WO2010049035A1

WO2010049035A1 - Method for conditioning ion cells and ion cells conditioned according to said method in a device for generating electric energy

Info

Publication number: WO2010049035A1
Application number: PCT/EP2009/006647
Authority: WO
Inventors: Jörg Raimund HEMPEL
Original assignee: Imp Gmbh
Priority date: 2008-10-27
Filing date: 2009-09-14
Publication date: 2010-05-06
Also published as: DE102008053407A1

Abstract

The invention relates to a method for conditioning ion cells comprising the following steps: (a) generation of a magnetic field in the vicinity of at least one ion cell; (b) charging of the ion cell or cells to a nominal capacity; and (c) short-circuiting of the ion cell or cells over a period in which no discernible heating occurs. The invention also relates to a device for generating electric energy comprising at least one ion cell (1) and means for generating a magnetic field in the vicinity of the ion cell or cells (1).

Description

METHOD FOR CONDITIONING ION CELLS AND THEREOF

PROCESS CONDITIONED ION CELLS IN A DEVICE

GENERATION OF ELECTRICAL ENERGY

The present invention relates to a method for conditioning ion cells as well as to this method conditioned ion cells, in particular lithium-ion accumulators in a device for generating electrical energy.

Of all currently known ion cells, in particular lithium-ion accumulators have recently become the focus of interest. Lithium-ion batteries, or lithium-ion batteries for short, also known as Lilon batteries, are characterized by their high energy density, which is several thousand Wh / kg higher than with all other accumulators. In addition, the lithium-ion battery is thermally stable, has a constant output voltage over the entire discharge period, a long life and has no (controversial) memory effect.

A lithium-ion battery generates an electromotive force due to the displacement of lithium ions.

During the charging process, positively charged lithium ions migrate through an electrolyte from the cathode between the anode (nC) plating planes (intercalation) while the charging current supplies the electrons across the external circuit. The ions form an intercalation compound (LixnC) with the carbon. When discharging the lithium ions migrate back into the metal oxide and the Electrons can flow to the cathode via the external circuit.

Essential to the functioning of the intercalation is the formation of a protective overcoat on the negative electrode which is permeable to the small lithium plus ions but impermeable to solvent molecules. If the cover layer is insufficiently formed, lithium + ions intercalate together with the solvent molecules, irreversibly destroying the graphite electrode. The protective cover layer consists of common lithium-ion batteries of graphite, which is also called active material of the negative electrode (anode). (See also: http: //www.ac.uni- kiel. De / bensch / research areas / intercalation chemistry)

Deep discharge can deactivate (de-form) the protective covering layer of active material. Also, by overcharging, the active material can also be reduced by destruction (e.g., corrosion), poisoning (e.g., sulfation), passivation (e.g., memory effect), shorting (e.g., dendrite formation), electrolyte decomposition (e.g., dehydration), and the like.

With the common lithium-ion batteries, therefore, care must be taken to ensure that no operating conditions such as over-discharge or over-charging, overheating and the like occur, which may have a negative impact on the capacity of the lithium-ion battery. The capacity of a lithium-ion battery is for each individual battery individually dependent on preconditions such as age, temperature and the like and its conditioning.

Conditioning in this context means a specific procedure during the initial loading and unloading of the Lithium-ion batteries, which its achievable capacity can be significantly influenced positively.

For example, after their manufacture, lithium-ion batteries are charged for the first time with a low current intensity until the minimum voltage which corresponds to the deep discharge voltage is reached. Then they are charged from the deep discharge voltage with a constant current until reaching the rated voltage. Thereafter, they continue to be charged at a constant voltage until the charging current falls below a certain threshold, for example 3% of the initial current or the charging is terminated when the charging current no longer drops.

When discharging a lithium-ion battery, according to most manufacturers' instructions, a discharge should not occur below a discharge voltage of approximately 20% to 25% below the rated voltage in order not to shorten the life of the lithium-ion battery or not to unnecessarily reduce its capacity.

The above-described conditioning of lithium-ion batteries thus serves to achieve and maintain a high charge capacity and care of the lithium-ion battery to increase its life.

The present invention has for its object to provide a method for conditioning of ionic cells and a device for generating electrical energy, which has conditioned by this method ion cells, indicate that to a significant increase in the efficiency of the ion cells or the Guide device. This object is achieved with the features of claims 1 and 14.

In the subclaims features of preferred embodiments of the present invention are characterized.

The intercalation reaction occurring in a lithium-ion battery, i. the reversible incorporation of lithium ions into a solid host matrix modifies the electronic and magnetic properties of the overall system.

For example, pronounced antiferromagnetic interactions within the host compound, i. e.g. within the graphite can be attenuated by an increasing lithium content until in the fully intercalated material finally ferromagnetic exchange interactions dominate.

The present invention is based on the finding that the application of a magnetic field to such an ion cell leads to interactions which, with appropriate conditioning of the thus modified ion cells, leads to a considerable increase in the efficiency of the ion cells.

In the following the invention will be explained in more detail with reference to the explanation of exemplary embodiments and comparative experiments with reference to the drawing. Show:

Fig. 1 shows an embodiment of an ion cell arrangement (Ia) according to the invention, in cross-section (Ib) and a plan view of the magnetic strip (Ic) used; 2 schematically shows the interconnection of an ion cell with magnetic strip to be attached with a laboratory power supply;

Fig. 3 is a table comparing results of measurements in the conventional lithium ion cells and ion cells prepared in accordance with the present invention;

Fig. 4 current and voltage curve in test no. 1;

Fig. 5 Current and voltage curve in test no. 2;

Fig. 6 Current and voltage curve in test no. 3;

Fig. 7 Current and voltage curve in test no. 4;

Fig. 8 Current and voltage curve in test no. 5;

Fig. 9 Current and voltage curve in test no. 6;

FIG. 10 shows the course of current and voltage in test no. 7; FIG.

and

Fig. 11 Current and voltage course in test no. 8.

FIGS. 1 a to 1 c show an exploded view (FIG. 1 a), a cross section (FIG. 1 b) of the ion cell arrangement according to the invention and a top view of the manet strip 1 used.

A commercially available lithium-ion battery 2, here of the type SAMSUNG SF US 18650 GR with a rated voltage of 3.7 V is fitted with two magnetic strips 1. Magnetic strips of type 3M 300LSE, permanent magnet strip MGO 1317 Piastinorm are cut to the length of the rechargeable battery 2 and mounted diametrically opposite to the longitudinal axis of the rechargeable battery on the rechargeable battery cover. As shown in Fig. Ic, the magnetic strips 1 have an alternating polarity which extends in each case parallel to the longitudinal extent of the magnetic strip. The battery used has no protection circuit.

As the cross section shown in Fig. Ib shows the battery 2 is enveloped together with the magnetic strip 1 of a dielectric film 3, on which according to an embodiment of the present invention, an aluminum foil is attached, which completely envelopes the cylinder jacket of the battery.

The lithium-ion battery shown here is wound, similar to an electrolytic capacitor. Since it may possibly come to different thicknesses of the electrolyte layer located between the electrodes during winding, it is conceivable that not every location on the cylinder jacket for the magnetic strip shows the same effect. It has been observed that attaching a magnetic stripe to the battery causes a slight increase in the voltage of the lithium-ion battery. However, this increase in voltage was slightly different in the experiments performed with some lithium-ion batteries depending on the location of the magnetic strip.

Fig. 2 shows a test set-up with which the optimum mounting location of the magnetic strip was determined. For this purpose, a laboratory power supply with variable internal resistance and separately adjustable voltage as well as limitable current was connected to the poles of the lithium-ion battery and adjusted so that an additionally integrated into the circuit current meter showed no current flow. The means that the voltage provided by the laboratory power supply corresponded exactly to the output voltage of the lithium-ion battery. Subsequently, a magnetic strip was placed on the cylindrical surface of the battery and moved on this circular. It was found that a slightly higher output voltage was already set by the approach of the magnetic strip on the battery and a low current of one milliamper flowed back into the power supply via the ampermeter 6. Circular translation of the magnetic stripe has shown that not every radial position of the magnetic stripe results in the same return flow. The magnetic strip was finally left in place on the cylinder jacket of the battery where the current flowing back into the power supply was greatest. Subsequently, a second magnetic strip was mounted on the diametrically opposite side of the cylinder jacket of the battery. By this measure, as will be discussed in more detail below, the efficiency of the inventive device for generating electrical energy could be further increased.

The following is an experiment in which a series circuit of six prepared as described above lithium-ion batteries were first subjected to conditioning, which will be explained in more detail below and then charging and discharging were made with this structure and with a series circuit compared to six identical, commercial lithium-ion batteries.

For conditioning of a device according to the invention for generating electrical energy contained therein, equipped with magnetic strips ion cells or the single ion cell are charged in a first step to their nominal capacity. This can be done by a conventional method, as described above. Subsequently, the ion cells or the ionic Cell short-circuited over a short period of time in which there is no noticeable heating of the cell yet. It has been found that this period should not exceed five seconds, preferably the short circuit takes place over two seconds. A strong warming of the ion cell, ie over more than a few degrees C ⁰ , is absolutely to be avoided, since this indicates irreversible destruction processes within the cell.

An ion cell conditioned in this way, in particular a lithium-ion accumulator, already exhibits a higher efficiency, i. an increased compared to a conventional non-conditioned ion cell charge and energy output. This effect can be further increased if the following conditioning steps follow the short-circuiting. This is followed by another charging with a charging current between 10 mA to max. 400 mA to the poles of the cell is a voltage which is about 10% above the rated voltage of the cell and the charging current has dropped below 10 mA. Subsequently, the ion cell with a current of 80 mA to max. 600 mA controlled discharge until an abrupt voltage and Entladestromabfall is observed. Subsequently, the charging process described above is repeated and the ion cell discharged again controlled until an accelerated voltage drop is observed.

Such conditioning was carried out on SAMSUNG SF US 18650 GR lithium-ion batteries, charging with a charging current of 80 mA until a voltage of 4 V was applied to the cell's poles (rated voltage of the cell 3.7 V) ) and the charge current had dropped to 10 mA. Then the lithium-ion cell was discharged with a current of 160 mA until the voltage at the poles of the cell had dropped to 2.5V. After renewed Charging, as described above, the lithium-ion cell was discharged to a voltage of 2.95V.

Six such lithium-ion batteries, conditioned according to the method described above, were connected in series. Each battery was here described with reference to FIG. 1 provided with two magnetic strips and wrapped with the interposition of an insulating film with an aluminum foil.

For comparison purposes, a series circuit of six standard lithium-ion batteries of the same type was created. This set of lithium-ion batteries will be referred to below as LITH 1, whereas the modified and conditioned set LITH 2 will be named.

The following measurements were carried out on the αiesen ΛKkusätzen made a by the Stuttgart Chamber of Commerce and Industry publicly appointed and sworn expert for EMC in his rooms.

Fig. 3 shows a summary of the Messergebriisse. FIGS. 4 to 10 show the individual respectively recorded measurement curves of the voltage and current profile.

In Test No. 1 and Test No. 2, the LITH 1 and LITH 2 battery packs were discharged each until a voltage of 20 V was applied to their poles. The rated voltage of the batteries used is according to the manufacturer in each case 3.7 V. A series connection of 6 batteries thus results in a nominal voltage of the arrangement of 22.2 V. As shown in FIG. 5, the battery pack LITH 1 had a voltage of 22 at the beginning of the discharge process, 58 V whereas the LITH 2 battery set had a much higher initial voltage of 24.03 V. The removed Amount of charge that results during discharge to a relaxation of 20 V each and the corresponding energy is reproduced for the two battery sets in the table in Fig. 3. It can already be seen that a significantly higher charge quantity was taken from the modified LITH 2 battery pack, namely 464 mAh compared to 264 mAh at LITH 1.

Subsequently, the LITH 1 and LITH 2 battery packs were recharged in Tests 3 and 4. The output voltage before charging LITH 1 was 20.46 V, which self-adjusts after removal of the load after discharge. LITH 1 and LITH 2 were over a period of about 39 min. continuously charged with a current of 400 mA, at the end of the charging process with LITH 1 a final voltage of 22.8 V was established. During this period, the LITH 1 battery pack was supplied with 5.69 Wh of electrical energy. In LITH 2, the output voltage, which sets itself, was already at 22.8 V. During the approximately 39 min. For continuous continuous charging, LITH 2 was supplied with 4.24 Wh of electrical energy with a final voltage of 23.68 volts.

Subsequently, the battery packs LITH 1 and LITH 2 were again discharged in tests Nos. 5 and 6 to a discharge end voltage of 20 V. The output voltage of LITH 1 was 22, 27 V and the corresponding output voltage of LITH 2 at 22, 18 V. Up to the discharge end voltage of 20 V, LITH 1 electrical energy in the amount of 5.24 Wh and LITH 2 electrical energy in the amount of 4.64 Wh taken.

What is striking about these measurements is that with the modified LITH 2 battery pack a significantly higher charge quantity (438.6 mAh) was taken off than with the LITH 1 (245.3 mAh) battery pack. Also, the discharged electrical energy of 4.67 Wh when discharging LITH 2 is more than 10% larger than the 4.24 Wh supplied electric energy during charging.

In tests 7 and 8, in a recharging operation starting from an output voltage of 21.47 V at LITH 1 and at 22.49 V at LITH 2 again electric charge and thus electrical energy were supplied. The energy input was 4.05 Wh for LITH 1 and 4, 26 Wh for LITH 2.

When discharged again (tests 9 and 10), the energy consumption for the LITH 1 battery set was 3.84 Wh and for the LITH 2 battery set 4.44 Wh.

Also for this test, LITH 2 has a positive energy balance (charged 4.26 Wh, discharging 4.44 Wh), whereas the LITH 1 battery set behaved "normally" (charged 4.05 Wh, discharging 3.84 Wh).

In summary, it can be stated that in the repeated charging and discharging processes, the lithium ion battery packs that were equipped with magnetic strips and conditioned in the manner described above have a significantly better energy take-off balance than conventional ones Set lithium-ion batteries of the same type as used in the modified battery packs.

What is ultimately based on the increase in efficiency of modified lithium-ion batteries is currently not fully understood. It can be assumed that the magnetic fields applied to the lithium-ion batteries have an influence on the intercalation process within the electrolyte of the battery. With increasing incorporation of lithium ions into the host lattice of the electrolyte, this system shows increasing ferromagnetic interactions that can be affected by the externally applied magnetic field.

It is believed that the special conditioning of lithium-ion batteries provided with permanent magnets can increase the mobility of the lithium ions, so that the effects of the magnetic interactions are enhanced.

Claims

claims

1. A method of conditioning ionic cells comprising the steps of:

(a) generating a magnetic field at the location of the at least one ion cell;

(b) loading the at least one ion cell to its nominal capacity; and

(c) short-circuiting the at least one ionic cell for a period of time during which no noticeable heating occurs.

2. The method according to claim 1, characterized in that the short-circuiting takes place over a period of less than 5 seconds, preferably less than 2 seconds.

3. The method according to claim 1 or 2, characterized in that the ion cell (s) has positively charged ions of the metals Li, Na, Mg, Pd, Al, Zn, Cd, Pb or of compounds of these metals or have.

4. The method according to any one of claims 1 to 3, characterized in that the ion cell is a lithium-ion secondary battery whose positive electrode ions of the compounds L1COO2; LiNiO2j LiNuχCo _x θ2; Linio, 85Coo, iAlo.o5θ2; Linio, 33Coo, 33Mno, 33θ2; LiMn2Ü4 spinel or LiFePO4 has.

5. The method according to any one of claims 1 to 4, characterized in that the magnetic field is generated by at least one permanent magnet attached to the ion cell.

6. The method according to any one of the preceding claims, characterized in that the ion cell is cylindrical and two strip-shaped permanent magnets are arranged on the cell jacket parallel to the cell axis and diametrically opposite one another.

7. The method according to any one of claims 1 to 5, characterized in that the cell housing has the shape of a cuboid and at least two strip-shaped permanent magnets are mounted on opposite sides of the cuboid.

8. The method according to any one of the preceding claims, characterized in that the ion cells and optionally the permanent magnets attached thereto are surrounded by a dielectric film on which a metal foil is attached.

9. The method according to claim 8, characterized in that the metal foil is an aluminum foil.

10. The method according to any one of claims 1 to 8, characterized in that the ion cell is a lithium-ion secondary battery and further comprises the following steps:

(d) after short-circuiting (c), a further charging is carried out with a charging current of at least 10 mA to a maximum of 400 raA until a voltage is applied to the cell poles, the is about 10% above the rated voltage and the charging current has dropped below 10 mA;

(e) the ionic cell is discharged in a controlled manner at a current of 80 mA to a maximum of 600 mA until an abrupt voltage and discharge current drop is observed; and

(f) repeating step (d) and then

(g) the ion cell is again discharged in a controlled manner until an accelerated voltage drop is observed.

1 1. A method according to claim 10, characterized in that the ion cell is a lithium-ion cell and in step (d), the charging is carried out with a charging current of 80 mA until a voltage at the poles of the cell of 4 V. is applied and the charge current has dropped to 10 mA, the ion cell is discharged in a controlled manner with a current of 160 mA until the voltage of the ion cell has dropped to 2.5 V and in step (g) the ion cell is reduced to one Voltage of 2.95 V is discharged.

12. The method according to claim 6 or 7, characterized in that:

- The ion cell is connected to a power supply with variable internal resistance and with separately adjustable voltage and limitable current and the voltage of the power supply is set so that between power supply and ion cell no longer flows, and

- A magnetic strip on the lateral surface of the ion cell is moved parallel to its longitudinal axis until a maximum current is set, which flows back from the ion cell in the power supply.

13. The method according to claim 5, characterized in that the magnetic strips have substantially the length of the ion cell and run alternately north and south poles parallel to the longitudinal axis of the magnetic strip.

14. Device for generating electrical energy with at least one ion cell (1) and

Means for generating a magnetic field at the location of the at least one ion cell (1).

15. The apparatus according to claim 14, characterized in that the ion cell (1) is a lithium-ion battery.

16. The apparatus of claim 14 or claim 15, characterized in that the ion cell is cylindrical or cuboidal and the means for generating a magnetic field have at least one permanent magnet strip which is mounted parallel to the longitudinal axis of the ion cell on the cell jacket.

17. The apparatus according to claim 16, characterized in that two magnetic strips are arranged on diametrically opposite sides of the ion cell.

18. The device according to claim 17, characterized in that the magnetic strips have substantially the length of the ion cell in the direction of the longitudinal axis and have alternating side by side in the longitudinal axis direction extending north and south poles.

19. The apparatus according to claim 14, characterized in that the means for generating a magnetic field comprise an electromagnet.

20. Device according to one of claims 14 to 19, characterized in that the ion cell is conditioned by the method according to one of claims 1 to 13.