DE102011102628A1 - Electrochemical cell - Google Patents

Abstract

Electrochemical cell comprising at least one negative electrode, at least one positive electrode and at least one electrolyte, the at least one negative electrode essentially having at least one carbon-containing electrochemical active material which is capable of a “solid electrolyte interface”, that is to say an SEI layer on at least To form parts of the surface of the electrode, the electrochemical cell has at least one stabilizing additive which is capable of stabilizing the SEI layer, at least one protective device being provided in the electrochemical cell, which has the at least one stabilizing additive and preferably configured as a storage container The at least one stabilizing additive is at least partially released from the at least one protective device if at least one predetermined parameter has been reached or exceeded with regard to the SEI layer which is undercut.

Description

The present invention relates to an electrochemical cell, wherein the electrochemical cell has at least one stabilizing additive. which is capable of stabilizing the SEI layer of the solid electrolyte interface (SEI). If necessary, this stabilizing additive is released from a protective device, in particular designed as a storage container. 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 the cells used, but especially those for the propulsion of automobiles, have to meet the 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 ,

The longevity of electrochemical cells is often dependent on the aging of the electrodes. In the aging process, the electrochemical cells lose capacity and performance. This process takes place to a greater or lesser extent in most common electrochemical cells, depending on the circumstances of use (temperature, storage conditions, state of charge, etc.), but also the quality and processing of the materials during the electrochemical cell manufacturing process. For example, high-quality processing of pure materials can lead to long-lasting electrochemical cells that age only slightly over a longer period of time, thus losing less capacity and performance.

However, such measures are often not sufficient to obtain a long-lived electrochemical cell, since chemical reactions take place inside the cell during the operation of a cell, which are partly irreversible, and which can lead to the capacity loss of the electrochemical cell.

An example of such a chemical reaction is the formation of the so-called SEI layer. The solid electrolyte interface (SEI) layer is formed at the interface between the active material of the cathode and / or the anode and the nonaqueous electrolyte during the first charging and discharging cycles, and consists essentially of reaction products of electrolyte and active material , Such reaction products may be, for example, Li ₂ O, LiF, polymeric compounds or (semi) carbonates such as Li ₂ CO ₃ . The initial formation of the SEI layer results in an initial irreversible capacity loss of the electrochemical cell.

Especially in those electrochemical cells in which the electrochemical active material of the negative electrode has substantially carbonaceous materials, the formation of a stable SEI layer on the surface of the electrochemical active material is of vital importance for the longevity of the cell. Some of the aforementioned reaction products, such as the (semi) carbonates, are metastable compounds which, under certain conditions (eg, heat), can be degraded to more stable products, such as LiF. This can lead to the formation of cracks within the SEI layer, as a result of which electrolyte can re-penetrate into the active material and further decompose it, which can lead to a further irreversible loss of capacity of the cell; the SEI layer is growing.

Overloading the cell can lead to the opposite process, namely the decomposition of the SEI layer. In both cases, the growth and decomposition of the SEI layer, the cell may experience a loss of capacity; the cell is aging.

However, the SEI layer plays not only a role in the aging of the cell but also in its safety by making lithium dendrite growth more difficult, if not impossible. For example, cracking within the SEI layer can cause lithium dendrites to grow through the cracks or pores, which can lead to cell shorting.

Therefore, a considerable effort is made to obtain a stable SEI layer as possible. In the publication US 2009/0106970 A For example, a six-step method for producing a lithium-ion battery having an SEI layer is described.

The aim of the present invention is therefore to provide a simple method for producing an electrochemical cell, which is particularly durable.

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.

The underlying object is achieved by an electrochemical cell comprising at least one negative electrode, at least one positive electrode and at least one electrolyte, wherein the at least one negative electrode substantially comprises at least one carbon-containing electrochemical active material which is capable of producing a "solid electrolyte interface". Thus, to form an SEI layer on at least parts of the surface of the electrode, wherein the electrochemical cell has at least one stabilizing additive which is capable of stabilizing the SEI layer, wherein in the electrochemical cell at least one protective device is provided which at least has a stabilizing additive and is preferably designed as a storage container, wherein the at least one stabilizing additive is at least partially released from the at least one protective device, if at least with regard to the SEI layer s reaches a predetermined parameter or exceeded or fallen short of.

An advantage of the electrochemical cell according to the invention is that the use of at least one protective device, which can interact with the SEI layer at least one stabilizing additive only when needed, and not before, for example, by unwanted chemical and / or physical processes during operation electrochemical cell is destroyed, and thus is not available or not in sufficient quantity when needed.

"Substantially" means that at least up to 50%, at least up to 75%, at least up to 90%, at least up to 99%, preferably up to 100% of the electrochemical active material is carbonaceous.

In a preferred embodiment, an electrochemical cell has at least one protective device which has a first shape and a second shape, wherein the at least one protective device transitions from the first to the second shape if, with regard to the SEI layer, at least one predetermined parameter, in particular a temperature, pressure, pH, content of a chemical compound, in particular HF, H ₂ O, CO ₂ , capacity loss of the cell or voltage or combinations thereof, is reached or exceeded or undershot, and wherein the protective device in the second form releases said stabilizing additive.

In a preferred embodiment, an electrochemical cell has at least one protective device which has at least one polymeric material.

In a preferred embodiment, an electrochemical cell has at least one protective device, which is designed as a storage container for the at least one stabilizing additive.

In a preferred embodiment, an electrochemical cell comprises at least one stabilizing additive selected from phenylene carbonate, vinylidene carbonate fluorine-containing or non-fluorine-containing lithium organoborates, lithium difluoro (oxalato) borate (LIDFOB) or lithium bis (oxalato) borate (LiBOB) and fluorine-containing or non-fluorine-containing lithium organophosphates, lithium tetrafluoro (oxalato) phosphate (LiTFOP), lithium tris (oxalato) phosphate (LiTOP), or kinetic and / or thermodynamically stable electrically insulating and / or ion-conducting compounds, kinetic and / or thermodynamically stable Lithium salts, inorganic lithium salts, LiF, LiOH, Li ₂ CO ₃ and Li ₂ O or mixtures thereof

In a preferred embodiment, an electrochemical cell has at least one negative electrode comprising at least one carbonaceous electrochemical active material selected from amorphous graphite, crystalline graphite, carbonaceous materials or mixtures thereof.

In a preferred embodiment, an electrochemical cell has at least one positive electrode which at least partially comprises at least one electrochemical active material selected from: 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 at least one spinel-type lithium metal oxide or lithium metal mixed oxide, wherein the metal is selected from cobalt, manganese or nickel; or at least one lithium metal oxide or lithium metal mixed oxide in a type different from spinel type, wherein the metal is selected from cobalt, manganese or nickel; or mixtures thereof.

SEI layer

An SEI layer according to the present invention is preferably formed during the first charge and discharge cycles at least partially on the surface of the electrochemical active material, in particular the electrochemical active material of the negative electrode, which preferably comprises substantially carbonaceous electrochemically active material.

The formation of the SEI layer can by reaction of a lithium ion-containing electrolyte with the surface of the active material. However, it is also possible for the formation of the SEI layer to take place by the reaction of an additive which influences SEI layer formation, such as LiBOB.

Preferably, up to 40%, preferably up to 70%, further preferably up to 100% of the surface area of the electrochemical active material, an SEI layer is formed.

Preferably, the SEI layer has an average thickness of greater than 0 nm up to 20 nm, preferably up to 30 nm, preferably up to 40 nm, preferably up to 50 nm, more preferably up to 60 nm.

In a preferred embodiment, the SEI layer has an average thickness of 30 nm and more and 50 nm and less.

Preferably, the SEI layer has electrically insulating and lithium ion conducting properties.

Preferably, the SEI layer at least partially comprises compounds of the following group: inorganic lithium salts, in particular LiF, LiOH, Li ₂ O, (semi) carbonates, in particular Li ₂ CO ₃ , ROCO ₂ Li (where R = alkyl, olefin, Alkenyl, or aromatic substituents) and (CH ₂ OCO ₂ Li) ₂ , polymeric compounds such as polyolefins, or mixtures thereof.

The term "stable" SEI layer is to be understood as meaning that the average volume change, in particular the average thickness of the SEI layer, does not change or does not change significantly as the number of charging and discharging cycles increases, for example becomes thicker or thinner to the average thickness during the first charge and discharge cycles. Furthermore, a "stable" SEI layer preferably has no cracks or pores which cause the surface of the active material to be exposed to the electrolyte. Preferably, a stable SEI layer has substantially kinetically and / or thermodynamically stable compounds, preferably LiF, LoOH, Li ₂ CO ₃ and Li ₂ O or mixtures thereof.

For example, one possible measurable parameter for a stable SEI layer may be a constant capacity of the line.

The term "unstable" SEI layer is to be understood as meaning that the average volume change, in particular the average thickness of the SEI layer, changes substantially as the number of charge and discharge cycles increases, for example has become thicker or thinner compared to the average Volume, in particular the average thickness during the first charge and discharge cycles. When the electrochemical cell is overcharged, for example, the SEI layer is decomposed. Furthermore, an unstable SEI layer may have cracks or pores which cause the surface of the active material to be exposed to the electrolyte. An unstable SEI layer has at least partially metastable compounds, such as ROCO ₂ Li or (CH ₂ OCO ₂ Li) ₂ , which decompose to more stable compounds under certain conditions, such as elevated temperatures, which can cause the above-mentioned cracks or pores , Furthermore, an unstable SEI layer does not resist, or does not sufficiently withstand, the ingrowth of lithium dendrites.

The term "volume change" is understood to mean the change in the extent of the SEI layer in all degrees of freedom.

Depending on the embodiment, the "instability" or "instability" of the SEI layer is defined by at least one predetermined parameter within the electrochemical cell which is reached or exceeded or undershot with respect to the SEI layer. Such a predetermined parameter may preferably be selected from: specific temperature, specific temperature range, specific pressure, specific pressure range, specific pH, range of pH, amount of volume change of the SEI layer, content of particular chemical compound (s), For example, HF, H ₂ O, CO ₂ , certain capacity loss of the cell, certain voltage, voltage range or combinations thereof.

For example, one possible measurable parameter for an unstable SEI layer may be an irreversible capacity loss of the cell.

Stabilizing additive

For the purposes of the present invention, the term "stabilizing additive" is to be understood essentially as meaning all additives known to the person skilled in the art which are capable of stabilizing the SEI layer and / or of being capable of forming a stable SEI layer. According to the prior art, such stabilizing additives are added to the electrolyte before or during the production of the electrochemical cell. These additives are already present when the SEI layer is formed during the first charging and discharging cycles.

In one embodiment, the at least one stabilizing additive is preferably selected from phenylene carbonate, vinylidene carbonate, fluorine-containing or non-fluorine-containing lithium organoborates, for example lithium difluoro (oxalato) borate (LiDFOB) or lithium bis (oxalato) borate (LiBOB) and fluorine-containing or non-fluorine-containing lithium organophosphates, for example lithium tetrafluoro (oxalato) phosphate ( LiTFOP) or lithium tris (oxalato) phosphate (LiTOP), or mixtures thereof.

In a preferred embodiment, the at least one stabilizing additive is selected from kinetic and / or thermodynamically stable electrically insulating and / or ion-conducting compounds, preferably kinetic and / or thermodynamically stable lithium salts, preferably inorganic lithium salts, preferably LiF, LiOH, Li ₂ CO ₃ and Li ₂ O or mixtures thereof.

The term "stabilize SEI layer" is to be understood that the at least one stabilizing additive interacts with the SEI layer, and thereby the SEI layer is at least partially, preferably completely stabilized, in particular restored to its original state.

In a preferred embodiment, the stabilization, in particular the recovery of the SEI layer, preferably takes place by incorporation and / or addition of at least one stabilizing additive into defect sites of the SEI layer. The at least one stabilizing additive preferably has electrically insulating and / or ion-conducting, in particular lithium-ion-conducting properties. Preferably, the at least one stabilizing additive is similar, preferably identical to at least one compound occurring in the SEI layer, preferably similar or identical to at least one thermodynamically and / or kinetically stable compound occurring in the SEI layer, preferably designed as at least an inorganic lithium salt, in particular LiF, Li ₂ CO ₃ or Li ₂ O.

The advantage of using at least one stabilizing additive, which is essentially present in the electrochemical cell, or formed therein, is that such additives only a small, preferably no disturbing influence on the running in the electrochemical cell chemical and physical processes.

guard

The term "protective device" in the sense of the present invention is to be understood as meaning at least one device which has the at least one stabilizing additive so that an interaction of the at least one stabilizing additive with the SEI layer is minimized, preferably prevented, until at least as long the SEI layer is or becomes unstable.

Particularly advantageous in one embodiment, the design of the protective device as a storage for the at least one stabilizing additive.

The advantage of this at least one protective device is that the at least one stabilizing additive can interact with the SEI layer only when necessary, and is not already destroyed, for example, by undesired chemical and / or physical processes during the operation of the electrochemical cell, and thus if necessary, not available or not available in sufficient quantity. A need for an interaction between the at least one stabilizing additive and the SEI layer is preferably present when the SEI layer is or becomes unstable, preferably when a parameter predetermined with respect to the SEI layer is reached or exceeded or undershot. Such a predetermined parameter in the sense of the present invention can preferably be selected from: specific temperature, specific temperature range, specific pressure, specific pressure range, specific pH, pH range, specific amount of volume change of the SEI layer, content of certain chemical Compound (s), for example, HF, H ₂ O, CO ₂ , specific capacity loss of the cell, particular voltage, voltage range, or combinations thereof.

Preferably, the at least one protective device has a first shape or a second shape, wherein the first shape differs from the second shape in that the first shape minimizes, preferably prevents, the interaction of the at least one stabilizing additive with the SEI layer the second form allows the interaction of the at least one stabilizing additive with the SEI layer, preferably reinforced.

Preferably, the at least one protection device is capable of changing from the first shape to the second shape under certain conditions, such as increasing the pH of the electrolyte solution, or elevated temperatures, or in the presence of certain compounds, such as HF or water.

A similar mechanism is known, for example, from pharmaceutical research. In this case, micelle capsules are formed in the interior of which a pharmaceutical active substance is located. The so-called "loaded" micelle capsules become the targeted "delivery" of pharmaceutical Active substance used to target cells. For example, it is understood that the target cells have structures, such as receptors, to which the micelle capsules "dock" and thereby release their contents. The concepts known from pharmaceutical practice to delay an active substance (comparable to the stabilizing additive which is relevant here) and / or to release it in response to certain physiological parameters can in principle be transferred to electrochemical cells.

In one embodiment, the at least one protection device at least partially comprises at least one material which is capable of participating in the formation of the first shape and / or the second shape of the at least one protection device.

By "material" is meant at least one compound or at least one compound mixture. The material may for example consist of one or more polymers.

The material must be chosen so that it will not be damaged during normal operation of the electrochemical cell, so that the stabilizing additive is released.

Preferably, the at least one material is at least partially capable of chemically and / or physically reacting under certain conditions, and thereby preferably involved in the first-to-second transformation process of the protection device and / or initiating the conversion process and / or the conversion process support.

Preferably, the at least one protective device at least partially comprises at least one polymeric material.

In one embodiment, the protective device at least partially comprises a material which melts from a certain temperature and / or changes its phase state, preferably at least one polymeric compound.

In one embodiment, the at least one protective device at least partially comprises at least one material which is capable of at least one chemical reaction. Preferably, the material is capable of reacting with at least one "undesirable" compound that is formed when the SEI layer becomes unstable or participates in the instability of the SEI layer. Such "undesired" compounds are, for example, acids, in particular protic acids, preferably HF, CO ₂ , H ₂ O or mixtures thereof.

The advantage of using materials which are capable of reacting with at least one "undesirable" compound, which arises when the SEI layer becomes unstable or is involved in the instability of the SEI layer, is that said compounds are at least partially characterized by a chemical Reaction "consumed", in particular degraded, and so reduces their harmful influence on the electrochemical cell is preferably prevented. Furthermore, it is advantageous that the at least one stabilizing additive is released in particular only in the presence of at least one corresponding "undesired" compound.

In a preferred embodiment, the at least one protective device at least partially comprises a material which has at least one ester bond R ₁ -C (= O) -OR ₂ . In this case, R ₁ and R _{2 may be} identical or different. In this case, the compound is preferably capable of entering into a chemical reaction with water and / or acids, in particular protic acids HR, which are preferably present at least partially in dissociated form, in particular as H ⁺ and R ^- , in particular an ester cleavage, in particular with formation of the corresponding alcohol ROH and the corresponding acid RCO ₂ H. Preferably, the protective device comprises at least partially polyester.

In a preferred embodiment, the at least one protective device at least partially comprises a material which has at least one ether bond (R ₁ -OR ₂ , R ₁ and R ₂ may be identical or different) which is capable of reacting with water and / or acids, in particular Proton _acids HR _acid , which are preferably present at least partially in dissociated form, in particular as H ⁺ and R _acid , to enter into a chemical reaction, in particular an ether cleavage, in particular with formation of the corresponding alcohol R _1/2 OH ^and R _1/2 -R _acid . Preferably, the protective device comprises at least partially polyether.

In a preferred embodiment, the at least one protective device at least partially comprises a material which has at least one disulfide bond R ₁ -SSR ₂ . R ₁ and R _{2 may be} identical or different. In this case, the compound is preferably capable of undergoing a chemical reaction, in particular under reductive conditions, in particular with cleavage of the disulfide bond, for example with thiol formation R _1/2 -SH.

In a preferred embodiment, the at least one protective device at least partially comprises a material which is at least partially capable of binding CO ₂ . This can preferably achieved by the presence of epoxide groups or amine groups.

In one embodiment, the at least one protective device is at least partially designed as a sheath.

In a further embodiment, the at least one protective device is at least partially formed as a release film.

The at least one protective device having the at least one stabilizing additive is preferably arranged inside the electrochemical cell.

In one embodiment, the at least one protective device having the at least one stabilizing additive is at least partially disposed in the electrolyte. This is preferably done by adding the at least one protective device comprising the at least one stabilizing additive to the electrolyte, which is subsequently introduced into the electrochemical cell. This has the advantage that the at least one protective device comprising the at least one stabilizing additive is distributed substantially homogeneously within the electrochemical cell, preferably within the electrochemical active material of the negative electrode. Preferably, the at least one protective device having the at least one stabilizing additive has a maximum spread of a few micrometers, preferably of a few nanometers, preferably less than 100 μm, more preferably less than 75 μm, further preferably less than 50 μm, further preferably less than 10 μm further preferably less than 500 nm, more preferably less than 250 nm, further preferably less than 100 nm, more preferably less than 50 nm, such that the at least one protective device comprising the at least one stabilizing additive preferably does not close the pores of the separator or can clog. As a result, the maximum intake of a protective device is limited to stabilizing additive.

In a further embodiment, the at least one protective device having the at least one stabilizing additive is arranged at least partially on at least one component, preferably the at least one sheath and / or the at least one negative electrode, of the electrochemical cell. This has the advantage that the dimensioning and thus the maximum intake quantity of stabilizing additive of the at least one protective device can be selected substantially freely.

In a further embodiment, at least one first protective device having at least one stabilizing additive is arranged at least partially in the electrolyte and / or at least one second protective device has at least one stabilizing additive at least partially on at least one component, preferably the at least one coating and / or the at least one negative Electrode arranged. The at least first protective device may be different from the at least second protective device, or at least have a stabilizing additive which is different from the stabilizing additive in the second protective device. However, the at least first and the at least second protective devices can also be identical or the stabilizing additives present in the protective devices can be identical.

In one embodiment, the at least one protective device having at least one stabilizing additive is at least partially net-like, wherein in the net-like structure at least partially regions are formed which are capable of having the at least one stabilizing additive, preferably by forming cavities. Zeolites or similar matrix structures are particularly preferred as a protective device, furthermore also carbon nanotubes.

In one embodiment, the at least one protective device having at least one stabilizing additive is at least partially connected to the SEI layer by chemical and / or physical interactions, such as electrostatic or covalent or non-covalent interactions, in particular so connected that the at least one protective device in the Essentially non-destructive from the surface of the SEI layer is separable.

This has the advantage that thereby the mechanical stability of the SEI layer can be improved by the at least one protective device being arranged at least partially on the surface exposed to the electrolyte, the SEI layer, such that a volume change of the SEI layer can be reduced, preferably minimized, preferably prevented, and further, the at least partially occurring cracks or pores within the SEI layer by the at least one stabilizing additive which is in spatial proximity to the formed cracks or pores, at least partially closed even before the electrolyte can react with the surface of the electrochemical active material exposed to cracking.

Through the functionalization of the surface SEI layer exposed to the electrolyte, at least in part chemical and / or physical interactions of this surface with the at least one protective device comprising at least one stabilizing additive can be formed.

By "functionalization" it is meant herein that chemical and / or physical measures are taken with respect to the surface of the SEI layer which have the goal of being at least partially capable of chemical and / or physical interaction on the surface of the SEI layer Atoms, molecules, groups, ions or mixtures thereof, form. This can be done, for example, by using ionizing radiation, heat, ozone, deposition processes, acids or bases, oxidative or reductive processes, or mixtures thereof. The material from which the protective device is at least partially formed, should be selected according to the applied functionalization in order to obtain a corresponding chemical and / or physical interaction between the surface of the SEI layer and the at least one protective device, or vice versa, one must Material of the protective device appropriate functionalization method can be selected.

In one embodiment, this is preferably achieved by the following steps: providing an electrochemical cell and generating a stable SEI layer on the electrochemical active material of the negative electrode, for example by methods known in the art. This is followed by a step of disassembling the electrochemical cell to obtain the stable SEI layer located on the electrochemical active material of the negative electrode. Subsequently, the formation of a functionalization layer is performed by applying a functionalization step to the surface of the SEI layer which does not face the electrochemical active material of the negative electrode. Subsequent application of the protective device comprising the at least one stabilizing additive on the functionalized surface of the SEI layer.

In one embodiment, the at least one protective device is designed as a storage container for at least one stabilizing additive. Preferably, the protective device configured as a storage container at least partially has an enclosure which is capable of at least partially enclosing the at least one stabilizing additive such that the at least one stabilizing additive is capable of release from the at least one protective device, at least in part. to interact with the SEI layer. The release of the at least one stabilizing additive is effected by at least partial destruction of the protective device. The at least partial destruction of the envelope can in turn be carried out by performing mechanical work, such as tensile work and / or by chemical processes, such as degradation reactions, such as ester cleavage, disulfide cleavage or ether cleavage, and / or by physical processes, such as melting the cladding.

In one embodiment, the at least one protection device is in contact, preferably in thermal and / or electrical contact with at least one battery monitoring device, preferably a battery management system (BMS), wherein the battery monitoring device is capable of detecting an irreversible capacity loss of the electrochemical cell. Preferably, the contact, preferably the thermal and / or electrical contact of the at least one protection device with the at least one battery monitoring device via a transmission device, such as a wire or a wire mesh. If the electrochemical cell according to the invention undergoes an irreversible loss of capacity during operation, this irreversible capacity loss of the electrochemical cell is detected by the BMS, which can be in contact with another battery monitoring system, and a signal, preferably a thermal and / or electrical signal, preferably by means of the transmission device , which is preferably designed as a wire or wire mesh, sent to the at least one protection device. In response to the signal, which is preferably a thermal and / or electrical signal, the at least one protection device at least partially releases the at least one stabilizing additive. This is preferably done by heating the at least one protective device, whereby it is at least partially destroyed, preferably by at least partial melting.

electrolyte

In one embodiment, the electrochemical cell has at least one electrolyte.

The electrolyte used can be a nonaqueous electrolyte consisting of at least one organic solvent and at least one alkali metal-containing, preferably lithium ion-containing, inorganic or organic salt.

In principle, all solvents known to the person skilled in the art may serve as organic solvents, which are used in electrolytes of electrochemical cells.

Preferably, the organic solvent is selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acrylate (MA), methyl butyrate (MB ), Ethyl acetate (EA), 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,3-dioxane, sulfulane, ethylmethylsulfone (EMS), tetramethylenesulfone (TMS), butylsulfone (BS), ethylvinylsulfone (EVS), 1-fluoro-2- (methylsulfonyl) benzene (FS), acetonitrile or phosphoric acid esters, or mixtures of these solvents.

Preferably, the alkali ion-containing, preferably 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 ] ^- , [B (C ₆ H ₅ ) ₄ ] ^- , Cl ^- , Br ^- , AlCl ₄ ^- , CF ₃ SO ₃ ^- , C ₄ F ₉ SO ₃ ^- , [(CF ₃ SO ₂ ) ₃ C] ^- , [(CF ₃ SO ₂ ) ₂ N] ^- , [(C ₂ F ₅ SO ₂ ) N] ^- , [(CN) ₂ N] ^- , ClO ₄ ^- , SiF ₆ ^- , or mixtures thereof.

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.

Ionic liquids are ionic compounds which are in a liquid state at room temperature. Ionic liquids consist of anions and cations, with the size ratio between cations and anions chosen so that they do not dispose at room temperature in a crystal lattice, whereby a liquid at room temperature salt can be obtained, which is referred to as ionic liquid. The ionic liquid typically has "large" organic cations, such as the ethylmethylimidazolium cation, and relatively "small" anions, such as the tetrafluoroborate anion. By suitable combination of cations and anions, the properties of the ionic liquid can also be influenced. For example, if a basic anion such as the cyanato anion OCN ^{- is} used, the ionic liquid is also more basic in nature.

Preferably, ionic liquids are used which have cationic imidazole-containing derivatives, in particular the cation ethyl-methyl-imidazolium. Preferred anions can be selected from the group AlCl ₄ , Al ₂ Cl ₇ , F, F × HF, NO ₂ , NO ₃ , BF ₄ , AlF ₄ , PF ₆ , AsF ₆ , SbF ₆ , NbF ₆ , TaF ₆ , WF ₇ , CH ₃ CO ₂ , CF ₃ CO ₂ , C ₃ F ₇ CO ₂ , CH ₃ SO ₃ , CF ₃ SO ₃ , C ₄ F ₉ SO ₃ , (CF ₃ CO) (CF ₃ SO ₃ ) N, CF ₃ SO ₂ ) ₂ N, (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ) N, (C ₂ F ₅ SO ₂ ) ₂ N, (CF ₃ SO ₂ ) ₃ C, (CN) ₂ N, (CN) ₃ C, CF ₃ BF ₃ , C ₂ F ₅ BF ₃ , C ₃ F ₇ BF ₃ , C ₄ F ₉ BF ₃ or mixtures thereof.

Furthermore, the electrolyte may have 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.

Furthermore, the electrolyte preferably contains additives preferably phenylene carbonate, fluorine-containing or non-fluorine-containing lithium organoborates, for example lithium difluoro (oxalato) borate (LiDFOB) or lithium bis (oxalato) borate (LiBOB) and fluorine-containing or non-fluorine-containing lithium organophosphates, for example lithium tetrafluoro (oxalato) phosphate (LiTFOP) or lithium tris (oxalato) phosphate (LiTOP), which may affect the formation of the SEI layer on the electrodes.

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.

In a preferred embodiment, the electrochemical cell has at least one positive electrode, at least one negative electrode and at least one separator which separates the positive from the negative electrode and which are at least partially surrounded by at least one sheath.

electrodes

The term "negative electrode" means that the electrode emits electrons when connected to a consumer, such as an electric motor. Thus, the negative electrode, according to this convention, the anode, Preferably, the negative electrode has at least one electrochemical active material, which is suitable for the storage and / or outsourcing of redox components, in particular of lithium ions.

In one embodiment, the electrochemical active material of the negative electrode is selected from amorphous graphite, crystalline graphite, carbonaceous materials, or mixtures thereof.

Preferably, in addition to the electrochemical active material, the negative electrode also has at least one further additive, preferably an additive for increasing the conductivity, for example based on carbon, for example carbon black, and / or a redox-active additive which, if the electrochemical cell is overcharged, destroys the electrochemical active material reduced, preferably minimized, preferably prevented.

Preferably, the negative electrode has a metallic substrate. Preferably, this metallic substrate is at least partially coated with electrochemical active material.

In one embodiment, the negative electrode comprises a binder capable of enhancing adhesion between electrochemical active material and a metallic substrate. 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 ^®.

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.

The positive electrode of the electrochemical cell preferably has at least one electrochemical active material which is suitable for incorporation and / or removal of redox components, in particular of lithium ions.

In one embodiment, the electrochemical active material of the positive electrode is selected from at least one oxide, preferably a mixed oxide, which has one or more elements selected from nickel, manganese, cobalt, aluminum, phosphorus, iron or titanium.

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

The at least one 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 parent 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 LiNiCo0 _second , which can not be in the spinel type or in the spinel type.

Preferably, in addition to the electrochemical active material, the positive electrode also has at least one further additive, preferably an additive for increasing the conductivity, for example based on carbon, for example carbon black, and / or a redox-active additive which, if the electrochemical cell is overcharged, destroys the electrochemical active material reduced, preferably minimized, preferably prevented.

Preferably, the positive electrode comprises a binder capable of enhancing adhesion between electrochemical active material and a metallic substrate. 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 ^®.

Preferably, the positive electrode has a metallic substrate. Preferably, this metallic substrate is at least partially coated with electrochemical active material.

The term "metallic substrate" preferably refers to that component of an electrochemical cell known as "electrode carrier" and "collector". In the present case, the metallic substrate is suitable for applying electrochemical active composition and is essentially of a metallic nature, preferably of a completely metallic nature.

Preferably, at least one electrode has at least partially a metallic substrate. Preferably, this metallic substrate is at least partially designed as a film or as a network structure or as a fabric, preferably comprising a metal.

In one embodiment, a metallic substrate comprises copper or a copper-containing alloy. In a further embodiment, a metallic substrate comprises aluminum. In one embodiment, the metallic substrate can be configured as a film, mesh structure or fabric, which preferably comprises at least partially plastics.

Preferably, up to 30%, preferably up to 50%, preferably up to 70%, preferably up to 100%, of the total surface of a metallic substrate has at least one layer which has at least one electrochemical active material which is suitable for incorporation and / or removal of lithium ions suitable is.

separator

In one embodiment, 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 more 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, sulfates, aluminosilicates with at least one of zirconium, aluminum, lithium and more preferably zirconium oxide.

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.

The invention likewise provides a method for operating an electrochemical cell, the electrochemical cell having at least one stabilizing additive which is at least partially released from the at least one protective device when the SEI layer is or becomes unstable, in particular as soon as a predetermined parameter is reached or exceeded or is fallen short of.

• • Bereitstellen mindestens einer positiven Elektrode
• • Bereitstellen mindestens einer negativen Elektrode, wobei die mindestens eine negative Elektrode im Wesentlichen mindestens ein kohlenstoffhaltiges elektrochemisches Aktivmaterial aufweist, welches befähigt ist, eine SEI-Schicht auf zumindest Teilen der Oberfläche auszubilden
• • Bereitstellen mindestens eines stabilisierenden Zusatzes welcher befähigt ist, eine SEI-Schicht zu stabilsieren
• • Bereitstellen mindestens einer Schutzeinrichtung, welche befähigt ist den mindestens einen stabilisierenden Zusatz zumindest teilweise aufzunehmen

wobei der mindestens eine stabilisierende Zusatz aus der mindestens einen Schutzeinrichtung freigesetzt wird, wenn im Hinblick auf die SEI-Schicht mindestens ein vorbestimmter Parameter erreicht oder überschritten oderThe present invention also relates to a process for the production of the electrochemical cell according to the invention, which comprises the following steps:

• • Provide at least one positive electrode
• Providing at least one negative electrode, wherein the at least one negative electrode substantially comprises at least one carbon-containing electrochemical active material capable of forming an SEI layer on at least parts of the surface
• Providing at least one stabilizing additive capable of stabilizing an SEI layer
• Provision of at least one protective device which is capable of at least partially accommodating the at least one stabilizing additive

wherein the at least one stabilizing additive is released from the at least one protective device when, with regard to the SEI layer, at least one predetermined parameter is reached or exceeded or

The electrochemical cell of the present invention can be used to power mobile information equipment, tools, electric powered automobiles, and hybrid drive automobiles.

1 shows schematically the structure of an embodiment of an electrochemical cell according to the invention

2 schematically shows the structure and arrangement of an embodiment of a negative electrode with SEI layer and protective device as part of the electrochemical cell according to the invention at the time before and after the unstable become the SEI layer

3 schematically shows the structure and arrangement of an embodiment of a protective device and a negative electrode with SEI layer as part of the electrochemical cell according to the invention at the time before and after the unstable SEI layer

1 shows an electrochemical cell according to the invention 100 consisting of a positive electrode with active material 110 a separator 120 , a serving 160 , a negative electrode with active material 150 , one, on the surface of the negative electrode with active material 150 located SEI layer 170 and a stabilizing additive or a stabilizing additive mixture 180 , which of a protective device 190 which acts as a separation between SEI layer 170 and stabilizing additive 180 is configured, between parts of the serving 160 is included. Furthermore, the electrochemical cell 100 a battery management system 131 on which with the positive electrode 110 and the negative electrode 150 and a battery monitoring system 132 in contact. Via a transmission device 140 is the battery monitoring system 132 with the protective device 190 connected. Parts of the transmission device 140 stand with the protective device 190 in operative relation. This offers the advantage that when measuring an irreversible capacity loss of the electrochemical cell 100 (which can be regarded as a visible to the outside sign that the SEI layer 107 is unstable or will) by the battery management system 131 to the battery monitoring system 132 which is capable of a signal via the transmission device 140 to the protective device 190 to convey. The signal is preferably an electrical signal which is transmitted to the transmission device 140 is transmitted. In this case, the transmission device 140 at least in the area in which the transmission device 140 in operative relation with the protective device 190 is formed as an electrical resistance, which converts electrical energy, ie the electrical signal, into heat energy, which due to the operative relationship between the transmission device 140 and protective device 190 , this heat energy to the protective device 190 at least partially releases, whereby the stabilizing additive or the stabilizing additive mixture 180 from the protective device 190 is released. In this case, the protective device 190 is at least partially destroyed, for example, is destroyed by melting. Thus, the stabilizing additive or the stabilizing additive mixture 180 with the SEI layer 170 interact, and the SEI layer 170 preferably stabilize. The protective device 190 has at least one polymer having a melting temperature higher than the temperature during normal operation of the electrochemical cell 100 prevails in the same, but less than the temperature, of the resistance range of the transmission device 140 is produced.

2 shows a negative electrode of an electrochemical cell according to the invention 201 and after 202 the release of the stabilizing additive or the stabilizing additive mixture 250 from parts of the protective device 231 . 232 (Parts of the protective device before the release of the stabilizing additive 250 : 231 ; Parts of the protective device after the release of the stabilizing additive 250 : 232 ). The negative electrode 201 . 202 has an electrochemical active material 210 at least partially with an SEI layer 220 is coated. Die, the electrochemical active material 210 turned away side of the SEI layer 220 has been functionalized (not in 2 pictured), whereby parts of the protective device 231 . 232 through connections 240 essentially non-destructive of the SEI layer 220 are removable. These connections 240 For example, they may be covalent bonds, electrostatic bonds or other strong interactions or bonds. Furthermore, parts of the protective device 231 . 232 containing the stabilizing additive or the stabilizing additive mixture 250 included, also via connections 260 connected together so that the parts of the protective device 231 . 232 essentially non-destructively separable from each other. Furthermore, it is possible that parts of the protective device 231 . 232 vulnerability 271 . 272 have, on which the parts of the protective device 231 . 232 preferably destroyed. This is preferably done when the SEI layer 220 becomes unstable, such as with a volume change of the SEI layer 220 accompanied. After now parts of the protective device 231 . 232 with both the SEI layer 220 about essentially non-destructively releasable compounds 240 as well as with each other about essentially non-destructive releasable compounds 260 connected to each other, are the previously substantially intact parts of the protective device 231 containing the stabilizing additive or the stabilizing additive mixture 250 included, so damaged 232 in that the stabilizing additive or the stabilizing additive mixture 250 is released, and the SEI layer 220 stabilize and preferably can also repair by moving into parts of the SEI layer 220 intercalates. Damage to parts of the protective device 232 preferably finds weak spots 270 instead of.

3 shows a negative electrode of an electrochemical cell according to the invention 301 and after 302 the release of the stabilizing additive or the stabilizing additive mixture 340 from protective devices 331 . 332 , The negative electrode 301 . 302 consists of electrochemical active material 310 which at least partially with an SEI layer 320 is coated. The protective devices 331 . 332 are preferably in the electrolyte solution 350 , Now if the SEI layer 320 It can become unstable to crack or pore formation within the SEI layer 320 come, causing the electrochemical active material 310 the electrolyte solution 350 at least partially exposed. Now if the SEI layer 320 becomes unstable becomes the stabilizing additive or the stabilizing additive mixture 340 released from the protective devices 332 , and in the SEI layer 320 stored, whereby this is stabilized again.

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

• US 2009/0106970 A [0009]
• EP 1017476 [0109]
• DE 19501271 A1 [0110]
• EP 1852926 [0116]
• EP 1783852 [0117]

Claims (9)

Electrochemical cell comprising at least one negative electrode, at least one positive electrode and at least one electrolyte, wherein the at least one negative electrode substantially comprises at least one carbon-containing electrochemical active material which is capable of a "solid electrolyte interface", ie an SEI layer on at least Forming parts of the surface of the electrode, characterized in that the electrochemical cell has at least one stabilizing additive which is capable of stabilizing the SEI layer, wherein in the electrochemical cell at least one protective device is provided which has the at least one stabilizing additive and is preferably configured as a storage container wherein the at least one stabilizing additive is at least partially released from the at least one protective device, if with regard to the SEI layer at least one predetermined parameter e is reached or exceeded or fallen short of. An electrochemical cell according to claim 1, characterized in that the at least one protection device has a first shape, and a second shape, wherein the at least one protection device merges from the first to the second shape, if with respect to the SEI layer at least one predetermined parameter , in particular a temperature, pressure, pH, content of a chemical compound, in particular HF, H ₂ O, CO ₂ , capacity loss of the cell or voltage or combinations thereof, is reached or exceeded or undershot, and wherein the protective device in the second Release form said stabilizing additive. Electrochemical cell according to at least one of the preceding claims, characterized in that the at least one protective device comprises at least one polymeric material. Electrochemical cell according to at least one of the preceding claims, characterized in that the at least one stabilizing additive is selected from phenylene carbonate, vinylidene carbonate fluorine-containing or non-fluorine-containing lithium organoborates, lithium difluoro (oxalato) borate (LiDFOB) or lithium bis (oxalato) borate ( LiBOB) and fluorine-containing or non-fluorine-containing lithium organophosphates, lithium tetrafluoro (oxalato) phosphate (LiTFOP), lithium tris (oxalato) phosphate (LiTOP), or kinetic and / or thermodynamically stable electrically insulating and / or ion-conducting compounds, kinetic and / or or thermodynamically stable lithium salts, inorganic lithium salts, LiF, LiOH, Li ₂ CO and Li ₂ O or mixtures thereof. Electrochemical cell according to at least one of the preceding claims, characterized in that the negative electrode comprises at least one carbon-containing electrochemical active material which is selected from amorphous graphite, crystalline graphite, carbonaceous materials or mixtures thereof. Electrochemical cell according to at least one of the preceding claims, characterized in that the positive electrode at least partially comprises at least one electrochemical active material which is selected from: • 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 • at least one spinel-type lithium metal oxide or lithium metal mixed oxide, wherein the metal is selected from cobalt, manganese or nickel; or • 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. Method for operating an electrochemical cell according to at least one of the preceding claims, characterized in that the at least one stabilizing additive is at least partially released from the at least one protective device when the SEI layer is or becomes unstable, in particular as soon as a predetermined parameter is reached or exceeded or falls below. Method for operating an electrochemical cell according to at least one of Claims 1 to 6, comprising the following steps: • Provide at least one positive electrode Providing at least one negative electrode, wherein the at least one negative electrode substantially comprises at least one carbon-containing electrochemical active material capable of forming an SEI layer on at least parts of the surface Providing at least one stabilizing additive capable of stabilizing an SEI layer Provision of at least one protective device which is capable of at least partially accommodating the at least one stabilizing additive characterized in that the at least one stabilizing additive is released from the at least one protective device when, with regard to the SEI layer, at least one predetermined parameter is reached or exceeded or undershot. Use of the electrochemical cell according to one of claims 1 to 6 for the energy supply of a consumer, in particular in mobile information devices, tools, electrically driven automobiles or automobiles with hybrid drive.

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