JP2014503951A - Electrochemical cell - Google Patents

Abstract

  An electrochemical cell comprising at least one negative electrode, at least one positive electrode, at least one separator separating the positive electrode from the negative electrode, and at least one electrolyte. The negative electrode is at least partially provided with metallic lithium and is at least partially coated.

Description

  The entire contents of the priority application DE102010054610.0 dated 15 December 2010 are hereby incorporated by reference into the present application.

  The present invention relates to an electrochemical cell in which the negative electrode comprises at least partly metallic lithium and is preferably coated with a protective film. The cell can preferably be used to drive an electric motor, preferably a hybrid drive or a “plug-in” drive vehicle.

  Electrochemical cells, especially lithium secondary batteries, are used in mobile information devices such as mobile phones, tools, or vehicles with electric drives, hybrid drives due to their high energy density and high capacity. Used as energy store. Even though the field of use of electrochemical cells is so diverse, all cells used must meet the same high demands. That is, the highest possible capacitance and energy density that remains as stable over many charge and discharge cycles, with as little weight as possible.

  Particularly high energy densities for lithium ion batteries can be achieved through the use of a lithium metal anode. However, the use of a lithium metal anode is associated with considerable problems. A particularly serious problem is that the lithium metal anode tends to grow dendrites (solidified needle-like crystals), which can lead to battery shorts and, in the worst case, battery explosions.

Japanese Patent Laying-Open No. 2005-071999 JP 2004-134403 A European Patent No. 1017476 German Patent Application Publication No. 19501271 EP 1852926 European Patent No. 1783852

D. Linden, T. B. Edited by T. B. Reddy, “Handbook of Batteries”, 3rd edition, McGraw-Hill, 35.7.1

  The object of the present invention is therefore to provide an improved and particularly safe electrochemical cell comprising a lithium metal anode.

  This is achieved according to the invention by the teachings of the independent claims. Preferred further embodiments of the invention are the subject matter of the dependent claims.

  To solve this problem, as described in detail below, at least one negative electrode, at least one positive electrode, at least one separator separating the negative electrode from the positive electrode, and at least one electrolyte, An electrochemical cell comprising is intended. The negative electrode is at least partially provided with metallic lithium and is at least partially coated.

  The term “negative electrode” means that the electrode emits electrons when connected to a consumer, such as an electric motor. Therefore, according to this convention, the negative electrode is the anode.

  The term “positive electrode” means that the electrode accepts electrons when connected to a consumer, such as an electric motor. Therefore, according to this convention, the positive electrode is the cathode.

  Suitably, the at least one electrode comprises an electrode support. Preferably, the electrode support is at least partly configured as a foil or network structure or woven fabric, preferably comprising copper or an alloy containing copper. In a further embodiment, the electrode support comprises aluminum. In a further embodiment, the negative electrode support preferably comprises an electrode support comprising a metal that does not form an alloy with lithium metal. Preferably, up to 30%, preferably up to 50%, preferably up to 70%, preferably up to 100% of the entire surface of the electrode support is used for lithium ion intercalation and deintercalation. A suitable at least one electrochemically active material is provided.

  Preferably, the electrochemically active material is at least partially coupled in material connection with the surface of the electrode support.

  In one embodiment, the at least one electrode, preferably the positive electrode, comprises a suitable binder to improve adhesion between the electrochemically active material and the electrode support. Preferably, such a binder comprises a polymer, preferably a fluorinated polymer, preferably polyvinylidene fluoride sold under the trade name Kainer® or Dinion®.

  In one embodiment, the electrode support may be configured as a foil or mesh structure or woven fabric, preferably at least partially comprising plastic.

  The term “metallic lithium” can be understood as lithium in which the oxidation state is approximately “0”, ie present as elemental lithium. In that case, it is not impossible that the metallic lithium is additionally, at least partly, in another oxidation state. In addition to elemental lithium, further materials may be included that are preferably used to improve the conductivity or safety or long life of the electrode. Thus, preferably the elemental lithium is embedded in a matrix consisting of a polymer matrix or carbon matrix or silicon wire, preferably silicon nanowires, in order to prevent volume changes during the charging or discharging process.

The use of lithium metal alloys, preferably lithium-tin alloys such as Li ₂₂ Sn ₅ , or lithium-aluminum alloys such as LiAl is particularly preferred.

  An “electrochemical cell” can be understood as various devices for storing energy electrically. The term thereby specifically defines primary or secondary type electrochemical cells, but also defines other forms of energy storage, such as capacitors. Suitably an electrochemical cell may be understood as a lithium ion battery / cell.

  The coating according to the invention of a negative electrode (particularly configured as a protective film) comprising at least partly metallic lithium is a lithium dendrite (also called lithium whisker) that may be formed from a lithium metal anode (negative electrode) in some circumstances. It has the function of reducing formation, preferably minimizing and preferably preventing. Preferably, the coating is at least partly, preferably completely, at the macroscopic level (dendritic size and / or dendritic diameter in the millimeter range), preferably at the microscopic level (dendritic size and / or in the micrometric range). Alternatively, dendrite diameter) more preferably prevents the formation of metallic lithium dendrite at the nano level (dendritic size and / or dendrite diameter in the nanometer range).

  The coating preferably comprises at least partly an inorganic, ion-conducting material, in particular lithium ion-conducting material, having at least one element of zirconium, aluminum, lithium, oxide, phosphate, sulfuric acid A ceramic material, preferably at least partly, preferably comprising at least one compound selected from the group consisting of salts, titanates, silicates, aluminosilicates, particularly preferably zircon oxide, aluminum oxide, silicon oxide. Be prepared.

In a particularly preferred embodiment, the coating comprises at least partly an inorganic, ion-conducting material, in particular lithium ion-conducting material, preferably aluminum oxide and / or silicon oxide, preferably Al _2. O ₃ and / or SiO ₂ , preferably a ceramic material. Such a protective film has the advantage that the use of solid polymer electrolytes can be stopped in connection with electrodes comprising metallic lithium.

  More preferably, the inorganic and ion conductive material is at least partially ion conductive in the temperature range of −40 ° C. to 200 ° C.

  Solid polymer electrolytes are currently the most effective way to prevent lithium dendrite growth according to the prior art, so lithium metal anodes can often only be used in combination with solid polymer electrolytes . However, solid polymer electrolytes have the disadvantage of aging very quickly (due to the transition from amorphous to crystalline) and exhibiting ionic conductivity only above a certain temperature (activation temperature).

  In this case, the coating of the lithium metal anode (“protective film”) allows the use of a liquid non-aqueous electrolyte, such as an ionic liquid, or an organic solvent having an organic or inorganic salt containing lithium, and It is also preferable in the gist.

  U.S. Patent No. 6,057,034 describes a coating of a lithium metal anode with lithium fluoride based on a lithium sulfur battery to hinder dendrite growth.

  U.S. Patent No. 6,099,056 describes the coating of a lithium metal anode with a polymer film.

  Preferably, the coating (“protective film”) completely covers the lithium metal anode. Suitably, the coating may at least partially cover the lithium metal anode, in particular the coating at least partially covers the lithium metal anode at the contact point or contact surface or contact area between the lithium metal anode and the separator and / or electrolyte. Cover.

  Preferably, the coating further comprises an inorganic, ionically conductive material, preferably at least partly, preferably completely, configured as fibers or particles or fibers and particles.

  Preferably, the coating is at least partially composed of an inorganic, ionically conductive material, preferably comprising particles with a maximum average diameter of <100 nm, preferably <50 nm, preferably <20 nm, preferably <10 nm. Prepare for. However, the maximum average diameter may be larger or smaller.

  Preferably the fibers comprise an average diameter of up to 50 μm, up to 25 μm, up to 10 μm, up to 5 μm, or larger or smaller.

  In one preferred embodiment, the fibers are configured as a fleece, which may or may not be woven.

  In a further embodiment, the coating is configured as a woven or non-woven fleece that additionally includes particles of an inorganic, ionically conductive material, the material being The fleece may be different or identical to the inorganic and ionically conductive material at least partially provided.

  The advantages of using a fleece are high tensile strength and recoverable shape accuracy.

  In one embodiment, the coating may comprise an additive material, such as a binder or a conductive additive. In one embodiment, the protective film additionally comprises plastic.

  Preferably, the inorganic and ionically conductive material is up to 30%, preferably up to 50%, preferably up to 70%, preferably up to 95%, preferably up to 100% of the entire surface of the lithium metal anode. % Coating.

  “Coating” means that the coating is preferably at least partially, preferably completely bonded in material connection to the surface of the lithium metal anode.

  Preferably, the coating corresponds to the average thickness of the anode, preferably three quarters of the average thickness of the anode, preferably half the average thickness of the anode, preferably one quarter of the average thickness of the anode. However, preferably the average thickness of the coating may be larger or smaller.

  For the use of the term coating, the coating may comprise a plurality of layers, preferably comprising the materials and configurations described above, preferably up to 2, preferably up to 5, preferably up to 7 layers or more. It is included. The layers may be the same or different with respect to their construction and materials. The configuration and material selection of the layers may preferably be made dependent on one another or independently of one another.

  The choice of separator material can also make a decisive contribution to the safety of the electrochemical cell. For example, if the separator has holes or pores that are too large, when lithium dendrite grows, these dendrites can grow through the separator and then contact the positive electrode, thereby causing an internal short circuit. Can eventually lead to the destruction of the battery.

  It is therefore advantageous to use a separator that reaches a certain temperature ("shutdown temperature"), whose pore structure is destroyed, so that ions can no longer be transported through the separator, but it uses a polymer. Can be achieved. If the polymer material is additionally coated with an inorganic material, further improvements in battery safety are guaranteed. This prevents the polymer material from completely dissolving when a certain temperature, the so-called “breakdown temperature” (temperature higher than the “shutdown temperature”) is reached. Thereby, a wide range of shorts is avoided.

  Preferably, a separator is used which comprises a support which separates the positive electrode from the negative electrode and which has no or low electronic conductivity and is at least partially permeable to matter. The support is preferably coated on at least one side with an inorganic material. Preferably, an organic material is used, preferably configured as a non-woven fleece, as an at least partly material-permeable support.

  Suitably a polymer, particularly preferably an organic material comprising one or more polymers selected from polyethylene terephthalate (PET), polyolefins or polyetherimides, is coated with an inorganic, preferably ion-conducting material. The material is more preferably ionically conductive in the temperature range of −40 ° C. to 200 ° C., preferably an oxide, phosphate, at least one element of zirconium, aluminum, lithium It comprises at least one compound selected from the group consisting of silicates, titanates, sulfates, aluminosilicates, particularly preferably zircon oxide.

  Such a separator is sold in Germany, for example, under the trade name Eparonic Separion®.

  Preferably, the inorganic, ionically conductive material of the separator comprises particles having a maximum diameter of less than 100 nm, preferably 0.5 μm to 7 μm, preferably 1 μm to 5 μm, preferably 1.5 μm to 3 μm. .

  In one embodiment, the separator comprises a porous inorganic coating on and within the fleece, the coating having an average particle size of 0.5 μm to 7 μm, preferably 1 μm to 5 μm, very particularly preferably 1 Aluminum oxide particles having an oxide of Zr or Si of 5 to 3 μm are provided.

  In order to achieve the highest possible porosity, preferably more than 50% by weight of the total particles, particularly preferably more than 80% by weight, are within the above-mentioned boundaries of the average particle size. Preferably, the maximum particle size is preferably one third to one fifth, particularly preferably less than one tenth or equal to one tenth of the thickness of the fleece used .

  Suitable polyolefins are preferably polyethylene, polypropylene or polymethylpentene. Particularly preferred is polypropylene. The use of polyamide, polyacrylonitrile, polycarbonate, polysulfone, polyethersulfone, polyvinylidene fluoride, polystyrene as an organic support material can likewise be envisaged. Mixtures of polymers may also be used.

  A separator having PET as a support material is available on the market under the name Separion®. The separator can be manufactured according to a method as disclosed in Patent Document 3.

  The term “nonwoven fleece” means that the polymer is in the form of a non-woven fabric. Such fleeces are known from the prior art and / or can be produced according to known methods, for example by the spunbond method or the melt-blow method as reported in US Pat.

  Preferably the separator comprises a fleece with an average thickness of 5 μm to 30 μm, preferably 10 μm to 20 μm. The fleece is preferably configured flexibly. Preferably the fleece has a homogeneous pore radius distribution, and preferably at least 50% of the pores have a pore radius of 75 μm to 100 μm. Preferably the porosity of the fleece is 50%, preferably 50% to 97%.

  “Porosity” is defined as the volume of the fleece (100%) minus the volume of the fleece fibers (corresponding to the volume of the fleece not occupied by the material). At that time, the volume of the fleece can be calculated from the dimensions of the fleece. The fiber volume is derived from the measured fleece weight taken into account and the density of the polymer fibers. If the porosity of the fleece is high, the porosity of the separator can also be higher, and therefore it can be achieved that the separator accepts more electrolyte.

  In a further embodiment, the separator comprises polyethylene glycol terephthalate, polyolefin, polyetherimide, polyamide, polyacrylonitrile, polycarbonate, polysulfone, polyethersulfone, polyvinylidene fluoride, polystyrene, or mixtures thereof. Preferably the separator comprises a polyolefin or a mixture of polyolefins. Particularly preferred in this embodiment is a separator made of a mixture of polyethylene and polypropylene.

  Preferably such a separator has a thickness of 3 μm to 14 μm.

  The polymer is preferably present in the form of a fiber fleece, and the polymer fibers preferably have an average diameter of 0.1 μm to 10 μm, preferably 1 μm to 4 μm.

  The term “mixture” of polymers means that the polymers are preferably present in the form of fleeces joined together in layers. Such a fleece or fleece complex is disclosed, for example, in US Pat.

  In a further embodiment of the separator, the separator consists of an inorganic material. As the inorganic material, magnesium, calcium, aluminum, silicon, titanium oxide, silicate and zeolite, borate and phosphate are preferably used. Such a material for the separator and a method for manufacturing the separator are disclosed in US Pat. In a preferred embodiment of this embodiment of the separator, the separator consists of magnesium oxide.

  In a further embodiment of the separator, from 50% to 80% by weight of magnesium oxide may comprise calcium oxide, barium oxide, barium carbonate, lithium phosphate, sodium phosphate, potassium phosphate, magnesium phosphate, calcium phosphate, phosphorus Barium acid or lithium borate, sodium borate, potassium borate, or a mixture of these compounds may be substituted.

  Preferably, the separator of this embodiment has a film thickness of 4 μm to 25 μm.

  In one embodiment, the separator comprises the same inorganic and ion conductive material as the inorganic and ion conductive material provided in the protective film. However, the inorganic and ion-conductive material of the separator may be different from the inorganic and ion-conductive material of the protective film.

  Preferably, the positive electrode of the electrochemical cell comprises an electrochemically active material, which material is selected from at least one oxide, preferably nickel, manganese, cobalt, phosphorus, iron or titanium. It is selected from mixed oxides comprising one or more elements.

In one embodiment, the positive electrode comprises a compound having the chemical formula LiMPO ₄ and M is at least one transition metal cation, preferably a transition metal cation in the first column of the periodic table.

The transition metal cation is preferably selected from the group consisting of manganese, iron, nickel, cobalt or titanium or a combination of these elements. The compound preferably has an olivine structure, preferably a superior olivine, with iron or cobalt, preferably LiFePO ₄ or LiCoPO ₄ being particularly preferred. However, the compound may have a structure different from the olivine structure.

In a further embodiment, the positive electrode comprises an oxide, preferably a transition metal oxide or a transition metal mixed oxide, preferably a spinel type transition metal mixed oxide, preferably lithium manganate, preferably LiMn ₂ O. ₄ , lithium cobaltate, preferably LiCoO ₂ , or lithium nickelate, preferably LiNiO ₂ , or a mixture of two or three of these oxides. However, the oxide may be different from the spinel type.

More preferably, in addition to the transition metal oxide described above, the positive electrode is only a lithium transition metal mixed oxide containing manganese, cobalt and nickel, preferably lithium cobalt manganate, preferably LiCoMnO ₄ , preferably Is lithium nickel manganate, preferably LiNi _0.5 Mn _1.5 O ₄ , preferably lithium nickel manganese cobalt oxide, preferably LiNi _0.33 Mn _0.33 Co _0.33 O ₂ , or lithium nickel cobalt The oxide may preferably comprise LiNiCoO ₂ , which may not be spinel-type, or may be present in spinel-type.

  Preferably, the positive electrode comprises, in addition to the electrochemically active material, further substances such as conductive additives such as carbon containing materials, copper flakes or aluminum flakes.

  As the electrolyte, a non-aqueous electrolyte composed of an organic solvent and an inorganic salt or organic salt containing lithium ions may be used.

  Preferably, the organic solvent is ethylene carbonate, propylene carbonate, diethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxirane, sulfolane, acetonitrile, or phosphorus. It is selected from acid esters or mixtures of these solvents.

Preferably, the salt containing lithium ions is AsF ₆ ⁻ , PF ₆ ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , PF ₃ (CF ₃ ) ₃ ⁻ , BF ₄ ⁻ , BF ₂ (CF ₃ ). ^{_{2 -, BF 3 (CF 3}} ) -, [B (COOCOO) 2 -], CF 3 SO 3 -, C 4 F 9 SO 3 -, [(CF 3 SO 2) 2 N] -, [(C 2 One or a plurality of counter ions selected from F ₅ SO ₂ ) N] ⁻ , [(CN) ₂ N] ⁻ and ClO ₄ ^— .

  Preferably, the electrochemical cell separator is impregnated with electrolyte. In one embodiment, the separator is impregnated with an electrolyte that is configured as an ionic liquid. Moreover, the electrolyte may include auxiliary substances commonly used in electrolytes for lithium ion batteries. For example, it is a free radical scavenger such as biphenyl, a flame retardant additive such as an organic phosphate ester or hexamethyl phosphoric acid amide, or an acid scavenger such as an amine.

  Additives such as phenylene carbonate that can affect the formation of a “solid electrolyte interface” membrane (SEI) at the electrode can be used as well.

The present invention likewise relates to a method for producing an electrochemical cell according to the present invention, which method comprises the following steps:
-Preparing a positive electrode;
-Providing a negative electrode comprising at least partially metallic lithium;
-At least partially, preferably completely coating the negative electrode;
-Preparing a separator;
-Infiltrating the separator with electrolyte;
-Assembling the prepared positive electrode with the separator and negative electrode, depending on the order of negative electrode / separator / positive electrode layer, or vice versa;
Is provided.

  These steps may be performed in any order with the exception of the last step. The principle by which such an electrochemical cell can be produced is known to the person skilled in the art from the prior art, for example Non-Patent Document 1.

  The electrochemical cell according to the present invention can be used to power mobile information devices, tools, electrically powered vehicles, and vehicles with hybrid drives.

Claims (15)

In an electrochemical cell comprising at least one negative electrode, at least one positive electrode, at least one separator separating the positive electrode from the negative electrode, and at least one electrolyte,
The negative electrode comprises at least partially metallic lithium;
An electrochemical cell wherein the negative electrode is at least partially coated.   The coating reduces or prevents the formation of lithium dendrite on or at the negative electrode, the coating preferably comprising at least partly an inorganic and ion-conductive material. The electrochemical cell according to claim 1.   The coating is selected from the group consisting of oxide, phosphate, sulfate, titanate, silicate, aluminosilicate having at least one element of zirconium, aluminum, lithium or a mixture thereof. The electrochemical cell according to claim 2, further comprising at least partially a ceramic material comprising at least one compound.   The electrochemical cell according to any one of claims 1 to 3, wherein the coating is at least partially bonded to the surface of the negative electrode in material connection.   5. The electrochemical cell according to claim 1, wherein the coating is provided at least partially between the negative electrode and the separator. 6. The positive electrode includes at least in part at least one electrochemically active material, the electrochemically active material comprising:
a. At least one compound LiMPO _{4 wherein} M is at least one transition metal cation selected from manganese, iron, cobalt, titanium or combinations of these elements, or b. At least one lithium metal oxide or lithium metal mixed oxide of the spinel type, wherein the metal is selected from cobalt, manganese or nickel, or a lithium metal oxide or lithium metal mixed oxide, or c. At least one lithium metal oxide or lithium metal mixed oxide of a type different from the spinel type, wherein the metal is selected from cobalt, manganese or nickel, lithium metal oxide or lithium metal mixed oxide,
Alternatively, the electrochemical cell according to any one of claims 1 to 5, wherein the electrochemical cell is selected from a mixture thereof. The separator is
a. A separator, preferably consisting of at least one support that is either non-electron-conducting or poorly electron-conductive and at least partially permeable to matter, said support being made of an inorganic material on at least one side. An organic material, preferably coated as an at least partly material permeable support, preferably configured as a non-woven fleece, is preferably used, which is preferably a polymer, Particularly preferably, it comprises one or more polymers selected from polyethylene terephthalate, polyolefin or polyetherimide, the organic material being coated with an inorganic and ion conductive material, and the inorganic and ion conductive material. Some materials preferably have ionic conductivity in the temperature range of −40 ° C. to 200 ° C. The inorganic ion-conductive material is preferably an oxide, phosphate, silicate, titanate, sulfate, aluminosilicate having at least one element of zirconium, aluminum, and lithium. A separator comprising at least one compound selected from the group consisting of, particularly preferably zircon oxide, wherein the inorganic material preferably comprises particles having a maximum diameter of less than 100 nm, or b. A separator comprising polyethylene terephthalate, polyolefin, polyetherimide, polyamide, polyacrylonitrile, polycarbonate, polysulfone, polyethersulfone, polyvinylidene fluoride, polystyrene, or mixtures thereof; or c. The electrochemical cell according to any one of claims 1 to 6, wherein the electrochemical cell is selected from separators comprising an inorganic material.   The electrochemical cell according to claim 1, wherein the electrochemical cell includes an electrolyte.   The electrochemical cell according to claim 8, wherein the electrolyte includes an organic solvent and lithium ions, or is configured as a non-aqueous electrolyte including an ionic liquid.   10. An electrochemical cell according to any one of the preceding claims, wherein the at least one electrode comprises an electrode support that is at least partially coated with an electrochemically active material. The electrode support is at least partially configured as a foil, a mesh structure, or a woven fabric.
a. At least one metal or metal alloy, preferably copper, an alloy containing copper or aluminum, or b. At least a metal that cannot form an alloy with lithium, or c. The electrochemical cell according to claim 10, comprising a material selected from at least one plastic or a mixture of the materials a to c.   The electrochemical cell according to any one of claims 1 to 11, wherein the negative electrode at least partially contains elemental lithium or a lithium alloy. A method for producing an electrochemical cell according to any one of claims 1 to 12, comprising the following steps:
-Preparing a positive electrode;
-Providing a negative electrode comprising at least partially metallic lithium;
-At least partially, preferably completely coating the negative electrode;
-Preparing a separator;
-Infiltrating the separator with electrolyte;
-Assembling the prepared positive electrode with the separator and negative electrode, depending on the negative electrode / separator / positive electrode layer or vice versa;
A method comprising:   13. Use of an electrochemical cell according to any one of claims 1 to 12 for supplying energy to a consumer.   15. Use according to claim 14, in a mobile information device, a tool, an electrically powered vehicle or a vehicle with a hybrid drive.