DE102018216521A1 - Battery cell with at least one electrochemical cell and method for producing the same - Google Patents

Abstract

The invention relates to a battery cell (102) with at least one electrochemical cell (100), which is an anode (108) and cathode 110) acting electrodes (104), at least one of the electrodes (104) on the side facing away from the separator (106) being electrically conductively connected to a flat, electrically conductive conductor (112), between the electrode (104) and the arrester (112) has a laterally open, electrically conductive, porous layer (122) for discharging gases.

Description

Field of the Invention

The invention relates to a battery cell with at least one electrochemical cell and a method for producing a battery cell with at least one electrochemical cell.

State of the art

In a battery cell, an electrolyte material can be used between an anode material and a cathode material. A single electrochemical cell of the battery cell has a stack of at least three layers, the anode material being contained in a first layer, but the electrolyte material being neither contained in the anode material nor the cathode material, and the cathode material being contained in a third layer . The stack is electrically connected to the two poles of the battery cell on opposite sides. The electrical connection can be made by so-called arresters, which are arranged as electrically conductive foils on the opposite sides.

Disclosure of the invention

Against this background, the approach presented here presents a battery cell with at least one electrochemical cell and a method for producing a battery cell with at least one electrochemical cell according to the independent claims. Advantageous further developments and improvements of the approach presented here result from the description and are described in the dependent claims.

Advantages of the invention

Embodiments of the present invention can advantageously make it possible to remove gases generated during a formation process or during the operation of a battery cell from a cell stack of the battery cell. Accumulation of the gases on electrically conductive foils acting as diffusion obstacles in the cell stack can be prevented, as a result of which process reliability can be increased and a reject rate can be reduced.

A battery cell with at least one electrochemical cell is proposed, the cell being formed by two electrodes which are electrically separated using a separator made of solid electrolyte and which interact chemically and act as an anode and cathode, at least one of the electrodes being electrical on the side facing away from the separator is conductively connected to a flat, electrically conductive arrester, at least one laterally open, electrically conductive, porous layer for discharging gases being arranged between the electrode and the arrester.

Furthermore, a method for producing a battery cell with at least one electrochemical cell is proposed, the cell being constructed by two electrodes which are electrically separated and chemically interacting using an separator and act as anode and cathode, at least one of the electrodes on that of the separator opposite side is electrically conductively connected to a flat, electrically conductive arrester, and a laterally open, electrically conductive, porous layer for discharging gases is arranged between the electrode and the arrester, the battery cell being formed using a forming process using the porous layer is degassed and an envelope of the battery cell is sealed in a fluid-tight manner after degassing.

Ideas for embodiments of the present invention can be viewed, inter alia, as based on the ideas and knowledge described below.

A battery cell can be understood as an energy store for storing electrical energy in chemical form. An electrochemical cell is the smallest functional unit of the battery cell. The battery cell can have a plurality of electrochemical cells connected in parallel and / or electrically connected in series. Several battery cells can be combined to form a battery, for example a traction battery for a vehicle.

The cell has a layer sequence of different electrochemically active materials and electrochemically inert materials. Electrodes of the cell have the electrochemically active materials. A separator arranged between the electrodes has electrochemically inert material.

To build up the cell, the materials can be arranged in layers one above the other. Prefabricated layers can be stacked and / or layers can be created on site. Layers can be cut off from a blank, for example as disks. Layers can also be created from liquids or pastes. The liquids or pastes can be dispersions of one or more of the materials in a solvent which form the layer by removing the solvent. Likewise, the layers can be formed by a reaction of two or more components from the liquid or change into a solid state. The layers can also be produced by solidification of the molten melt. Layers can also be produced by reshaping, for example rolling, pressing or drawing a blank.

The various electrochemically active materials have an electrochemical potential difference. Depending on the material pairing, one of the electrodes acts as an anode and the other electrode acts as a cathode. An electrical current flow between the anode and the cathode within the cell is prevented by the separator. During charging and discharging of the battery cell, ions of the electrochemically active materials move between the anode and cathode as charge carriers through the separator.

An arrester can be designed as a metallic layer or foil. The arrester can act as an obstacle to diffusion. A porous layer can have interconnected cavities in a border area between the electrode and the arrester. The porous layer can thus in particular be open-pore. The porous layer can extend up to a lateral edge of the conductor or the electrode and can be open to an environment of the cell or be in contact with the environment. Ambient conditions in the vicinity of the cell in the area of the interface can act via the porous layer. For example, if there is a low ambient pressure in the environment, such as an approximate vacuum, the low ambient pressure also exists in the porous layer.

In a formation process, the battery cell can be switched from a manufacturing state to an operating state. During the formation process, the at least one electrochemical cell can be arranged outside an envelope of the battery cell or can already be arranged in the envelope. The casing can still be open or already closed. The covering can be a film or a solid housing. For forming, at least one electrical potential can be applied to the poles of the battery cell in order to cause at least one desired reaction in the electrochemical cells. For example, at least one undesired substance can be oxidized or reduced on at least one of the electrodes in order to change into a gaseous state and to be removed through the porous layer. After the gas has been removed, the at least one electrochemical cell can be arranged in the open casing provided. The open envelope with the cell in it is closed after the gas has been removed. An already closed envelope is opened and closed again to discharge the gas.

The porous layer can be formed by coating the arrester. The arrester can be coated with a layer material and a pore-forming material. The pore-forming material can then be removed. The layer material and the pore-forming material can be applied to the arrester in a liquid or pasty state. The layer material can be electrically conductive. The layer material can solidify on the arrester to form a porous structure, the pores of which are filled by the pore-forming material. The pore-forming material can, for example, be brought into a gaseous state by an increase in temperature and can thus be removed from the pores. The pore-forming material can also be washed out of the pores using a solvent.

As an alternative, the porous layer can be provided as a prefabricated disk and can be connected in an electrically conductive manner to the arrester and the electrode. For example, the disk can be cut off from a blank.

The porous layer can be formed in regions between the electrode and the arrester. Adjacent to an area with the porous layer, at least one other area can be arranged without the porous layer. In other words, the porous layer cannot extend over the entire contact area between the electrode and the arrester. In a portion of the area, the electrode and the arrester can also be directly connected to one another. The area with the porous layer can be designed as at least one laterally open channel. The channel can be straight or curved.

The porous layer can be formed in strips. Stripes with the porous layer and stripes without the porous layer can alternate. In particular, the strips with the porous layer can be arranged at regular intervals. This allows the resulting gas to be easily directed to the edge of the cell.

At least the porous layer can have a surface made of a carbon material. The porous layer can be carbon coated. The carbon material can improve the electrical conductivity of the porous layer. The arrester can be coated with the layer of carbon material through the porous layer.

The porous layer can have a thickness of less than 10 μm, in particular less than 5 μm, in particular less than 2 μm. Pore formers are preferred fibers with long unidirectional expansion. For example, the x / y dimension is less than the layer thickness, preferably less than half the layer thickness.

The z dimension can be larger than ten times the diameter. The arrester can have a thickness of less than 20 µm.

The arrester can be electrically conductively connected to a further electrode on a side opposite the electrode. On both sides of the arrester, a laterally open porous layer can be arranged between the electrode and the arrester. The arrester can have a resistance-optimized thickness, or the conductor cross section of the arrester can be adapted to an expected current flow through the arrester. This can reduce the amount of material used. The further electrode is part of an adjacent electrochemical cell of the battery cell.

It is noted that some of the possible features and advantages of the invention are described herein with respect to different embodiments. A person skilled in the art recognizes that the features of the battery cell and of the method can be combined, adapted or exchanged in a suitable manner in order to arrive at further embodiments of the invention.

Figure list

• 1 zeigt eine Darstellung einer Schichtenfolge für eine Batteriezelle mit einer elektrochemischen Zelle gemäß einem Ausführungsbeispiel.

Embodiments of the invention are described below with reference to the accompanying drawing, wherein neither the drawing nor the description are to be interpreted as limiting the invention.

• 1 shows an illustration of a layer sequence for a battery cell with an electrochemical cell according to an embodiment.

The figure is only schematic and not to scale.

Electrical energy can be stored using batteries. Batteries convert chemical reaction energy into electrical energy. A distinction is made here between primary batteries and secondary batteries. Primary batteries are only functional once, while secondary batteries, also known as accumulators, can be recharged. A battery comprises one or more battery cells. So-called lithium-ion battery cells are used in particular in an accumulator. These are characterized, among other things, by high energy densities, thermal stability and extremely low self-discharge. Lithium-ion battery cells are used in motor vehicles, in particular in electric vehicles (EV), hybrid vehicles (hybrid electric vehicles, HEV) and plug-in hybrid vehicles (plug-in hybrid electric vehicles, PHEV). Lithium-ion battery cells have a positive electrode, which is also called a cathode, and a negative electrode, which is also called an anode. The cathode and the anode can each comprise a current conductor to which an active material is attached. The active material for the cathode can be a metal oxide, for example. The active material for the anode can be, for example, metallic lithium, graphite, amorphous carbon (hard carbon), silicon or a mixture of the three aforementioned materials or Li-titanate.

Lithium-based batteries typically require materials with very low levels of contamination (battery-grade). The main reason for this is that, depending on the electrochemical stability, contaminants react on the electrodes, for example, they are reduced at the anode or oxidized at the cathode. This can lead to solid reaction products on the solid electrolyte interface (SEI) or mobile species in the electrolyte. Both of these normally result in adverse battery properties. Batteries with metallic lithium as anode, which has the lowest electrochemical potential of all elements (-3.04 V vs SHE), are particularly demanding. Most molecules are reduced at this potential. Among other things, water molecules or solvent molecules are reduced, which, for example, can be located in the battery electrodes due to the process. Depending on the reaction, a reaction product thereof can be hydrogen. Hydrogen is known to react with lithium to form lithium hydride (LiH). Lithium hydride primarily forms coarse structures on the anode, some of which protrude from the surface of the anode and can lead to contact with the cathode and a short circuit if the separator breaks. It is therefore advantageous to remove either the water and / or the solvent molecules / contaminants before they reach the Li-metal anode.

Discharge foils can be coated with carbon coatings, for example. These coatings primarily serve to reduce the contact resistance and / or to protect the aluminum from corrosion. These coatings are not open-pore and do not necessarily cover the entire area.

Today's lithium ion batteries are based on a liquid electrolyte that is filled into the battery at the end of production. In order to produce a targeted SEI on the anode and cathode, the battery is subjected to a forming step immediately afterwards (i.e. before the first charge), in which certain potentials are applied to the anode and cathode in order to advantageously oxidize or reduce certain species in the liquid electrolyte. Contamination can also be removed in the same way. After formation, all gases are removed from the cell and the battery sealed gas-tight. The Li-ion battery is thus formed before the first cell cycling.

A type of formation can also be used with solid electrolyte-based battery cells (e.g. with a polymer electrolyte) to prevent contamination e.g. to remove by reduction. One possibility is pre-discharge, in which the potential at the cathode is reduced to below 1.5 V vs Li / Li +, which means e.g. Water and residual organic solvent molecules are reduced to gaseous species. In contrast to liquid electrolyte-based cells, this gas is enclosed within the polymer at the cathode and can form gas bubbles. The approach presented here simplifies the removal of this gas.

Embodiments of the invention

1 shows a representation of a section of an electrochemical cell 100 a battery cell 102 according to an embodiment. The electrochemical cell 100 consists of two electrodes 104 that have different electrochemical potentials and with different electrical poles of the battery cell 102 are electrically connected. Between the electrodes 104 is a separator 106 arranged of the electrodes 104 electrically separated from each other, but chemically combined. Between the electrodes 104 or the poles, an electrical voltage can be tapped. The separator 106 here has a solid electrolyte material. The electrodes 104 become dependent on their potential as an anode 108 or cathode 110 designated.

The battery cell 102 has a fluid-tight, liquid-tight and gas-tight envelope, which is not shown here, and which covers the cell 100 or several cells 100 the battery cell 102 encloses. The poles of the battery cell 102 are led through the casing to the outside. The wrapper can be, for example, a foil pouch, which can be referred to as a pouch. Likewise, the envelope can be formed by a fixed housing. The housing can vary depending on the type of battery cell 102 be shaped differently. The housing can for example be circular cylindrical or prismatic. The sheath can be electrically conductive with one of the poles of the battery cell 102 be connected or the pole of the battery cell 102 form.

One of the electrodes 104 is electrically conductive with an electrically conductive arrester 112 connected. The arrester 112 is with that of the electrode 104 assigned pole electrically connected. The arrester 112 is on one of the separators 106 opposite side of the the electrode 104 arranged. The arrester 112 is electrochemically ineffective and is used to transfer electrical charges with the lowest possible electrical losses between the electrodes 104 and to transport the connected pole. For example, the arrester 112 from a metal foil.

In the exemplary embodiment shown here, the arrester is 112 with the cathode 110 connected since the cathode 110 has a limited electrical conductivity and an electrical current flow through the cathode when charging or discharging the battery cell 102 for heating the cathode 110 and the cell 102 or the battery cell 102 would lead.

The cathode 110 has an electrically conductive cathode material 114 and an electrically insulating polymer material + conductive salt 116 on. Particles of the cathode material 114 are in the polymer material + conductive salt 116 embedded. The separator 106 can be made of the same polymer material 116 consist. The polymer material 116 can then be used as a polymer electrolyte 118 be designated. A material of the arrester 112 can on the cathode material 114 be coordinated.

The anode 108 can be an electrically conductive anode material 120 and the polymer electrolyte 118 exhibit. Then one of the separators can 106 facing back of the anode 108 also an arrester 112 be arranged. In the illustrated embodiment, the anode 108 pure anode material 120 and is therefore electrically conductive.

On the back of the anode 108 can be the next separator here 106 a next cell and then a next cathode 110 the next cell to be arranged to form a cell stack. Likewise, on one of the cathode 110 opposite side of the arrester 112 another cathode 110 another cell and then another separator 106 and another anode 108 be arranged in the further cell. the cell stack can therefore have a regular layer structure.

Between the arrester 112 and the electrode connected to it in an electrically conductive manner 104 is a laterally open, electrically conductive, porous layer 122 arranged. The porous layer 122 is designed to remove gases laterally from the cell 100 or to be removed laterally from the cell stack. The porous layer 122 has interconnected recesses or pores 124 on that are free of a layer material 126 the porous layer 122 are. The layer material 126 can be electrically conductive. The layer material 126 can also be coated in an electrically conductive manner. The porous layer 122 runs at least with one end to an edge of the cell 100 or the cell stack, whereby the gases can be drawn off at the edge. For example, the gases in a battery cell manufacturing process 102 in the electrode 104 arise and are peeled off before the wrapper is sealed. A vacuum or approximately a vacuum around the cell can be used to draw off the gases 100 or the cell stack are generated. Because the porous layer 122 is open laterally and the pores 124 hence with the environment of the cell 100 or the cell stack are connected, also prevails in the pores 124 the negative pressure, which increases the gases through the electrode 104 to the porous layer 122 diffuse.

The pores 124 can be formed by removing a pore former material. The pore-forming material can, for example, with the layer material 126 together as a paste or liquid on the drain 112 or the electrode 104 be dosed. The layer material can have a solvent and particles. The solvent is used to harden the layer material 126 evaporated, for example. The particles can be electrically conductive. The layer material 126 can also set chemically. The layer material 126 can be hardened in a hardening process by an external influence. The pore-forming material can be present, for example, as spheres. The balls can be evenly round or irregular. The balls can be of different sizes or the same size. In the paste or liquid, the balls touch and hold continuous connections between the later pores at the points of contact 124 free of the layer material 126 . After the layer material has hardened 126 the pore former material can be removed, causing the pores 124 in the layer material 126 stay behind. The pore-forming material can, for example, be removed thermally. The pore-forming material can also be removed chemically.

In other words, a continuous or laterally open gas diffusion layer on the back contact film of a polymer electrode is proposed, by means of which a targeted discharge of gases from the battery stack is made possible. Manufacturing processes are presented for the gas diffusion layer. Furthermore, a process for gas generation and removal (formation) is presented. The layer is a uniform, flat, porous, "quasi-2D" gas diffusion layer made of an open-pore particle layer.

In 1 a structure of a polymer battery according to an embodiment is shown in section. The individual layers are firmly connected to each other, there is almost no open-pore volume. The polymer battery consists of an anode 108 , Solid electrolyte separator 106 and cathode 110 on a metallic arrester 112 . The anode 108 can be, for example, a composite of polymer electrolyte and graphite or a metallic lithium foil. The separator 106 consists of pure polymer electrolyte 116 . The cathode 110 consists of a composite of cathode particles 114 , such as LFP, NCA or NCM, polymer electrolyte 116 and lead black. The arrester 112 consists of a metal foil. This can also be coated. For example, the arrester 112 be coated with a carbon coating. This coating is a few µm thick and not open-pored. The polymer electrolyte 116 consists of a polymer and a conductive salt.

If gas is generated in this polymer battery, for example due to pre-discharge, during cycling or when heating to the operating temperature, the gas normally collects between the cathode 110 and arrester 112 . Without the porous layer 122 the gas may not find a way out of the layer composite and can thus destroy the layer structure.

Here is a section through a battery layer stack on an additional gas diffusion layer or porous layer 122 on the arrester 112 shown. The layer 122 can the complete arrester 112 cover. An open-pore coating is understood here as a gas diffusion layer. This consists, for example, of particles which are held together by a binder material. Due to the open structure, gases can be directed out of the layer structure. If necessary, the open-pored structure can be applied to a thin, flat carbon layer as corrosion protection.

The arrester foil has a total height of <20 µm. The layer thickness of the gas diffusion layer is as small as possible at <10 μm, the layer being preferred 122 <5 µm thin, the layer is more preferred 122 <2 µm thin. The secondary particles have a diameter that is significantly smaller than the layer height. It is preferably in the range of <1 μm, more preferably the diameter is in the range <500 nm. The porosity of the layer 122 is> 20%, preferably> 40%.

The porous layer 122 has sufficient electrical conductivity, open, continuous pores, a height of at least 2 µm, mechanical stability, oxidation stability in the range 3 V to 5 V against lithium, no solubility in the electrolyte of the battery and is chemically inert.

The particles can consist, for example, of carbon-based materials such as graphite or carbon black, conductive oxides such as SnO2 and / or corrosion-stable metals such as titanium. The binder can be made of PVDF or cellulose, for example.

To produce the gas diffusion layer on the conductor foil, the particles can be dissolved in a solvent together with a binder material. The suspension can be flat on the arrester 112 applied and the solvent can then be evaporated. In order to improve the open porosity, auxiliary substances such as fibers or particles can be added, which are referred to as pore formers. The auxiliary substances can be removed in a subsequent baking step.

The cathode composite made of cathode particles 114 for example from LFP, NCA or NCM, polymer electrolyte 116 and conductive carbon black can, for example, be liquid-processed or dry-processed on the structured conductor foil. In the liquid process, the composite materials are liquefied in a solvent. The suspension is applied to the discharge foil and the solvent is evaporated. So that the suspension or the future cathode does not cover the pores 124 can penetrate and clog the pores 122 small dimensions or specially coated. The pores 124 can be coated with PTFE, for example, which creates the pores 124 cannot be wetted inside with the solvent. In the drying process, the cathode composite is processed into a thin film without solvent. This film is laminated onto the coated arrester film. Clogging of the pores 124 is almost impossible.

A formation (predischarge) before the first charging can effectively reduce the content of impurities in the battery. The cell can be used to form 100 in an open or closed pouch (depending on the ambient conditions). The cell 100 is contacted and the potential at the cathode is reduced. This reduces certain species, such as water or solvent molecules in the battery. During the formation, gases, such as hydrogen, are emitted from the cell due to their large volume due to the porous structure 100 be directed. The closed pouch is opened, the gases are released, the pouch is evacuated and closed. The open pouch is evacuated and closed.

In conclusion, it should be pointed out that terms such as "showing", "comprehensive", etc. do not exclude other elements or steps and terms such as "one" or "one" do not exclude a large number. Reference signs in the claims are not to be viewed as a restriction.

Claims (9)

Battery cell (102) with at least one electrochemical cell (100), which is provided by two electrodes (104), which are electrically separated and chemically interact using a separator (106) made of solid electrolyte (118) and act as anode (108) and cathode (110) is formed, wherein at least one of the electrodes (104) on the side facing away from the separator (106) is electrically conductively connected to a flat, electrically conductive arrester (112), one laterally between the electrode (104) and the arrester (112) open, electrically conductive, porous layer (122) for discharging gases is arranged. Battery cell (102) according to Claim 1 , in which the porous layer (122) is formed in regions between the electrode (104) and the conductor (112), an area with the porous layer (122) being adjacent to at least one area without the porous layer (122). Battery cell (102) according to Claim 2 , in which the porous layer (122) is formed in strips. The battery cell (102) according to any one of the preceding claims, wherein at least the porous layer (122) has a surface made of a carbon material. Battery cell (102) according to one of the preceding claims, in which the porous layer (122) has a thickness of less than 10 µm, in particular less than 5 µm, in particular less than 2 µm. Battery cell (102) according to one of the preceding claims, in which the arrester (112) has a thickness of less than 20 µm. Battery cell (102) according to one of the preceding claims, in which the conductor (112) is electrically conductively connected to a further electrode on a side opposite the electrode (104), wherein on both sides of the conductor (112) between the electrode (104) and a laterally open porous layer (122) is arranged on the arrester (112). A method of manufacturing a battery cell (102), comprising at least one electrochemical cell (100) by two, using one Separators (106) are electrically separated and chemically interacting electrodes (104) designated as anode (108) and cathode (110), at least one of the electrodes (104) on the side facing away from the separator (106) being electrically conductive with a flat surface , electrically conductive arrester (112) is connected, and at least one laterally open, electrically conductive, porous layer (122) for discharging gases is arranged between the electrode (104) and the arrester (112), the battery cell (102) below Is formed using a forming process, is degassed using the porous layer (122) and an envelope of the battery cell (102) is sealed in a fluid-tight manner after degassing. Procedure according to Claim 8 , in which the porous layer (122) is formed by coating the arrester (112), the arrester (112) being coated with a layer material (126) and a pore former material and the pore former material being subsequently removed.

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