WO2021195881A1 - 负极极片与包含其的电化学装置 - Google Patents

负极极片与包含其的电化学装置 Download PDF

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WO2021195881A1
WO2021195881A1 PCT/CN2020/082187 CN2020082187W WO2021195881A1 WO 2021195881 A1 WO2021195881 A1 WO 2021195881A1 CN 2020082187 W CN2020082187 W CN 2020082187W WO 2021195881 A1 WO2021195881 A1 WO 2021195881A1
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Prior art keywords
negative electrode
electrode framework
layer
framework layer
lithium
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PCT/CN2020/082187
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English (en)
French (fr)
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陈茂华
李大光
谢远森
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宁德新能源科技有限公司
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Priority to JP2022552979A priority Critical patent/JP2023516415A/ja
Priority to PCT/CN2020/082187 priority patent/WO2021195881A1/zh
Priority to EP20928298.7A priority patent/EP4131509A4/en
Priority to KR1020227033834A priority patent/KR20220140004A/ko
Publication of WO2021195881A1 publication Critical patent/WO2021195881A1/zh
Priority to US17/956,473 priority patent/US20230043821A1/en

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Definitions

  • This application relates to the field of energy storage technology, and more specifically, to a negative pole piece and an electrochemical device containing the same.
  • electrochemical devices are playing an increasingly important role in our daily lives.
  • lithium-ion batteries are widely used in the field of consumer electronics due to their advantages of large specific energy, high working voltage, low self-discharge rate, small size, and light weight.
  • people have higher and higher requirements for the energy density, safety, and cycle performance of electrochemical devices.
  • volume energy density and mass energy density are important parameters to measure the performance of electrochemical devices.
  • Lithium metal is the metal with the lowest relative atomic mass (6.94) and the lowest standard electrode potential (-3.045V) among all metal elements, and its theoretical gram capacity can reach 3860mAh/g. Therefore, using lithium metal as the negative electrode of the electrochemical device, combined with some high energy density positive electrode materials, can greatly increase the energy density of the electrochemical device and its working voltage. However, in real commercial applications, lithium metal used as the negative electrode of an electrochemical device may have various problems during the charge and discharge cycle, thereby preventing the commercialization of lithium metal as a negative electrode active material.
  • Lithium metal is very active, and it is very easy to have side reactions with the electrolyte in the electrochemical device, resulting in the simultaneous consumption of lithium metal and the electrolyte, making the cycle coulombic efficiency much lower than that of general electrochemical devices that use graphite as the negative electrode active material ;
  • lithium metal will be deposited on the surface of the negative pole piece. Due to the inhomogeneity of the current density and the concentration of lithium ions in the electrolyte, the deposition rate will be too fast at some points, forming a sharp lithium dendritic structure; the formation of lithium dendrites will lead to the energy density of the electrochemical device It may even pierce the diaphragm in the electrochemical device and cause a short circuit, which may cause safety problems;
  • the negative pole piece will expand and contract violently; according to the current general design of commercial lithium-ion batteries, in the process of the electrochemical device from the fully charged state to the fully discharged state,
  • the thickness of the negative electrode coated with lithium metal varies from 8 ⁇ m to 100 ⁇ m; this will cause the interface between the active layer of the lithium metal negative electrode and its adjacent structure (for example, the current collector) to peel off, which greatly increases the impedance of the electrochemical device. Decrease the stability of electrochemical devices.
  • the present application provides a negative pole piece and an electrochemical device containing the same in an attempt to solve at least one of the above-mentioned problems at least to some extent.
  • the present application provides a negative electrode sheet, which includes: a current collector; a negative electrode framework on the current collector; wherein the negative electrode framework includes at least a first negative electrode framework layer and a second negative electrode framework layer
  • the first negative electrode framework layer is located between the current collector and the second negative electrode framework layer, and the porosity of the first negative electrode framework layer is greater than the porosity of the second negative electrode framework layer.
  • the present application provides an electrochemical device, which includes the negative pole piece in the above embodiments.
  • the present application provides an electronic device, which includes the electrochemical device in the above-mentioned embodiments.
  • This application constructs a special negative electrode framework for lithium metal negative electrodes, wherein the negative electrode framework is located on the current collector and includes at least two layers with different porosities, namely the first negative electrode framework layer (for example, it is close to the
  • the current collector may also be referred to as the "inner layer”
  • the second negative electrode framework layer for example, it is farther from the current collector than the first negative electrode framework layer, and may also be referred to as the "outer layer”
  • the first negative electrode framework layer described in the present application has a relatively large porosity, and can achieve the following functions:
  • the first negative electrode framework layer has a large porosity, which can provide sufficient space for the deposition of lithium metal during charging; and during discharge, it forms a stable structural support during the continuous reduction of negative electrode metal lithium.
  • the negative pole piece will not change drastically or even change its volume. Therefore, this alleviates or even eliminates the drastic volume change of the lithium metal negative electrode during the charging and discharging process of the electrochemical device.
  • the first negative electrode framework layer has a larger porosity, which can provide a good transport channel for ions and electrons; in addition, the first negative electrode framework layer has a higher specific surface area, which can effectively disperse the charge and discharge process.
  • the current reduces the current density and forms a more uniform electric field, thereby improving the uniformity of lithium deposition and inhibiting the growth of lithium dendrites.
  • the first negative electrode framework layer has a larger porosity, which can provide a large number of nucleation sites and reduce the current density, thereby effectively improving the density of deposited lithium.
  • the second negative electrode framework layer described in the present application has a relatively small porosity, and can achieve the following functions:
  • first negative electrode framework layer Similar to the first negative electrode framework layer, it can provide deposition space for lithium metal during charge and discharge, and greatly reduce or eliminate drastic changes in volume; at the same time, it can reduce the current density, inhibit the growth of lithium dendrites, and improve The deposition density of lithium.
  • the first negative electrode framework layer has a denser framework structure, which helps to form a dense electrode surface, reduces side reactions between lithium metal and electrolyte, and improves the cycle stability of the electrode;
  • a negative electrode protective layer is further formed on the dense electrode surface of the second negative electrode framework layer to further reduce the side reaction between the lithium metal and the electrolyte and improve the cycle stability of the electrode.
  • Fig. 1 is a schematic top view of a punched negative current collector according to some embodiments of the present application
  • FIG. 2 is a schematic top view of a first negative electrode framework layer constructed on the negative electrode current collector shown in FIG. 1 according to some embodiments of the present application;
  • FIG. 3 is a schematic top view of a second negative electrode framework layer constructed on the first negative electrode framework layer shown in FIG. 2 according to some embodiments of the present application;
  • FIG. 4 is a schematic cross-sectional view of a negative pole piece cut along the line AA' shown in FIG. 3 according to some embodiments of the present application;
  • Fig. 5 is a schematic cross-sectional view of a negative pole piece with a negative frame provided on both sides of a current collector according to some embodiments of the present application;
  • FIG. 6 is a schematic cross-sectional view of a negative pole piece including more layers of negative pole frames according to some embodiments of the present application;
  • FIG. 7 is a schematic cross-sectional view of a negative electrode piece with a negative electrode protective layer provided on the surface of a negative electrode skeleton according to some embodiments of the present application.
  • the term when used in conjunction with a value, can refer to a range of variation less than or equal to ⁇ 10% of the stated value, such as less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, Less than or equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%.
  • a list of items connected by the terms “at least one of”, “at least one of” or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (exclude B); B and C (exclude A); or all of A, B, and C.
  • Project A can contain a single component or multiple components.
  • Project B can contain a single component or multiple components.
  • Item C can contain a single component or multiple components.
  • an electrochemical device for example, a lithium ion battery
  • using lithium metal as the negative electrode of the electrochemical device can increase the energy density of the battery and the operating voltage of the battery.
  • the use of lithium metal as a negative pole piece may cause various problems, such as side reactions between lithium metal and electrolyte, formation of lithium dendrites, and negative pole pieces
  • the violent expansion and contraction of the volume will easily cause the interface between the negative pole piece and other adjacent structures to peel off, resulting in a sharp increase in impedance and severely reducing the safety and stability of the electrochemical device.
  • the application provides a negative electrode framework with a multilayer structure.
  • the negative electrode framework has two or more layers, wherein by adopting a different porosity design for each layer, the negative electrode framework layer close to the current collector has a higher porosity and the negative electrode framework layer far away from the current collector has a lower porosity. Porosity.
  • the negative pole piece of this application can be a single-sided structure or a double-sided structure.
  • the single-sided structure means that the negative electrode frame described in this application is provided only on one side of the current collector, and the double-sided structure refers to the two sides of the current collector. Both sides are provided with the negative electrode framework described in the present application.
  • Figures 1-4 are a top view and a cross-sectional view of a negative pole piece with a single-sided structure according to some embodiments of the present application.
  • FIG. 1 shows a top view of the negative electrode current collector 101 that has been punched out.
  • the current collector 101 may be a negative electrode current collector commonly used in the art, which includes, but is not limited to, nickel foil, tin foil, copper foil, lithium foil, and lithium-coated copper foil.
  • the first negative electrode framework layer 102 with a relatively large porosity is disposed on the surface of the current collector 101.
  • the second negative electrode skeleton layer 103 with a smaller porosity is disposed on the surface of the first negative electrode skeleton layer 102.
  • FIG. 3 schematically shows only a part of the second negative electrode framework. ⁇ 103.
  • the second negative electrode framework layer 103 should completely cover the surface of the first negative electrode framework layer 102.
  • FIG. 4 shows a cross-sectional view of the negative pole piece cut along the line AA′ in FIG. 3.
  • the negative electrode piece of the present application includes: a current collector 101 and a negative electrode skeleton on the current collector 101, wherein the negative electrode skeleton includes at least a first negative electrode framework layer 102 and a second negative electrode framework layer 103, wherein the first A negative electrode framework layer 102 is located between the current collector 101 and the second negative electrode framework layer 103, and the porosity of the first negative electrode framework layer 102 is greater than the porosity of the second negative electrode framework layer 103.
  • the first negative electrode skeleton layer 102 may also be referred to as an inner layer and the second negative electrode skeleton layer 103 may be referred to as an outer layer.
  • the pores existing in the first negative electrode framework layer 102 and the second negative electrode framework layer 103 reserve space for the deposition of lithium metal.
  • the severe volume change caused by the insertion and extraction of lithium ions can be alleviated or even eliminated, thereby effectively It avoids interfacial peeling and improves the safety and stability of electrochemical devices.
  • the first negative electrode framework layer 102 has a relatively large porosity, which can provide a good conduction channel for the transmission of ions and electrons, and improve the rate performance of the electrochemical device.
  • the first negative electrode framework layer 102 has a relatively high specific surface area, effectively disperses the current in the charge and discharge process, reduces the current density, improves the uniformity of lithium deposition, and inhibits the formation of lithium dendrites.
  • the second negative electrode framework layer 103 has a denser framework structure than the first negative electrode framework layer 102.
  • the dense structure of the second negative electrode framework layer 103 can at least bring the following advantages: (1) It can also provide deposition space for lithium metal during the charge and discharge process, greatly reducing or eliminating drastic changes in volume; at the same time, it can reduce the current density and suppress Lithium dendrites grow to increase the deposition density of lithium; (2) help to further form a dense negative electrode protective layer on its surface, reduce the difficulty of forming the negative electrode protective layer, reduce side reactions between lithium metal and electrolyte, and further Improve the strength and stability of the lithium metal negative electrode, and improve the coulombic efficiency and cycle life of electrochemical devices.
  • the porosity of the first negative electrode framework layer ranges from about 55% to about 90%.
  • the porosity of the second negative electrode framework layer ranges from about 10% to about 50%. In some embodiments, the porosity of the second negative electrode framework layer ranges from about 20% to about 50%. In some other embodiments, the porosity of the second negative electrode framework layer ranges from about 20% to about 40%.
  • the porosity of the first negative electrode framework layer may be a substantially fixed percentage or a percentage that varies within the above-mentioned range. In some embodiments, when the porosity of the first negative electrode framework layer changes, the porosity preferably decreases as the relative distance from the current collector increases.
  • the porosity of the second negative electrode framework layer may be a substantially fixed percentage or a percentage that varies within the above-mentioned range. In some embodiments, when the porosity of the second negative electrode framework layer changes, the porosity preferably decreases as the relative distance from the current collector increases.
  • the total thickness of the negative electrode skeleton ranges from about 5 ⁇ m to about 100 ⁇ m. In some embodiments, the thickness of the first negative electrode framework layer ranges from about 1 ⁇ m to about 95 ⁇ m. In some embodiments, the thickness of the second negative electrode framework layer ranges from about 0.1 ⁇ m to about 50 ⁇ m.
  • the thickness of the negative electrode framework and the porosity of the negative electrode framework satisfy the following relationship:
  • t is the total thickness of the negative electrode framework/ ⁇ m
  • x is the distance from any plane parallel to the surface of the current collector in the negative electrode framework to the surface of the current collector (integral element)/ ⁇ m
  • p is the pores of the negative electrode framework Rate.
  • the above formula 1 indicates that the cumulative thickness of the pores provided by the negative electrode skeleton is in the range of 5 ⁇ m to 50 ⁇ m. It can also be understood that the cumulative thickness of lithium metal that can be deposited on the negative electrode framework ranges from 5 ⁇ m to 50 ⁇ m.
  • the above formula 2 indicates that the porosity of the negative electrode skeleton decreases from the inside to the outside.
  • the above formula 3 indicates that the porosity of the negative electrode skeleton is in the range of 20% to 90%.
  • the above formula 4 indicates that the thickness of the negative electrode skeleton is in the range of 5 ⁇ m to 100 ⁇ m. It should be noted that the porosity described in the present application is only calculated based on the material of the negative electrode framework itself, and does not include the lithium metal that is pre-replenished in the negative electrode framework before the first charge and discharge.
  • the present application provides a negative electrode framework whose porosity gradually decreases from the inside to the outside. That is, the thickness and porosity of the negative electrode skeleton satisfy the relationship described in the above formula (2).
  • the negative electrode framework described in the present application also satisfies at least one of the above formulas (1), (3) and (4).
  • the negative electrode piece further includes lithium metal pre-intercalated (ie, pre-replenished) into the negative electrode framework to serve as the negative electrode active material of the electrochemical device, wherein the amount of the pre-intercalated lithium metal The range is about 0.001 mg/cm 2 to about 6 mg/cm 2 .
  • Pre-intercalation refers to the lithium metal pre-embedded into the negative electrode frame before the negative pole piece is charged and discharged for the first time.
  • a range of pre-doping amount of the lithium metal is from about 0.005mg / cm 2 to about 3mg / cm 2.
  • the amount of the pre-intercalated lithium metal may be about 0.005 mg/cm 2 , about 0.01 mg/cm 2 , about 0.1 mg/cm 2 , about 0.5 mg/cm 2 , about 1 mg/cm 2 , about 1.5 mg /cm 2 , about 2 mg/cm 2 , about 2.5 mg/cm 2 and about 3 mg/cm 2 .
  • Fig. 5 is a cross-sectional view of a negative pole piece with the negative frame of the present application provided on both sides of a current collector according to some embodiments of the present application.
  • a first negative electrode framework layer 102 and a second negative electrode framework layer 103 are provided on both sides of the current collector 101, wherein the first negative electrode framework layer 102 is located in the current collector 101. And the second negative electrode framework layer 103.
  • the negative electrode frameworks provided on both sides of the current collector 101 may be two different negative electrode frameworks.
  • FIG. 6 is a cross-sectional view of a negative electrode sheet including more layers of negative electrode skeletons according to some embodiments of the present application.
  • the negative pole piece of the present application further includes at least one third negative frame layer 104. As shown in FIG. 6, the third negative electrode framework layer 104 is located on the surface of the second negative electrode framework layer 103.
  • FIG. 6 is an exemplary embodiment in which the negative electrode framework of the present application has more than two-layer structure.
  • FIG. 6 only illustrates a negative electrode skeleton with a three-layer structure, those skilled in the art can adjust the number of negative electrode framework layers in the negative electrode sheet according to specific needs through the teachings of this application, and it is obviously not affected by the drawings of this application. The limit of the number of layers of the negative electrode skeleton shown.
  • the first negative electrode framework layer, the second negative electrode framework layer, and the third negative electrode framework layer each independently include at least one of the following materials: polymer materials, carbon materials, metals Materials, or inorganic materials.
  • the polymer material includes at least one of the following: polyethylene oxide, polyimide, polyacrylic acid, polyethylene, polypropylene, polyacrylonitrile, polystyrene, poly Vinyl fluoride, polyether ether ketone, polyester, polyvinylidene chloride, polytetrafluoroethylene, polyethylene terephthalate, or derivatives of one or more of the above-mentioned polymer materials.
  • the carbon material includes at least one of the following: porous carbon, carbon nanotubes, carbon fibers, graphene and its derivatives, or hollow carbon spheres.
  • the metal material includes at least one of the following: copper, nickel, chromium, titanium, tungsten, zirconium, or an alloy composed of two or more of the foregoing materials.
  • the inorganic material includes at least one of the following: lithium phosphate (Li 3 PO 4 ); LiPON; Li 2 O; LiF; LiOH; Li 2 CO 3 ; LiAlO 2 ; Li 4 SiO 4 ; Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2 -GeO 2 ceramics; lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , where 0 ⁇ x ⁇ 2 and 0 ⁇ y ⁇ 3); lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , where 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 1, and 0 ⁇ z ⁇ 3); Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 , where 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1; lithium lanthanum titanate (Li x La y TiO 3 , where 0 ⁇
  • the first negative electrode framework layer, the second negative electrode framework layer, and the third negative electrode framework layer are each independently composed of a composite material, wherein the composite material is two or more of the following materials Any combination of those: polymer materials, carbon materials, metal materials, and inorganic materials.
  • the negative electrode skeleton may include: a basic skeleton prepared from a polymer material or a carbon material and an inorganic material further deposited on the basic skeleton.
  • the inorganic material covers the inner and outer surfaces of the porous structure of the material in the form of particles or coatings.
  • the inorganic material includes at least one of the following: HfO 2 , SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, BaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2 O 3 , TiO 2 , SiO 2 , CuO, or AgO.
  • the inorganic material can serve as a deposition site to guide lithium deposition inside the porous structure.
  • the preparation method of the composite material may be a common preparation method in the art, which includes, but is not limited to, atomic layer deposition (ALD) and electrochemical deposition.
  • ALD atomic layer deposition
  • electrochemical deposition electrochemical deposition
  • the negative pole piece further includes one or more negative protective layers on the surface of the negative frame.
  • one or more negative electrode protective layers 105 may be further formed on the surface of the second negative electrode framework layer 103.
  • the role of the negative electrode protective layer is to protect the negative electrode.
  • the negative electrode protective layer 105 can isolate the electrolyte from the negative electrode active material lithium metal, greatly reduce the side reaction between the electrolyte and the lithium metal, and improve the cycle stability of the electrochemical device.
  • the framework of the second negative electrode framework layer is denser, which reduces the difficulty of forming the negative electrode protective layer and is beneficial to further build on the surface of the negative electrode framework.
  • a dense negative electrode protective layer is formed.
  • the porosity of the negative electrode protective layer ranges from about 0% to about 10%.
  • the material used for the negative electrode protective layer includes at least one of the following: inorganic substances, silicon, metals, or organic substances.
  • the inorganic substance includes at least one of the following: lithium phosphate (Li 3 PO 4 ); LiPON; Li 2 O; LiF; LiOH; Li 2 CO 3 ; LiAlO 2 ; Li 4 SiO 4 ; Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2 -GeO 2 ceramics; lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , where 0 ⁇ x ⁇ 2 and 0 ⁇ y ⁇ 3); lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , where 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 1, and 0 ⁇ z ⁇ 3); Li 1+x+y (Al,Ga) x (Ti,Ge) 2-x Si y P 3-y O 12 , where 0 ⁇ x ⁇ 1 and 0 ⁇ y ⁇ 1; lithium lanthanum titanate (Li x La y TiO 3 , where 0 ⁇
  • the metal includes at least one of the following: Au, Pt, Ag, Al, In, Sn, or an alloy composed of two or more of the foregoing materials.
  • the organic substance includes at least one of the following: polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene carbonate (PPC) ), polyvinyl carbonate (PEC), polycaprolactone (PCL), tetraethylene glycol diacrylate (TEGDA), perfluorosulfonic acid resin (Nafion), polyacrylonitrile (PAN), poly Dimethylsiloxane (PDMS) or derivatives of the above-mentioned organic substances.
  • PEO polyethylene oxide
  • PVDF polyvinylidene fluoride
  • PMMA polymethyl methacrylate
  • PPC polypropylene carbonate
  • PCL polyvinyl carbonate
  • PCL polycaprolactone
  • TAGDA tetraethylene glycol diacrylate
  • PAN polyacrylonitrile
  • PDMS poly Dimethylsiloxane
  • an electrochemical device comprising the negative pole piece of the above-mentioned embodiment.
  • the electrochemical device also includes a positive pole piece and a separator between the positive pole piece and the negative pole piece.
  • the positive pole piece or separator is not particularly limited, and may be a positive pole piece and a separator commonly used in the art. Isolation film.
  • the electrochemical device is a lithium ion battery.
  • the positive pole piece includes a positive current collector and a positive active material layer on the surface thereof, wherein the positive active material layer includes a positive active material, a conductive agent, and a binder.
  • the positive current collector includes, but is not limited to, aluminum foil or nickel foil.
  • examples of the positive active material may include, but are not limited to, lithium cobaltate, lithium iron phosphate, lithium iron manganese phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadyl phosphate, At least one of sodium vanadyl phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based materials, lithium nickel cobalt aluminate, and lithium titanate.
  • the chemical formula of lithium cobaltate can be Li a Co b M 1c O 2-d , where M 1 includes nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), Boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), At least one of strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr) or silicon (Si), the values of a, b, c and d are in the following ranges: 0.8 ⁇ a ⁇ 1.2, 0.8 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 0.2, -0.1 ⁇ d ⁇ 0.2;
  • the chemical formula of lithium nickelate can be Li e Ni f M 2g O 2-h , where M 2 includes cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), Boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), At least one of strontium (Sr), tungsten (W), zirconium (Zr) or silicon (Si), the values of e, f, g and h are in the following ranges: 0.8 ⁇ e ⁇ 1.2, 0.3 ⁇ f ⁇ 0.98 , 0.02 ⁇ g ⁇ 0.7, -0.1 ⁇ h ⁇ 0.2;
  • the chemical formula of lithium manganate is Li i Mn 2-j M 3j O 4-k , where M 3 includes cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), Boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), At least one of strontium (Sr) or tungsten (W), the values of i, j, and k are in the following ranges: 0.8 ⁇ i ⁇ 1.2, 0 ⁇ j ⁇ 1.0, and -0.2 ⁇ k ⁇ 0.2.
  • the conductive agent includes at least one of conductive carbon black, carbon fiber, acetylene black, Ketjen black, graphene, and carbon nanotubes.
  • the isolation film includes, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, or aramid.
  • polyethylene includes at least one component of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • polyethylene and polypropylene they have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect.
  • separators widely used in lithium-ion batteries are suitable for this application.
  • the above-mentioned lithium ion battery further includes an electrolyte.
  • the electrolyte may be in a gel state or a liquid state, and the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt includes LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC At least one of (SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB, or lithium difluoroborate.
  • LiPF 6 is selected for lithium salt because it can give high ionic conductivity and improve cycle characteristics.
  • the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
  • the carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • examples of the chain carbonate compound are diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, ethyl methyl carbonate, or a combination thereof.
  • examples of the cyclic carbonate compound are ethylene carbonate, propylene carbonate, butylene carbonate, vinyl ethylene carbonate, propyl propionate, or a combination thereof.
  • fluorocarbonate compound examples include fluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Ester, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluorocarbonate -1-Methyl ethylene, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof.
  • examples of carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, ⁇ -butyrolactone, decanolide , Valerolactone, mevalonolactone, caprolactone, methyl formate or a combination thereof.
  • examples of ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane , Ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran or a combination thereof.
  • examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl -2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid ester or a combination thereof.
  • Some embodiments of the present application provide a method for preparing a lithium ion battery, which includes: winding or stacking the above-mentioned positive pole piece, separator, and negative pole piece of the present application in order to form a battery core, and then inserting, for example, aluminum plastic Into the membrane, electrolyte is injected, formed, and encapsulated to form a lithium-ion battery.
  • the electrochemical device of the present application further includes any other suitable electrochemical device.
  • the electrochemical device in the embodiments of the present application includes any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, solar cells, or capacitors.
  • the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
  • electrochemical device of the present application is not particularly limited, and it can be used for any purpose known in the prior art.
  • electronic devices including the electrochemical device of the present application include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, Portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles , Motorcycles, power-assisted bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.
  • the positive electrode active material lithium iron phosphate (LiFePO 4 ), conductive carbon black (Super P), polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent , Formulated into a slurry with a solid content of 55%, and stirred evenly.
  • the slurry is uniformly coated on the positive electrode current collector aluminum foil and dried at 90° C. to obtain a positive electrode pole piece.
  • the load capacity of the positive electrode is 1 mAh/cm 2 . After coating, cut the pole piece into (38mm ⁇ 58mm) specifications for later use.
  • LiTFSI lithium bistrifluoromethanesulfonimide
  • a polyethylene with a thickness of 15 ⁇ m was used as the separator, and the double-layer coated negative electrode piece, the separator, and the single-layer coated positive electrode piece in the example and the comparative example were sequentially stacked. After the stacking is completed, the four corners of the entire laminate structure are fixed with tape, and then placed in the aluminum plastic film. After top-side sealing, liquid injection, and packaging, the lithium metal laminates of the following examples and comparative examples are finally obtained. Slice battery.
  • the frame to be tested is placed in an automatic mercury porosimeter (model AutoPore V9610) for testing, and the porosity of the sample is obtained.
  • the pressure range is 0.5-30,000psia.
  • the pole piece to be tested is punched into a small round piece with a diameter of 14 mm, which is used as the positive electrode.
  • the copper foil was punched into a small disc with a diameter of 18 mm as the negative electrode.
  • a polyethylene with a thickness of 15 ⁇ m and a diameter of 20 mm is used as the separator, and 60 ⁇ L of the above-mentioned electrolyte is added to assemble a button cell.
  • the button cell is charged at a current density of 0.1 mA/cm 2 , and the charging voltage is in the range of 0-1V.
  • the laminated battery was charged and discharged for one cycle at a rate of 0.1C at 60°C to form the laminated battery, and then the battery was subjected to a charge-discharge cycle at room temperature.
  • the number of cycles of the lithium ion battery in the comparative example and the example was tested when the discharge capacity was 80% of the first discharge capacity.
  • the porosity of the first negative electrode framework layer ie, the inner layer
  • the thickness was 45 ⁇ m
  • the second negative electrode framework layer That is, the outer layer
  • the above-mentioned two layers of polyacrylonitrile fibers were heated at a temperature of 210°C for 1 hour in an atmosphere, and then heated at a temperature of 900°C for 3 hours in an argon atmosphere to obtain a carbon film.
  • the preparation method and raw materials are the same as in Example 1, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 2 is 55%.
  • Example 3 The preparation method and raw materials are the same as in Example 1, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 3 is 80%.
  • the preparation method and raw materials are the same as in Example 1, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 4 is 90%.
  • the preparation method and raw materials are the same as in Example 1, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 5 is 95%.
  • the preparation method and raw materials are the same as in Example 1, except that the porosity of the second negative electrode framework layer (ie, the outer layer) in Example 6 is 20%.
  • Example 7 The preparation method and raw materials are the same as in Example 1, except that the porosity of the second negative electrode framework layer (ie, the outer layer) in Example 7 is 40%.
  • Example 8 The preparation method and raw materials are the same as in Example 1, except that the porosity of the second negative electrode framework layer (ie, the outer layer) in Example 8 is 10%.
  • Comparative Example 1 The difference between Comparative Example 1 and Examples 1-8 is that no negative electrode framework is provided, only lithium metal is placed on the current collector, and the two are tightly combined by rolling.
  • the thickness of the pre-filled lithium metal is 10 ⁇ m.
  • Comparative Example 2 only provides a negative electrode framework layer with a porosity of 30% and a thickness of 50 ⁇ m on both surfaces of the current collector.
  • Comparative Example 3 only provided a negative electrode framework layer with a porosity of 70% and a thickness of 50 ⁇ m on both surfaces of the current collector.
  • the amount of pre-supplementing lithium is related to the porosity of the negative electrode frame.
  • the porosity provided by the negative electrode framework is low, the space available for lithium deposition is small, so the amount of pre-replenished lithium will be correspondingly reduced.
  • the electrochemical device prepared using the negative electrode pieces of Examples 1-8 of the present application has better cycle stability than the electrochemical device prepared using the negative electrode pieces of Comparative Examples 1-3.
  • Comparative Example 1 since no framework was constructed for metallic lithium, the cycle stability of its electrochemical device was the worst.
  • Comparative Examples 2 and 3 built a layer of framework (it can also be understood as two layers of frameworks with the same porosity).
  • the cycle stability of the electrochemical device is improved.
  • the inner layer has a higher porosity than the outer layer, which can further improve the cycle stability of the electrochemical device compared to Comparative Examples 2 and 3 .
  • Example 5 Compared Example 5 with other examples, it can be seen that the cycle stability of the electrochemical device of Example 5 is relatively poor. Deposition provides strong support. However, even so, the cycle stability of the electrochemical device of Example 5 is still better than that of Comparative Examples 1-3.
  • the foamed copper with a porosity of 70% was used as the first negative electrode framework layer (ie, the inner layer) with a thickness of 45 ⁇ m; the foamed copper with a porosity of 30% was used as the second negative electrode framework layer (ie, the outer layer) with a thickness of 5 ⁇ m.
  • the pole piece is cut into (40mm ⁇ 60mm) specifications for use.
  • Example 10 The preparation method and raw materials are the same as in Example 9, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 10 is 80%.
  • the porosity of the first negative electrode skeleton layer ie, the inner layer
  • the thickness was 45 ⁇ m
  • the second negative electrode The porosity of the framework layer (ie, the outer layer) was 30%, and the thickness was 5 ⁇ m.
  • the pole piece is cut into (40mm ⁇ 60mm) specifications for use.
  • Example 12 The preparation method and raw materials are the same as in Example 11, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 12 is 80%.
  • the foamed copper having a porosity of 70% was used as the first negative electrode framework layer (ie, the inner layer), and the thickness was 45 ⁇ m.
  • polyacrylonitrile is used as a precursor to prepare a fiber layer with a porosity of 30% as the second negative electrode framework layer (ie, outer layer), with a thickness of 5 ⁇ m.
  • the polyacrylonitrile fiber layer was heated at a temperature of 210°C for 1 hour in an atmosphere, and then heated at a temperature of 900°C for 3 hours in an argon atmosphere, to obtain a carbon film with a thickness of 5 ⁇ m.
  • Example 14 The preparation method and raw materials are the same as in Example 13, except that the porosity of the first negative electrode framework layer (ie, the inner layer) in Example 14 is 80%.
  • the inner and outer layers of the negative electrode framework of Examples 1-8 are made of carbon materials.
  • a metal material for example, Cu
  • a polymer material for example, polyimide
  • the cycle performance of the electrochemical devices of Examples 9-14 has been improved, which shows that the anode framework made of metal materials and polymer materials can provide a deposition framework and a carbon material for lithium metal like carbon materials. support.
  • the metal Cu is used to prepare the negative electrode framework, the cycle stability of the obtained electrochemical device is slightly worse than that of the electrochemical device using the negative electrode framework layer made of carbon materials and/or polymer materials.
  • Example 15 is an improvement of Example 1 on the basis of Example 1.
  • the specific improvement items are: after heating the above two polyacrylonitrile fiber layers to obtain a carbon film, the atomic layer deposition technique is used to cover the inner and outer surfaces of the pore structure of the carbon film with a zinc oxide coating with a thickness of 20 nm.
  • Example 16 is an improvement of Example 9 on the basis of Example 9.
  • the specific improvement items are: the use of atomic layer deposition technology to cover the inner and outer surfaces of the pore structure of the two foamed copper materials with a layer of aluminum oxide coating with a thickness of 20 nm.
  • Embodiment 17 is an improvement of Embodiment 11 on the basis of Embodiment 11.
  • the specific improvement items are: using atomic layer deposition technology to cover the inner and outer surfaces of the pore structure of the polyimide fiber layer with a copper oxide coating with a thickness of 20 nm.
  • Example 18 is an improvement of Example 13 on the basis of Example 13.
  • the specific improvement items are: using atomic layer deposition technology to cover the inner and outer surfaces of the pore structure of carbon film and copper foam with a layer of titanium dioxide coating with a thickness of 20 nm.
  • Examples 15-18 involve further covering the inner and outer surfaces of the pore structure of the framework formed in Examples 1, 9, 11 and 13 with a layer of inorganic substance (for example, ZnO, Al 2 O 3 , CuO, and TiO 2 ) coating. That is, the structure of the negative electrode framework of Examples 15-18 can be described as: firstly, the basic negative electrode framework is formed by using carbon materials/metal materials/polymer materials; ⁇ Material. That is, the negative electrode skeletons of Examples 15-18 were formed of composite materials. Correspondingly comparing the electrochemical data of Examples 15-18 with Examples 1, 9, 11 and 13, it can be seen that by further wrapping or depositing inorganic materials on the inner and outer surfaces of the pore structure of the framework, the performance of the electrochemical device can be further improved. Cycle stability.
  • inorganic substance for example, ZnO, Al 2 O 3 , CuO, and TiO 2
  • Example 19 is an improvement of Example 1 on the basis of Example 1.
  • the specific improvement items are: after pre-replenishing lithium, a layer of LiF negative electrode protective layer with a thickness of 1 ⁇ m is deposited on the surface of the second negative electrode framework layer by means of magnetron sputtering. See Figure 7 for a schematic diagram of the specific structure.
  • Embodiment 20 is an improvement of Embodiment 19 on the basis of Embodiment 19.
  • the specific improvement items are: using atomic layer deposition technology to cover a layer of ZnO coating with a thickness of 20nm on the inner and outer surfaces of the pore structure of the negative electrode framework.
  • Example 21 The difference between Examples 21 and 22 and Example 20 is that the material of the negative electrode protective layer is replaced with metal In and organic PEO, respectively.
  • Embodiment 23 is an improvement of Embodiment 9 on the basis of Embodiment 9.
  • the specific improvement items are: after pre-replenishing lithium, a layer of LiF negative electrode protective layer with a thickness of 1 ⁇ m is deposited on the surface of the second negative electrode framework layer by means of magnetron sputtering.
  • Embodiment 24 is an improvement of Embodiment 23 on the basis of Embodiment 23.
  • the specific improvement items are: using atomic layer deposition technology to cover a layer of ZnO coating with a thickness of 20nm on the inner and outer surfaces of the pore structure of the negative electrode framework.
  • Example 25 The difference between Examples 25 and 26 and Example 24 is that the material of the negative electrode protective layer is replaced with metal In and organic PEO, respectively.
  • Embodiment 27 is an improvement of Embodiment 11 on the basis of Embodiment 11.
  • the specific improvement items are: after pre-replenishing lithium, a LiF negative electrode protective layer with a thickness of 1 ⁇ m is deposited on the surface of the second negative electrode framework layer by means of magnetron sputtering.
  • Embodiment 28 is an improvement of Embodiment 27 on the basis of Embodiment 27.
  • the specific improvement items are: using atomic layer deposition technology to cover a layer of ZnO coating with a thickness of 20nm on the inner and outer surfaces of the pore structure of the negative electrode framework.
  • Example 29 The difference between Examples 29 and 30 and Example 28 is that the material of the negative electrode protective layer is replaced with metal In and organic PEO, respectively.
  • Embodiment 31 is an improvement of Embodiment 13 on the basis of Embodiment 13.
  • the specific improvement items are: after pre-replenishing lithium, a layer of LiF negative electrode protective layer with a thickness of 1 ⁇ m is deposited on the surface of the second negative electrode framework layer by means of magnetron sputtering.
  • Embodiment 32 is an improvement of embodiment 31 on the basis of embodiment 31.
  • the specific improvement items are: using atomic layer deposition technology to cover a layer of ZnO coating with a thickness of 20nm on the inner and outer surfaces of the pore structure of the negative electrode framework.
  • Example 33 The difference between Examples 33 and 34 and Example 33 is that the material of the negative electrode protective layer is replaced with metal In and organic PEO, respectively.
  • Examples 19, 23, 27, and 31 a negative electrode protective layer was deposited on the surface of the negative electrode framework of Examples 1, 9, 11, and 13, respectively. Compared with Examples 1, 9, 11, and 13, the cycle stability of Examples 19, 23, 27, and 31 has been further improved. This is because the negative electrode protective layer has a good effect on the negative electrode framework and the negative electrode active material.
  • the protective effect of the lithium metal can reduce or even isolate the contact between the lithium metal and the electrolyte, greatly reduce the side reactions between the lithium metal and the electrolyte, and improve the cycle stability of the electrode and the electrochemical device.
  • the present application provides a novel negative electrode piece and an electrochemical device and an electronic device containing the same.
  • the present application provides a lithium metal negative electrode with a negative framework layer having two or more layers, wherein the negative framework layer close to the current collector has a higher porosity and the negative framework layer far away from the current collector has a lower porosity Rate.
  • references in the specification of this application to “embodiments”, “partial examples”, “one embodiment”, “another example”, “examples”, “specific examples” or “partial examples” mean what they represent It is at least one embodiment or example in the embodiments of the present application that includes the specific feature, structure, material, or characteristic described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: “in some embodiments”, “in embodiments”, “in one embodiment”, “in another example”, “in an example “In”, “in a specific example” or “exemplary”, which are not necessarily quoting the same embodiment or example in the embodiments of the present application.
  • the specific features, structures, materials or characteristics herein can be combined in one or more embodiments or examples in any suitable manner.

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Abstract

涉及负极极片与包含其的电化学装置。具体地，所述负极极片包括：集流体（101）；位于所述集流体（101）上的负极骨架；其中所述负极骨架至少包括第一负极骨架层（102）和第二负极骨架层（103），所述第一负极骨架层（102）位于所述集流体（101）与所述第二负极骨架层（103）之间，且其中所述第一负极骨架层（102）的孔隙率大于所述第二负极骨架层（103）的孔隙率。通过采用这种设计，能够减少锂金属与电解液之间的副反应、抑制锂枝晶的形成以及大幅度地缓解甚至消除由锂离子的嵌入和脱出带来的负极极片体积的剧烈膨胀和收缩，从而能够增强电化学装置的安全性和稳定性。

Description

负极极片与包含其的电化学装置 技术领域
本申请涉及储能技术领域，更具体地，涉及负极极片与包含其的电化学装置。
背景技术
伴随着科技的不断进步和对环保要求的不断提高，电化学装置在我们日常生活中扮演着越来越重要的角色。其中，锂离子电池凭借其具有比能量大、工作电压高、自放电率低、体积小、重量轻等优势而在消费电子领域中广泛应用。然而，随着电动汽车和可移动电子设备的高速发展，人们对电化学装置的能量密度、安全性、循环性能等方面的要求越来越高。其中，体积能量密度与质量能量密度是衡量电化学装置性能的重要参数。
锂金属是所有金属元素中相对原子质量最小(6.94)、标准电极电位(-3.045V)最低的金属，其理论克容量可达到3860mAh/g。因此，使用锂金属作为电化学装置的负极，配合一些高能量密度的正极材料，可以大大提高电化学装置的能量密度及其工作电压。然而，在真正的商业化应用中，锂金属作为电化学装置的负极极片在充放电循环过程中可能会存在各种问题，从而阻止锂金属作为负极活性材料的商业化。
发明内容
本申请发现在锂金属作为电化学装置的负极活性材料时，在电化学装置的充放电过程中可能会遇到如下问题：
(1)锂金属很活泼，非常容易与电化学装置中的电解液发生副反应，导致锂金属和电解液的同时消耗，使得循环库伦效率大大低于一般以石墨为负极活性材料的电化学装置；
(2)在电化学装置充放电的过程中，锂金属会在负极极片表面沉积。由于电流密度和电解液中锂离子浓度的不均匀性，会出现在某些点位沉积速度过快的现象，形成尖锐的锂枝晶结构；锂枝晶的形成会导致电化学装置的能量密度降低，甚至可能会刺穿电化学装置中的隔膜而导致短路，引发安全问题；
(3)在电化学装置充放电的过程中，负极极片会发生剧烈的膨胀和收缩；按照目前商 用锂离子电池的一般设计，在电化学装置自满充状态至满放状态的过程中，单面涂敷有锂金属的负极的厚度变化范围为8μm至100μm；这会导致锂金属负极活性层与其相邻结构(例如，集流体)之间的界面发生剥离，大大增加电化学装置的阻抗，降低电化学装置的稳定性。
鉴于上述问题，本申请提供一种负极极片与包含其的电化学装置以试图在至少某种程度上解决上述至少一个问题。
在一些实施例中，本申请提供了一种负极极片，其包括：集流体；位于所述集流体上的负极骨架；其中所述负极骨架至少包括第一负极骨架层和第二负极骨架层，所述第一负极骨架层位于所述集流体与所述第二负极骨架层之间，且其中所述第一负极骨架层的孔隙率大于所述第二负极骨架层的孔隙率。
在一些实施例中，本申请提供了一种电化学装置，其包括上述实施例中的负极极片。
在一些实施例中，本申请提供了一种电子装置，其包含上述实施例中的电化学装置。
本申请构建了一种特殊的负极骨架以用于锂金属负极，其中所述负极骨架位于集流体上且包括具有不同孔隙率的至少两层，即第一负极骨架层(例如，其靠近所述集流体，也可称之为“内层”)和第二负极骨架层(例如，其相较于第一负极骨架层而远离所述集流体，也可称之为“外层”)。其中，本申请所述的第一负极骨架层具有较大的孔隙率，能够实现以下作用：
(1)第一负极骨架层具有较大的孔隙率，能够在充电时为锂金属的沉积提供充足的空间；而在放电时，在负极金属锂不断减少的过程中，形成稳定的结构支撑，使得在电化学装置充放电的过程中负极极片不会发生剧烈的体积变化，甚至不发生体积变化。因此，这就缓解甚至消除了在电化学装置的充放电过程中锂金属负极发生的剧烈的体积变化。
(2)第一负极骨架层具有较大的孔隙率，能够为离子和电子提供良好的传输通道；此外，第一负极骨架层具有较高的比表面积，这可以有效地分散充放电过程中的电流，减小电流密度，形成更均匀的电场，从而改善锂沉积的均匀性，抑制锂枝晶的生长。
(3)第一负极骨架层具有较大的孔隙率，这可以提供大量形核位点，降低电流密度，从而有效改善沉积锂的致密度。
其中，本申请所述的第二负极骨架层具有较小的孔隙率，能够实现以下作用：
(1)与第一负极骨架层类似，可以在充放电过程中为锂金属提供沉积空间，并大幅度地降低或消除体积的剧烈变化；同时可以减小电流密度，抑制锂枝晶生长，提高锂的沉积密度。
(2)相较于第一负极骨架层具有更致密的骨架结构，有助于形成致密的电极表面，减少锂金属和电解液之间的副反应，提高电极的循环稳定性；此外，可于第二负极骨架层的致密的电极表面上进一步形成负极保护层，进一步减少锂金属和电解液之间的副反应，提高电极的循环稳定性。
附图说明
在下文中将简要地说明为了描述本申请实施例或现有技术所必要的附图以便于描述本申请的实施例。下文描述中的附图仅只是本申请中的部分实施例。
图1是根据本申请一些实施例的冲切好的负极集流体的俯视示意图；
图2是根据本申请一些实施例的在图1所示的负极集流体上构建的第一负极骨架层的俯视示意图；
图3是根据本申请一些实施例的在图2所示的第一负极骨架层上构建的第二负极骨架层的俯视示意图；
图4是根据本申请一些实施例的沿着图3所示的A-A'线切割的负极极片的剖视示意图；
图5是根据本申请一些实施例的在集流体的两侧设置负极骨架的负极极片的剖视示意图；
图6是根据本申请一些实施例的包含有更多层的负极骨架的负极极片的剖视示意图；
图7是根据本申请一些实施例的在负极骨架的表面上设置负极保护层的负极极片的剖视示意图。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合本申请实施例，对本申请的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施 例，而不是全部的实施例。基于本申请提供的技术方案及所给出的实施例，本领域技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
在本说明书中，除非经特别指定或限定之外，相对性的用词例如：“中央的”、“纵向的”、“侧向的”、“前方的”、“后方的”、“右方的”、“左方的”、“内部的”、“外部的”、“较低的”、“较高的”、“水平的”、“垂直的”、“高于”、“低于”、“上方的”、“下方的”、“顶部的”、“底部的”以及其衍生性的用词(例如“水平地”、“向下地”、“向上地”等等)应该解释成引用在讨论中所描述或在附图中所描示的方向。这些相对性的用词仅用于描述上的方便，且并不要求将本申请以特定的方向建构或操作。
再者，为便于描述，“第一”、“第二”、“第三”等等可在本文中用于区分一个图或一系列图的不同组件。“第一”、“第二”、“第三”等等不意欲描述对应组件。
在本申请具体实施方式及权利要求书中，术语“大致”、“大体上”、“实质”及“约”用以描述及说明小的变化。当与事件或情形结合使用时，所述术语可指代其中事件或情形精确发生的例子以及其中事件或情形极近似地发生的例子。举例来说，当结合数值使用时，术语可指代小于或等于所述数值的±10％的变化范围，例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％。
另外，有时在本文中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
在具体实施方式及权利要求书中，由术语“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一种”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一种”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个组分或多个组分。项目B可包含单个组分或多个组分。项目C可包含单个组分或多个组分。
在电化学装置(例如，锂离子电池)中，使用锂金属作为电化学装置的负极极片，可以提高电池的能量密度以及电池的工作电压。然而，在电化学装置的充放电循环的过程中，使用锂金属作为负极极片可能会导致各种问题，例如，锂金属与电解液之间的副反应、锂枝晶的形成以及负极极片的体积的剧烈膨胀和收缩。其中，负极极片的体积的剧烈膨胀和收缩会容易导致负极极片与其他相邻结构之间的界面发生剥离，使得阻抗的剧烈升高，严重降低电化学装置的安全性和稳定性。
本申请提供了一种具有多层结构的负极骨架。该负极骨架具有两层或更多层，其中通过对每一层采用不同的孔隙率设计，使得靠近集流体的负极骨架层具有较高的孔隙率而远离集流体的负极骨架层具有较低的孔隙率。
以下将结合图1-4来说明本申请实施例负极极片的结构以及其有益效果。
本申请负极极片可以是单面结构，也可以是双面结构，其中单面结构是指仅在集流体的一侧设置本申请所述的负极骨架，双面结构是指在集流体的两侧均设置本申请所述的负极骨架。图1-4是根据本申请一些实施例的单面结构的负极极片的俯视图和剖视图。
图1-3示出了本申请的负极极片的其中一种制备过程的示意图。首先，图1示出了冲切好的负极集流体101的俯视图。根据本申请的实施例，所述集流体101可以是本领域常用的负极集流体，其包括，但不限于，镍箔、锡箔、铜箔、锂箔、覆锂铜箔。
如图2所示，将孔隙率较大的第一负极骨架层102设置在集流体101的表面上。
如图3所示，将孔隙率较小的第二负极骨架层103设置在第一负极骨架层102的表面上。其中为了清楚地显示负极骨架的层状结构(即，为了清楚地显示被第二负极骨架层103覆盖的第一负极骨架层102)，图3仅示意性地示出了一部分的第二负极骨架层103。而在本申请的一个或多个实施例中，第二负极骨架层103应完全覆盖在第一负极骨架层102的表面上。
图4示出了沿着图3中的A-A'线切割的负极极片的剖视图。如图4所示，本申请的负极极片包括：集流体101和位于集流体101上的负极骨架，其中负极骨架至少包括第一负极骨架层102以及第二负极骨架层103，其中所述第一负极骨架层102位于所述集流体101与所述第二负极骨架层103之间，且其中所述第一负极骨架层102的孔隙率大于所述第二负极骨架层103的孔隙率。按照图4中的由内到外的箭头指示的方向，也可将第一负极骨架层102称作内层并将第二负极骨架层103称作外层。
所述第一负极骨架层102和所述第二负极骨架层103内部所存在的孔隙为锂金属的沉积预留了空间。在电化学装置充放电的过程中，通过使负极活性材料锂金属在本申请构建的负极骨架内嵌入或脱出，可以缓解甚至消除锂离子的嵌入和脱出所带来的剧烈的体积变化，从而有效地避免界面剥离并提高电化学装置的安全性和稳定性。
另外，第一负极骨架层102具有较大的孔隙率，能够为离子和电子的传输提供良好的导通通道，改善电化学装置的倍率性能。此外，第一负极骨架层102具有较高的比表面积，有效地分散充放电过程中的电流，减小电流密度，改善锂沉积的均匀性，抑制锂枝晶的形成。
第二负极骨架层103相较于第一负极骨架层102具有更致密的骨架结构。第二负极骨架层103的致密结构至少能够带来以下优势：(1)同样可在充放电过程中为锂金属提供沉积空间，大幅降低或消除体积的剧烈变化；同时可以减小电流密度，抑制锂枝晶生长，提高锂的沉积密度；(2)有助于在其表面上进一步形成致密的负极保护层，降低负极保护层的形成难度，减少锂金属和电解液之间的副反应，进一步提高锂金属负极的强度和稳定性，改善电化学装置的库伦效率和循环寿命。
在一些实施例中，所述第一负极骨架层的孔隙率的范围为约55％至约90％。
在一些实施例中，所述第二负极骨架层的孔隙率的范围为约10％至约50％。在一些实施例中，所述第二负极骨架层的孔隙率的范围为约20％至约50％。在另一些实施例中，所述第二负极骨架层的孔隙率的范围为约20％至约40％。
所述第一负极骨架层的孔隙率可为大体上固定的百分比或是在上述范围中变化的百分比。在一些实施例中，当所述第一负极骨架层的孔隙率有变化时，所述孔隙率优选地为随着与集流体的相对距离增加而减少。所述第二负极骨架层的孔隙率可为大体上固定的百分比或是在上述范围中变化的百分比。在一些实施例中，当所述第二负极骨架层的孔隙率有变化时，所述孔隙率优选地为随着与集流体的相对距离增加而减少。
在一些实施例中，所述负极骨架的总厚度的范围为约5μm至约100μm。在一些实施例中，所述第一负极骨架层的厚度的范围为约1μm至约95μm。在一些实施例中，所述第二负极骨架层的厚度的范围为约0.1μm至约50μm。
在一些实施例中，所述负极骨架的厚度与所述负极骨架的孔隙率满足以下关系：
Figure PCTCN2020082187-appb-000001
Figure PCTCN2020082187-appb-000002
20％≤p≤90％  (式3)
5≤t≤100  (式4)
其中t为所述负极骨架的总厚度/μm，x为所述负极骨架中任一与集流体表面平行的平面至集流体表面的距离(积分元)/μm，p为所述负极骨架的孔隙率。
其中，上述式1表示所述负极骨架提供的孔隙的累计厚度的范围为5μm至50μm。这也可理解为，在所述负极骨架上可沉积锂金属的累计厚度的范围为5μm至50μm。参照图4示出的由内到外的方向箭头，上述式2表示负极骨架的孔隙率由内而外变小。上述式3表示负极骨架的孔隙率的范围为20％至90％。上述式4表示负极骨架的厚度的范围为5μm至100μm。应注意，本申请所述孔隙率在计算时仅以负极骨架的材料本身计算，并不包含在首次充放电之前预先在负极骨架内补充的锂金属。
在一些实施例中，本申请提供了一种孔隙率由内向外逐渐减小的负极骨架。亦即，负极骨架的厚度和孔隙率满足上述式(2)所述的关系。在本申请的一些实施例中，本申请所述的负极骨架还满足上述式(1)、(3)和(4)中的至少一者。
在一些实施例中，所述负极极片进一步包括预嵌入(即，预先补充)至所述负极骨架内的锂金属以作为电化学装置的负极活性物质，其中所述预嵌入的锂金属的量的范围为约0.001mg/cm 2至约6mg/cm 2。“预嵌入”是指在负极极片首次充放电之前，预先嵌入至负极骨架内的锂金属。在一些实施例中，所述预嵌入的锂金属的量的范围为约0.005mg/cm 2至约3mg/cm 2。例如，所述预嵌入的锂金属的量可以为约0.005mg/cm 2、约0.01mg/cm 2、约0.1mg/cm 2、约0.5mg/cm 2、约1mg/cm 2、约1.5mg/cm 2、约2mg/cm 2、约2.5mg/cm 2和约3mg/cm 2。
图5是根据本申请一些实施例的在集流体的两侧上分别设置本申请所述的负极骨架的负极极片的剖视图。
如图5所示，所述集流体101的两侧的表面上均设置了第一负极骨架层102以及第二负极骨架层103，其中所述第一负极骨架层102位在所述集流体101与所述第二负极骨架层103之间。在一些实施例中，所述集流体101两侧所设置的负极骨架可为两种不同的负极骨架。
图6是根据本申请一些实施例的包含有更多层的负极骨架的负极极片的剖视图。
在一些实施例中，本申请负极极片进一步包含至少一个第三负极骨架层104。如图6所示，所述第三负极骨架层104位于所述第二负极骨架层103的表面上。
应理解，图6为本申请负极骨架具有多于两层结构的示范性实施例。尽管图6只是演示了具有三层结构的负极骨架，但是本领域技术人员通过本申请的教导，可以根据具体需求调整负极极片中的负极骨架层的层数，而显然不受本申请附图所示的负极骨架层数的限制。
根据本申请的实施例，所述第一负极骨架层、所述第二负极骨架层和所述第三负极骨架层各自独立地包括以下材料中的至少一种：高分子材料、碳材料、金属材料、或无机材料。
在一些实施例中，所述高分子材料包括以下各者中的至少一种：聚环氧乙烷、聚酰亚胺、聚丙烯酸、聚乙烯、聚丙烯、聚丙烯腈、聚苯乙烯、聚氟乙烯、聚醚醚酮、聚酯、聚偏二氯乙烯、聚四氟乙烯、聚对苯二甲酸乙二醇酯、或上述高分子材料中的一者或多者的衍生物。
在一些实施例中，所述碳材料包括以下各者中的至少一种：多孔碳、碳纳米管、碳纤维、石墨烯及其衍生物、或中空碳球。
在一些实施例中，所述金属材料包括以下各者中的至少一种：铜、镍、铬、钛、钨、锆、或上述材料中的两者或更多者组成的合金。
在一些实施例中，所述无机材料包括以下各者中的至少一种：磷酸锂(Li 3PO 4)；LiPON；Li 2O；LiF；LiOH；Li 2CO 3；LiAlO 2；Li 4SiO 4；Li 2O-Al 2O 3-SiO 2-P 2O 5-TiO 2-GeO 2陶瓷；锂钛磷酸盐(Li xTi y(PO 4) 3，其中0<x<2且0<y<3)；锂铝钛磷酸盐(Li xAl yTi z(PO 4) 3，其中0<x<2，0<y<1，且0<z<3)；Li 1+x+y(Al,Ga) x(Ti,Ge) 2-xSi yP 3-yO 12，其中0≤x≤1且0≤y≤1；锂镧钛酸盐(Li xLa yTiO 3，其中0<x<2且0<y<3)；锂锗硫代磷酸盐(Li xGe yP zS w，其中0<x<4，0<y<1，0<z<1，且0<w<5)；锂氮化物(Li xN y，其中0<x<4，0<y<2)；SiS 2玻璃(Li xSi yS z，其中0≤x<3，0<y<2，且0<z<4)；P 2S 5玻璃(Li xP yS z，其中0≤x<3，0<y<3，且0<z<7)；或石榴石陶瓷(Li 3+xLa 3M 2O 12，其中0≤x≤5，且M为Te、Nb、或Zr中的至少一种)。
在一些实施例中，所述第一负极骨架层、所述第二负极骨架层和所述第三负极骨架层各自独立地由复合材料构成，其中复合材料为以下材料中的两者或者更多者的任意组合：高分子材料、碳材料、金属材料、及无机材料。例如，负极骨架可以包括：由高分子材料或者碳材料制备的基本骨架和在所述基本骨架上进一步沉积的无机材料。在一些实施例中，所述无机材料以颗粒或者涂层的形式覆盖在所述材料的多孔结构的内外表面上。在一些实施例中，所述无机材料包括以下各者中的至少一种：HfO 2、SrTiO 3、SnO 2、 CeO 2、MgO、NiO、CaO、BaO、ZnO、ZrO 2、Y 2O 3、Al 2O 3、TiO 2、SiO 2、CuO、或AgO。在至少一个方面，所述无机材料可以作为沉积位点，引导锂沉积在多孔结构的内部。
在一些实施例中，所述复合材料的制备方法可以是本领域常见的制备方法，其包含，但不限于，原子层沉积技术(Atomic layer deposition，ALD)及电化学沉积法等。
在一些实施例中，所述负极极片进一步包括位于所述负极骨架表面上的一层或多层负极保护层。如图7所示，可以在所述第二负极骨架层103的表面上进一步形成一层或多层负极保护层105。顾名思义，负极保护层的作用在于对负极实施保护。例如，负极保护层105可以隔绝电解液与负极活性物质锂金属的接触，大大降低电解液与锂金属的副反应，提高电化学装置的循环稳定性。此外，值得注意的是，相较于第一负极骨架层的多孔结构，第二负极骨架层的骨架更为致密，这就降低了负极保护层的形成难度，有利于在负极骨架的表面上进一步形成致密的负极保护层。
在一些实施例中，所述负极保护层的孔隙率的范围为约0％至约10％。
在一些实施例中，所述负极保护层所采用的材料包括以下各者中的至少一种：无机物、硅、金属、或有机物。
在一些实施例中，所述无机物包括以下各者中的至少一种：磷酸锂(Li 3PO 4)；LiPON；Li 2O；LiF；LiOH；Li 2CO 3；LiAlO 2；Li 4SiO 4；Li 2O-Al 2O 3-SiO 2-P 2O 5-TiO 2-GeO 2陶瓷；锂钛磷酸盐(Li xTi y(PO 4) 3，其中0<x<2且0<y<3)；锂铝钛磷酸盐(Li xAl yTi z(PO 4) 3，其中0<x<2，0<y<1，且0<z<3)；Li 1+x+y(Al,Ga) x(Ti,Ge) 2-xSi yP 3-yO 12，其中0≤x≤1且0≤y≤1；锂镧钛酸盐(Li xLa yTiO 3，其中0<x<2且0<y<3)；锂锗硫代磷酸盐(Li xGe yP zS w，其中0<x<4，0<y<1，0<z<1，且0<w<5)；锂氮化物(Li xN y，其中0<x<4，0<y<2)；SiS 2玻璃(Li xSi yS z，其中0≤x<3，0<y<2，且0<z<4)；P 2S 5玻璃(Li xP yS z，其中0≤x<3，0<y<3，且0<z<7)；或石榴石陶瓷(Li 3+xLa 3M 2O 12，其中0≤x≤5，且M为Te、Nb、或Zr中的至少一种)。
在一些实施例中，所述金属包括以下各者中的至少一种：Au、Pt、Ag、Al、In、Sn、或上述材料中的两者或更多者组成的合金。
在一些实施例中，所述有机物包括以下各者中的至少一种：聚氧化乙烯(PEO)、聚偏氟乙烯(PVDF)、聚甲基丙烯酸甲酯(PMMA)、聚碳酸丙烯酯(PPC)、聚碳酸乙烯酯(PEC)、聚己内酯(PCL)、四乙二醇二丙烯酸酯(tetraethylene glycol diacrylate；TEGDA)、全氟磺酸树脂(Nafion)、聚丙烯腈(PAN)、聚二甲基硅氧烷(PDMS)或上述有机物的 衍生物。
本申请的一些实施例提供一种电化学装置，所述电化学装置包含上述实施例的负极极片。此外，所述电化学装置还包括正极极片和位于正极极片和负极极片之间的隔离膜，所述正极极片或隔离膜并没有特别限制，可以是本领域常用的正极极片及隔离膜。在一些实施例中，所述电化学装置为锂离子电池。
根据本申请一些实施例，所述正极极片包含正极集流体以及在其表面上的正极活性物质层，其中正极活性物质层包含了正极活性材料、导电剂及粘结剂。在一些实施例中，所述正极集流体包括，但不限于，铝箔或镍箔。
在一些实施例中，所述正极活性材料的实例可以包括，但不限于，钴酸锂、磷酸铁锂、磷酸锰铁锂、磷酸铁钠、磷酸钒锂、磷酸钒钠、磷酸钒氧锂、磷酸钒氧钠、钒酸锂、锰酸锂、镍酸锂、镍钴锰酸锂、富锂锰基材料、镍钴铝酸锂及钛酸锂中的至少一种。
在上述正极活性材料中，钴酸锂的化学式可以为Li aCo bM 1cO 2-d，其中，M 1包括镍(Ni)、锰(Mn)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)、钨(W)、钇(Y)、镧(La)、锆(Zr)或硅(Si)中的至少一种，a、b、c和d值分别在以下范围内：0.8≤a≤1.2、0.8≤b≤1、0≤c≤0.2、-0.1≤d≤0.2；
在上述正极活性材料中，镍酸锂的化学式可以为Li eNi fM 2gO 2-h，其中，M 2包括钴(Co)、锰(Mn)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)、钨(W)、锆(Zr)或硅(Si)中的至少一种，e、f、g和h值分别在以下范围内：0.8≤e≤1.2、0.3≤f≤0.98、0.02≤g≤0.7、-0.1≤h≤0.2；
在上述正极活性材料中，锰酸锂的化学式为Li iMn 2-jM 3jO 4-k，其中M 3包括钴(Co)、镍(Ni)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)或钨(W)中的至少一种，i、j和k值分别在以下范围内：0.8≤i≤1.2、0≤j<1.0和-0.2≤k≤0.2。
在上述正极活性材料中，镍钴锰酸锂的化学式为LiNi lCo mMn nO 2，其中l、m和n值分别在以下范围内：0<l<1.0、0<m<1.0和0<n<1.0，且l+m+n＝1。
在一些实施例中，所述导电剂包括导电碳黑、碳纤维、乙炔黑、科琴黑、石墨烯、 碳纳米管中的至少一种。本领域技术人员应当理解，广泛使用于锂离子电池的各种正极极片都适用于本申请，而不受其限制。
根据本申请一些实施例，所述隔离膜包括，但不限于，聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。举例来说，聚乙烯包括高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种组分。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。本领域技术人员当能理解，广泛使用于锂离子电池的各种隔离膜都适用于本申请。
根据本申请的一些实施例，上述锂离子电池还包括电解液，电解液可以呈现凝胶态或者液态，所述电解液包括锂盐和非水溶剂。
在一些实施例中，锂盐包括LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB或二氟硼酸锂中的至少一种。例如，锂盐选用LiPF 6，因为它可以给出高的离子电导率并改善循环特性。
在一些实施例中，非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。
在一些实施例中，碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。
在一些实施例中，链状碳酸酯化合物的实例为碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸甲乙酯或其组合。所述环状碳酸酯化合物的实例为碳酸亚乙酯、碳酸亚丙酯、碳酸亚丁酯、碳酸乙烯基亚乙酯、丙酸丙酯或其组合。所述氟代碳酸酯化合物的实例为碳酸氟代亚乙酯、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯或其组合。
在一些实施例中，羧酸酯化合物的实例为乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯、甲酸甲酯或其组合。
在一些实施例中，醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃或其组合。
在一些实施例中，其它有机溶剂的实例为二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯、和磷酸酯或其组合。
本申请的一些实施例提供了一种锂离子电池的制备方法，其包括：将上述正极极片、隔离膜以及本申请负极极片按顺序卷绕或堆叠成电芯，之后装入例如铝塑膜中，注入电解液，化成、封装，即制成锂离子电池。
本领域的技术人员将理解，以上描述的电芯的结构以及锂离子电池的制备方法仅是示范性实施例。在不背离本申请公开的内容的基础上，可以采用本领域常用的其他方法作为锂离子电池或者其它电化学装置的制备方法。
本领域的技术人员将理解，虽然上面以锂离子电池进行了举例说明，本申请的电化学装置进一步包含其他任何合适的电化学装置。在不背离本申请公开的内容的基础上，本申请实施例中的电化学装置包括发生电化学反应的任何装置，它的具体实例包括所有种类的一次电池、二次电池、太阳能电池或电容。特别地，所述电化学装置是锂二次电池，包括锂金属二次电池、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。
本申请电化学装置的用途没有特别限定，其可用于现有技术中已知的任何用途。根据本申请的一些实施例，包含本申请的电化学装置的电子装置包括，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。
下面结合对比例及具体实施例对本发明的技术方案作进一步的说明，但并不局限于此。本领域的技术人员将理解，本申请中描述的制备方法仅是示范实施例，凡是对本发明技术方案进行修改或者同替换，而不脱离本发明技术方案的范围，均应涵盖在本发明的保护范围中。
具体实施例
正极极片的制备
将正极活性材料磷酸铁锂(LiFePO 4)、导电炭黑(Super P)、聚偏二氟乙烯(PVDF) 按照重量比97.5:1.0:1.5进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成为固含量为55％的浆料，并搅拌均匀。将浆料均匀涂覆在正极集流体铝箔上，90℃条件下烘干，得到正极极片。正极的负载量为1mAh/cm 2。涂布完成后，将极片裁切成(38mm×58mm)的规格待用。
电解液的制备
在干燥氩气气氛中，首先将二氧环戊烷(DOL)和二甲醚(DME)以1:1的体积比混合，然后在有机溶剂中加入双三氟甲烷磺酰亚胺锂(LiTFSI)作为锂盐进行溶解并混合均匀，得到锂盐的浓度为1M的电解液。
锂离子电池的制备
采用厚度为15μm的聚乙烯作为隔离膜，并将实施例与对比例中的双层涂布的负极极片、隔离膜以及单层涂布的正极极片依序堆叠。堆叠好后，用胶带将整个叠片结构的四个角固定好后，置入铝塑膜中，经顶侧封、注液、封装后，最终得到以下各实施例和对比例的锂金属叠片电池。
材料和锂离子电池的测试方法
(一)孔隙率测试
将待测的骨架放置到全自动压汞仪(型号为AutoPore V9610)中进行测试，得到该样品的孔隙率。其中，压力范围为0.5–30,000psia。
(二)负极骨架层的厚度测试
将待测的极片裁切成约10mm×5mm的大小，放入离子研磨抛光机中对该极片的横截面进行抛光，然后将所得极片转移到扫描电子显微镜(SEM)中，在合适的放大倍率下观测抛光后的横截面，并测量负极骨架层的厚度。
(三)锂金属预沉积量测试
将待测的极片冲切成直径为14mm的小圆片，作为正极。将铜箔冲切成直径为18mm的小圆片作为负极。采用厚度为15μm、直径为20mm的聚乙烯作为隔离膜，并加入60μL的上述电解液，组装成扣式电池。以0.1mA/cm 2的电流密度对扣式电池进行充电，充电电压的范围为0-1V。通过测得的充电容量，结合锂的克容量3860mAh/g，即可计算得到单位面积上锂金属的预沉积量。
(四)锂离子电池的循环性能测试
将叠片电池在60℃下以0.1C的倍率充放电一圈以对叠片电池进行化成，然后在 常温下对电池进行充放电循环。其中，首先对电池进行恒流充电，充电电流为1C，截止电压为3.8V；其次对电池进行恒压充电至截止电流为0.05C；接着对电池进行恒流放电，放电电流为1C，截止电压为2.7V。以这种方式，测试当放电容量为首次放电容量80％时，对比例和实施例中的锂离子电池的循环圈数。
负极极片的制备
实施例1
使用静电纺丝技术，以聚丙烯腈为前驱体分别制备两层聚丙烯腈纤维层：第一负极骨架层(即，内层)的孔隙率为70％，厚度为45μm；第二负极骨架层(即，外层)的孔隙率为30％，厚度为5μm。将上述两层聚丙烯腈纤维层在大气环境中以210℃的温度加热1小时，然后在氩气环境中以900℃的温度加热3小时，得到碳膜。按照本申请图5所述的方式对镍箔集流体、第一负极骨架层和第二负极骨架层进行排序，并将锂箔放置于负极骨架的两个外表面上，加热到300度，使锂融化进入到骨架内部，进行预补锂。最后将极片裁切成(40mm×60mm)的规格待用。
实施例2
与实施例1的制备方法和原料相同，不同之处在于：实施例2中的第一负极骨架层(即，内层)的孔隙率为55％。
实施例3
与实施例1的制备方法和原料相同，不同之处在于：实施例3中的第一负极骨架层(即，内层)的孔隙率为80％。
实施例4
与实施例1的制备方法和原料相同，不同之处在于：实施例4中的第一负极骨架层(即，内层)的孔隙率为90％。
实施例5
与实施例1的制备方法和原料相同，不同之处在于：实施例5中的第一负极骨架层(即，内层)的孔隙率为95％。
实施例6
与实施例1的制备方法和原料相同，不同之处在于：实施例6中的第二负极骨架层(即，外层)的孔隙率为20％。
实施例7
与实施例1的制备方法和原料相同，不同之处在于：实施例7中的第二负极骨架层(即，外层)的孔隙率为40％。
实施例8
与实施例1的制备方法和原料相同，不同之处在于：实施例8中的第二负极骨架层(即，外层)的孔隙率为10％。
对比例1
对比例1和实施例1-8的区别在于：不设置任何负极骨架，仅仅将锂金属放置于集流体上，并通过辊压的方式使两者紧密结合在一起。预补锂金属的厚度为10μm。
对比例2
与实施例1的制备方法和原料相同，不同之处在于：对比例2仅在集流体的两个表面上设置孔隙率为30％，厚度为50μm的负极骨架层。
对比例3
与实施例1的制备方法和原料相同，不同之处在于：对比例3仅在集流体的两个表面上设置孔隙率为70％，厚度为50μm的负极骨架层。
上述实施例1-8以及对比例1-3的实验参数和测量结果如下表1所示。
表1
Figure PCTCN2020082187-appb-000003
在对负极骨架进行预补锂时，预补锂的量与负极骨架的孔隙率有关。一般而言，当负极骨架提供的孔隙率较低时，可供沉积锂的空间较小，因此预补锂量也会相应减 少。如表1所示，采用本申请实施例1-8的负极极片制备的电化学装置相较于采用对比例1-3的负极极片制备的电化学装置具有更好的循环稳定性。在对比例1中，由于没有为金属锂构建任何骨架，其电化学装置的循环稳定性最差。对比例2和3搭建了一层骨架(也可理解为，搭建了两层孔隙率相同的骨架)，相较于对比例1，其电化学装置的循环稳定性有所改善。然而，本申请的实施例1-8通过搭建两层孔隙率不同的骨架，其中内层孔隙率大于外层孔隙率，能够相较于对比例2和3，进一步改善电化学装置的循环稳定性。
此外，对比实施例5和其它实施例可以看出，实施例5的电化学装置的循环稳定性相对较差，这主要是由于实施例5的内层孔隙率过大，不能够为金属锂的沉积提供有力的支撑。然而，即便如此，实施例5的电化学装置的循环稳定性仍然优于对比例1-3。
实施例9
将孔隙率为70％的泡沫铜作为第一负极骨架层(即，内层)，厚度为45μm；将孔隙率为30％的泡沫铜作为第二负极骨架层(即，外层)，厚度为5μm。按照本申请图5所述的方式对镍箔集流体、第一负极骨架层和第二负极骨架层进行排序，并将锂箔放置于负极骨架的两个外表面上，加热到300度，使锂融化进入到骨架内部，进行预补锂。最后将极片裁切成(40mm×60mm)的规格待用。
实施例10
与实施例9的制备方法和原料相同，不同之处在于：实施例10中的第一负极骨架层(即，内层)的孔隙率为80％。
实施例11
使用静电纺丝技术，以聚酰亚胺为前驱体分别制备两层聚酰亚胺纤维层：第一负极骨架层(即，内层)的孔隙率为70％，厚度为45μm；第二负极骨架层(即，外层)的孔隙率为30％，厚度为5μm。按照本申请图5所述的方式对镍箔集流体、第一负极骨架层和第二负极骨架层进行排序，并将锂箔放置于负极骨架的两个外表面上，加热到300度，使锂融化进入到骨架内部，进行预补锂。最后将极片裁切成(40mm×60mm)的规格待用。
实施例12
与实施例11的制备方法和原料相同，不同之处在于：实施例12中的第一负极骨架层(即，内层)的孔隙率为80％。
实施例13
将孔隙率为70％的泡沫铜作为第一负极骨架层(即，内层)，厚度为45μm。使用静电纺丝技术，以聚丙烯腈为前驱体制备孔隙率为30％的纤维层作为第二负极骨架层(即，外层)，厚度为5μm。将聚丙烯腈纤维层在大气环境中以210℃的温度加热1小时，然后在氩气环境中以900℃的温度加热3小时，得到厚度为5μm碳膜。按照本申请图5所述的方式对镍箔集流体、第一负极骨架层和第二负极骨架层进行排序，并将锂箔放置于负极骨架的两个外表面上，加热到300度，使锂融化进入到骨架内部，进行预补锂。最后将极片裁切成(40mm×60mm)的规格待用。
实施例14
与实施例13的制备方法和原料相同，不同之处在于：实施例14中的第一负极骨架层(即，内层)的孔隙率为80％。
上述实施例9-14的实验参数和测量结果如下表2所示。
表2
Figure PCTCN2020082187-appb-000004
实施例1-8的负极骨架的内外层均采用了碳材料。与之不同，实施例9-14采用了金属材料(例如，Cu)和高分子材料(例如，聚酰亚胺)制备了负极骨架。和对比例1相比，实施例9-14的电化学装置的循环性能均得到了改善，这说明了由金属材料和高分子材料制备的负极骨架能够与碳材料一样为金属锂提供沉积框架和支撑。然而，当采用金属Cu制备负极骨架时，所得到的电化学装置的循环稳定性稍稍差于采用碳材料和/或高分子材料制备的负极骨架层的电化学装置，这主要是由于Cu对锂的润湿性较差，在电化学充放电循环过程中，锂倾向于沉积在极片的表面，导致负极骨架的作用 无法完全发挥。若在Cu的表面增加润湿层/保护层，例如氧化层，则电化学装置的循环稳定性会大幅度的提升(例如，可参见下述实施例16和18中的电化学数据)。
实施例15
实施例15是在实施例1的基础上对实施例1进行的改进。具体改进事项为：在将上述两层聚丙烯腈纤维层加热得到碳膜后，使用原子层沉积技术在碳膜的孔隙结构的内外表面覆盖一层厚度为20nm的氧化锌涂层。
实施例16
实施例16是在实施例9的基础上对实施例9进行的改进。具体改进事项为：使用原子层沉积技术在两种泡沫铜材料的孔隙结构的内外表面覆盖一层厚度为20nm的氧化铝涂层。
实施例17
实施例17是在实施例11的基础上对实施例11进行的改进。具体改进事项为：使用原子层沉积技术在聚酰亚胺纤维层的孔隙结构的内外表面覆盖一层厚度为20nm的氧化铜涂层。
实施例18
实施例18是在实施例13的基础上对实施例13进行的改进。具体改进事项为：使用原子层沉积技术在碳膜和泡沫铜的孔隙结构的内外表面覆盖一层厚度为20nm的二氧化钛涂层。
上述实施例15-18的实验参数和测量结果如下表3所示。
表3
Figure PCTCN2020082187-appb-000005
实施例15-18涉及在实施例1、9、11和13所形成的骨架的孔隙结构的内外表面进一步覆盖一层无机物(例如，ZnO、Al 2O 3、CuO和TiO 2)涂层。也即，实施例15-18的负极骨架的结构可以描述为：首先采用碳材料/金属材料/高分子材料形成基础负极骨 架；再在所形成的基础负极骨架的孔隙结构的内外表面上形成无机物材料。也即，实施例15-18的负极骨架是由复合材料形成的。相应地比较实施例15-18与实施例1、9、11和13的电化学数据，可以看出通过在骨架的孔隙结构的内外表面进一步包裹或者沉积无机物材料，能够进一步改善电化学装置的循环稳定性。
实施例19
实施例19是在实施例1的基础上对实施例1进行的改进。具体改进事项为：在预补锂之后，用磁控溅射的方式，在第二负极骨架层的表面上沉积一层厚度为1μm的LiF负极保护层。具体结构的示意图可参见图7。
实施例20
实施例20是在实施例19的基础上对实施例19进行的改进。具体改进事项为：使用原子层沉积技术在负极骨架的孔隙结构的内外表面覆盖一层厚度为20nm的ZnO涂层。
实施例21和22
实施例21和22与实施例20的不同之处在于：将负极保护层的材料分别替换为金属In和有机物PEO。
实施例23
实施例23是在实施例9的基础上对实施例9进行的改进。具体改进事项为：在预补锂之后，用磁控溅射的方式，在第二负极骨架层的表面上沉积一层厚度为1μm的LiF负极保护层。
实施例24
实施例24是在实施例23的基础上对实施例23进行的改进。具体改进事项为：使用原子层沉积技术在负极骨架的孔隙结构的内外表面覆盖一层厚度为20nm的ZnO涂层。
实施例25和26
实施例25和26与实施例24的不同之处在于：将负极保护层的材料分别替换为金属In和有机物PEO。
实施例27
实施例27是在实施例11的基础上对实施例11进行的改进。具体改进事项为：在预补锂之后，用磁控溅射的方式，在第二负极骨架层的表面上沉积一层厚度为1μm的 LiF负极保护层。
实施例28
实施例28是在实施例27的基础上对实施例27进行的改进。具体改进事项为：使用原子层沉积技术在负极骨架的孔隙结构的内外表面覆盖一层厚度为20nm的ZnO涂层。
实施例29和30
实施例29和30与实施例28的不同之处在于：将负极保护层的材料分别替换为金属In和有机物PEO。
实施例31
实施例31是在实施例13的基础上对实施例13进行的改进。具体改进事项为：在预补锂之后，用磁控溅射的方式，在第二负极骨架层的表面上沉积一层厚度为1μm的LiF负极保护层。
实施例32
实施例32是在实施例31的基础上对实施例31进行的改进。具体改进事项为：使用原子层沉积技术在负极骨架的孔隙结构的内外表面覆盖一层厚度为20nm的ZnO涂层。
负极实施例33和34
实施例33和34与实施例33的不同之处在于：将负极保护层的材料分别替换为金属In和有机物PEO。
上述实施例19-34的实验参数和测量结果如下表4所示。
表4
Figure PCTCN2020082187-appb-000006
Figure PCTCN2020082187-appb-000007
实施例19、23、27和31分别在实施例1、9、11和13的负极骨架的表面上沉积了负极保护层。和实施例1、9、11和13相比，实施例19、23、27和31的循环稳定性得到了进一步的改善，这是由于负极保护层能够对负极骨架和负极活性物质起到很好的保护作用，降低甚至隔绝锂金属和电解液之间的接触，大幅降低锂金属和电解液之间的副反应，提高电极和电化学装置的循环稳定性。
将实施例20、24、28和32分别与实施例19、23、27和31进行比较，实施例20、24、28和32的负极极片的改进之处在于在基础负极骨架上进一步覆盖了ZnO涂层。此外，对比电化学数据可以得出在基础负极骨架上进一步沉积无机物材料有助于进一步改善电化学装置的循环稳定性。实施例21和22、实施例25和26、实施例29和30以及实施例33和34分别选取了金属材料和高分子材料作为负极保护层。参见这些实施例的电化学数据可知，采用金属材料和高分子材料能够和无机物材料一样对负极骨架和负极活性物质形成很好的保护。
通过本申请上述实施例与对比例的说明应可了解，本申请提供了一种新颖的负极极片和包含其的电化学装置及电子装置。具体地，本申请为锂金属负极提供了具有两层或更多层的负极骨架层，其中靠近集流体的负极骨架层具有较高的孔隙率而远离集流体的负极骨架层具有较低的孔隙率。通过采用这种设计，能够减少锂金属与电解液之间的副反应、抑制锂枝晶的形成以及大幅度地缓解甚至消除由锂离子的嵌入和脱出带来的负极极片体积的剧烈膨胀和收缩，从而能够增强电化学装置的安全性和稳定性。
在本申请说明书中对“实施例”、“部分实施例”、“一个实施例”、“另一举例”、“举例”、“具体举例”或“部分举例”的引用，其所代表的意思是在本申请实施例中的至少一个实施例或举例包含了该实施例或举例中所描述的特定特征、结构、材料或特性。因此，在整个说明书中的各处所出现的描述，例如：“在一些实施例中”、“在实施例中”、“在一个实施例中”、“在另一个举例中”，“在一个举例中”、 “在特定举例中”或“举例”，其不必然是引用本申请实施例中的相同的实施例或示例。此外，本文中的特定特征、结构、材料或特性可以以任何合适的方式在一个或多个实施例或举例中结合。
上文说明摘要整理出数个实施例的特征，这使得所属技术领域中具有通常知识者能够更加理解本申请的多种方面。所属技术领域中具有通常知识者可轻易地使用本申请作为基础，设计或修改内容以便实现与此处申请的实施例相同的目的及/或达到相同的优点。
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、原理及范围的情况下对实施例进行改变，替代和修改。

Claims (15)

  1. 一种负极极片，其包括：
    集流体；
    位于所述集流体上的负极骨架；
    其中所述负极骨架至少包括第一负极骨架层和第二负极骨架层，所述第一负极骨架层位于所述集流体与所述第二负极骨架层之间，且
    其中所述第一负极骨架层的孔隙率大于所述第二负极骨架层的孔隙率。
  2. 根据权利要求1所述的负极极片，其中所述第一负极骨架层的孔隙率的范围为55％至90％。
  3. 根据权利要求1所述的负极极片，其中所述第二负极骨架层的孔隙率的范围为10％至50％。
  4. 根据权利要求1所述的负极极片，其中所述负极骨架的厚度与所述孔隙率满足以下关系：
    Figure PCTCN2020082187-appb-100001
    Figure PCTCN2020082187-appb-100002
    20％≤p≤90％
    5≤t≤100
    其中t为所述负极骨架的总厚度/μm，x为所述负极骨架中任一与集流体表面平行的平面至集流体表面的距离(积分元)/μm，p为所述负极骨架的孔隙率。
  5. 根据权利要求1所述的负极极片，其进一步包括嵌入至所述负极骨架内的锂金属，其中所述锂金属的量为0.001至6mg/cm 2。
  6. 根据权利要求1所述的负极极片，其中所述第一负极骨架层和所述第二负极骨架层各自独立地包括以下材料中的至少一种：高分子材料、碳材料、金属材料、或无机材料。
  7. 根据权利要求6所述的负极极片，其中，
    所述高分子材料包括以下各者中的至少一种：聚环氧乙烷、聚酰亚胺、聚丙烯酸、聚乙烯、聚丙烯、聚丙烯腈、聚苯乙烯、聚氟乙烯、聚醚醚酮、聚酯、聚偏二氯乙烯、聚四氟乙烯、聚对苯二甲酸乙二醇酯、或上述材料中的一者或多者的衍生物；
    所述碳材料包括以下各者中的至少一种：多孔碳、碳纳米管、碳纤维、石墨烯及其衍生物、或中空碳球；
    所述金属材料包括以下各者中的至少一种：铜、镍、铬、钛、钨、锆、或上述材料中的两者或更多者组成的合金；
    所述无机材料包括以下各者中的至少一种：
    Li 3PO 4；
    LiPON；
    Li 2O；
    LiF；
    LiOH；
    Li 2CO 3；
    LiAlO 2；
    Li 4SiO 4；
    Li 2O-Al 2O 3-SiO 2-P 2O 5-TiO 2-GeO 2陶瓷；
    Li xTi y(PO 4) 3，其中0<x<2且0<y<3；
    Li xAl yTi z(PO 4) 3，其中0<x<2，0<y<1，且0<z<3；
    Li 1+x+y(Al,Ga) x(Ti,Ge) 2-xSi yP 3-yO 12，其中0≤x≤1且0≤y≤1；
    Li xLa yTiO 3，其中0<x<2且0<y<3；
    Li xGe yP zS w，其中0<x<4，0<y<1，0<z<1，且0<w<5；
    Li xN y，其中0<x<4，0<y<2；
    Li xSi yS z，其中0≤x<3，0<y<2，且0<z<4；
    Li xP yS z，其中0≤x<3，0<y<3，且0<z<7；或
    Li 3+xLa 3M 2O 12，其中0≤x≤5，且M为Te、Nb、或Zr中的至少一种。
  8. 根据权利要求1所述的负极极片，所述负极骨架进一步包括在所述负极骨架上沉积的无机材料。
  9. 根据权利要求8所述的负极极片，其中所述无机材料包括以下各者中的至少一种：HfO 2、SrTiO 3、SnO 2、CeO 2、MgO、NiO、CaO、BaO、ZnO、ZrO 2、Y 2O 3、Al 2O 3、TiO 2、SiO 2、CuO、或AgO。
  10. 根据权利要求1所述的负极极片，其进一步包括位于所述负极骨架上的一层或多层负极保护层。
  11. 根据权利要求10所述的负极极片，其中所述负极保护层的孔隙率约为0％至10％。
  12. 根据权利要求10所述的负极极片，其中所述负极保护层所采用的材料包括以下各者中的至少一种：无机物、硅、金属、或有机物。
  13. 根据权利要求12所述的负极极片，其中，
    所述无机物包括以下各者中的至少一种：
    Li 3PO 4；
    LiPON；
    Li 2O；
    LiF；
    LiOH；
    Li 2CO 3；
    LiAlO 2；
    Li 4SiO 4；
    Li 2O-Al 2O 3-SiO 2-P 2O 5-TiO 2-GeO 2陶瓷；
    Li xTi y(PO 4) 3，其中0<x<2且0<y<3；
    Li xAl yTi z(PO 4) 3，其中0<x<2，0<y<1，且0<z<3；
    Li 1+x+y(Al,Ga) x(Ti,Ge) 2-xSi yP 3-yO 12，其中0≤x≤1且0≤y≤1；
    Li xLa yTiO 3，其中0<x<2且0<y<3；
    Li xGe yP zS w，其中0<x<4，0<y<1，0<z<1，且0<w<5；
    Li xN y，其中0<x<4，0<y<2；
    Li xSi yS z，其中0≤x<3，0<y<2，且0<z<4；
    Li xP yS z，其中0≤x<3，0<y<3，且0<z<7；或
    Li 3+xLa 3M 2O 12，其中0≤x≤5，且M为Te、Nb、或Zr中的至少一种；
    所述金属包括以下各者中的至少一种：Au、Pt、Ag、Al、In、Sn、或上述材料中的两者或更多者组成的合金；
    所述有机物包括以下各者中的至少一种：PEO、PVDF、PMMA、PPC、PEC、PCL、TEGDA、Nafion、PAN、PDMS或上述有机物的衍生物。
  14. 一种电化学装置，其包括根据权利要求1-13中任一项所述的负极极片。
  15. 一种电子装置，其包括根据权利要求14所述的电化学装置。
PCT/CN2020/082187 2020-03-30 2020-03-30 负极极片与包含其的电化学装置 WO2021195881A1 (zh)

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