WO2013045567A1

WO2013045567A1 - Electrochemical cell

Info

Publication number: WO2013045567A1
Application number: PCT/EP2012/069115
Authority: WO
Inventors: Martin Winter; Stefano Passerini; Simon LUX; Peter Bieker; Tobias PLACKE; Hinrich-Wilhelm MEYER
Original assignee: Westfälische Wilhelms-Universität Münster
Priority date: 2011-09-30
Filing date: 2012-09-27
Publication date: 2013-04-04
Also published as: DE102011054122A1

Abstract

The invention relates to an electrochemical cell comprising an electrode which reversibly absorbs and emits lithium ions, an electrode which reversibly absorbs and emits anions, and an electrolyte comprising a lithium salt and a solvent, wherein the electrode which reversibly absorbs and emits lithium ions comprises lithium titanate as the electrode material which reversibly absorbs and emits lithium ions.

Description

Electrochemical cell

The invention relates to an electrochemical cell, in particular a secondary

electrochemical cell based on the dual-ion insertion principle.

Secondary electrochemical cells are commonly referred to as rechargeable batteries and are distinguished from primary electrochemical cells by their rechargeability. Lithium-ion technology is currently the leading technology in the field of rechargeable battery storage systems, especially for applications in portable electronics. Lithium-ion batteries include two electrodes separated by a separator. The charge transport is via an electrolyte containing a lithium salt dissolved in a nonaqueous organic solvent. In lithium-ion batteries, lithium ions are reversibly stored or removed from the electrode active materials. When charging a lithium-ion battery Li ⁺ - ions are transported from the cathode to the anode and the discharge process, the Li ⁺ ions change back from the anode to the cathode.

However, common lithium-ion batteries have various disadvantages. Thus, metal oxides of mixtures of nickel and cobalt are often used in lithium-ion batteries as electrode material, whereby the production costs are greatly increased by the use of nickel and especially by cobalt. In addition, the heavy metals nickel and cobalt have a high toxicity. An alternative to conventional lithium-ion batteries form the so-called dual graphite systems, which are based on a storage of lithium in a graphite anode and an incorporation of anions in a graphite cathode. The graphite electrodes are also separated in dual graphite systems by a separator and the charge transport via an electrolyte containing a lithium salt. When charging a dual graphite system, however, the lithium ion from the electrolyte in the

Anodenaktivmaterial and parallel an anion, usually the lithium salt, in the

Cathode active material stored. Therefore, this process is also referred to as dual insertion or dual-ion insertion principle. In the charged state, the electrolyte of the dual graphite system is thus depleted of Li ⁺ and anion, since these are as charge carriers in the two electrode active materials. During discharge, the ions are simultaneously released back to the electrolyte and thus the ion concentration is increased again.

A disadvantage of dual graphite systems, however, is that they use very high lithium salt concentrations. These high concentrations decrease at low levels

Temperatures the conductivity and thus the capacity of the cells. Due to the dual incorporation of Li ⁺ and anion, the function of such a cell is particularly strong on the interaction of the individual components, in particular the electrodes and the

Lithium salt and its concentration dependent. Another disadvantage of dual graphite systems is that they have a high capacity loss during the first cycle.

The present invention was therefore based on the object to provide an electrochemical cell which overcomes at least one of the aforementioned disadvantages of the prior art. In particular, the present invention was based on the object of providing an electrochemical cell which operates within the thermodynamic stability window of organic electrolytes. This object is achieved by an electrochemical cell, in particular a secondary electrochemical cell, comprising a lithium ion reversibly receiving and donating electrode, anions reversibly receiving and donating electrode and a

An electrolyte comprising a lithium salt and a solvent, wherein the lithium ion reversibly receiving and donating electrode comprises lithium titanate as lithium ion reversibly receiving and donating electrode material.

Another object of the invention relates to the use of lithium titanate as lithium ion reversibly receiving and donating electrode material in an electrochemical cell, in particular a secondary electrochemical cell comprising a lithium ions reversibly receiving and donating electrode and anions reversibly receiving and donating electrode.

Further advantageous embodiments of the invention will become apparent from the dependent claims.

Surprisingly, it has been found that an electrochemical cell based on the dual-ion insertion principle, comprising a lithium cation reversibly receiving and donating lithium titanate electrode, at relatively low concentrations of the lithium salt of 1 M, even at low temperatures, a good conductivity and thus have good capacity ,

It is advantageous that the, in particular secondary, electrochemical cell can operate reversibly within the thermodynamic stability window of the organic electrolyte with good capacity. Of great advantage is that, in particular secondary, electrochemical cell high efficiency of the charge / discharge after the first

Cycle and has only a very small capacity loss. In particular, it is further advantageous that the electrochemical cell can provide increased security. It is of particular advantage that the especially secondary electrochemical cell has a good fast charging and in particular discharging capability. In particular, the electrochemical cell has the further advantage of being able to be operated even at low temperatures, for example in a temperature range from -40 ° C. to + 55 ° C. This is particularly advantageous for use in portable electronics. Furthermore, the particular secondary electrochemical cell with lithium titanate electrode has a long service life. In particular, this system is less toxic than nickel and cobalt-containing lithium ion systems and therefore more environmentally friendly. The environmental friendliness of this cell, which manages without cobalt and nickel-containing compounds, is a major advantage over current lithium-ion batteries.

For the purposes of the present invention, the term "lithium titanate" means spinels of the formula Li _x Ti _y 0 ₄ , where 0.8 <x <1.4 and 1.6 <y <2.2. A preferred one

Lithium titanate is Li ^ isO ^.

The electrodes of the electrochemical cell can reversibly absorb and release lithium ions or anions. For the purposes of the present invention, the term "reversibly take up and release" is understood to mean that the active materials of the electrodes can reversibly store and disperse lithium cations or anions, intercalate and deintercalate, or take up and release by compound formation or alloy formation. For the purposes of the present invention, the term reversibly "intercalate and deintercalate" is understood to mean that a graphite or a carbon-based electrode can absorb and release lithium cations or anions. The electrodes are usually composite electrodes, which may contain binders and additives in addition to the materials reversibly receiving and donating or intercalating and deintercalating the respective ions. These electrode materials are mostly on a metal foil or a carbon-based current collector foil, which acts as a current conductor, applied.

In preferred embodiments, the lithium ion reversibly receiving and donating electrode comprises lithium titanate in the range of> 50 wt% to <98 wt%, preferably in the range of> 75 wt% to <95 wt%, preferably in the range from> 80 wt .-% to <95 wt .-%, based on the total weight of the electrode.

Advantageously, cells having a lithium ion reversibly receiving and donating electrode comprising lithium titanate in such a range can have a particularly good rapid charging and discharging capability.

In preferred embodiments, the lithium ion reversibly receiving and donating electrode comprises lithium titanate particles having a size or average

Diameter in the range of> 0.1 nm to <10 μιη, preferably in the range of> 0.5 nm to <5 μιη, more preferably in the range of> 1 nm to <800 nm, most preferably in the range of> 100 nm up to <500 nm.

Typical further constituents of an electrode are, in addition to the lithium ion reversibly receiving and donating electrode or active material additives and binders. The total weight of the lithium titanate electrode therefore includes the lithium ion reversibly receiving and donating electrode material lithium titanate, and further additives and / or binders.

Suitable binders are, for example, polytetrafluoroethylene (PTFE), polyvinylidene difluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene-butadiene elastomer (SBR),

Carboxymethylcelluloses (CMC), in particular sodium carboxymethylcellulose (Na-CMC), or polyvinylidene difluoride (PVDF). Suitable additives are in particular Conductivity additives such as metal particles, for example copper particles, in particular metal particles with a size in the nanometer range, as well as conductive carbon materials, in particular carbon blacks, carbon fibers, graphites, carbon nanotubes or mixtures thereof. Suitable carbon blacks are, for example, the finely divided industrial carbon blacks known by the name carbon black.

The positive electrode, the cathode, the electrochemical cell can reversibly absorb and release anions. In the cells of the invention, the positive electrode preferably comprises one

Compound into which the anion can be stored. In particular, are suitable

Carbon or metal compounds, in particular alkali, alkaline earth or

Transition metal compounds such as oxides, halides, phosphates, chalcogenides such as sulfides and selenides, silicates, aluminates or hydroxides. These compounds, in particular aluminates and hydroxides, are often layered compounds which can incorporate anions between the layers.

Preferably, the anion is reversibly receiving and donating electrode material selected from the group comprising

Carbon, graphite, graphene, or carbon nanotubes,

fluorinated carbons of the formula (CF _x ) _n where x is in the range of 0.01 to 1.24 and n is in the range of 1 to 1000,

Carbon oxides of the formula (CO _y ) _m , which are solid at room temperature and where y is in the range of 0.01 to 1 and m is in the range of 1 to 100,

Sulfides M _z S _y of transition metals M selected from the group comprising Ti, V,

Cr, Mn, Fe, Co, Cd, Ta, Ni, Cu, Zn, Zr, Nb, Mo, Sn and / or Al, where y is in the range from 1 to 10 and z is in the range from 1 to 3, Selenide M _z Se _y of transition metals M selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cd, Ta, Ni, Cu, Zn, Zr, Nb, Mo, Sn and / or AI where y in the range from 1 to 10 and z ranges from 1 to 3,

Telluride M _z Te _y of transition metals M selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cd, Ta, Ni, Cu, Zn, Zr, Nb, Mo, Sn and / or AI where y in the range from 1 to 10 and z ranges from 1 to 3,

complex halides of metals selected from the group comprising Na, Mg, Al, Si, P, S, K, Ca, Ti, Zn, Cu, Ni, Co, Fe, Mn, Cr, V, Zr, Nb, Mo and / or Sn, anion-introducing metal oxides of the transition metals, preferably selected from the group comprising W, Mo, Cr, V and / or Ti,

Metal silicates of the formula Me _n [(Si _x O _y ) ^{4x "2y} ] where Me is selected from the group consisting of Fe, Li, Ni, Ti, Na, K, Ba, Ca, Mg, Mn, Co, Al, Sn, Ag, Au, Cu and / or Sb, and 1 <x <65, 1 <y <130 and 1 <n <12, where Si can be replaced by Al up to a ratio of 1: 1,

Metal aluminates of the formula (MeAl (OH) _x ) where Me is selected from the group consisting of Fe, Li, Ni, Ti, Na, K, Ba, Ca, Mg, Mn, Co, Al, Sn, Ag, Au, Cu and / or Sb and 2 <x <7, and / or

Layered, mixed metal hydroxides corresponding essentially to the general formula: M _m DdT (OH) _{(3 + m +} d ₎ , wherein

M is a metal cation selected from the group of alkaline earth metals and alkali metals, preferably Li, Na, Mg, Ca, and / or K, particularly preferably Li and Ca and particularly preferably Ca, and m is in the range from 0 to 8,

D is at least one bivalent metal cation from the group comprising Mg, Ca,

Mn, Fe, Co, Ni, Cu and / or Zn, and d is in the range of 0 to 8,

T is a unit amount of at least one trivalent metal cation selected from the group comprising Al, Ga, Fe and / or Cr, and

(3 + m + d) corresponds to the number of OH groups which are essentially the

Satisfies valency requirements of M, D and T, where m + d is not equal to zero. One group of advantageously usable anions reversibly accepting and donating compounds are transition metal chalcogenides. Preference is given to sulfides, selenides and tellurides of the formulas M _z S _y , M _z Se _y and M _z Te _y of transition metals M selected from the group comprising Ti, V, Cr, Mn, Fe, Co, Cd, Ta, Ni, Cu , Zn, Zr, Nb, Mo, Sn and / or Al, wherein y is in the range of 1 to 10 and z is in the range of 1 to 3. Preferred transition metals M are selected from the group comprising Ti, V, Cr, Ni and / or Mo. Sulfides such as TiS ₂ and NiS are particularly advantageous. Also useful are selenides such as TiSe ₂ .

Also preferably usable are complex halides of metals selected from the group consisting of Na, Mg, Al, Si, P, S, K, Ca, Ti, Zn, Cu, Ni, Co, Fe, Mn, Cr, V, Zr, Nb , Mo and / or Sn. For the purposes of the present invention, the term "complex halides" is to be understood as meaning compounds in which the halides are present as complex ligands In particular, the complex halides are insoluble in the electrolyte and are solid at room temperature (20 ± 2 ° C.) preferably usable complex halides are selected from the group comprising chiolith (Na ₅ Al ₃ Fi ₄ ), usovite (Ba ₂ CaMgAl ₂ Fi ₄ ) and / or cryptophalite ((NH ₄ ) ₂ SiF ₆ ) Metal oxides of the transition metals, preferably of transition metals selected from the group comprising W, Mo, Cr, V and / or Ti. Particularly preferred are metal oxides

selected from the group comprising MoO, Mo0 ₂ , Ti0 ₂ and / or W0 ₂ . Also useful compounds are in particular layered metal silicates of the formula Me _n [(Si _x O _y ) ^4x_2y ], wherein Me is selected from the group consisting of Fe, Li, Ni, Ti, Na, K, Ba, Ca, Mg, Mn, Co, Al, Sn, Ag, Au, Cu and / or Sb, 1 <n <12 and 1 <x <65 and 1 <y <130. For the metal silicates of the formula Me "[(Si _x O _y ) ^{4x 2y} ] can Si up to one Ratio of 1: 1 to be replaced by AI. Preferred metals Me are selected from the group comprising Li, Na, Ca, Ba and / or Fe, in particular Li, Na and Fe are preferred. Metal silicates selected from the group comprising Li ₂ FeSiO ₄ , Li ₂ CoSiO ₄ , Li ₂ MnSiO ₄ and / or NaFeSi ₄ are particularly advantageously usable.

Further usable compounds are, in particular, layered metal aluminates of the formula (MeAl (OH) _x ) where Me is selected from the group consisting of Fe, Li, Ni, Ti, Na, K, Ba, Ca, Mg, Mn, Co, Al, Sn, Ag, Au, Cu and / or Sb and 2 <x <7. Preference is given to NaAl (OH) ₄ and KAl (OH) ₄ .

Further usable compounds are, in particular, layered metal hydroxides corresponding essentially to the general formula M _m DdT (OH) _{(3 + m +} d ₎ , where M is a metal cation selected from the group of alkaline earth metals and alkali metals, and m is in the range from 0 to 8 D is at least one divalent metal cation selected from the group consisting of Mg, Ca, Mn, Fe, Co, Ni, Cu and / or Zn, and d is in the range of 0 to 8, T is a unit amount of at least one trivalent metal cation selected from the group comprising Al, Ga, Fe and / or Cr, and (3 + m + d) corresponds to the number of OH groups that substantially satisfy the valence requirements of M, D and T, where m + d is not equal to zero ,

These metal hydroxides are also referred to as "mixed" metal hydroxides due to the various metal cations M, D and T. The term "substantially" has in the context of the present invention with respect to the general formula M _m DdT (OH) _{(3 + m +} d ₎ the meaning that the sum of the valences of the electropositive and electronegative elements equalize.

Preference is given to metal hydroxides of alkaline earth metals and alkali metals selected from the group comprising Li, Na, Mg, Ca and / or K, more preferably lithium and / or Calcium, and more preferably calcium. A further preferred metal hydroxide is [MgdAl (OH) ₃₊ d] where d is between 0.5 and 4.

Preferably, the anions are carbon-based reversibly receiving and donating electrode material. For the purposes of the present invention, the term "carbon-based" is to be understood as meaning a carbonaceous material such as graphite, pitch or tar, pitch coal, coke, synthetic graphite, carbon black, lamellar graphite, or mixtures thereof. Further preferably usable carbon compounds are fluorinated carbons of the formula (CF _x ) _n where x is in the range of 0.01 to 1.24 and n is in the range of 1 to 1000, and carbon oxides of the formula (CO _y ) _m , which at room temperature and y is in the range of 0.01 to 1 and m is in the range of 1 to 100. An example of such carbon oxides are temperature- and oxygen-treated graphites.

Preferably, the anions are carbon-based reversibly receiving and donating electrode material. The incorporation of anions or lithium ions in a

Carbon based electrode material is also referred to as intercalation. For the purposes of the present invention, the term "carbon-based" is to be understood as meaning a carbonaceous material such as graphite, pitch or tar, pitch coal, coke, synthetic graphite, carbon black, lamellar graphite, or mixtures thereof.

In preferred embodiments, the anions are reversibly receiving and donating electrode material formed of a material selected from the group consisting of carbon, graphite, graphene or carbon nanotubes.

Carbon and graphite show particularly good intercalating and deintercalating

Properties for anions. Anions that reversibly take up the anions and In particular, the anions which comprise the electrolyte, in particular the anions of the lithium salt, are.

The anions from the electrolyte may intercalate between the layer lattice planes of the graphite and / or deposit or intercalate with graphite layers of disordered carbons. Carbon materials are particularly well suited if they have a partial graphitic structure. But even porous carbon-rich material can intercalate reversible anions within its crystal lattice. The intercalating carbons or graphites preferably intercalate the anions without their solvation sheath.

In particular, used in the technical processing of carbon fibers such as carbon black, activated carbon, amorphous carbon, carbon fibers, graphites, graphene,

Graphite oxides, as well as carbon nanotubes, carbon manure foam, amorphous carbon or mixtures thereof.

Carbon particles can be amorphous, crystalline or partially crystalline, so-called soft or hard carbons. Examples of amorphous carbon are, for example, Ketjenblack,

Acetylene black or carbon black. Preference is given to using crystalline

Carbon modifications, such as graphite, carbon nanotubes, so-called carbon nanotubes, as well as fullerenes or mixtures thereof. Also preferably usable as crystalline carbon modifications is so-called VGCF carbon (vapor grown carbon fibers). Further preferably usable are temperature-treated carbons such as graphene oxides. A heat treatment of carbonaceous or -rich materials increases their

Crystallinity and may increase the ability to store anions. Temperature treated carbons are preferably solid at room temperature. Graphene, graphite and / or partially graphitized carbons are preferred. Graphite and partially graphitized carbons can be particularly good anions between the

Interleave layer lattice planes of graphite.

Useful graphite or carbon particles preferably have a middle one

Diameter in the range of> 2 nm to <50 μιη, preferably in the range of> 10 nm to <30 μιη, more preferably in the range of> 30 nm to <30 μιη, on.

Useful are discrete particles, for example in the form of spheres, such as spheroidal graphite, flakes, grains or rods, so-called nanotubes. The graphite or

Carbon material is particularly useful in powder form. In particular, powdered carbon and graphite can be well processed with a binder into a composite electrode.

Preferably, the anion is reversibly intercalating and deintercalating

Electrode material carbon-based. Preferably, the anions comprise reversibly intercalating and deintercalating electrode carbon and / or graphite in the range of> 70 wt .-% to <100 wt .-%, preferably in the range of> 80 wt .-% to <98 wt .-%, preferably in the range of> 90 wt .-% to <97 wt .-%, based on the total weight of the electrode.

The proportion of> 70% by weight of the electrode formed in a dual intercalation cell of the carbon and / or graphite anion intercalation compound makes a significant difference to conventional lithium ion battery cathodes containing carbon and graphite as an additive contained only in small amounts of about 10% by weight. The electrochemical cell furthermore has in particular a separator. The separator separates the electrodes from each other. Preferably, the separator is disposed between the electrodes. The particularly secondary electrochemical cell preferably comprises a lithium ion reversibly receiving and donating electrode, an anion reversibly receiving and donating electrode, a separator and an electrolyte comprising a lithium salt and a solvent. The separator is permeable to the ions of the electrolyte. Suitable materials for the separator are for example microporous plastics, for example poly-ethylene-tetrafluoroethylene, nonwovens made of glass fibers or polyethylene. Preference is given to microporous films, for example porous ethylene-tetrafluoroethylene film or nonwovens. Particularly suitable are nonwovens of glass fibers, in particular nonwoven glass fiber nonwoven.

The separator may further be a gel polymer separator. A gel polymer separator can be prepared, for example, by admixing a polymer, in particular selected from the group consisting of polypropylene, polytetrafluoroethylene and / or polyvinylidene difluorides, preferably polyethylene oxides, into the electrolyte.

The charge transport in electrochemical energy storage takes place via an electrolyte. A liquid electrolyte is usually substantially one in one

Solvent or a mixture of several solvents dissolved lithium secondary salt formed.

Suitable lithium salts are in preferred embodiments selected from the group consisting of LiF, LiCl, LiBr, LiI, LiNO ₃ , LiSO ₄ , LiPF ₆ , LiAsF ₆ , LiC 10 ₄ , LiSbF ₆ , LiPtCk, Li (CF ₃ ) SO ₃ (LiTf), LiC (SO ₂ CF ₃ ) ₃ , LiPF ₃ (CF ₃ ) ₃ (LiF AP), LiPF ₄ (C ₂ O ₄ ) (LiTFOB), LiBF ₄ , LiB (C ₂ O ₄ ) ₂ (LiBOB), LiBF ₂ (C ₂ O ₄ ) (LiDFOB), LiB (C ₂ O ₄ ) (C ₃ O ₄ ) (LiMOB), Li (C ₂ F ₅ BF ₃ ) (LiF AB), Li ₂ Bi ₂ Fi ₂ (LiDFB) , LiN (SO ₂ F) ₂ (LiFSI), LiN (SO ₂ CF ₃ ) ₂ (LiTFSI) and / or

LiN (S0 ₂ C ₂ F ₅ ) ₂ (LiBETI). Preferred lithium salts are selected from the group comprising LiPF ₆ , Li (SO ₂ F) ₂ (LiFSI), LiN (SO ₂ CF ₃ ) ₂ (LiTFSI) and / or LiB (C ₂ O ₄ ) ₂ (LiBOB). In particular, LiN (S0 ₂ F) ₂ (LiFSI), LiN (S0 ₂ CF ₃ ) ₂ (LiTFSI), and LiB (C ₂ 0 ₄ ) ₂ (LiBOB) can lead to improved electrochemical cell performance and performance

Temperature resistance has.

Preferably, the anion of the lithium salt does not decompose to a potential of at least 3.5 V, preferably at least 4 V, preferably 5 V, relative to the potential of lithium. In particular, the anion of the lithium salt preferably does not decompose in a potential range of> 4.55 V to <5.6 V, preferably not a potential range of> 5.1 V to <5.6 V, compared to the potential of lithium. This is particularly advantageous since the electrochemical cell according to the invention, which is based on the dual-ion insertion principle, is preferably operated at high cell voltages of at least 3.5 V, preferably at least 4 V, preferably 5 V, compared to the potential of lithium. In preferred embodiments, the inventive electrochemical cell is operated at a cell voltage in the range of> 3 V to <4 V, preferably in the range of> 3.5 V to <4 V, against lithium titanium oxide. Preferably, the anion is selected from the group comprising F ^~ , Cl ^~ , Br ^~ , Γ, N0 ₃ ^~ , SO, ^" PF ₆ -, BF, ^" B (C ₂ 0 ₄ ) ₂ ^" (BOB), BF ₂ ( C ₂ O ₄ ) ^" (DFOB), B (C ₂ O ₄ ) (C ₃ O ₄ ) ^" (MOB),

(C ₂ F ₅ BF ₃ ) ^" (FAB), (CF ₃ ) S0 ₃ -, B ₁₂ F ₁₂ ² - (DFB), N (S0 ₂ F) ₂ ^" (FSI), N (S0 ₂ CF ₃ ) ₂ ^" (TFSI) and / or N (S0 ₂ C ₂ F ₅ ) ₂ ^~ (LiBETI) Preferably, the anion is selected from the group consisting of PF ₆ ^" , N (SO ₂ F) ₂ ^" (FSI), N ( S0 ₂ CF ₃ ) ₂ ^" (TFSI) and / or B (C ₂ 0 ₄ ) ₂ ^" (BOB).

Advantageously, it has been found that in the dual storage system according to the invention comprising a lithium titanate anode and large anions such N (S0 ₂ F) ₂ ^~ , N (S0 ₂ CF3) ₂ ^~ and B (C ₂ 04) ₂ ^~ can be incorporated. This is particularly advantageous, since it was hitherto assumed that only very small or smaller anions such as fluoride, PF ₆ or BF ^~ ₄ ^~ be reversibly intercalated in graphite electrodes. This allows the electrochemical cell to have improved capacity and temperature resistance.

Preferably, the lithium salt is dissolved in the solvent. Preferably, the concentration of the lithium salt in the electrolyte is in the range of> 0.5 M to <19 M, preferably in the range of> 0.65 M to <12 M, more preferably in the range of> 1 M to <5 M. Preferably the concentration of the lithium salt, in particular a lithium salt comprising an organic anion selected from the group comprising B (C ₂ O ₄ ) ₂ - (BOB), BF ₂ (C ₂ O ₄ ) - (DFOB), B (C ₂ 0 ₄ ) (C ₃ O ₄ ) - (MOB), (C ₂ F ₅ BF ₃ ) ^" (FAB),

(CF ₃ ) S0 ₃ ^~ Bi ₂ Fi ₂ ^{2 "} (DFB), N (S0 ₂ F) ₂ ^" (FSI), N (S0 ₂ CF ₃ ) ₂ ^" (TFSI) and / or N (S0 ₂ C ₂ F ₅ ) ₂ ^" (LiBETI), in the electrolyte in the range of> 0.5 M to <2.5 M, preferably in the range of> 0.65 M to <2 M, particularly preferably in the range of> 1 M to < 1.5 M.

The use of lithium titanate as the anode material reduces the risk that the salts and / or solvents will decompose and lead to an exothermic decomposition of the cell. This reduces the security risk in the operation of the cell. In particular, it is advantageous that no passivation layers form on lithium titanate anodes which would lead to irreversible salt loss. In addition, lower salt concentrations reduce the cost of manufacturing the cell.

Preferably, the electrolyte is a substantially anhydrous, organic

liquid or liquid electrolyte. Preferably, the solvent is an organic solvent. Suitable organic solvents are, for example, selected from the group comprising aliphatic hydrocarbons, in particular pentane, aromatic hydrocarbons, in particular toluene, alkenes, in particular hexene, Alkynes, in particular heptin, halogenated hydrocarbons, in particular chloroform or fluoromethane, alcohols, in particular ethanol, glycols, in particular ethylene glycol and diethylene glycol, ethers, in particular diethyl ether and tetrahydrofuran, esters, in particular ethyl acetate, carbonates, in particular diethyl carbonate, lactones, in particular gamma-butyrolactone and gamma-valerolactone, acetates, in particular sodium acetate, Sulfones, in particular sulfolane, sulfoxides, in particular dimethyl sulfoxide, amides, in particular acetic acid (trimethylsilyl) amide, nitriles, in particular acetonitrile, amines, in particular dimethylamine, ketones, in particular acetone, aldehydes, in particular hexanal, sulfides, in particular carbon disulfide, carbonic acid esters, in particular dimethyl carbonate and ethylene carbonate, carboxylic acids, in particular formic acid, and / or urea derivatives in particular dimethylpropyleneurea

Preferred organic solvents are selected from the group comprising

Ethylene carbonate, fluoroethylene carbonate, propylene carbonate, diethyl carbonate,

Dimethyl carbonate, ethyl methyl carbonate, acetonitrile, glutaronitrile, adiponitrile, pimelonitrile, gamma-butyrolactone, gamma-valero lactone, dimethoxyethane, 1,3-dioxalane,

Dimethyl sulfoxide, vinylene carbonate, vinylene ethylene carbonate, methyl acetate and / or

Mixture thereof, preferably from the group comprising ethylene carbonate, diethyl carbonate, dimethyl carbonate and / or mixtures thereof.

Preference is given to mixtures of ethylene carbonate and at least one other

Solvent, more preferably with diethyl carbonate or dimethyl carbonate. In preferred embodiments, the solvent is a mixture of ethylene carbonate and dimethyl carbonate. Particularly preferred as the solvent is a mixture of ethylene carbonate and dimethyl carbonate in equal parts by weight. In one

Solvent mixture of ethylene carbonate and dimethyl carbonate in the ratio 1: 1, a good conductivity in a temperature range of -20 ° C to + 60 ° C can be achieved in an advantageous manner. Another object of the invention relates to the use of lithium titanate as lithium ion reversibly receiving and donating electrode material in an electrochemical cell, in particular a secondary electrochemical cell, comprising a lithium ion reversibly receiving and donating electrode and anions reversibly receiving and donating electrode and an electrolyte comprising a lithium salt and a solvent.

The electrochemical cell is particularly suitable for a lithium-based

Energy storage. Another object of the invention relates to the use of lithium titanate as the anode material in a based on the dual-ion insertion principle lithium-based energy storage. Lithium-based energy stores are preferably selected from the group comprising lithium batteries, lithium-ion batteries, lithium-ion accumulators, lithium-polymer batteries and / or lithium-ion capacitors, in particular lithium-ion batteries or lithium ions

Accumulators.

Examples and figures which serve to illustrate the present invention are given below.

Here are the figures:

Figure 1 shows the discharge capacity and efficiency of the electrochemical cell against

the number of charge / discharge cycles.

Figure 2 shows the current / voltage curve of the electrochemical cell versus time.

example 1

Preparation of an electrochemical cell with lithium titanate anode For the production of the lithium titanate electrode, based on the total weight of the electrode, 85% by weight of lithium titanate Li ₄ TisOi ₂ (battery grade / battery grade purity,

Südchemie, Munich, Germany), 10% by weight of carbon (Super-P Li, TIMCAL®, Bodio, Switzerland) and, as binder, 5% by weight of polyvinylidene difluoride (Kynar® Flex 761,

Arkema®, France) dissolved in N-methyl-2-pyrrolidone (Acros Organics, 99.5%, Extra Dry) as a solvent. The mixture was homogenized at 8000 rpm for 1.5 hours using a T25 digital Ultra-Turrax stirrer and a S 25 N-18 G dispersing tool (both ^IKA® , Staufen, Germany). The mixture was then applied using a doctor blade on an aluminum foil of a thickness of 20 μιη (99.88% pure, Evonik-Degussa ^® ) as a current collector with a layer thickness of 175 μιη. The electrode was dried at 80 ° C for 12 hours. Subsequently, an electrode having a diameter of 12 mm was punched and dried for 24 hours at 120 ° C under vacuum. The surface loading was> 3 mg / cm ² . The surface load was determined by weighing the pure aluminum foil and the punched electrodes.

For the preparation of the graphite electrode were based on the total weight of

Electrode, 90% by weight graphite (graphite KS6, TIMCAL®, Bodio, Switzerland), 5% by weight

Carbon (Super-P Li, TIMCAL®, Bodio, Switzerland) and, as a binder, 5% by weight of sodium carboxymethycellulose (Walocel® CRT 2000 PPA 12, Dow Wolff Cellulosics, The Dow

Chemical Company, Midland, MI, USA) in deionized water as a solvent. The mixture was homogenized at 5000 rpm for 1 hour with the aid of a T25 digital Ultra-Turrax stirrer and a S 25 N-18 G dispersing tool (both ^IKA® , Staufen, Germany). The mixture was then applied using a doctor blade on an aluminum foil of a thickness of 20 μιη (99.88% pure, Evonik-Degussa ^® ) as a current collector with a layer thickness of 200 μιη. The electrode was dried at 80 ° C for 12 hours. Subsequently, a round electrode with a diameter of 12 mm, or an area of 1.13 cm ² , punched out and for 24 hours at 120 ° C under Vacuum dried. The surface loading was 1.5 mg / cm ² . The surface load was determined by weighing the pure aluminum foil and the punched electrodes. The separator used was a glass fiber separator from Whatman (Whatman GF / D, GE Healthcare®, Great Britain). The electrolyte was a mixture of

Ethylene carbonate and dimethyl carbonate in equal parts by weight (1: 1). Both solvents were purchased in a "battery grade" grade from Übe®, Yamaguchi, Japan Lithium hexafluorophosphate LiPF ₆ (Übe®,

Yamaguchi, Japan) at a concentration of 1 mol / l

Example 2

Electrochemical investigation of the electrochemical cell with lithium titanate anode The electrochemical examination of the electrochemical cell prepared according to Example 1 was carried out in a cell made of a modified gas valve of the company

Swagelok ^® with the exclusion of oxygen and water. The potentiostat / galvanostat used was a Maccor 4000 series instrument or a BaSyTec MDS battery test system. The electrodes used in the measuring cell were round with a diameter of 12 mm, respectively an area of 1.13 cm ² .

The assembly of the cell was carried out in a glove box filled with an inert gas atmosphere of argon and an oxygen and water content of less than 1 ppm. After this

Assembly, the cell was equilibrated for 24 hours at room temperature (20 ± 2 ° C).

To charge the cell, a galvanostatic current was then applied, which corresponded to a specific current density of 50 mA / g with respect to the active material of the graphite electrode. The cell was charged to a final charge voltage of 3.3V and then discharged to 1.8 V with the same galvanostatic current, wherein the data in V respectively refer to the cell voltage between the graphite and the lithium titanate electrode. This charge / discharge process is one cycle and has been repeated 20 times at 20 ± 2 ° C.

FIG. 1 shows the discharge capacity and the efficiency of the charging / discharging process of the electrochemical cell as a function of the number of cycles applied on the x-axis. In this case, the left y-axis shows the value of the discharge capacity, represented as a black circle, and the right y-axis, the efficiency of the charge / discharge, shown as

Triangle.

It was found that the charge / discharge process was more than 97% reversible after the first cycle, based on a maximum efficiency of 100%. Furthermore, based on the graphite electrode, a discharge capacity greater than 30 mAh / g could be achieved.

This shows that, in contrast to common dual-graphite systems, a very high efficiency could be achieved, and this in addition to the use of relatively high charge and discharge currents in these systems, which were previously unrealizable, since the

Graphite anode operates below the thermodynamic stability window of the electrolyte.

Figure 2 shows the current / voltage curve of the cell versus that on the x-axis

applied time. The voltage of the cell is shown in full lines on the left y-axis and the current in dashed lines on the right y-axis. Positive currents refer to the charging process, whereas negative currents represent the discharging process. FIG. 2 shows the first 10 charging / discharging operations.

The shape of the potential shows that the ion storage in a limited

Potential range occurred. Also, the difference between the potential of charging and Discharge process low compared to conventional dual-graphite systems and thus the electrical efficiency higher.

The results show that the use of lithium titanate anodes in a dual ion insertion cell offers significant advantages over the classic dual-graphite cell and a lithium-ion battery. In particular, by using

Lithium titanate anodes are worked in a Potentialarbeitsbereich in which the organic electrolyte is thermodynamically stable, but the total cell voltage was still above 3 volts. Furthermore, there was no formation of a passivation layer on the anode. Furthermore, high charging and discharging currents could be realized.

Claims

An electrochemical cell comprising a lithium ion reversibly receiving and donating electrode, an anion reversibly receiving and donating electrode and an electrolyte comprising a lithium salt and a solvent, characterized

characterized in that the lithium ion reversibly receiving and donating electrode comprises lithium titanate as lithium ion reversibly receiving and donating electrode material.

2. An electrochemical cell according to claim 1, characterized in that the

Lithium ion reversibly receiving and donating lithium titanate in the range of> 50 wt .-% to <98 wt .-%, preferably in the range of> 75 wt .-% to <95 wt .-%, preferably in the range of> 80 wt. -% to <95 wt .-%, based on the

Total weight of the electrode.

3. Electrochemical cell according to claim 1 or 2, characterized in that the anions reversible receiving and donating electrode material is formed from a material selected from the group comprising carbon, graphite, graphene or

Carbon nanotubes.

4. Electrochemical cell according to one of the preceding claims, characterized

in that the lithium salt is selected from the group consisting of LiF, LiCl, LiBr, LiI, LiNO ₃ , LiSO ₄ , LiPF ₆ , LiAsF ₆ , LiC 10 ₄ , LiSbF ₆ , LiPtCk, Li (CF ₃ ) SO ₃ ,

LiC (S0 ₂ CF ₃ ) ₃ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₄ (C ₂ 0 ₄ ), LiBF ₄ , LiB (C ₂ 0 ₄ ) ₂ , LiBF ₂ (C ₂ 0 ₄ ),

LiB (C ₂ O ₄ ) (C ₃ O ₄ ), Li (C ₂ F ₅ BF ₃ ), Li ₂ B ₁₂ F ₁₂ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ and / or

LiN (S0 ₂ C ₂ F ₅ ) ₂ , preferably selected from the group comprising LiPF ₆ , Li (S0 ₂ F) ₂ , LiN (S0 ₂ CF ₃ ) ₂ and / or LiB (C ₂ 0 ₄ ) ₂ .

5. Electrochemical cell according to one of the preceding claims, characterized in that the anion of the lithium salt does not decompose to a potential of at least 3.5 V, preferably of at least 4 V, preferably of 5 V above the potential of lithium, wherein the Anion is preferably selected from the group comprising F ^~ , Cr, ΒΓ, I ^" , PF ₆ -, BF ₄ -, B (C ₂ 0 ₄ ) ₂ ^" , BF ₂ (C ₂ 0 ₄ ) -, B (C ₂ 0 ₄ ) (C ₃ O ₄ ) -, (C ₂ F ₅ BF ₃ ) -, (CF ₃ ) S0 ₃ ^" Bi ₂ F ₁₂ ² -, N (S0 ₂ F) ₂ -, N (S0 ₂ CF ₃ ) ₂ - and / or N (S0 ₂ C ₂ F ₅ ) ₂ -

6. An electrochemical cell according to one of the preceding claims, characterized

in that the anion of the lithium salt is selected from the group comprising PF ₆ ^" , N (SO ₂ F) ₂ ^" , N (SO ₂ CF ₃ ) ₂ ^" and / or B (C ₂ 0 ₄ ) ₂ ^" .

7. An electrochemical cell according to one of the preceding claims, characterized

in that the solvent is an organic solvent, wherein the organic solvent is preferably selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate,

Ethyl methyl carbonate, acetonitrile, glutaronitrile, adiponitrile, pimelonitrile, gamma-butyrolactone, gamma-valero lactone, dimethoxyethane, 1,3-dioxalane, dimethyl sulfoxide, vinylene carbonate, vinylene ethylene carbonate, methyl acetate and / or a mixture thereof, preferably from the group comprising ethylene carbonate, diethyl carbonate,

Dimethyl carbonate and / or mixtures thereof.

8. Use of lithium titanate as lithium ion reversibly receiving and donating electrode material in an electrochemical cell comprising a

Lithium ion reversible receiving and donating electrode and an anion reversible receiving and donating electrode and an electrolyte comprising a lithium salt and a solvent.

9. Use of lithium titanate as the anode material in a based on the dual-ion insertion principle lithium-based energy storage.