次电池中，所述隔离膜设置在正极极片和负极极片之间， 起到隔离的作用。其中，所述隔离膜的种类并不受到具体的限制，可以是现有电池中使用的任何隔离膜材料，例如聚乙烯、聚丙烯、聚偏氟乙烯以及它们的多层复合膜，但不仅限于这些。
在本发明的二次电池中，所述电解液包括电解质盐以及有机溶剂，其中电解质盐和有机溶剂的具体种类并不受到具体的限制，可根据实际需求进行选择。所述电解液还可包括添加剂，所述添加剂种类没有特别的限制，可以为负极成膜添加剂，也可为正极成膜添加剂，也可以为能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
下面结合具体实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
实施例1
(1)正极极片的制备
将正极活性物质(详见表1)、导电剂Super P、粘结剂聚偏氟乙烯(PVDF)按一定质量比进行混合，加入溶剂N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌至体系呈均一状，获得正极浆料；将正极浆料均匀涂覆在正极集流体铝箔的两个表面上，室温晾干后转移至烘箱继续干燥，然后经过冷压、分切得到正极极片。
(2)负极极片的制备
将负极活性物质(详见表1)、导电剂Super P、增稠剂羧甲基纤维素钠(CMC)、粘结剂丁苯橡胶(SBR)按一定质量比进行混合，加入溶剂去离子水，在真空搅拌机作用下搅拌至体系呈均一状，获得负极浆料；将负极浆料均匀涂覆在负极集流体铜箔的两个表面上，室温晾干后转移至烘箱继续干燥，然后经过冷压、分切得到负极极片。
(3)电解液的制备
将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照按体积比1:1:1进行混合得到有机溶剂，接着将充分干燥的锂盐LiPF 6溶解于混合后的有机溶剂中，配制成浓度为1mol/L的电解液。
(4)隔离膜的制备
选用聚乙烯膜作为隔离膜。
(5)电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后卷绕得到裸电芯；将裸电芯置于外包装壳中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，获得电池。
实施例2-27以及对比例1-6的电池均按照与实施例1类似的方法进行制备，具体区别示出在表1中。
表1：实施例1-27和对比例1-6的参数
Figure PCTCN2019110992-appb-000001
Figure PCTCN2019110992-appb-000002
在本发明的极片中涉及的各参数及电池性能参数可按如下方法进行测试，也可按照本领域其它公知的方法进行测试，得到的测试结果均在误差范围内：
1、极片参数测试：
(1)负极膜片的比表面积
负极膜片的比表面积测试可参考国家标准GB/T 19587-2004气体吸附BET法测定固态物质比表面积。
(2)负极膜片的压实密度
负极膜片的压实密度＝负极膜片单位面积质量/负极膜片厚度。其中，负极膜片单位面积质量可通过标准天平称量，负极膜片厚度可通过万分尺测 量。
(3)负极膜片与负极集流体之间的粘结力
负极膜片与负极集流体之间的粘结力测试可参考国家标准GB/T2790-1995胶粘剂180°剥离强度试验方法。具体测试时可利用高铁拉力机以50mm/min的剥离速度进行180°剥离力测试，取长度为60mm的负极膜片从负极集流体上完全剥离时所采集的剥离力平均值作为负极膜片与负极集流体之间的粘结力。
(4)负极膜片的孔隙率
负极膜片的孔隙率采用气体置换法测量，具体可参考国家标准GB/T24586-2009铁矿石表观密度、真密度和孔隙率的测定。孔隙率P＝(V 1-V 2)/V 1×100％，V 1表示表观体积，V 2表示真实体积。
(5)正极极片单位面积的电阻
采用HIOKI内阻仪的四端子交流法进行测试。测试端子直径为14mm，测试压力为25MPa，采点时间为15s，加载电流后，可测量得到电压。正极极片单位面积的电阻＝电压/电流/测试端子的面积。
2、电池性能测试：
(1)动力学性能测试
在25℃下，将实施例和对比例制备得到的电池以x C满充、以1C满放重复10次后，再将电池以x C满充，然后拆解出负极极片并观察负极极片表面的析锂情况。如果负极表面未析锂，则将充电倍率x C以0.1C为梯度递增再次进行测试，直至负极表面析锂，停止测试，此时的充电倍率x C减去0.1C即为电池的最大充电倍率。
然后在25℃下，将实施例和对比例制备得到的电池以上述最大充电倍率恒流充电至截止电压，再在此电压下恒压充电至0.05C，记录此次恒流和恒压充电的总时间。
若总时间小于40min，认为电池动力学性能优秀；若总时间大于等于40min而小于等于50min，认为电池动力学性能良好；若总时间大于50min，认为电池动力学性能较差。
(2)循环性能测试
在25℃下，将实施例和对比例制备得到的电池以1.6C倍率充电、以1C 倍率放电，进行满充满放循环测试，直至电池的容量小于初始容量的80％，记录电池的循环圈数。
(3)实际能量密度测试
在25℃下，将实施例和对比例制备得到的电池以1C倍率满充、以1C倍率满放，记录此时的实际放电能量；在25℃下，使用电子天平对该电池进行称重；电池1C实际放电能量与电池重量的比值即为电池的实际能量密度。
其中，实际能量密度小于目标能量密度的80％时，认为电池实际能量密度非常低；实际能量密度大于等于目标能量密度的80％且小于目标能量密度的95％时，认为电池实际能量密度较低；实际能量密度大于等于目标能量密度的95％且小于目标能量密度的105％时，认为电池实际能量密度适中；实际能量密度大于等于目标能量密度的105％且小于目标能量密度的120％时，认为电池实际能量密度较高；实际能量密度为目标能量密度的120％以上时，认为电池实际能量密度非常高。
各实施例和对比例的测试结果详见表2。
表2：实施例1-27和对比例1-6的性能测试结果
Figure PCTCN2019110992-appb-000003
Figure PCTCN2019110992-appb-000004
从表2的测试结果可以看出：实施例1-27的电池中负极极片均满足0.3≤a×(1.1/b+0.02×c)≤6.0，负极多孔电极的孔道结构发达但不疏松，负极膜片可提供足够多的嵌锂通道，负极膜片与负极集流体之间的粘结力可保证负极极片优异的电子传导性能，因此锂离子在负极多孔电极孔道内部的液相传导阻力较小、锂离子与电子在负极活性物质表面的电荷交换阻抗较小，因此负极极片具有良好的动力学性能以及高体积能量密度特点，由此可以使电池在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。
与实施例1-27相比，在对比例1-6中，a×(1.1/b+0.02×c)均不在所给范围 内，电池无法同时兼顾动力学性能、循环性能及能量密度。
进一步地，在负极极片具有良好动力学性能的前提下，通过合理匹配正、负极的动力学性能，使电池满足0.10≤P/(2-R×0.9)≤0.30，电池的动力学性能和循环性能还能得到进一步提升，这是由于电池充电过程中锂离子脱出和嵌入难易程度更加匹配。从表2的测试结果可以看出，实施例1-18的综合性能要优于实施例19-20。
进一步地，负极膜片的比表面积a优选为0.3m 2/g～6.0m 2/g，在上述优选范围内，可以在更好地提升电池动力学性能的同时保证电池长循环寿命优势。负极膜片的压实密度b优选为0.8g/cm 3～2.0g/cm 3，在上述优选范围内，可以在更好地提升电池动力学性能的同时保证电池高能量密度优势，同时负极极片保有电解液的能力也更好，负极活性物质和电解液之间的界面电荷转移阻抗也更低，电池循环性能也能得到进一步提升。负极膜片与负极集流体之间的粘结力c优选为1N/m～20N/m，在上述优选范围内，负极极片可具有良好的电子传导能力，锂离子与电子在负极活性物质表面进行电荷交换速度较快，进而锂离子能更容易嵌入负极活性物质体相内部。
但当负极膜片的比表面积a、负极极片压实密度b、负极膜片与负极集流体之间的粘结力c中的一个或几个参数未能满足上述优选范围时，只要保证0.3≤a×(1.1/b+0.02×c)≤6.0，结合实施例21-23，电池仍可在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。
从实施例24-27以及对比例3-6中可知，当电池选用不同的正、负极活性物质时，只要负极极片满足0.3≤a×(1.1/b+0.02×c)≤6.0，电池即可在不牺牲能量密度的前提下具有良好的动力学性能和循环性能。
根据上述说明书的揭示和教导，本领域技术人员还可以对上述实施方式进行变更和修改。因此，本发明并不局限于上面揭示和描述的具体实施方式，对本发明的一些修改和变更也应当落入本发明的权利要求的保护范围内。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本发明构成任何限制。

Claims (10)

  1. 一种负极极片，包括负极集流体以及设置在负极集流体至少一个表面上且包括负极活性物质的负极膜片；
    其特征在于，
    所述负极极片还满足：0.3≤a×(1.1/b+0.02×c)≤6.0；
    其中，
    a表示负极膜片的比表面积，单位为m 2/g；
    b表示负极膜片的压实密度，单位为g/cm 3；
    c表示负极膜片与负极集流体之间的粘结力，单位为N/m；
    优选地，所述负极极片满足：0.6≤a×(1.1/b+0.02×c)≤3.5。
  2. 根据权利要求1所述的负极极片，其特征在于，所述负极膜片的比表面积a满足0.3m 2/g≤a≤6.0m 2/g，优选满足0.8m 2/g≤a≤3.5m 2/g。
  3. 根据权利要求1所述的负极极片，其特征在于，所述负极膜片的压实密度b满足0.8g/cm 3≤b≤2.0g/cm 3，优选满足1.0g/cm 3≤b≤1.6g/cm 3。
  4. 根据权利要求1所述的负极极片，其特征在于，所述负极膜片与所述负极集流体之间的粘结力c满足1N/m≤c≤20N/m，优选满足2N/m≤c≤10N/m。
  5. 根据权利要求1所述的负极极片，其特征在于，所述负极膜片的孔隙率P满足20％≤P≤55％，优选满足25％≤P≤40％。
  6. 根据权利要求1所述的负极极片，其特征在于，
    所述负极活性物质选自碳材料、硅基材料、锡基材料、钛酸锂中的一种或几种；
    优选地，所述负极活性物质选自碳材料、硅基材料中的一种或几种。
  7. 一种二次电池，其特征在于，包括根据权利要求1-6中任一项所述的 负极极片。
  8. 根据权利要求7所述的二次电池，其特征在于，所述电池还包括正极极片，所述正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包括正极活性物质的正极膜片，所述二次电池还满足0.10≤P/(2-R×0.9)≤0.30，优选满足0.11≤P/(2-R×0.9)≤0.25；
    其中，
    P为负极膜片的孔隙率；
    R为正极极片单位面积的电阻，单位为Ω/cm 2。
  9. 根据权利要求8所述的二次电池，其特征在于，所述正极极片单位面积的电阻R满足0.02Ω/cm 2≤R≤1.20Ω/cm 2，优选满足0.08Ω/cm 2≤R≤0.60Ω/cm 2。
  10. 根据权利要求8所述的二次电池，其特征在于，所述正极活性物质选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、橄榄石结构的含锂磷酸盐中的一种或几种。
PCT/CN2019/110992 2018-10-17 2019-10-14 负极极片及二次电池 WO2020078307A1 (zh)

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