DE102009027397A1 - Battery cell of a rechargeable battery, battery and method for enabling a deep discharge of the battery cell - Google Patents

Abstract

The invention relates to a battery cell (2) of a rechargeable battery (1) having a positive electrode (4) having a first active material (8) and a negative electrode (5) having a second active material (10), each of the electrodes ( 4, 5) is assigned a respective potential range (17, 18) of its electrical potential, which enables a permanently reversible redox reaction of the active materials (8, 10). It is provided that the battery cell (2) at least one further material (13, 14) for forming an additional redox system, the at least one of the potentials of the electrodes (4, 5) by means of a further redox reaction in its associated potential region (17, 18). stable holds.
The invention further relates to a corresponding rechargeable battery (1) and a corresponding method for enabling a deep discharge of a battery cell (2).

Description

The The invention relates to a battery cell of a rechargeable battery with a positive electrode having a first active material and a negative electrode having a second active material, wherein each of the electrodes is a respective potential region of its associated with electrical potential, which is a permanently reversible Redox reaction of the active materials allows.

State of the art

A Such a battery cell is a battery cell, for example secondary Lithium-ion battery known. The positive electrode of such a battery cell For example, lithium cobalt dioxide is the first active material and a positive current collector made of aluminum and the negative For example, electrode includes graphite as the second active material and a negative current collector of copper, wherein between the electrodes a separator is arranged. The first active material and the second active material consist of a single component or of several components.

battery cells secondary Lithium-ion batteries (secondary Lithium cells that do not contain lithium metal) are currently in use electrical energy storage and currently come, for example, in portable electrical appliances such as cell phones, laptops, camcorders, MP3 players and electric hand tools (Powertools) are used. The use of these batteries for food of electric drive machines in the vehicle sector is also already realized. The term secondary lithium cells covers all Rechargeable lithium cells of different geometry and Cell chemistry.

The secondary Lithium-ion battery is superior to other battery technologies a comparatively high energy density. It is thermally stable, delivers over the discharge period is a substantially constant voltage.

The Charging this designed as rechargeable batteries electrical Memory is done by means of a charger or integrated in memory Loading units. When loading need among other things, according to the respective cell type specific maximum Charging current values, temperatures and end-of-charge voltages to obtain the functionality and for the warranty the safe operation of the battery cell are maintained. When discharging have to Cell parameters such as current limits, temperature limits and End-of-discharge voltages of the individual battery cells monitored and be respected. Essential for the unloading is in particular the compliance with the manufacturer Discharge voltage.

The Adhering to the cell parameters requires electronic control and Protective devices, which with costs but also an additional space requirement accompanied.

Disclosure of the invention

According to the invention, it is provided that the battery cell at least one further material for training an additional one Redox system having at least one of the potentials of the electrodes by means of a further redox reaction in its associated potential range stable. Such an extra Redox system allows thus a deep discharge of the battery cell up to a voltage well below a given by the manufacturer of the battery Discharge voltage. Under deep discharge here is the discharge down to a cell voltage of 0 V understood. The extra Redox system stops the potential of the at least one electrode at least when falling below the final discharge voltage by means of the further redox reaction in their associated potential areas stable. Preferably, the extra holds Redox system both potentials of the electrodes in their associated Potential areas stable.

By the at least one further material of the battery cells, so a or more additive cell component (s), it is guaranteed that the Potentials of the positive and negative electrodes during discharge within their respective potential ranges for proper operation the battery cell (electrochemical stability window) remain.

conventional Battery cells with preset discharge voltage - like them for example in laptops or electric hand tools (Powertools) can be used - can through a deep discharge, however, be irreversibly damaged if the manufacturer specified respective potential ranges for proper operation or leave a resulting voltage window becomes. The associated "safety reserve" is used Among other things, to asymmetric aging of the To buffer electrodes. Particularly important is the content of the invention also for serially connected battery cells where not every single one Battery cell is monitored for their voltage level.

at a battery cell according to the invention can the monitoring effort by the further redox reaction described here, however, strong reduced or a surveillance Completely be omitted.

According to a preferred embodiment The invention provides that each of the electrical potentials in the course of a discharge of the battery cell enters a common potential window and both potentials are kept stable by the further redox reaction in this common potential window. In this case, provision is made in particular for the electrical potentials Φ to be kept stable by the further redox reaction at levels which deviate from one another by less than 0.3 V, preferably by less than 0.2 V and particularly preferably by less than 0.1 V. The potential Φp of the positive electrode is preferably at the same level or only slightly higher than the potential Φn of the negative electrode. This case has the advantage that the battery cell is stable and storable at about 0-0.3 V (Φp - Φn = 0 V ... 0.3 V) and furthermore a short circuit does not give any significant amounts of energy. In general, however, other potential layers of positive and negative electrodes are conceivable as long as the potential window of the electrodes is not left. Theoretically, the redox reaction at the positive electrode may also take place at a lower potential than that of the negative electrode, as long as the common potential window is not left.

With Advantage is provided that the positive electrode and / or the negative electrode and / or an electrolyte of the battery cell the has further material. The stabilization can be achieved by the further redox reaction within the positive and / or negative electrode but also within of the electrolyte happen.

Especially is provided that the positive electrode continues to be a positive Current collector of a first arrester material and the negative Electrode continues to have a negative current collector from a second Ableitermaterial has. In particular, it is provided that the positive current collector and / or the first active material and / or the negative current collector and / or the second active material and / or the electrolyte of the battery cell has the further material.

According to one preferred embodiment of Invention is provided that the rechargeable battery a secondary Lithium-ion battery is. Due to their high specific energy and power densities are battery cells of a secondary lithium ion Battery (lithium secondary cells) currently all possible Fields of application for grid electrical machinery and equipment to conquer. The spectrum of technologies used is included very large. So come the most diverse materials in the battery cells for use. This refers to all components of the cell, such as Example active and passive materials of positive and passive negative electrodes, the components of the electrolyte respectively the electrolyte solution, Separators, the current collectors and housing materials of a housing of the Battery cell.

The positive electrode of the battery cell of a secondary lithium ion For example, battery comprises lithium cobalt dioxide as the first active one Material and a positive current collector of aluminum on and For example, the negative electrode has graphite as the second active one Material and a negative current collector made of copper. Of the Electrolyte allows the movement of positively charged lithium ions. Between the electrodes the separator is arranged.

Furthermore There are many different types of battery cells that are not only the outer geometry but also affect the internal mechanical structure of the cells. The used positive and negative electrodes can be used for Example wrapped, stacked or generally in any Geometry, separated by a separator face. The cell types are mostly optimized for specific applications, such as high energy content, as with other laptop cells, or high Power deliveries, such as electric hand tools or HEV applications (HEV: hybrid electric vehicle).

When Designs of the battery cells come in particular the following forms in question: 18650, 26650, sub-C or other cylindrical housing, pouch cells, prismatic geometry. As cell types are both Li-ion, Li-polymer and cells with lithium metal and inorganic electrolyte solutions for Commitment.

electrochemical active substances are in particular graphites, amorphous carbon, Metals, alloys, lithable metal oxides, phosphates, sulfides, organic storage substances, sulfur compounds and mixtures it.

From Of particular interest are combinations of active components which size Lithium storage and a big one Possess cell voltage. this makes possible in the episode big Energy content for the battery cells. As an example, here is the well-known material combination Called graphite / lithium cobalt dioxide, which has an average cell voltage from about 3.6-3.8 V allows.

Due to safety and stability issues, positive electrode materials such as nickel / manganese / cobalt / aluminum mixed oxides, lithium metal phosphates or lithium manganese spinels are currently being used. Any mixtures of these are possible and can already be found in real use. The negative electrodes graphite and amorphous carbons are used, and hybrid electrodes with lithium alloy portions are ge bräuchlich. Lithium alloy electrodes are planned for the future, with tin, silicon, and their oxides as promising alloying components currently being discussed. For example, inorganic electrolyte solutions, ionic liquids and alloy electrodes are also under development in the future.

According to one further advantageous embodiment of the invention is provided that the further material of the battery cell is a lithium compound is. The admixture of a lithium compound (inorganic or also organic), which does not or only little to the energy content of the Cell contributes, but the potential of the positive and / or negative electrode in the holding electrochemically stable area is particularly advantageous.

With particular advantage, the lithium compound is a lithium metal oxide, in particular lithium titanate (Li ₄ Ti ₅ O ₁₂ ). In particular, the lithium metal oxide, preferably the lithium titanate, is added to the positive and / or negative electrode. During deep discharge, lithium is then removed from the lithium titanate on the side of the positive electrode and lithium is incorporated into the lithium titanate on the side of the negative electrode. In the charged state of the battery cell, the titanate on the negative electrode would be lithiated and delithiated on the positive electrode. The kinetics of the titanate charge or titanate discharge is not rate-determining, in order to ensure that during the dumping / storage potential of this additive, a stabilized level (holding point) occurs in the course of the discharge curve. If this were not the case, then the known damage would take place on the electrodes.

For the here described functionality come further all Lithium compounds (such as metal oxides) as another material in question, which in the discharged and / or charged state a sufficient ensure chemical and electrochemical stability and mechanically stable are and which are within the harmless potential window the used active materials on the negative and positive Electrode is located. Conceivable alternative materials further Materials are, for example, all other lithable transition metal oxides, Phosphates, u. s. w., such as vanadium compounds, Molybdenum, Titanium, chromium, niobium, rubidium, manganese and tungsten. Also mixed oxides, Mixed phosphates, oxide mixtures, phosphate mixtures, organic lithium compounds and combinations thereof can be used as other materials.

It in particular, localized in the positive and negative electrode Redox partners are used, which consist of the same base material, but also various redox systems are conceivable, the redox systems are to be selected according to their effective potential positions and stability ranges.

alternative it is envisaged that the battery cell at least two other materials to form the redox system. Such a redox system becomes close to or within the positive or the electrolyte given the negative electrode. Also lithium compounds are usable as further materials. This can be done, for example the uptake of these materials in gelified electrolytes the positive or negative side of the arranged between the electrodes Separators happen or as an addition to the solid electrode components such as binders, active components or conductivity components. For example can also redox systems are used similar to the currently discussed Substances for overcharge protection. When overload protection is however, diffusing these substances between positive and negative electrode required by a continuous shuttle mechanism to enable. The potential-stabilizing reactions must be fast enough can, to drift the electrode potentials into areas outside of the allowed potential window to avoid.

Especially it is envisaged that the redox system will be an inorganic redox system or an organic redox system. It is preferably provided that the redox system is a mobile redox system or an immobile Redox system is.

The The invention further relates to a rechargeable battery with at least one aforementioned battery cell. The battery preferably has a plurality of battery cells connected in series electrically on.

The Invention finally relates a method of enabling a deep discharge of at least one battery cell of a rechargeable battery. According to the invention, it is provided the battery cell has a first active material positive electrode and a second active material having having negative electrode, each of the electrodes being a respective one Potential range of their electrical potential is assigned, the one permitting a permanently reversible redox reaction of the active materials and wherein the battery cell at least one further material for training an additional one Redox system having at least one of the potentials of the electrodes by means of a further redox reaction in its associated potential range stable.

By the method according to the invention, the monitoring effort can be greatly reduced by the further redox reaction described here or a monitoring completely omitted.

According to one preferred embodiment of Invention is provided that each of the electrical potentials in the course of a discharge of the battery cell into a common Potential window passes and both potentials through the other Redox reaction kept stable in this common potential window become.

Especially It is intended that the rechargeable battery be a secondary lithium-ion battery is.

The The invention will be explained in more detail with reference to the accompanying drawings. It demonstrate:

1 the construction of a battery cell according to a preferred embodiment of the invention in a schematic representation and

2 a diagram in which the voltage of the electrodes in dependence on a state of charge of a battery cell according to the invention compared to a battery cell of a conventional secondary lithium-ion battery is applied.

The 1 shows the schematic structure of a secondary lithium-ion battery (lithium-ion battery) trained rechargeable battery 1 with a single battery cell 2 , The battery cell 2 is in a battery case 3 the battery 1 arranged and has a positive electrode 4 , a negative electrode 5 and one in the battery cell 2 between the electrodes 4 . 5 arranged separator 6 on. The positive electrode 4 has a positive current collector 7 and a first active material 8th on at least one surface of the positive current collector 7 on. The negative electrode 5 has a negative current collector 9 and a second active material 10 on at least one surface of the negative current collector 9 on. The two electrodes 4 . 5 are in the example of 1 via an external wiring 11 with one the voltage between the electrodes 4 . 5 measuring voltmeter electrically connected. Real electrodes usually require additions of binders and conductivity additives to electronically couple the volume. The first active material 8th and the second active material 10 can consist of a single component or of several components.

The positive current collector 7 consists in the illustrated embodiment of aluminum, the negative current collector 9 made of copper. On the one surface of the positive current collector 7 In particular, lithium cobalt dioxide (LiCoO ₂ ) is the first active material 8th arranged. Alternatively to the use of lithium cobalt dioxide as the first active material 8th It is also preferred to use lithium nickel dioxide (LiCoO ₂ ), manganese spinel (LiMn ₂ O ₄ ), NCM (LiNi _0.33 Co _0.33 Mn _0.33 O ₂ ) or a mixture of NCM and manganese spinel or another lithium metal oxide.

The potential of the current collector 7 . 9 For example, via conductivity additives to each area in the electrode volume of the electrode 4 . 5 brought. The active material 8th . 10 is connected via an "electron conductor" to the potential of the current collector (arrester).

The secondary Lithium-ion battery is characterized by high energy density (gravimetric and volumetric).

The operation of the secondary lithium-ion battery is based on a due to the different electrochemical potentials of lithium in the two electrodes 4 . 5 resulting source voltage. At the end of the cell reaction, lithium ions are then shifted from one electrode to the other electrode.

During the charging process, positively charged lithium ions (Li ⁺ ions) migrate through the electrolyte from the positive electrode 4 between the graphite planes of the second active material 10 the negative electrode 5 while a charge current drives the electrons across the external circuitry 11 supplies; The lithium ions form an intercalation compound (LixnC) with the carbon (graphite). During discharge, the lithium ions migrate back into the metal oxide formed as lithium cobalt dioxide, and the electrons can pass through the external wiring 11 the battery 1 positive electrode 4 flow.

For anodes (negative electrodes 5 ) with anode materials "high voltage position" applies: Essential for the functioning of the intercalation is the formation of a protective cover layer 12 on the negative electrode 5 which is permeable to the small lithium ions but impermeable to solvent molecules.

Real electrodes 4 . 5 In most cases they are coated on both sides, porous and have cover layers on nearly all active materials 12 on. Due to the required porosity are the outer layers 12 also present in the electrode volume.

• a) die elektrochemische Auflösung des negativen Stromkollektors 9 (Beispiel: Kupfer-Ableiter, dadurch u. a. Kontaktverlust des zweiten aktiven Materials 10),
• b) die Auflösung der Deckschicht 12 auf der negativen Elektrode 5 mit Graphit als zweitem aktivem Material 10 (dadurch u. a. irreversibler Lithiumverlust während der Zyklisierung),
• c) die irreversible elektrochemische Reduktion des ersten aktiven Materials 8 (Beispiel: Lithium-Metall-Oxid, oder Lithium-Metall-Phosphat),
• d) die Lithierung des positiven Stromkollektors 7 (Beispiel Aluminium-Ableitermaterial, dadurch unter anderem starke Volumenarbeit und Strukturinstabilität),
• e) irreversible oder passivierende Phasenumwandlungen in den aktiven Materialien (Beispiel: Manganspinell) und
• f) die Lithierung von Leitfähigkeitszusätzen in der positiven Elektrode 4, dadurch unter anderem strukturelle Schädigungen und mechanischer Stress.

battery cells 2 Of secondary lithium batteries, which are allowed to deliver 3-4 V voltage mostly only up to cell voltages ≤ (not greater than) one in 2 discharge voltage Vls (V cell ≦ Vls) in the range of about 2.0 to 2.7 V are discharged. Being deeper discharged can cause various irreversible damage, such as for example:

• a) the electrochemical dissolution of the negative current collector 9 (Example: copper arrester, thereby, inter alia contact loss of the second active material 10 )
• b) the resolution of the topcoat 12 on the negative electrode 5 with graphite as the second active material 10 (thereby irreversible lithium loss during cyclization)
• c) the irreversible electrochemical reduction of the first active material 8th (Example: lithium metal oxide, or lithium metal phosphate),
• d) the lithiation of the positive current collector 7 (Example aluminum arrester material, thereby among other things strong volume work and structural instability),
• e) irreversible or passivating phase transformations in the active materials (example: manganese spinel) and
• f) the lithiation of conductivity additives in the positive electrode 4 , among other things, structural damage and mechanical stress.

All these effects are in their occurrence (potential position, damage rate, etc.) also dependent on the environment in which they are operated. This applies in particular to the type of solvent and the conductive salts (electrolyte solution) contained therein and to all other additives in the electrolyte and in the electrode materials (here, for example, binders and conductivity additives). Furthermore, residual moisture in the battery cell 2 and other contaminants that affect damage processes and damage kinetics.

To a these effects avoiding deep discharge capacity of the battery cell according to the invention 2 to reach includes the positive electrode 4 next to the first active material 8th in the example of 1 also lithium titanate (Li ₄ Ti ₅ O ₁₂ ) as another material 13 , On the one surface of the negative current collector 9 is next to intercalation enabling carbon in the form of graphite as the second active material 10 also lithium titanate as another material 14 arranged. This further material 14 is part of the negative electrode 5 ,

The 2 shows a schematic representation of the course 15 the potential Φp of the positive electrode 4 and the course 16 the potential Φn of the negative electrode 5 - Measured against lithium reference potential - during a discharge of the battery cell 2 (Course 16 . 17 the discharge curves). It must be ensured that the respective course 15 . 16 of the potential always in a respective potential range 17 . 18 remains to the permanently reversible redox reaction of the active materials 8th . 10 to ensure. By introducing the other material 13 . 14 (Li ₄ Ti ₅ O _{12 in this case} ), an additional redox system is formed, which enhances the potentials of the electrodes 4 . 5 after falling below the difference of these potentials below the discharge final voltage Vls in a common potential window 19 the potential areas 17 . 18 at a first level 20 the potential of the positive electrode 4 and a second level 21 the potential of the negative electrode 5 stable. Depending on the amount of added additional material 13 . 14 This condition can be guaranteed for a longer or shorter time.

In 2 Furthermore, the course of the electrode potentials is given, as would occur in a current non-inventive Li-ion cell. course 15 schematically shows the potential of the positive electrode 4 as it might occur when using a Ni / Co oxide. The extension 22 of the course 16 schematically indicates the course of the potential of the negative electrode 5 as it might occur in the case of a carbon-based intercalation electrode. In the direction of large discharge capacity values C is leaving the common potential window 19 positive or negative electrode 4 . 5 outlined as it is when over-discharging the conventional battery cell 2 can occur.

In addition, the inventive delaying the harmful leaving the potential window 19 outlined. With continuous over-discharge, this condition would persist until the capacity reserves of the inserted component (s) are exhausted. This represents the stability / safety margin of the invention. As an example of one in the positive and negative electrodes 4 . 5 inserted further material 13 . 14 be here in 1 listed lithium titanate. This component has a redox potential of about 1.5V vs. Lithium potential. In normal operation of the cell, this component would be in the negative electrode 5 present in the lithiated state, in the positive electrode 4 then in the delithiated state. In addition, lithium titanate can also be designed sufficiently fast kinetically to also accommodate discharge currents of high-performance battery cells.

By the further material 13 . 14 Thus, the following additional property of the battery cell according to the invention results 2 the rechargeable battery 1 :
Each of the electrodes 4 . 5 is a respective potential area 17 . 18 associated with their electrical potential Φ, which is a permanently reversible redox reaction of the active materials 8th . 10 allows the battery cell 2 at least one more material 13 . 14 to form an additional redox system having both potentials of the electrodes 4 . 5 falls below a discharge final voltage Vls by means of a further redox reaction in each case arranged potential area 17 . 18 - here in the common potential window 19 - keeps stable.

Each of the electrical potentials Φ passes in the course of a discharge of the battery cell 2 into the common potential window 19 where both potentials by the further redox reaction in this common potential window 19 are kept stable and the electrical potentials are kept stable by the further redox reaction to levels that differ by less than 0.1 V from each other.

Will you also dissolve the topcoat 12 on the negative electrode 5 Prevent, reduces the usable potential window 19 in general. For this case, the use of redox pairs of different potential position for each considered positive and negative electrode 4 . 5 meaningful. In this case, no discharge to 0 V is possible, but you still get a performance and safety advantage over standard cells, as most of the degeneration mechanisms remain off.

The cited invention may reduce the energy density of the battery cell 2 (depending on the weight and volume of the attached materials and the overall design of the cell components), since the additive added other materials 13 . 14 are not involved in the actual cell reaction. However, considering long cell / battery life, the invention may contribute to a longer useful life as damage mechanisms are bypassed. Furthermore, it should be noted that even current cell types on the market usually do not manage without surpluses of active materials to a safe and stable buoyancy of the battery cell 2 to ensure in the long run. This effort may optionally be limited by the invention described herein in return. Furthermore, this invention increases the level of security of the battery cell 2 , as over-discharge states of standard cells (associated with the potentials 22 . 23 ) for destruction, up to a mechanical destruction, the battery cell 2 being able to lead.

The invention is particularly in series-connected battery cells 2 (not shown) useful or to increase the inherent security and performance reserves to use. Overdischarges are major causes of capacity losses and internal resistance increases in systems without single voltage monitoring. Avoiding these degeneration mechanisms increases the life of the cells 2 and critical safety areas of the battery 1 are avoided.

Claims (13)

Battery cell of a rechargeable battery ( 1 ) with a first active material ( 8th ) having positive electrode ( 4 ) and a second active material ( 10 ) having negative electrode ( 5 ), each of the electrodes ( 4 . 5 ) a respective potential range ( 17 . 18 ) is assigned to its electrical potential (Φ), which is a permanently reversible redox reaction of the active materials ( 8th . 10 ), characterized by another material ( 13 . 14 ) for forming an additional redox system which has at least one of the potentials of the electrodes ( 4 . 5 ) by means of a further redox reaction in its associated potential range ( 17 . 18 ) keeps stable. Battery cell according to claim 1, characterized in that each of the electrical potentials in the course of a discharge of the battery cell ( 2 ) into a common potential window ( 19 ) and both potentials through the further redox reaction in this common potential window ( 19 ) are kept stable. Battery cell according to claim 2, characterized in that the electrical potentials by the further redox reaction at levels ( 20 . 21 ), which deviate from each other by less than 0.3V. Battery cell according to one of the preceding claims, characterized in that the positive electrode ( 4 ) and / or the negative electrode ( 5 ) and / or an electrolyte of the battery cell ( 2 ) the further material ( 13 . 14 ) having. Battery cell according to one of the preceding claims, that the positive electrode ( 4 ) continue to have a positive current collector ( 7 ) of a first arrester material and the negative electrode ( 5 ) continue to have a negative current collector ( 9 ) comprises a second arrester material. Battery cell according to one of the preceding claims, characterized in that the rechargeable battery ( 1 ) is a secondary lithium-ion battery. Battery cell according to one of the preceding claims, characterized in that the further material ( 13 . 14 ) of the battery cell is a lithium compound. Battery cell according to claim 7, characterized that the lithium compound is a lithium metal oxide, in particular Lithium titanate is. Battery cell according to one of claims 1 to 6, characterized in that the battery cell ( 2 ) at least two other materials ( 13 . 14 ) to form the redox system. Battery cell according to one of the preceding claims, characterized characterized in that the redox system is an inorganic redox system or an organic redox system. Battery cell according to one of the preceding claims, characterized in that the redox system is a mobile redox system or an immobile redox system is. Rechargeable battery with at least one battery cell according to one of the preceding claims. Method for enabling a deep discharge at least one battery cell of a rechargeable battery, wherein the battery cell has a first active material positive electrode and a second active material having and wherein each of the electrodes is a respective one Potential range of their electrical potential is assigned, the a permanently reversible redox reaction of the active materials allows wherein the battery cell at least one further material for training an additional one Redox system having at least one of the potentials of the electrodes by means of a further redox reaction in its associated potential range stable.

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