DE102010054610A1 - Electrochemical cell - Google Patents

Abstract

Electrochemical cell, having at least one negative electrode, at least one positive electrode, at least one separator which separates the positive electrode from the negative electrode, and at least one electrolyte. The negative electrode has at least partially metallic lithium and is at least partially coated.

Description

The present invention relates to an electrochemical cell whose negative electrode has at least partially metallic lithium, and is coated, preferably coated with a protective layer. The cell can preferably be used for driving a vehicle with an electric motor, preferably with hybrid drive or in "plug-in" operation.

Electrochemical cells, especially lithium secondary batteries, find because of their high energy density and high capacity as energy storage in mobile information devices such. As mobile phones, in tools or in electrically powered cars and in automobiles with hybrid drive application. Despite these very different fields of application of electrochemical cells, all cells used must meet similar high requirements: the highest possible electrical capacity and energy density, which remains stable over a high number of charging and discharging cycles, with the lowest possible weight.

Particularly high energy densities for lithium-ion batteries can be achieved by using a lithium-metal anode. The use of a lithium-metal anode, however, involves considerable problems. A particularly relevant problem is that lithium-metal anodes tend to dendrite growth (solidified acicular crystals), which can lead to short circuit of the battery and in the worst case to explosion of the same.

The invention is therefore based on the object to provide an improved, in particular safe electrochemical cell having a lithium-metal anode.

This is achieved according to the invention by the teaching of the independent claims. Preferred developments of the invention are the subject of the dependent claims.

To achieve this object, as described in detail below, an electrochemical cell is provided which has at least one negative electrode, at least one positive electrode, at least one separator which separates the negative electrode from the positive electrode, and at least one electrolyte. The negative electrode has at least partially 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. Thus, according to this convention, the negative electrode is the anode.

The term "positive electrode" means that the electrode receives electrons when connected to a consumer, such as an electric motor. Thus, according to this convention, the positive electrode is the cathode.

Preferably, at least one electrode has an electrode carrier. Preferably, this electrode carrier is at least partially designed as a film or as a network structure or as a fabric, preferably comprising copper or a copper-containing alloy. In another embodiment, an electrode carrier comprises aluminum. In a further embodiment, the electrode carrier of the negative electrode has an electrode carrier, which preferably has a metal which does not form alloys with metallic lithium. Preferably, up to 30%, preferably up to 50%, preferably up to 70%, preferably up to 100%, of the total surface of an electrode carrier has at least one electrochemical active material which is suitable for incorporation and removal of lithium ions.

Preferably, the electrochemical active material is at least partially bonded cohesively to the surface of the electrode carrier.

In one embodiment, at least one electrode, preferably the positive electrode, has a binder capable of enhancing the adhesion between electrochemical active material and electrode carrier. Preferably, such a binder comprises a polymer, preferably a fluorinated polymer, preferably polyvinylidene fluoride on, which is sold under the trade names Kynar ^® or Dyneon ^®.

In one embodiment, the electrode carrier can be configured as a film, network structure or fabric, which preferably comprises at least partially plastics.

The term "metallic lithium" is to be understood as lithium, which is essentially present in the oxidation state "0", that is to say as elemental lithium. It is not excluded that the metallic lithium also additionally exists at least partially in other oxidation states. Furthermore, in addition to elemental lithium, other substances may also be present which preferably serve to increase the conductivity or the safety or longevity of the electrode. Thus, preferably elemental lithium is in a polymer or carbon matrix or in a matrix of silicon wires, preferably silicon nanowires embedded to counteract a volume change during the loading or unloading process.

Particularly preferred is the use of a lithium metal alloy, preferably a lithium-tin alloy, for example Li ₂₂ Sn ₅ , or a lithium-aluminum alloy, for example LiAl.

An "electrochemical cell" is any type of device for the electrical storage of energy to understand. The term defines in particular electrochemical cells of the primary or secondary type, but also other forms of energy storage, such as capacitors. Preferably, an electrochemical cell is to be understood as a lithium-ion battery / cell.

The coating according to the invention of the negative electrode, which at least partially comprises metallic lithium (in particular provided as a protective layer) has the function of forming lithium dendrites (also called lithium whiskers), which may be of the lithium metal anode (negative electrode ) can be reduced, preferably minimized, preferably to prevent. Preferably, the coating at least partially, preferably completely, prevents the formation of metallic lithium dendrites at the macroscopic level (dendrite size and / or diameter in the millimeter range), preferably also at the microscopic level (dendrite size and / or diameter in the micrometer range, more preferably nanoscopic Plane (dendrite size and / or diameter in the nanometer range).

The coating preferably has at least partially an inorganic, ion-conducting, in particular lithium ion-conductive material, preferably at least partially a ceramic material, which preferably at least one compound from the group of oxides, phosphates, sulphates, titanates, silicates, aluminosilicates, aluminosilicates with at least one of the elements Zirconium, aluminum, lithium, more preferably zirconia, alumina, silica.

In a particularly preferred embodiment, the coating has at least partially inorganic, ion-conductive, in particular lithium-ion-conductive material, preferably ceramic material, which preferably comprises aluminum oxide and / or silicon oxide, preferably Al ₂ O ₃ and / or SiO ₂ . Such a protective layer has the advantage that it can be dispensed with the use of a solid polymer electrolyte in connection with the electrode having metallic lithium.

Further preferably, the inorganic, ion-conducting material in a temperature range of -40 ° C to 200 ° C is at least partially ion-conducting.

Solid polymer electrolytes are currently the most effective method of preventing lithium dendrite growth in the art, and lithium metal anodes can often be used only in combination with solid polymer electrolytes. However, solid polymer electrolytes have the disadvantage that they age very rapidly (due to the transition from the amorphous to the crystalline) and develop above a certain temperature (activation temperature), the ionic conductivity.

In the present case, by the coating of the lithium-metal anode ("protective layer"), the use of a liquid, non-aqueous electrolyte, for example an ionic liquid or an organic solvent with a lithium-containing organic or inorganic salt, possible and also for the purposes of the present invention.

JP 2005 071999 describes using a lithium-sulfur battery, the coating of a lithium-metal anode with lithium fluoride to counteract dendrite growth.

JP 2004 134403 describes the coating of a lithium-metal anode with a polymeric layer.

Preferred embodiments

Preferably, the coating ("protective layer") completely envelops the lithium metal anode. Preferably, the coating may at least partially encase the lithium metal anode, in particular the coating at least partially encloses the lithium metal anode at the contact points, areas or regions of the lithium metal anode with the separator and / or the electrolyte.

Preferably, the coating comprises inorganic, ion-conductive material, which is further preferably at least partially, preferably completely configured as fibers or particles or fibers and particles.

Preferably, the coating comprises at least partially inorganic, ion-conducting material, which preferably comprises particles having a largest average diameter of <100 nm, preferably <50 nm, preferably <20 nm, preferably <10 nm. The largest average diameter but also bigger or smaller.

The fibers preferably have an average diameter of up to 50 μm, of up to 25 μm, of up to 10 μm, of up to 5 μm or larger or smaller.

In a preferred embodiment, the fibers are configured as non-woven, which may be woven or non-woven.

In a further embodiment, the coating is configured as a woven or non-woven non-woven, which additionally contains particles of an inorganic, ion-conductive material, which may be different from or identical to the inorganic, ion-conductive material, which at least partially comprises the nonwoven.

The advantage of using a nonwoven is the high tear resistance and reversible shape retention.

In one embodiment, the coating may include additional materials, such as binders or conductivity additives. In one embodiment, the protective layer additionally comprises plastics.

Preferably, the inorganic ion conducting material wraps up to 30%, preferably up to 50%, preferably up to 70%, preferably up to 95%, preferably up to 100%, of the total surface area of the lithium metal anode.

"Encapsulation" means that the coating is preferably at least partially bonded to the surface of the lithium-metal anode, preferably completely.

Preferably, the coating has an average thickness corresponding to the average thickness of the anode, preferably equal to 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, preferably the average Thickness of the coating but also be larger or smaller.

The use of the term coating also implies that the coating may have multiple layers, preferably up to two layers, preferably up to five layers, preferably up to seven or more layers, which preferably have the aforementioned materials and configurations. The layers may be identical or different with respect to their designs and materials. The choice of configurations and materials which comprise the layers can preferably be done as a function of one another or independently of one another.

The choice of separator material can also contribute significantly to the safety of the electrochemical cell. For example, if a separator has too large holes or pores, in the case of lithium dendrite growth, these dendrites may grow through the separator to contact the positive electrode, resulting in an internal short, and thus destruction the battery can come.

Therefore, it is advantageous to use a separator whose pore structure is destroyed upon reaching a certain temperature ("shut-down temperature"), and thus no more ions can be transported through the separator, which can be achieved by the use of polymers , A further increase in the safety of the battery is ensured if the polymer material is additionally coated with inorganic material. This prevents, upon reaching a temperature, the so-called "break-down temperature" (which is higher than the "shut-down temperature") that the polymer material melts completely. Thus, a large-area short circuit is avoided.

Preferably, a separator is used which separates the positive electrode from the negative electrode and is not or only poorly electron-conducting, and which consists of an at least partially permeable carrier. The support is preferably coated on at least one side with an inorganic material. As at least partially permeable carrier is preferably an organic material is used, which is preferably designed as a non-woven fabric.

The organic material, which preferably comprises a polymer and particularly preferably one or more polymers selected from polyethylene terephthalate (PET), polyolefin or polyetherimide, is coated with an inorganic, preferably ion-conducting material, which is more preferably in a temperature range of -40 ° C is at least 200 ° C ion conducting, and preferably at least one compound selected from the group of oxides, phosphates, silicates, titanates, sulphates, aluminosilicates with at least one of zirconium, aluminum, lithium and more preferably zirconium oxide.

Such a separator is marketed in Germany, for example, under the trade name Separion ^® from Evonik AG.

The inorganic, ion-conducting material of the separator preferably has particles with a size diameter below 100 nm, preferably from 0.5 to 7 μm, preferably from 1 to 5 μm, preferably from 1.5 to 3 μm.

In one embodiment, the separator has a porous inorganic coating on and in the nonwoven, the aluminum oxide particles having an average particle size of from 0.5 to 7 μm, preferably from 1 to 5 μm and very particularly preferably from 1.5 to 3 μm, which are bonded to an oxide of the elements Zr or Si.

In order to achieve the highest possible porosity, preferably more than 50% by weight and more preferably more than 80% by weight of all particles are within the abovementioned limits of average particle size. Preferably, the maximum particle size is preferably 1/3 to 1/5 and more preferably less than or equal to 1/10 of the thickness of the nonwoven fabric used.

Suitable polyolefins are preferably polyethylene, polypropylene or polymethylpentene. Particularly preferred is polypropylene. The use of polyamides, polyacrylonitriles, polycarbonates, polysulfones, polyethersulfones, polyvinylidene fluorides, polystyrenes as organic carrier material is also conceivable. It is also possible to use mixtures of the polymers.

A separator with PET as carrier material is commercially available under the name Separion ^® . It can be made by methods such as those in the EP 1 017 476 are disclosed.

The term "nonwoven web" means that the polymers are in the form of nonwoven fibers (non-woven fabric). Such nonwovens are known from the prior art and / or can be produced by the known processes, for example by a spunbonding process or a meltblowing process such as, for example, in US Pat DE 195 01 271 A1 referenced.

Preferably, the separator comprises a nonwoven having an average thickness of 5 to 30 microns, preferably from 10 to 20 microns. Preferably, the fleece is flexible. Preferably, the nonwoven fabric has a homogeneous pore radius distribution, preferably at least 50% of the pores have a pore radius of 75 to 100 μm. Preferably, the web has a porosity of 50%, preferably from 50 to 97%.

"Porosity" is defined as the volume of the web (100%) minus the volume of the fibers of the web (corresponds to the fraction of the volume of the web that is not filled by material). The volume of the fleece can be calculated from the dimensions of the fleece. The volume of the fibers results from the measured weight of the fleece considered and the density of the polymer fibers. The large porosity of the web also allows for a higher porosity of the separator, therefore a higher uptake of electrolytes with the separator can be achieved.

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

Preferably, such separators have a layer thickness of 3 to 14 .mu.m.

The polymers are preferably in the form of fiber webs, wherein the polymer fibers preferably have an average diameter of 0.1 to 10 microns, preferably from 1 to 4 microns.

The term "mixture" or "mixture" of the polymers means that the polymers are preferably in the form of their nonwovens, which are bonded together in layers. Such nonwovens or nonwoven composites are, for example, in EP 1 852 926 disclosed.

In a further embodiment of the separator, this consists of an inorganic material. Preferably, the inorganic material used are oxides of magnesium, calcium, aluminum, silicon and titanium, as well as silicates and zeolites, borates and phosphates. Such materials for separators and processes for the preparation of the separators are in EP 1 783 852 disclosed. In a preferred embodiment of this embodiment of a separator, the separator consists of magnesium oxide.

In a further embodiment of the separator 50 to 80 wt .-% of the magnesium oxide by calcium oxide, barium oxide, barium carbonate, lithium, sodium, potassium, magnesium, calcium, barium phosphate or by lithium, sodium, potassium borate, or Mixtures of these compounds, be replaced.

The separators of this embodiment preferably have a layer thickness of 4 to 25 μm.

In one embodiment, the separator comprises an inorganic, ion-conductive material, which is identical to the inorganic, ion-conductive material, which is exhibited by the protective layer. However, the inorganic, ion-conductive material of the separator may also be different from the inorganic, ion-conductive material of the protective layer.

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

In one embodiment, the positive electrode comprises a compound of the formula LiMPO ₄ wherein M is at least one transition metal cation, preferably a transition metal cation of the first row of the Periodic Table of the Elements.

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 higher olivine, with iron or cobalt being particularly preferred, preferably LiFePO ₄ or LiCoPO ₄ . However, the compound may also 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 of the spinel type, preferably a lithium manganate, preferably LiMn ₂ O ₄ , a lithium cobaltate, preferably LiCoO ₂ , or a lithium Nickelate, preferably LiNiO ₂ , or a mixture of two or three of these oxides. However, the oxides can also be different from the spinel type.

Further preferably, the positive electrode in addition to the aforementioned transition metal oxides or exclusively a lithium transition metal mixed oxide containing manganese, cobalt and nickel, preferably a lithium cobalt manganate, preferably LiCoMnO ₄ , preferably a lithium nickel manganate, preferably LiNi _{0 , 5} Mn _1.5 O ₄ , preferably a lithium-nickel-manganese-cobalt oxide, preferably LiNi _0.33 Mn _0.33 Co _0.33 O ₂ , or a lithium-nickel-cobalt oxide, preferably LiNiCoO ₂ , which can not be in the spinel type or in the spinel type.

Preferably, the positive electrode has, in addition to the electrochemically active material, further substances, for example conductivity additives such as carbonaceous materials, copper or aluminum shavings.

As the electrolyte, a non-aqueous electrolyte consisting of an organic solvent and a lithium ion-containing, inorganic or organic salt can be used.

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

Preferably, the lithium ion-containing salt has one or more counterions selected from 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 F ₅ SO ₂ ) N] ^- , [(CN) ₂ N] ^- , ClO ₄ ^- .

Preferably, the separator of the electrochemical cell is impregnated with the electrolyte. In one embodiment, the separator is impregnated with an electrolyte which is designed as an ionic liquid. Furthermore, the electrolyte may include adjuvants that are commonly used in electrolytes for lithium-ion batteries. For example, these are free-radical scavengers such as biphenyl, flame retardant additives such as organic phosphoric acid esters or hexamethylphosphoramide, or acid scavengers such as amines.

Additives such as phenylene carbonate, which may affect the formation of the solid electrolytes interface (SEI) layer on the electrodes, are also useful.

• • Bereitstellen einer positiven Elektrode
• • Bereitstellen einer negativen Elektrode, welche zumindest teilweise metallisches Lithium aufweist
• • Zumindest teilweiser, vorzugsweise vollständiger Beschichtungen der negativen Elektrode
• • Bereitstellen eines Separators
• • Durchtränken des Separators mit Elektrolyt
• • Zusammenfügen der bereitgestellten positiven Elektrode mit dem Separator und der negativen Elektrode entsprechend der Lagenfolge negative Elektrode/Separator/positive Elektrode oder umgekehrt.

The present invention also relates to a method for producing the electrochemical cell according to the invention, which comprises the following steps:

• • Provide a positive electrode
• Providing a negative electrode which at least partially comprises metallic lithium
• At least partial, preferably complete, negative electrode coatings
• • Provision of a separator
• • soaking the separator with electrolyte
• • Assembling of the provided positive electrode with the separator and the negative electrode according to the sequence of positions negative electrode / separator / positive electrode or vice versa.

The steps, except for the last step, can be performed in any order. The principles by which such an electrochemical cell can be made are known to those skilled in the art, such as " Handbook of Batteries, Third Edition, McGraw-Rill, Editors: D. Linden, TB Reddy, 35.7.1 ":
The electrochemical cell of the present invention can be used to power mobile information equipment, tools, electric powered automobiles, and hybrid drive automobiles.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2005071999 [0022]
• JP 2004134403 [0023]
• EP 1017476 [0045]
• DE 19501271 A1 [0046]
• EP 1852926 [0052]
• EP 1783852 [0053]

Cited non-patent literature

• Handbook of Batteries, Third Edition, McGraw-Rill, Editors: D. Linden, TB Reddy, 35.7.1 [0069]

Claims (15)

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 characterized in that the negative electrode comprises at least partially metallic lithium and that the negative electrode at least partially coated. An electrochemical cell according to claim 1, characterized in that the coating reduces or prevents the formation of lithium dendrites on or at the negative electrode, the coating preferably comprising at least partially an inorganic, ion-conductive material. Electrochemical cell according to claim 2, characterized in that the coating comprises at least partially ceramic material having at least one compound which is selected from the group of oxides, phosphates, sulphates, titanates, silicates, aluminosilicates with at least one of zirconium, aluminum , Lithium or mixtures thereof. Electrochemical cell according to at least one of the preceding claims, characterized in that the coating is connected at least partially cohesively to the surface of the negative electrode. Electrochemical cell according to at least one of the preceding claims, characterized in that the coating is arranged at least partially between the negative electrode and separator. Electrochemical cell according to at least one of the preceding claims, characterized in that the positive electrode at least partially comprises at least one electrochemically active material which is selected from: a. at least one compound LiMPO ₄ , wherein M is at least one transition metal cation selected from manganese, iron, cobalt, titanium or a combination of these elements; or b. at least one spinel-type lithium metal oxide or lithium metal mixed oxide, wherein the metal is selected from cobalt, manganese or nickel; or c. at least one lithium metal oxide or lithium metal mixed oxide in a type other than spinel type, wherein the metal is selected from cobalt, manganese or nickel; or mixtures thereof. Electrochemical cell according to at least one of the preceding claims, characterized in that the separator is selected from: a. A separator, which preferably consists of at least one at least partially permeable carrier, which is not or only poorly electron-conducting, wherein the carrier is coated on at least one side with an inorganic material, wherein as at least partially permeable carrier preferably an organic material is used, which is preferably configured as a non-woven fabric, wherein the organic material is preferably a polymer and more preferably one or more polymers selected from polyethylene terephthalate, polyolefin or polyetherimide, wherein the organic material is coated with an inorganic, ion-conducting material, which is preferably in a Temperature range of -40 ° C to 200 ° C ion-conducting, and wherein the inorganic, ion-conducting material preferably at least one compound selected from the group of oxides, phosphates, silicates, titanates, sulphates, aluminosilicates with at least one the elements comprise zirconium, aluminum, lithium and more preferably zirconium oxide, and wherein the inorganic material preferably has particles with a largest diameter below 100 nm; or b. A separator comprising a polyethylene terephthalate, a polyolefin, a polyetherimide, a polyamide, a polyacrylonitrile, a polycarbonate, a polysulfone, a polyethersulfone, a polyvinylidene fluoride, a polystyrene or mixtures thereof; or c. A separator comprising an inorganic material. Electrochemical cell according to at least one of the preceding claims, characterized in that the cell comprises an electrolyte. Electrochemical cell according to claim 8, characterized in that the electrolyte is designed as a non-aqueous electrolyte which comprises an organic solvent and lithium ions, or comprises an ionic liquid. Electrochemical cell according to at least one of the preceding claims, characterized in that at least one electrode has an electrode carrier, which is at least partially coated with electrochemically active material. Electrochemical cell according to claim 10, characterized in that the electrode carrier is at least partially designed as a film or network structure or fabric, which preferably comprises a material selected from: a. At least one metal or metal alloy, preferably copper, copper-containing alloy or aluminum, or b. At least metal which is not capable of forming an alloy with lithium, or c. At least one plastic, or d. Mixtures of the materials from a to c. Electrochemical cell according to at least one of the preceding claims, characterized in that the negative electrode contains at least partially elemental lithium or a lithium alloy. A process for producing an electrochemical cell according to any one of the preceding claims, comprising the following steps: • Provide a positive electrode Providing a negative electrode which at least partially comprises metallic lithium At least partial, preferably complete, negative electrode coatings • Provision of a separator • soaking the separator with electrolyte • Assembling of the provided positive electrode with the separator and the negative electrode corresponding to the layer of negative electrode / separator / positive electrode or vice versa. Use of the electrochemical cell according to one of the preceding claims for supplying energy to a consumer. Use according to claim 14 in mobile information devices, tools, electrically powered automobiles or hybrid-powered automobiles.