HK1173267B

HK1173267B - Rechargeable electrochemical cell

Info

Publication number: HK1173267B
Application number: HK13100538.4A
Authority: HK
Inventors: Laurent Zinck; Christian Pszolla; Christiane Ripp; Markus Borck; Claudia Wollfahrt
Original assignee: Innolith Assets Ag
Priority date: 2010-02-12
Filing date: 2011-02-04
Publication date: 2016-12-16

Description

Rechargeable electrochemical battery cell

The invention relates to a rechargeable lithium battery cell having a positive electrode, a negative electrode and an electrolyte containing a conductive salt.

Rechargeable battery cells are very important in many technical fields. They are used in many cases for applications in which only a relatively low current strength is required, for example in mobile telephones. Furthermore, battery cells are also highly desirable in high current applications, where electric drive of motor vehicles is particularly important. The invention relates in particular to batteries which are also suitable for high current applications.

An important requirement is a high energy density. The battery should contain as much electrical energy per unit of weight and volume as possible. Lithium is particularly advantageous as the active metal in this respect.

In practice, rechargeable batteries are almost exclusively lithium ion batteries. Their negative electrodes consist of carbon coated on copper, into which lithium ions are intercalated during charging. The positive electrode also includes an intercalation material that is adapted to absorb ions of the active metal. Typically, the positive electrode is based on lithium cobalt oxide, which is coated on a current collector element made of aluminum. Both electrodes are very thin (thickness typically less than 100 μm). During charging, ions of the active metal are extracted from the positive electrode and inserted into the negative electrode. The reverse process occurs during the discharge. The transport of ions between the electrodes is performed by the electrolyte, which ensures the desired ion mobility. Lithium ion batteries contain an electrolyte consisting of a lithium salt (e.g. LiPF) dissolved in an organic solvent or solvent mixture (e.g. based on ethylene carbonate)₆) And (4) forming. The battery is hereinafter also referred to as an "organic lithium ion battery".

The safety of the organic lithium ion battery is problematic. The safety risk is caused in particular by organic electrolytes. If the lithium ion battery catches fire or even explodes, the organic solvent of the electrolyte forms a combustible material. To avoid such risks, additional measures have to be taken, in particular to precisely control the charging and discharging processes and to take additional safety measures in the battery construction. For example, the battery may contain a composition that melts and flowcoats the battery pack with molten plastic in the event of failure. However, these measures lead to an increase in cost and an increase in volume and weight, thereby reducing the energy density.

This problem is particularly acute when developing battery cells for high current applications. The requirements in terms of stability and long-term operational safety are particularly high. The term "high current battery" is used herein to denote a battery whose current carrying capacity (at rated voltage) relative to the electrode area (hereinafter "current carrying capacity per unit area") is at least 10mA/cm²Preferably at least 50mA/cm²And particularly preferably at least 150mA/cm²。

There is a great need for improved rechargeable battery cells which meet, inter alia, the following requirements:

very good electrical power data, in particular high energy density and at the same time high extractable current (power density).

Safety, also under difficult environmental conditions of the motor vehicle.

Long service life, in particular a very high number of available charge-discharge cycles.

-as low price as possible: inexpensive materials and production methods which are as simple as possible.

Other important requirements for practice, such as overcharge capability and deep discharge capability.

The present invention is based on the technical problem of providing battery cells which, as a whole, better satisfy these sometimes conflicting requirements than those hitherto.

The object is achieved by an electrochemically rechargeable lithium battery cell having a housing, a positive electrode, a negative electrode and an electrolyte containing a conductive salt, wherein the electrolyte is based on SO₂And the positive electrode contains Li_xM'_yM”_z(XO₄)_aF_bActive material of (2)A material therein

M' is at least one metal selected from the group consisting of: ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn,

m' is at least one metal selected from the group consisting of group IIA, IIIA, IVA, VA, VIA, IB, IIB, IIIB, IVB, VB, VIB and VIIIB metals,

x is selected from the group consisting of the elements P, Si and S,

x is larger than 0, and x is larger than 0,

y is greater than 0 and the ratio of y,

z is greater than or equal to 0 and,

a is greater than 0 and

b is greater than or equal to 0.

The active material is preferably a phosphate and the ingredient X is also phosphorus. The metal M' is particularly preferably iron. According to a further preferred embodiment, a is equal to 0, the active material further being free of fluorine.

"at least one metal" is understood to mean this: the components M' and M "may each consist of two or more of said metals. The subscripts y and z refer to the total number of metals represented by M' and M ". Of course, charge neutral conditions must be noted. The sum of the positive charges of the components Li, M' and M "must also be equal to the component (XO)₄) And (optionally) the sum of the negative charges of F.

For the sake of simplicity, the following references to lithium iron phosphate and the abbreviation "LEP" used herein are also typically applicable to the other compounds covered by the above definitions, and are not limiting with respect to generality.

In the context of the present invention, the term "SO-based₂The electrolyte of (1) denotes an electrolyte in which SO is present₂Not only in low concentrations but at least partly by SO₂Ensuring the mobility of the ions of the conductive salt contained in the electrolyte and functioning for charge transport. The electrolyte is preferably substantially free of organic material, wherein "substantially free" is to be interpreted asThis is done: the amount of any organic materials present is so small that they do not pose any safety risk. With the proviso that₂Hereinafter referred to as Li-SO₂A battery.

SO-based lithium batteries for lithium batteries have been discussed for a long time₂The electrolyte of (1). SO-based is indicated in (1) "handbook of batteries", David Linden (ed.), 2 nd edition, McGraw-Hill, 1994₂High ion conductivity of the inorganic electrolyte of (2). It is stated that this electrolyte is also advantageous in other electrical data. And further wherein said to have SO-based₂Have been long studied and are still attractive for certain applications. Further commercial applications are said to be limited, however, particularly because the electrolyte is toxic and highly corrosive.

With SO₂Battery cells of electrolytes are described in the following documents, for example:

(2) US patent 5213914

(3) WO00/44061 and US patent 6709789

(4) WO00/79631 and US 6730441

(5) WO2005/031908 and US2007/0065714

(6) L. Zinck et al, "purification Process for inorganic retrieval of lithium batteries and electrically of African disposal", J.Appl.Electrochem., 2006, 1291-

(7) WO2008/058685 and US patent application 2010/0062341

(8)WO2009/077140。

In the working examples described in these documents, the positive electrode is always based on lithium metal oxides, in particular on lithium cobalt oxide.

It has also been known for a long time to use lithium metal phosphates as positive electrode materials for lithium ion batteries with organic electrolytes. Early experimental studies were reported below:

(9) US patent 5910382

(10) Padhi et al, "phosphorus-olivinesa phosphorus-electric materials for rechargeable lithium batteries", J.Electrochem.Soc., 1997, 1188-1194

In (9) and (10), a cathode material for a lithium battery, which comprises Polyanion (PO)₄)^3-. This study relates to compounds with the metals Mn, Fe, Co and Ni, which are present in two different structures: olivine structure and NASICON structure. The effect of the structure on lithium intercalation is described and in it is reported an experiment using a battery cell in which a low number of charging cycles (25 cycles maximum) was performed.

(9) And (10) also address the problems associated with using LEP electrodes in lithium ion batteries. It is described that the cell voltage is only 3.5V even for a very small current load per unit area of 0.05mA/cm 2. In contrast, the cell voltage with the lithium cobalt oxide electrode was 4V and thus was about 14% higher. Furthermore, the conductivity of LEP is very poor. This results in a significant reduction in battery voltage even when low current loads are used. The capacity of the cell also shows a strong dependence on the current load and even has a capacity of less than 0.2mA/cm²Has been reduced to a value that renders the battery substantially unusable when loaded with current per unit area.

According to the (11) US patent 7338734,

it is believed that in lithium ion batteries with organic electrolytes, these problems are solved as follows: the specific surface area of the active material of the positive electrode is enlarged (in other words, a material consisting of very small particles is used) and instead of pure lithium iron phosphate, a material is used which is doped with one of the elements of groups IIA, IIIA, IVA, VA, VIA and IIIB of the periodic table of the elements, in particular with niobium.

This results in a significant improvement in electrical data compared to previously known organic lithium ion batteries having a positive LEP electrode. However, the manufacture of such cells is very complicated, in particular due to the required doping of the LEP material, due to the production of very fine LEP fractions, due to the casting of thin (film-type) electrode layers and due to the assembly of cells with thin electrode layers.

Within the scope of the present invention it has surprisingly been found that very good electrical power data (as well for high current applications) can be obtained by applying Li-SO₂LEP positive electrodes are used in the battery for much simpler implementation. The invention allows the use of lithium iron phosphate even without doping and still ensures a high current-carrying capacity. It is also not necessary to use very fine particle LEP. In the context of the present invention, it has been found to be advantageous to use a specific surface area of not more than 40m²(ii) a LEP/g, the specific surface area being measured according to the Brunauer-Emmett-Teller (BET) method, it also being possible advantageously to use a specific surface area of not more than 30m²Material per g and even not more than 15m²Material per gram. The preferred mean particle size is at least 0.2 μm, wherein materials with a mean particle size of at least 0.5 μm, at least 1 μm or even at least 2 μm can also be advantageously used.

The positive electrode of the present invention is preferably porous. However, the porosity should preferably not be too high. Thus, the following maximum values of porosity are particularly preferred in this order: 50%, 45%, 40%, 35%, 30%, 25%, 20%.

During operation, the pores of the positive electrode are preferably completely filled with electrolyte. Suitable conductive salts of the electrolyte are in particular aluminates, halides, oxalates, borates, phosphates, arsenates and gallates of alkali metals or alkaline earth metals. In the context of the present invention, lithium tetrahalo-aluminates are preferably used, and lithium tetrachloroaluminate is particularly preferred.

The electrolyte preferably contains at least 2.0 moles of SO₂Per mole of conductive salt, the following values are in order further preferred: at least 2.5 mol SO₂Per mole of conductive salt, at least 3.0 moles of SO₂Per mole of conductive salt, at least 4.0 moles of SO₂Per mole of conductive salt. In the context of the present invention, it has surprisingly been found that there is a relatively low concentration of leadElectrolytes of the electro-salts, despite the associated higher vapor pressure, are advantageous, in particular with regard to stability over multiple cycles.

The cell according to the invention is particularly advantageous if the thickness of the positive electrode is at least 0.25mm, preferably at least 0.3mm, further preferably at least 0.4mm, further preferably at least 0.5mm and particularly preferably at least 0.6 mm. The amount of active material should also be high based on the area of the positive electrode ("loading"). It is preferably at least 30mg/cm²The following values are in order further preferred: 40mg/cm²，60mg/cm²，80mg/cm²，100mg/cm²，120mg/cm²And 140mg/cm²。

Significant advantages are associated with large cathode thicknesses and correspondingly high active material loadings. In particular, the capacitance with respect to the area of the positive electrode ("capacity per unit area") is very high. The theoretical capacity of the LEP is 169 mAh/g. In experimental tests of the present invention, it has been found that this theoretical value is in Li-SO₂This is achieved in very good approximation (greater than 90%) in the cell. The positive electrode preferably has a capacity per unit area of at least 5mAh/cm²The following minimum values are in order further preferred: 7.5mAh/cm²，10mAh/cm²，12.5mAh/cm²，15mAh/cm²，20mAh/cm²，25mAh/cm²。

Within the scope of the present invention, it has been found that by combining an LEP electrode with an SO-based electrode₂In combination with electrolytes, it is possible to produce an electrochemical battery cell which is significantly improved in respect of the above-mentioned requirements as a whole, said cell being particularly suitable for applications relating to electromigration (for example batteries and hybrid vehicles):

the high load of the positive electrode and the accompanying high capacity per unit area make it possible to produce batteries with a high total capacity and with a relatively small electrode area. The loading may well exceed the minimum values mentioned above and reach values greater than 100mg/cm²The value of (c). Therefore, only 60cm is required for a capacity of 1Ah²The area of (a). Need to makeHas an electrode area of one third of that of the conventional LEP electrode for an organic lithium ion battery, a thickness of 50 to 90 μm, and a loading per unit area of 4 to 6mAh/cm²And which therefore requires 170-²To provide a capacitance of 1 Ah. As a result of the reduction in the area of the positive electrode, the areas of the separator and the negative electrode are also reduced. Further, for example, in the case of a prismatic cell having multiple electrodes, a small number of current collector tabs are required to connect with the cell ends. Also the interconnection of the electrodes in the housing is very simple when a small number of electrodes are used.

The current carrying capacity is very high. The positive electrode of the present invention can provide, for example, 300mA/cm²Current load per unit area.

In practice, a capacity of at least 90% of the theoretical capacity of the positive electrode can be used. This means that lithium ions can be almost completely extracted from the positive electrode during charging and re-inserted into the positive electrode during discharging. The invention also allows good values to be achieved, even in terms of the dependence of the capacitance on the current-carrying capacity. In other words, a large portion of the initial capacity of the battery is available even under high current load conditions. In summary, the actual useful capacity of the cells of the invention is higher than that of the lithium cobalt oxide electrode over the life of the cell, although the theoretical capacity of the LEP is only 60% compared to lithium cobalt oxide.

Multiple charge-discharge cycles required for electromigration applications are possible. A complete cycle of greater than 9000 was achieved in the experimental tests.

It is not necessary to regenerate the electrolyte by overcharging the battery such as described in document (8), for example. Thereby improving coulometric (coulometric) efficiency. However, the batteries of the present invention are also capable of being overcharged if required in a particular application.

The self-discharge of the cells of the invention is extremely low. It can therefore be stored for long periods under charging conditions and used immediately without recharging. In addition, the safety risk of "thermal runaway" related to self-discharge as described in document (2) is eliminated.

The stability of the carbon negative electrode preferably used in the context of the present invention is significantly improved. The negative electrode can even be manufactured without using a binder.

It is not necessary to use a relatively high content of carbon-based conductivity improver in the active material of the positive electrode, as described in documents (9), (10) and (11). Specifically, a relatively small amount of conductivity improver is sufficient. The carbon content of the positive electrode is preferably less than 10% by weight, wherein the following maximum values are in order further preferred: 7 wt%, 5 wt%, 2 wt%.

The content of binder can also be very low. The positive electrode preferably contains not more than 10% of a binder, with the following values being further preferred in order: 7 wt%, 5 wt%, 2 wt%.

Based on the information available prior to the present invention, Li-SO with LEP as the active material of the positive electrode could not have been expected₂The battery will be functional and even particularly advantageous.

As mentioned, the cell voltage of the lithium ion battery with LEP is almost 15% lower than the cell voltage of the lithium ion battery with lithium cobalt oxide. Accordingly, a correspondingly lower energy density value is contemplated.

Previously published on Li-SO₂The literature of batteries always describes the presence of a positive electrode based on oxides, in particular lithium cobalt oxide, in combination with SO₂The electrolyte phase is advantageous when combined. In document (5), it is recommended to use an activated cleaning method to improve the electrode performance.

The electrodes are in contact with the electrolyte in the cell and may therefore only react predominantly with the electrolyte. The electrolyte is thus decisive for the possible reactions of the materials contained in the electrodes. Based on SO, as described in document (1)₂The problematic property of the electrolyte of (a) is its high corrosiveness. The chemical behavior of LEP in organic electrolytes cannot be deduced about its significantly different SO-based₂Any information on stability in the inorganic electrolyte of (1). Because of the lithium oxideCobalt is already in Li-SO₂The battery proves itself and in any case will find a substitute in chemically similar oxide compounds.

As being based on SO₂The most important advantage of the electrolyte of (2) is that good conductivity can be observed. On the other hand, LEP is known as an electrode material having very poor conductivity. Based on this, when developing battery cells for high current applications, it seems illogical to combine the electrolyte (which is advantageous in terms of the internal resistance of the cell) with the electrode material (which is clearly disadvantageous in this respect).

Li-SO has already been mentioned in the literature (1)₂The choice of positive electrode material for the battery is limited to compounds whose potential decreases to a greater extent than SO₂The degree of potential reduction. Since the reduction in LEP reduction potential (2.9V) is significantly lower than lithium cobalt oxide (3.5V), there is only a narrow voltage range in which the battery should be charged and discharged as completely as possible. When LEP is tested in an organic battery according to documents (9) and (10), only about 60% of lithium is extracted from LEP, although 50 μ a/cm is loaded with a very low current per unit area²To perform charging and discharging.

Both LEP-based positive electrodes and carbon-based negative electrodes are intercalation electrodes that absorb active metallic lithium into their lattice structures during charge and discharge. A preferred embodiment of the invention relates to such intercalation electrodes, and in general also other intercalation electrodes suitable for taking up lithium in their interior, according to which an SO-based intercalation electrode is provided₂In the battery cell of the electrolyte of (1), at least one electrode is an intercalation electrode adapted to absorb lithium ions, which is subjected to a pretreatment for reducing the capping layer. Such an embodiment is advantageous for the rechargeable lithium battery cell with LEP positive electrode described above, but for SO-based rechargeable lithium battery cells₂Is also important for the entire embedded electrode in the electrolyte.

The pretreatment for reducing the capping layer involves forming the capping layer on the surface of the embedded electrode during the primary charging cycle. The formation of the cover layer not only consumes the charging current but also leads to an irreversible consumption of the active components of the battery system and thus to a reduction of the capacity during the service life of the remaining battery. The capacitance loss associated with the formation of the capping layer is reduced by a pretreatment for reducing the capping layer.

The invention is explained in more detail below on the basis of the drawings. The features shown and described herein can be used alone or in combination to produce preferred embodiments of the present invention. In the drawings:

fig. 1 shows a cross-sectional view of a battery cell of the present invention;

FIG. 2 shows a cross-sectional view of a metal foam suitable for the present invention;

FIG. 3 shows a cross-sectional view of the positive electrode;

FIG. 4 shows the discharge capacity as a function of cycle number for tests carried out with the positive electrode;

FIG. 5 shows the discharge capacity versus discharge rate for tests performed with the positive electrode compared to published results;

FIG. 6 shows the resistance of the electrode as a function of cycle number for tests performed with the positive electrode;

FIG. 7 shows capacity versus cycle number for experiments with two different anodes;

FIG. 8 shows capacity versus cycle number for additional experiments with two different anodes;

FIG. 9 shows discharge capacity versus cycle number for tests performed with two different batteries;

FIG. 10 shows capacity versus cycle number for long term testing;

fig. 11 shows the voltage versus charge capacity for three different preconditioned cathodes.

The housing 1 of the rechargeable battery cell 2 shown in fig. 1 comprises an electrode arrangement 3 comprising a plurality (three in the shown case) of positive electrodes 4 and a plurality (four in the shown case) of negative electrodes 5. The electrodes 4, 5 are connected to respective end connections 9, 10 of the battery by means of electrode leads 6, 7 in a conventional manner. The battery is filled with SO-based in such a way₂Electrolyte (not shown in the figure): so that the electrolyte penetrates as completely as possible into all pores, in particular into the electrodes 4, 5.

Typically, the electrodes 4, 5 are formed in a flat shape: i.e. to form a layer of lower thickness compared to its planar extension. Which are in each case separated from one another by partitions 11. The housing 1 of the prismatic cell shown is substantially cuboid, the electrodes and the walls shown in cross-section in fig. 1 extend perpendicular to the plane of the drawing and are substantially straight and flat. However, the battery of the present invention may also be designed as a wound battery.

As is conventional, the electrodes 4, 5 comprise current collector elements (Ableitelement) which are made of metal and serve to provide the required electrically conductive connection to the respective electrode active material. The current collector elements are in contact with the active materials involved in the electrode reactions of the respective electrodes. Preferably, the current collector element of the positive electrode, particularly preferably also of the negative electrode, is provided in the form of a three-dimensional porous metal structure, particularly a metal foam. The term "three-dimensional porous metal structure" denotes in the present context individual structures made of metal which extend not only over the length and width of the planar electrode as a thin sheet but also over its thickness dimension and which are porous in such a way that: the active material of the electrode may be mixed into the pores.

Figure 2 shows an electron micrograph of a metal foam structure suitable for the present invention. Based on the dimensions shown, it is clear that the average diameter of the pores P is greater than 100 μm and is therefore relatively large. Instead of the metal foam, it is also possible to use different three-dimensional metal structures, for example in the form of metal nonwovens or metal cloths (metallgembe).

During electrode fabrication, LEP material is incorporated into the porous structure of the current collector element so that it uniformly fills the pores of the current collector element throughout the thickness of the metal structure. The material is then pressed under high pressure, the thickness after the pressing process preferably being not more than 50%, particularly preferably not more than 40%, of the initial thickness.

The resulting electrode structure is shown in fig. 3, again in the form of an electron micrograph. The electrode material was cooled in liquid nitrogen and then pulverized to prevent the cutting operation from damaging the structural features. Although the material is damaged to some extent by the pulverization, the main feature of the structure of the positive electrode of the present invention is apparent from fig. 3.

The electrodes are much thicker than known LEP electrodes. In the example shown here, the thickness d is about 0.6 mm. The three-dimensional porous metal structure 13 of the current collector element extends substantially throughout the thickness d of the current collector element and the active LEP material 15 is substantially uniformly distributed therein. With regard to the two stated conditions, "substantially" is to be interpreted as such: the battery function is only slightly impaired by possible deviations. In any case, the porous metal structure should extend over at least 70%, preferably at least about 80%, of the thickness of the electrode.

The positive electrode includes a binder to improve its mechanical strength. In the context of the present invention, fluorinated binders, in particular THV (terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene 1, 1-difluoride) and PVDF (polyvinylidene 1, 1-difluoride) have proven suitable. Advantageously, it is sufficient that the binder is contained in the electrode in a relatively low concentration.

The negative electrode preferably contains carbon as an active material in a form suitable as an intercalation material for absorbing lithium ions. The structure is preferably similar to the positive electrode in the following features:

for the negative electrode as well, the current collector element preferably has a three-dimensional porous metal structure, in particular in the form of a metal foam.

It is relatively thick, having a thickness of at least 0.2mm, the following values being in order further preferred: 0.3mm, 0.4mm, 0.5mm, 0.6 mm.

The amount of negative active material is at least 10mg/cm based on its area²The following values are in order further preferred: 20mg/cm²，40mg/cm²，60mg/cm²，80mg/cm²，100mg/cm²。

-a capacity per unit area of preferably at least 2.5mAh/cm²The following values are in order further preferred: 5mAh/cm²，10mAh/cm²，15mAh/cm²，20mAh/cm²，25mAh/cm²，30mAh/cm²。

It is preferably porous, with a porosity of not more than 50%, the following values being further preferred in order: 45%, 40%, 35%, 30%.

The binder proportion is preferably not more than 5% by weight, more preferably not more than 3% by weight and particularly preferably not more than 1% by weight. Very particular preference is given to a negative electrode which does not contain any binder.

Additional information regarding the present invention and its preferred embodiments is provided based on the following experiments.

Test 1:

the following components were used to produce the paste:

94% by weight undoped lithium iron phosphate with a carbon surface coating; average particle size of about 2-3 μm

2% by weight of carbon black as conductivity enhancer

4% by weight of THV as binder,

the binder is first dissolved in acetone, then the carbon black is added to the solution with stirring, and finally the active substance and the further solvent are added alternately, likewise with stirring.

The paste was homogeneously mixed into a metal foam having an initial porosity of more than 90% and dried at 50 ℃ for 1 hour. After cooling, the electrode material was compressed by means of a calender from an initial thickness of 1.6mm to a thickness of 0.6 mm. It is then subjected to a tempering process at 180 ℃. The electrode material formed has a cross-section corresponding to fig. 3.

Cutting 1cm from the electrode material²A block of size. The capacity of the block is about 13 mAh. They were then tested in an E-cell with a three electrode arrangement in which the reference and counter electrodes were made of metallic lithium. Composition of electrolyte used in E-cell LiAlCl₄*1.5SO₂。

To determine the discharge capacity of the electrodes at different current loads, 40 charge-discharge cycles were carried out in the E-cell, with charging being carried out at the same charge rate of 1C in each case ("C" denoting the number of times the rated capacity was charged or discharged in 1 hour). Discharge was performed after each charging operation, and the battery was discharged in 40 cycles at the following rate:

10 cycles, 1C

4 cycles of 2C, 4C, 8C, 10C, 15C each

10 cycles, 1C.

Charging was carried out up to a voltage of 3.7V. The charging was terminated at a voltage of 3.2V.

FIG. 4 shows the discharge capacity Q as a function of the number of cycles as an average of 8 tests_D(unit mAh/g). It is clear from the figure that even with very high discharge rates, it is still possible to utilize most of the rated capacity. If, for example, the battery is discharged quickly with a 6 minute (10C) drain, it can still extract two thirds of the rated capacity.

FIG. 5 summarizes the results shown in FIG. 4, showing the discharge capacity Q as a function of the discharge rate C_D(FIG. A). Curve B represents values from the following publications:

(12) porcher et al, "DesignafAqueousProcessdeTeckLiFePO₄CompositeElectrodesforHigh-EnergyLithiumBattery，J.Electrochem.Soc.，2009，A133-A144

This publication describes the production of relatively thick electrodes for organic lithium-ion batteries, where a thickness of 0.2mm has been considered thick (compared to the hitherto usual thicknesses). The electrodes are fabricated with a water-soluble binder in an aqueous suspension. The resulting capacity per unit area ("capacity density") was 20mg/cm at load²And 3mAh/cm when the electrode thickness is 200 μm². The measurement data plotted in fig. 5 is taken from fig. 1 of the publication at page a135 for their best materials ("CMC"). It is clear that the capacity decreases with discharge rate much faster than the electrode of the present invention. For a discharge rate of 10C, the discharge capacity of the positive electrode for an organic lithium ion battery described in this publication, for example, is 18mAh/g, which is in contrast to 100mAh/g of the present invention. The comparison is summarized in table 1 below:

table 1:

	the invention	Porcher et al
			Capacity per unit area [ mAh/cm²]	13	3
Active substance load [ mg/cm²]	76	20
			Thickness of electrode [ mu ] m]	500	200
Specific discharge capacity [ mAh \| g for 10C]	100	18

Fig. 6 shows the resistance R value of the electrode measured on the E-cell after charging as a function of the number of cycles. The resistance of the electrode is maintained substantially constant in the range of 0.6-0.8 ohms despite the very high discharge rate.

Test 2:

for this test, a wound battery of the SubC type was produced, the electrode having a thickness of 17mAh/cm²Capacity (positive electrode with LEP substance as in experiment 1).

The electrodes were wound into a roll with the separator between them and placed in a SubC housing. Then using a composition of LiAlCl₄·6SO₂The electrolyte solution of (a) fills them.

The battery was charged to 831mAh at a charge rate of 0.7C. The discharge current is 10A, which corresponds to a discharge rate of 7C. The discharge was stopped at a battery voltage of 2V, and the extraction capacity was 728 mAh. This corresponds to a charge capacity of 88%. It can therefore demonstrate high current carrying capacity.

Test 3:

using the positive electrode of the present invention and a positive electrode containing lithium cobalt oxide as an active material but having otherwise the same characteristics, the relationship of capacity in an E-cell to the number of charge-discharge cycles (each having 1C) was determined.

FIG. 7 shows the use of a catalyst containing 1.5 mol of SO₂SO per mole of conductive salt (lithium aluminum tetrachloride)₂The results obtained with the electrolyte. Discharge capacity Q_D(percentage of theoretical value) is plotted against the number of charges and discharges performed,here curve a relates to the LEP electrode and curve B relates to the lithium cobalt oxide electrode. It is clear that almost the entire theoretical capacity can be used practically with LEP electrodes, while on average only about 60% of the theoretical capacity can be used in practice for comparative electrodes. This essentially compensates for the higher theoretical capacity of lithium cobalt oxide (273mAh/g) compared to LEP (170 mAh/g).

Fig. 8 shows the results of a test which differs from the test on which fig. 7 is based only in the concentration of the conductive salt in the electrolyte. In this case, it is 4.5 mol SO₂Molal LiAlCl₄. It is clear that LEP electrodes also perform very well in electrolytes containing low concentrations of conductive salts (curve a), while for lithium cobalt oxide electrodes the capacity drops rapidly to an unacceptably low value (curve B).

Test 4:

FIG. 9 shows the results of an experiment in which a full cell (with carbon negative electrode, SO) of the present invention was used₂Electrolyte and capacity of 19mAh/cm of the invention²Was compared with a battery identical in terms of other values, having a positive electrode based on lithium cobalt oxide (curve B). In this case, the electrolyte contains 6 moles of SO₂Molal LiAlCl₄。

Discharge capacity Q_D(percentage of nominal value) is plotted against cycle number. After the initial decrease, the extractable capacity of the cells of the invention is almost constant, while the capacity of the comparative cells decreases rapidly to an unacceptably low value. This demonstrates the superiority of the cell of the invention, particularly with cells containing a relatively high proportion of SO₂This is especially true for the electrolyte combinations of (1).

In summary, it has been found to be advantageous in the context of the present invention to use an electrolyte having a relative SO content₂Relatively low conductive salt content in terms of amount. This is in contrast to what has been given in the publications to date in respect of lithium-SO₂The main recommended content of the battery is contradictory to the use of a battery with a relatively low SO₂The proportion of electrolyte, in particular, is in contradiction to the vapor pressure.

Instead of or in addition to high SO₂In addition to the content, the capacity stability of the invention can be improved by adding lithium halides, preferably lithium chloride, according to a further preferred embodiment such salts are contained in the active material of the positive electrode, in particular as admixtures.

FIG. 10 shows the results of a long-term test on the battery of curve A of FIG. 9, where the capacity Q to be extracted_DRe-plot for cycle number. The figure shows about 9700 cycles, where the reduction in extractable capacity per 100 cycles is extremely low: less than 0.4%.

Pretreatment of the reduction coating:

as mentioned above, the lithium-SO with at least one intercalation electrode, in particular an intercalation electrode, may be improved by means of a pretreatment of the at least one intercalation electrode for reducing the cover layer₂The capacity stability of the battery. There are different possibilities for this.

A first possibility is to subject the embedded electrode to a tempering treatment. This applies in particular to carbon electrodes which are tempered at a temperature of at least 900 ℃ for a long time (at least 10, preferably at least 20 and particularly preferably at least 40 hours) under an excess of oxygen, preferably under a protective gas.

Alternatively or additionally, the formation of a coating on the carbon anode may be reduced by using a graphite material having a relatively low specific surface area.

According to a further preferred embodiment, the pretreatment for reducing the cover layer is achieved by providing the respective electrode with a thin surface coating.

Such surface coatings can be realized in particular by means of atomic layer deposition. This approach has recently been used for a number of purposes. A review is given, for example, in the following publications:

(13)S.M.George“AtomicLayerDeposition：AnOverview”，Chem.Rev.2010，111-131

the process parameters have to be adapted to the requirements of the electrode. In the context of the present invention, it has been found that if the carbon electrode is used with NO₂-TMA (nitrogen dioxide-trimethylaluminum) pretreatment, particular advantages can be obtained. This implants a first functional layer on the carbon, which layer is advantageous for the subsequent ALD process. For this purpose, reference may be made to the following documents

(14) Sundaram et al, "LeadingEdgeAtomicLayerPaostion applications", ECSTRansactions, 2008, 19-27

Al is preferably applied by ALD₂O₃A thin layer. According to the state of the art, SiO may also be applied₂。

Another possibility suitable for applying a surface coating of the reduction coating is dip coating. For this purpose, the intercalation active material intended for processing into the electrode or the entire electrode is brought into contact with a reaction solution comprising the starting materials forming the appropriate layer. A tempering treatment is then performed to form and harden the layer. This can be done, for example, as follows:

isopropyl alcohol, water, 1 molar hydrochloric acid and tetraethyl orthosilicate were mixed in a ratio of 3: 1: 1: 1, were mixed. The solution was kept at room temperature. It was then mixed with isopropanol in a ratio of 1: 1, in a volume ratio. The electrode to be treated is immersed in the reaction solution for 30s, or if bubble formation is observed, until bubble formation ceases. The electrodes were then dried in a drying chamber at 200 ℃ for 48 hours without vacuum.

Fig. 11 shows the results of an experiment performed using the following electrode materials:

a negative electrode without pretreatment for reducing coating

B negative electrode, where the active material is pretreated to form SiO by means of dip coating before introduction into the electrode₂Layer(s)

C negative electrode, the whole of which is pretreated by dip coating to form SiO₂And (3) a layer.

Three test electrodes were tested in an E-cell and the voltage U (volts) of lithium was plotted against the charged state Q (as the rated capacity Q) during charging of the electrodes_NScores). The three curve sets shown represent the results of a number of experiments in each case using the electrodes described above. In fig. 11, the area under the curve corresponds to the loss of battery capacity due to the formation of the cover layer. It is clear that for both pre-treated electrodes, the capacity loss is significantly less than for the untreated electrode, with the electrode pre-treated in its entirety being slightly more dominant in both pre-treated electrodes.

Claims

1. A rechargeable lithium battery cell having a housing, a positive electrode, a negative electrode and an electrolyte containing a conductive salt, wherein the electrolyte comprises at least 2 moles SO₂The positive electrode comprises a composition of LiFePO per mole of conductive salt₄And the positive electrode has a current collector element with a three-dimensional porous metal structure.

2. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the positive electrode is at least 0.25 mm.

3. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the positive electrode is at least 0.3 mm.

4. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the positive electrode is at least 0.4 mm.

5. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the positive electrode is at least 0.5 mm.

6. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the positive electrode is at least 0.6 mm.

7. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises at least 30mg/cm based on its area²The active material of (1).

8. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises at least 40mg/cm based on its area²The active material of (1).

9. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises at least 60mg/cm based on its area²The active material of (1).

10. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises at least 80mg/cm based on its area²The active material of (1).

11. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises a lithium-based electrolyteThe area of the surface is at least 100mg/cm²The active material of (1).

12. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises at least 120mg/cm based on its area²The active material of (1).

13. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises at least 140mg/cm based on its area²The active material of (1).

14. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode is porous.

15. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 50%.

16. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 45%.

17. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 40%.

18. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 35%.

19. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 30%.

20. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 25%.

21. Rechargeable lithium battery cell according to claim 14, characterized in that the porosity of the positive electrode is not more than 20%.

22. Rechargeable lithium battery cell according to claim 1, characterized in that the three-dimensional porous metal structure is in the form of a metal foam.

23. Rechargeable lithium battery cell according to claim 1, characterized in that the porous metal structure extends over at least 70% of the electrode thickness.

24. Rechargeable lithium battery cell according to claim 1, characterized in that the active material is substantially homogeneously distributed in the three-dimensional porous metal structure, wherein "substantially" is interpreted as such: the battery function is only slightly impaired by possible deviations.

25. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the negative electrode is at least 0.2 mm.

26. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the negative electrode is at least 0.3 mm.

27. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the negative electrode is at least 0.4 mm.

28. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the negative electrode is at least 0.5 mm.

29. Rechargeable lithium battery cell according to claim 1, characterized in that the thickness of the negative electrode is at least 0.6 mm.

30. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises a binder.

31. Rechargeable lithium battery cell according to claim 30, characterized in that the binder comprises a fluorinated binder.

32. Rechargeable lithium battery cell according to claim 31, characterized in that the binder comprises polyvinylidene 1, 1-difluoride.

33. Rechargeable lithium battery cell according to claim 31, characterized in that the fluorinated binder comprises a terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene 1, 1-difluoride.

34. Rechargeable lithium battery cell according to claim 30, characterized in that the concentration of the binder is not more than 10% by weight.

35. Rechargeable lithium battery cell according to claim 30, characterized in that the concentration of the binder is not more than 7% by weight.

36. Rechargeable lithium battery cell according to claim 30, characterized in that the concentration of the binder is not more than 5% by weight.

37. Rechargeable lithium battery cell according to claim 30, characterized in that the concentration of the binder is not more than 2% by weight.

38. Rechargeable lithium battery cell according to claim 1, characterized in that the negative electrode comprises carbon for absorbing lithium ions.

39. Rechargeable lithium battery cell according to claim 1, characterized in that the amount of active material of the negative electrode is at least 10mg/cm based on its area²。

40. Rechargeable lithium battery cell according to claim 39, characterized in that the amount of active material of the negative electrode is at least 20mg/cm based on its area²。

41. Rechargeable lithium battery cell according to claim 39, characterized in that the amount of active material of the negative electrode is at least 40mg/cm based on its area²。

42. Rechargeable lithium battery cell according to claim 39, characterized in that the amount of active material of the negative electrode is at least 60mg/cm based on its area²。

43. Rechargeable lithium battery cell according to claim 39, characterized in that the amount of active material of the negative electrode is at least 80mg/cm based on its area²。

44. Rechargeable lithium battery cell according to claim 1, characterized in that the amount of active material of the negative electrode is at least 140mg/cm based on its area²。

45. Rechargeable lithium battery cell according to claim 1, characterized in that the negative electrode is porous.

46. The rechargeable lithium battery cell according to claim 45, characterized in that the porosity of the negative electrode is not more than 50%.

47. The rechargeable lithium battery cell according to claim 45, characterized in that the porosity of the negative electrode is not more than 45%.

48. The rechargeable lithium battery cell according to claim 45, characterized in that the porosity of the negative electrode is not more than 40%.

49. The rechargeable lithium battery cell according to claim 45, characterized in that the porosity of the negative electrode is not more than 35%.

50. The rechargeable lithium battery cell according to claim 45, characterized in that the porosity of the negative electrode is not more than 30%.

51. Rechargeable lithium battery cell according to claim 1, characterized in that the negative electrode comprises a binder.

52. Rechargeable lithium battery cell according to claim 51, characterized in that the binder comprises a fluorinated binder.

53. The rechargeable lithium battery cell according to claim 51, characterized in that the binder comprises polyvinylidene 1, 1-difluoride.

54. The rechargeable lithium battery cell according to claim 51, characterized in that the binder comprises a terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene 1, 1-difluoride.

55. The rechargeable lithium battery cell according to claim 51, characterized in that the concentration of the binder is not more than 5 weight percent.

56. The rechargeable lithium battery cell according to claim 51, characterized in that the concentration of the binder is not more than 3 weight percent.

57. The rechargeable lithium battery cell according to claim 51, characterized in that the concentration of the binder is not more than 1 weight percent.

58. Rechargeable lithium battery cell according to claim 1, characterized in that the electrolyte comprises at least 2.5 mol SO₂Per mole of conductive salt.

59. Rechargeable lithium battery cell according to claim 1, characterized in that the electrolyte comprises at least 3 moles of SO₂Per mole of conductive salt.

60. Rechargeable lithium battery cell according to claim 1, characterized in that the electrolyte comprises at least 4 mol SO₂Per mole of conductive salt.

61. Rechargeable lithium battery cell according to claim 1, characterized in that the electrolyte comprises as conductive salt a halide, oxalate, borate, phosphate, arsenate or gallate.

62. Rechargeable lithium battery cell according to claim 1, characterized in that the electrolyte comprises lithium tetrahaloaluminate as conductive salt.

63. Rechargeable lithium battery cell according to claim 1, characterized in that the electrolyte comprises lithium aluminum tetrachloride as conductive salt.

64. Rechargeable lithium battery cell according to claim 1, characterized in that the current carrying capacity of the cell is at least 10mA/cm based on the area of the positive electrode²。

65. Rechargeable lithium battery cell according to claim 1, characterized in that the current carrying capacity of the cell is at least 50mA/cm based on the area of the positive electrode²。

66. Rechargeable lithium battery cell according to claim 1, characterized in that the current carrying capacity of the cell is at least 150mA/cm based on the area of the positive electrode²。

67. Rechargeable lithium battery cell according to claim 1, characterized in that the positive electrode comprises a lithium halide.

68. Rechargeable lithium battery cell according to claim 67, characterized in that a lithium halide is mixed with the active material of the positive electrode.

69. Rechargeable lithium battery cell according to claim 67, characterized in that lithium chloride is mixed with the active material of the positive electrode.

70. A rechargeable lithium battery cell according to any of the preceding claims having a housing, a positive electrode, a negative electrode and an electrolyte containing a conductive salt, wherein the electrolyte is based on SO₂And at least one electrode is an intercalation electrode adapted to absorb lithium ions, which is subjected to a pretreatment for reducing the capping layer.

71. Rechargeable lithium battery cell according to claim 70, characterized in that at least one electrode is pre-treated for reducing the cover layer by means of a surface coating of the active material.

72. Rechargeable lithium battery cell according to claim 71, characterized in that the surface coating is applied by means of atomic layer deposition.

73. Rechargeable lithium battery cell according to claim 72, characterized in that the surface coating contains Al₂O₃Or SiO₂。

74. Rechargeable lithium battery cell according to claim 71, characterized in that the surface coating is applied by means of dip coating.

75. Rechargeable lithium battery cell according to claim 74, characterized in that the surface coating contains SiO₂。

76. Method for producing an electrode for a rechargeable lithium battery cell according to any of claims 1 to 65, characterized in that it is carried out by the following steps:

-producing a paste-like mass from the active material, optionally with addition of a binder and/or a conductivity improver;

-homogeneously mixing the pasty mass into a three-dimensional porous metal structure;

-pressurizing the three-dimensional metal structure containing the pasty mass in such a way that: so that its thickness is reduced.

77. Method for producing an electrode for a rechargeable lithium battery cell according to claim 76, characterized in that the three-dimensional metal structure containing the paste-like mass is pressurized in such a way that: such that its thickness is reduced by at least 20%.

78. An electrode produced according to the method of claim 76.