DE102009034674A1 - Lithium Ion Battery - Google Patents

Abstract

A lithium ion battery comprising: (i) a positive electrode comprising a lithium iron phosphate having an olivine structure; (ii) a negative electrode; (iii) a separator which separates the positive and negative electrodes from one another and is permeable to lithium ions; wherein the separator comprises a fleece made of non-woven, non-electrically conductive polymer fibers, which is coated on one or both sides with an ion-conductive inorganic material; (iv) a non-aqueous electrolyte. The battery has a high quick charge capability with high security.

Description

The The present invention relates to a secondary battery, in particular a lithium-ion battery that has a high rapid charge capability with high security.

It is already known to use in positive electrodes of secondary batteries, ie of rechargeable batteries (accumulators), in particular of lithium ion secondary batteries, lithium iron phosphate (LiFePO ₄ ) with olivine structure. With such electrodes, the fast charging ability can be increased.

US 2006/0134524 A1 proposes a secondary battery having a positive electrode containing lithium iron phosphate having olivine structure. As a separator separating the positive electrode from the negative electrode, a porous film of a synthetic resin such as a polyolefin and / or a ceramic porous film is used.

US 2007/0254209 A1 proposes a secondary battery having a positive electrode containing lithium iron phosphate having olivine structure, using as a separator a polyethylene film having thereon a porous layer containing inorganic particles.

US 2007/0284159 A1 discloses a secondary battery having a positive electrode which may contain lithium iron phosphate having olivine structure, wherein a nonwoven fiber of a synthetic resin may be used as a separator.

DE 11 2007 001 410 T5 discloses a lithium secondary battery which may contain lithium iron phosphate in the positive electrode and which has as a separator a porous material, a nonwoven fabric or the like. DE 10 2007 024 394 discloses an energy storage device which may include lithium iron phosphate in the positive electrode, the separator being selected from polyolefins, ceramic coated hydrocarbons, fiberglass, cellulose based materials.

Secondary batteries, In particular, lithium-ion secondary batteries are due to their high energy density and high capacity as a driving force for used mobile information devices. Furthermore Such batteries also come for tools, electric powered automobiles and for cars with hybrid drive for use. Consequently, such batteries are not only high Requirements for fast charging capacity, capacity and Energy density, but in particular safety and security Reliability.

task the present invention is a secondary battery, in particular, a lithium ion secondary battery to provide which allows a quick charge and the same time has a high security.

• (i) eine positive Elektrode umfassend ein Lithiumeisenphosphat mit Olivinstruktur;
• (ii) eine negative Elektrode;
• (iii) einen Separator, der die positive und die negative Elektrode voneinander trennt und für Lithium-Ionen durchlässig ist, wobei der Separator ein Vlies aus ungewebten, nicht elektrisch leitfähigen Polymerfasern umfasst, das ein- oder beidseitig mit einem ionenleitenden anorganischen Material beschichtet ist;
• (iv) einen nicht-wässerigen Elektrolyt.

This object is achieved with a lithium-ion battery, which comprises:

• (i) a positive electrode comprising a lithium iron phosphate having olivine structure;
• (ii) a negative electrode;
• (iii) a separator which separates the positive and negative electrodes and is permeable to lithium ions, the separator comprising a nonwoven web of nonwoven non-electrically conductive polymer fibers coated on one or both sides with an ionically conductive inorganic material;
• (iv) a nonaqueous electrolyte.

in the Hereinafter, the terms "lithium ion battery" and "lithium ion secondary battery" become synonymous used. The terms also include the terms "lithium battery", "lithium ion secondary battery" and "lithium ion cell". A lithium-ion secondary battery generally consists of a series or series connection of individual lithium-ion cells. This means, that the term "lithium-ion battery" as Collective term for the common in the art the above terms is used.

Of the Term "positive electrode" means the electrode, when connecting the battery to a consumer, for example to an electric motor capable of picking up electrons, thus represents the cathode. The term "negative electrode" means the electrode, which is capable of delivering electrons when in use, thus represents the anode.

For the lithium-ion battery according to the invention, a lithium iron phosphate with olivine structure of the empirical formula LiFePO ₄ can be used. However, it is also possible to use a lithium iron phosphate containing an element M selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, B and Nb. Furthermore, it is also possible that the lithium iron phosphate contains carbon to increase the conductivity.

In a further embodiment, the lithium iron phosphate used with the olivine structure for the production of the positive electrode has the empirical formula Li _x Fe _1-y M _y PO ₄ , wherein M represents at least one element selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Bund Nb, where 0.05 ≤ x ≤ 1.2 and 0 ≤ y ≤ 0.8.

In In one embodiment, x = 1 and y = 0.

The positive electrode contains the lithium egg senphosphat preferably in the form of nanoparticles. The nanoparticles can take any shape, that is, they can be coarse-spherical or elongated.

In one embodiment, the lithium iron phosphate has a particle size measured as D ₉₅ value of less than 15 microns. Preferably, the particle size is less than 10 microns.

In a further embodiment, the lithium iron phosphate has a particle size measured as D ₉₅ value between 0.005 .mu.m to 10 .mu.m.

In a further embodiment, the lithium iron phosphate has a particle size measured as D ₉₅ value of less than 10 μm, the D ₅₀ value being 4 μm ± 2 μm and the D ₁₀ value being less than 1.5 μm.

The indicated values were measured by using the static Laser light scattering (laser diffraction, laser diffractometry) determines as known from the prior art.

The negative electrode can be made of a variety of materials Be eligible for using a battery with lithium-ion electrolyte are suitable. For example, the negative electrode may be lithium metal or lithium in the form of an alloy, either in the form a film, a grid or in the form of particles passing through a suitable binder are held together. The usage of Lithium metal oxides such as lithium titanium oxide is also possible. In principle, all materials can be used which are capable of using lithium intercalation compounds to build. Suitable materials for the negative electrode then include, for example, graphite, synthetic graphite, carbon black, Mesocarbon, doped carbon, fullerenes, niobium pentoxide, Tin alloys, titanium dioxide, tin dioxide, and mixtures of these Substances.

In The positive electrode will be the lithium iron phosphate used and the materials used for the negative electrode i. A. by a binder, these materials on the electrode holds, held together. For example, polymeric Binders are used. As a binder, for example Polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, Polytetrafluoroethylene, polyacrylate, ethylene (propylene-diene monomer) copolymer (EPDM) and mixtures and copolymers thereof.

Of the For the battery used separator must be to the ion transport for lithium ions between the positive and the negative Ensure electrode for lithium ions be permeable. On the other hand, the separator for Be electrons insulating.

Of the Separator comprises a nonwoven web of nonwoven polymer fibers, also called "non woven fabrics known which are electrically non-conductive. The term "fleece" becomes synonymous with terms such as "knitted fabric" or "felt" used. Instead of the term "unwoven" is also the term "not interweaves ".

Preferably the fleece is flexible and has a thickness of less than 30 microns on. Processes for producing such nonwovens are known from the prior art known to the art.

Preferably the polymer fibers are selected from the group of Polymers consisting of polyacrylonitrile, polyolefin, polyester, Polyimide, polyetherimide, polysulfone, polyamide, polyether.

suitable Polyolefins are, for example, polyethylene, polypropylene, polytetrafluoroethylene, Polyvinylidene fluoride.

preferred Polyesters are, for example, polyethylene terephthalates.

The The fleece contained in the separator is on one or both sides with a coated with ion-conducting inorganic material. The term "coating" includes Also, that the ion-conducting inorganic material not only can be located on one side or both sides of the fleece, but also inside the fleece.

The Ion-conducting inorganic material is in a temperature range from -40 ° C to 200 ° C ion conducting, d. H. ion-conducting for the lithium ions.

The material used for the coating is at least a compound from the group of oxides, phosphates, sulfates, titanates, Silicates, aluminosilicates at least one of the elements zirconium, aluminum or lithium.

In a preferred embodiment comprises or consists the ion-conducting material of zirconia.

Furthermore, a separator may be used, which consists of an at least partially permeable carrier, which is not or only poorly electron-conducting. This support is coated on at least one side with an inorganic material. As at least partially permeable carrier an organic material is used, which is designed as a non-woven fleece. The organic material is in the form of polymer fibers, preferably polymer fibers of polyethylene terephthalate (PET). The nonwoven fabric is coated with an inorganic ion conducting material which is preferably ion conducting in a temperature range of -40 ° C to 200 ° C. The inorganic ion-conducting material preferably comprises at least one compound from the group of oxides, phosphates, sulfates, titanates, silicates, aluminosilicates with at least one of the elements zirconium, aluminum, lithium, particularly preferably zirconium oxide. The inorganic ion-conducting material preferably has particles with a maximum diameter of less than 100 nm.

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

Methods for producing such separators are known from the prior art, for example from the EP 1 017 476 B1 . WO 2004/021477 and WO 2004/021499 ,

electrolytes for lithium-ion batteries include a variety of Lithium salts. Preferred lithium salts have inert anions and are non-toxic. Suitable lithium salts are, for example Lithium hexafluorophosphate, lithium hexa-fluoroarsenate, lithium bis (trifluoromethylsulfonylimide), Lithium trifluoromethanesulfonate, lithium tris (trifluoromethylsulfonyl) methide, Lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate, Lithium chloride, and mixtures thereof.

Preferably the electrolyte is present as electrolyte solution. suitable Solvents are preferably inert. Suitable solvents include, for example, propylene carbonate, dimethyl carbonate, diethyl carbonate, 2-methyltetrahydrofuran, dioxolane, tetrahydrofuran, 1,2-dimethoxyethane, Ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide, Dimethylformamide, nitromethane, and mixtures thereof.

The production of lithium-ion battery according to the invention can be carried out by methods known in the art and are described, for example in the "Handbook of Batteries David Linden, Thomas B. Reddy, 3rd Edition, 2002 , McGraw-Hill Verlag.

For example For example, the lithium iron phosphate may be used to make the positive electrode deposited as a powder on the electrode and a thin Film are compacted, optionally using a binder. The other electrode may be laminated to the first electrode, wherein the separator in the form of a film previously on the negative or the positive electrode is laminated. It is also possible, the positive electrode, the separator and the negative electrode to be processed simultaneously with mutual lamination.

in the The following are particularly preferred embodiments of the battery used in the battery according to the invention Separators and advantages of the battery, especially in terms of safety summarized.

in principle can cause too large pores and holes in separators, which are used in secondary batteries, to an inner one Short circuit. The battery can then be in one dangerous reaction very quickly self-discharge. in this connection can such large electrical currents occur that a closed battery cell in the worst case can even explode. Because of this, the separator can be crucial safety or lack of safety of a high-performance lithium battery or lithium high-energy battery.

Polymeric prevent i. A. above a certain temperature (the so-called "shut-down temperature", which is at about 120 ° C) any electricity transport through the electrolyte. This happens because at that temperature the pore structure of the separator collapses and all Pores are closed. Because no ions are transported anymore can be, comes the dangerous reaction, which can lead to the explosion, to a halt. Will the cell but due to external circumstances heated, so at about 150 to 180 ° C, the so-called "break-down temperature" is exceeded. From this temperature, it melts the separator, wherein this is contracting. In many places in the battery cell comes it now leads to a direct contact between the two electrodes and thus to a large internal short circuit. This leads to the uncontrolled reaction, which with a Explosion of the cell may end, or the resulting pressure must through a pressure relief valve (a rupture disk) frequently be decomposed under fire phenomena.

at used in the battery according to the invention Separator comprising a non-woven fabric of non-woven polymer fibers and the inorganic coating can only be shut-down come when, due to the high temperature, the polymer structure of the carrier material melts and into the pores of the inorganic Material penetrates and thereby closes. To the Break-down (collapse) does not happen with the separator, because the inorganic particles ensure that a complete Melting of the separator can not occur. This ensures that that there are no operating states in which a large area Short circuit can occur.

Due to the nature of the fleece used, which is a particularly suitable combination of Thickness and porosity, separators can be made that can meet the requirements for separators in high-performance batteries, especially lithium high-performance batteries. By the simultaneous use of exactly matched in their particle size oxide particles for the production of porous (ceramic) coating a particularly high porosity of the final separator is achieved, the pores are still small enough to unwanted growth of "lithium whiskers" through to prevent the separator.

On Reason of high porosity in connection with the low Thickness of the separator, it is also possible the separator completely or at least almost completely soak with the electrolyte, so no dead spots in individual areas of the separator and thus in certain windings or Stratifications of the battery cells may arise in which no electrolyte is present. This is achieved in particular by that by adhering to the particle size of the Oxide particles, the resulting separators free or almost free of are closed pores, in which the electrolyte can not penetrate.

The In addition, separators used for the invention have the advantage of being on the inorganic surfaces partially deposit the anions of the conductive salt of the separator material, which leads to an improvement of the dissociation and thus to a better one Ion conductivity in the high current range leads. Another, not insignificant advantage of the separator is in the very good wettability. Due to the hydrophilic ceramic Coating, the wetting with electrolyte takes place very quickly, which also leads to improved conductivity.

Of the used for the battery according to the invention Separator comprising a flexible nonwoven with one on and in this Nonwoven porous inorganic coating, the material of the fleece being selected from nonwoven, non-electrically conductive polymer fibers, also stands out in that the fleece has a thickness of less than 30 μm, a porosity of more than 50%, preferably from 50 to 97% and a pore radius distribution, wherein at least 50% of the pores have a pore radius of 75 to 150 microns.

Especially Preferably, the separator comprises a nonwoven which has a thickness of 5 to 30 microns, preferably a thickness of 10 to 20 microns having. Particularly important is also a homogeneous distribution of pore radii in the fleece as indicated above. An even more homogeneous pore radius distribution in fleece leads in conjunction with optimally matched oxide particles certain size to an optimized porosity of the separator.

The Thickness of the substrate has a big influence on the properties the separator, because on the one hand the flexibility but also the sheet resistance of the soaked with electrolyte Separators depends on the thickness of the substrate. By the small thickness becomes a particularly low electrical resistance achieved the separator in the application with an electrolyte. The separator itself has a very high electrical resistance because it itself must have insulating properties. moreover Thinner separators allow increased packing density in a stack of batteries, so that in the same volume a larger Can save energy.

Preferably the nonwoven has a porosity of 60 to 90%, especially preferably from 70 to 90%. The porosity is defined as the volume of the fleece (100%) minus the volume of the fibers of the Fleece, so the proportion of the volume of the fleece that is not of material is completed. The volume of the fleece can be off the dimensions of the fleece are calculated. The volume of the fibers results from the measured weight of the considered fleece and the density of polymer fibers. The big porosity The substrate also allows a higher porosity of the separator, which is why a higher uptake of electrolytes can be achieved with the separator.

In order to a separator with insulating properties can be obtained has this as polymer fibers for the nonwoven preferably non-electrically conductive fibers of polymers such as defined above, which are preferably selected from polyacrylonitrile (PAN), polyester, such. As polyethylene terephthalate (PET) and / or Polyolefin (PO), such as. Polypropylene (PP) or polyethylene (PE), or mixtures of such polyolefins.

The Polymer fibers of the nonwovens preferably have a diameter of 0.1 to 10 microns, more preferably from 1 to 4 microns on.

Particularly preferred flexible nonwovens have a basis weight of less than 20 g / m ² , preferably from 5 to 10 g / m ² .

The separator has a porous, electrically insulating, ceramic coating on and in the fleece. The porous inorganic coating on and in the nonwoven preferably has oxide particles of the elements Li, Al, Si and / or Zr with an average particle size of 0.5 to 7 μm, preferably of 1 to 5 μm and very particularly preferably of 1 , 5 to 3 microns on. Particularly preferably, the separator has a porous inorganic coating on and in the nonwoven, the aluminum has umoxid particles having an average particle size of 0.5 to 7 microns, preferably from 1 to 5 microns and most preferably from 1.5 to 3 microns, which are bonded with 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. As already described above, the maximum particle size is preferably 1/3 to 1/5 and particularly preferably less than or equal to 1/10 of the thickness of the nonwoven used.

Preferably the separator has a porosity of 30 to 80%, preferably from 40 to 75%, and more preferably from 45 to 70%. The porosity refers to the achievable, so open pores. The Porosity can by means of the known method of Mercury porosimetry can be determined or may be from the volume and the density of the starting materials used, if it is assumed that only open pores are present.

The used for the battery according to the invention Separators are also characterized by the fact that they have a tensile strength of at least 1 N / cm, preferably of at least 3 N / cm and whole particularly preferably from 3 to 10 N / cm. The separators can be preferably without damage down to any radius down to 100 mm, preferably down to to 50 mm and most preferably bend down to 1 mm. The high tear strength and the good bendability of the separator have the advantage that when charging and discharging a battery occurring Changes in the geometries of the electrodes through the separator can be mitged without this damaged becomes. The bendability also has the advantage that with this separator commercially standardized wound cells can be produced. In these cells, the electrode / separator layers are standardized Size spirally wound together and contacted.

The Combination of the positive electrode containing a lithium iron phosphate with the separator comprising a nonwoven web of nonwoven polymeric fibers, the one or both sides with an ion-conducting inorganic material is coated in the lithium-ion battery according to the invention results in a lithium-ion battery, in addition to the high fast charge capability an extremely high level of security with high capacity having. This combination is for use as Driving force for mobile information devices, for Tools, electrically powered automobiles and for automobiles with hybrid drive extraordinarily cheap.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 2006/0134524 A1 [0003]
• US 2007/0254209 A1 [0004]
• US 2007/0284159 A1 [0005]
• - DE 112007001410 T5 [0006]
• - DE 102007024394 [0006]
• - EP 1017476 B1 [0034]
• WO 2004/021477 [0034]
• WO 2004/021499 [0034]

Cited non-patent literature

• - "Handbook of Batteries" David Linden, Thomas B. Reddy, 3rd Edition 2002 [0037]

Claims (12)

Lithium-ion battery comprising: (i) one positive electrode comprising a lithium iron phosphate having olivine structure; (Ii) a negative electrode; (iii) a separator containing the positive and the negative electrode separates and permeable to lithium ions is; wherein the separator is a nonwoven web of nonwoven, not electrical conductive polymer fibers, the one or both sides coated with an ion-conducting inorganic material; (Iv) a non-aqueous electrolyte. A battery according to claim 1, wherein said lithium iron phosphate has the molecular formula Li _x Fe _1-y M _y PO ₄ , wherein M represents at least one member selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, B and Nb, where 0.05 ≤ x ≤ 1.2 and 0 ≤ y ≤ 0.8. A battery according to claim 2, wherein x = 1 and y = 0. A battery according to any one of the preceding claims, wherein the lithium iron phosphate has a particle size measured as D ₉₅ value of less than 15 microns. A battery according to claim 4, wherein the particle size is less than 10 microns. A battery according to claim 4 or 5, wherein the particle size 0.005 μm to 10 μm. A battery according to any one of the preceding claims, wherein the lithium iron phosphate has a particle size measured as D ₉₅ value of less than 10 microns, wherein the D ₅₀ value is 4 microns ± 2 microns and the D ₁₀ value is less than 1.5 microns. Battery according to one of the preceding claims, wherein the polymer fibers are selected from the group consisting of polyacrylonitrile, polyolefin, polyester, polyimide, Polyetherimide, polysulfone, polyamide, polyether. Battery according to one of the preceding claims, wherein the ion-conductive inorganic material in a temperature range from -40 ° C to 200 ° C is ion-conducting, and at least one compound from the group of oxides, phosphates, Sulfates, titanates, silicates, aluminosilicates at least one of Elements Zr, Al, Li is. Battery according to one of the preceding claims, wherein the polymer fibers comprise a polyethylene terephthalate or consist of a polyethylene terephthalate. Battery according to one of the preceding claims, wherein the ionic conductive inorganic material comprises zirconia or zirconium oxide. The battery according to claim 1, wherein the separator is made of a permeable carrier, preferably partially permeable to substances, the carrier is not or only poorly electron-conducting, the carrier coated on at least one side with an inorganic material is where as at least partially permeable to material Carrier polymer fibers are used which are not woven fleece are designed, wherein the polymer fibers preferably comprise a polyethylene terephthalate, the Fleece coated with an inorganic ion-conducting material which is preferably in a temperature range of -40 ° C is conductive to 200 ° C, where the inorganic, Ion-conductive material preferably comprises at least one compound the group of oxides, phosphates, sulfates, titanates, silicates, aluminosilicates at least one of the elements Zr, Al, Li is, in particular zirconium oxide, and wherein the inorganic, ion-conducting material is preferably particles having a largest diameter below 100 nm.