DE102019001238A1 - Electrochemical cell - Google Patents

Abstract

The invention relates to an electrochemical cell (1) having an electrode stack, comprising at least one at least substantially flat anode current collector (3) and at least one substantially flat cathode current collector (4), which are stacked on top of each other, and at least one between the anode current collector (3 ) and the cathode current collector (4) arranged separator, wherein the anode current collector (3) at least one arranged on an end side Anodenstromableiterfahne (5) and the cathode current collector (4) at least one disposed on a front side Kathodenstromableiterfahne (6). According to the invention, a material thickness of the anode current collector (3) linearly decreases starting from the end face with the anode current collector lug (5) to an opposite end face and a material thickness of the cathode current collector (4) linearly decreases starting from the end face with the cathode current collector lug (6) to an opposite end face or the anode current collector (3) and the cathode current collector (4) each comprise a Stromleitstruktur (9, 10) which guide one of the Anodenstromableiterfahne (5) or the Kathodenstromableiterfahne (6) guided electric current (I) such that a way of the same increasing distance from Anodenstromableiterfahne (5) or the Kathodenstromableiterfahne (6) is increasingly non-linear formed.

Description

The invention relates to an electrochemical cell according to the preamble of claim 1.

From the US 2016/0285105 A1 For example, a current collector for an electrochemical cell and such an electrochemical cell are known. The current collector has a plurality of different thicknesses. The current collector includes a tab that extends along a tab length from a proximal tab portion to a distal tab portion. In this case, the proximal tab portion has a first thickness and the distal tab portion has a second thickness, wherein the second thickness of the distal tab portion is greater than the first thickness of the proximal tab portion, so that a step between the two tab portions is formed. The proximal tab portion is provided for coupling the current collector to an electrode of the electrochemical cell. The distal tab portion of the current collector is provided for coupling the current collector to a lead of the electrochemical cell.

The invention is based on the object of specifying an improved over the prior art electrochemical cell.

The object is achieved with an electrochemical cell having the features specified in claim 1.

Advantageous embodiments of the invention are the subject of the dependent claims.

An electrochemical cell having an electrode stack comprises at least one at least substantially flat anode current collector and at least one substantially flat cathode current collector, which are stacked one above the other. Furthermore, the individual cell comprises at least one separator arranged between the anode current collector and the cathode current collector, wherein the anode current collector comprises at least one anode current collector lug arranged on one end side and the cathode current collector at least one cathode current collector lug arranged on one end side.

According to the invention, a material thickness of the anode current collector linearly decreases starting from the end side with the anode current collector lug to an opposite end side, and a material thickness of the cathode current collector linearly decreases starting from the end side with the cathode current collector lug to an opposite end side. Alternatively, the anode current collector and the cathode current collector each comprise a current conducting structure which directs an electric current conducted by the anode current collector tab or tab such that a path thereof becomes increasingly non-linear with increasing distance from the anode tab or tab.

Assuming a homogeneous distribution of an electric current in the anode current collector and cathode current collector is a change in a current density from the Anodenstromableiterfahne to the opposite end or from the Kathodenstromableiterfahne to the opposite end face in the direction x constant according to $$\frac{\delta \overrightarrow{l}}{\delta x}=cOnst,$$

Because the gradient of the electrical potential is proportional to the current density, a twofold mathematical integration yields that the electrical potential along the direction x corresponds to a course of a quadratic function of x.

This dependence applies to both the anode and the cathode, only with different signs. Applied to the electrochemical cell is an electrical voltage resulting from a difference between an electric potential of the cathode current collector and an electric potential of the anode current collector. That is, the applied voltage across the cell is in the direction x not constant, but dependent on a respective spatial position.

For electrochemical cells, it is generally true that an electric current flowing through them is exponentially dependent on the applied voltage according to the so-called Butler-Volmer formula. As a result, the electrochemical cell, i. H. the anode current collector and cathode current collector are not homogeneously loaded. In this case, in regions which are located in the vicinity of the current discharge lugs, current densities are higher above electrochemically active layers than in the middle of the cell or the anode current collectors and cathode current collectors.

In particular, for electrochemical cells with comparatively large length dimension between Anodenstromableiterfahne to the opposite end or Kathodenstromableiterfahne to the opposite end, with anode current collectors and Kathodenstromsammlern with certain material thicknesses and for electrochemical cells in which a layer thickness of an active material has a certain thickness, there a so-called C-rate limit. The C rate is a quantification of rechargeable electrical energy storage, which indicates maximum allowable charging and discharging under certain conditions. From the stated C-rate limit, predominantly only the areas which are located in the vicinity of the Anodenstromableiterfahne or Kathodenstromableiterfahne, an electrochemical activity, wherein in a central region of the electrochemical cells and thus the Anodenstromableiterfahne and Kathodenstromableiterfahne almost no electrochemical activity is recorded. For example, this can lead to faster cyclic aging of the electrochemical cell.

By means of the inventively provided decrease in the material thickness of the anode current collector and cathode current collector starting from the end face with the respective Stromableiterfahne to the opposite end or alternatively by means of inventively provided Stromleitstruktur a linear course of the electrical potential of the current density is achieved. That is, at different locations in the electrochemical cell, the same voltage is applied, so that a difference between electric potential in the anode and cathode is independent of location coordinates and thus each location element of the electrochemical cell can be charged and discharged with the same electric current. This makes it possible to realize even large-capacity and thus high-capacity electrochemical cells with simultaneously high C-rates and high energy density, while at the same time minimizing cyclical aging of the cells. In doing so, a loss of cell capacity during cyclic operation is minimized.

Embodiments of the invention are explained in more detail below with reference to drawings.

• 1 schematisch ein erstes Ausführungsbeispiel einer elektrochemischen Zelle,
• 2 schematisch ein zweites Ausführungsbeispiel einer elektrochemischen Zelle,
• 3 schematisch ein drittes Ausführungsbeispiel einer elektrochemischen Zelle,
• 4 schematisch ein Diagramm mit einem Verlauf eines elektrischen Potenzials entlang einer Richtung zwischen einer Anodenstromableiterfahne und einer gegenüberliegenden Stirnseite eines Anodenstromsammlers und zwischen einer Kathodenstromableiterfahne und einer gegenüberliegenden Stirnseite eines Kathodenstromsammlers,
• 5 schematisch eine Draufsicht einer Flachseite eines Anodenstromsammlers mit einer Stromleitstruktur und
• 6 schematisch eine Draufsicht einer Flachseite eines Kathodenstromsammlers mit einer Stromleitstruktur.

Showing:

• 1 schematically a first embodiment of an electrochemical cell,
• 2 schematically a second embodiment of an electrochemical cell,
• 3 schematically a third embodiment of an electrochemical cell,
• 4 3 is a schematic diagram showing a profile of an electrical potential along a direction between an anode current collector lug and an opposite end side of an anode current collector and between a cathode current collector lug and an opposite end side of a cathode current collector;
• 5 schematically a plan view of a flat side of an anode current collector with a Stromleitstruktur and
• 6 schematically a plan view of a flat side of a cathode current collector with a Stromleitstruktur.

Corresponding parts are provided in all figures with the same reference numerals.

In 1 is a first embodiment of an electrochemical cell 1 , also referred to as a single cell, shown.

The electrochemical cell 1 is designed as a so-called lithium-ion pouch cell, which is a housing formed from film sections 2 having.

Inside the case 2 is arranged in a manner not shown an electrode stack, which has a plurality of film-like and formed in 5 closer illustrated anode current collector 3 as well as several foil-like and in 6 closer illustrated cathode current collector 4 comprises, which are alternately stacked with the interposition of an electrically non-conductive separator on top of each other. Here are the anode current collector 3 for example, copper and the cathode current collector 4 For example, formed of aluminum and are each coated with at least one active material. Furthermore, it is located inside the housing 2 an electrolyte.

The anode current collector 3 each comprise at least one arranged on an end face and in 5 Anode Stromableiterfahne illustrated in more detail 5 , The cathode current collector 4 each comprise at least one arranged on an end face and in 6 Kathodenstromableiterfahne shown in detail 6 ,

The stacked Anodenstromableiterfahnen 5 the stacked anode current collector 3 are doing with a common anode current collector 7 coupled. The stacked Kathodenstromableiterfahnen 6 the stacked cathode current collector 4 are with a common cathode current collector 8th coupled.

In the illustrated first embodiment of the cell 1 are the anode current 7 and the cathode current collector 8th on an end face of the housing 2 with larger length dimension from the housing 2 led out and form a positive pole or a negative pole of the cell 1 ,

2 shows a second embodiment of the cell 1 , Unlike the in 1 The first embodiment shown are the anode current collector 7 and the cathode current collector 8th on opposite ends of the housing 2 with larger length dimension from the housing 2 led out and form the positive pole or the negative pole of the cell 1 , The longer end sides extend at least substantially in one direction y whereas the remaining shorter end faces of the case 2 at least essentially in one direction x extend.

In 3 is a third embodiment of the cell 1 shown. Unlike the in 2 illustrated second embodiment, the anode current collector 7 and the cathode current collector 8th on opposite ends of the housing 2 with shorter length dimension from the housing 2 led out and form the positive pole or the negative pole of the cell 1 ,

Assuming a homogeneous distribution of an electric current in the anode current collector 3 and cathode current collector 4 is a change in a current density starting from the anode current collector lug 5 to an opposite end side or starting from the Kathodenstromableiterfahne 6 to an opposite end in the direction x constant according to $$\frac{\delta \overrightarrow{l}}{\delta x}=cOnst,$$

Because the gradient of in 4 detailed electrical potential φ is proportional to the current density, results from a two-fold mathematical integration that the electric potential φ along the direction x a course of a quadratic function of x equivalent.

This dependence applies to both the anode current collector 3 as well as for the cathode current collector 4 , only with different signs. It is believed that the coating of active materials of the anode current collector 3 and cathode current collector 4 is formed of an infinite number of infinitesimal thin cells and is connected to the electrochemical cell 1 an electrical voltage is applied, which is a difference between an electrical potential φ of the cathode current collector 4 (shown in 4 ) and an electrical potential φ of the anode current collector 3 (shown in 4 ), it follows that the applied voltage to the cell 1 in the direction x not constant, but is dependent on a respective spatial position.

4 shows the courses of the electrical potential φ of the anode current collector 3 (broken line) and the electrical potential φ of the cathode current collector 4 (solid line) in response to a position starting from the Anodenstromableiterfahne 5 or Kathodenstromableiterfahne 6 to the opposite end face of the anode current collector 3 or cathode current collector 4 in the direction x ,

The same applies to the electrochemical cell 1 in that an electric current flowing through it I of the applied voltage according to the so-called Butler-Volmer formula is exponentially dependent. As a result, the electrochemical cell 1 ie the anode current collector 3 and cathode current collector 4 not be charged homogeneously. In this case, in regions which are in the vicinity of the respective current collector lugs, current densities are higher above electrochemically active layers than in the middle of the cell 1 or the anode current collector 3 and cathode current collector 4 ,

In the event that the two parabolas indicate the course of electrical potentials φ along the direction x for the anode current collector 3 and cathode current collector 4 describe a linear progression is a dispersion of current densities through electrochemically active layers along the direction x negligible. In particular, this is the case when there is a gap between anode current collector tab 5 or Kathodenstromableiterfahne 6 and the respective opposite end face of the anode current collector 3 or cathode current collector 4 is comparatively small, a thickness of the anode current collector 3 or cathode current collector 4 is sufficient, a layer thickness of the active material is comparatively low and / or the cell 1 operated at a relatively low C rate.

For electrochemical cells 1 with comparatively large distances between Anodenstromableiterfahne 5 to the opposite end or Kathodenstromableiterfahne 6 to the opposite end, with anode current collector 3 and cathode current collectors 4 with certain material thicknesses and for electrochemical cells 1 , in which the layer thickness of an active material has a certain thickness, there is a so-called C-rate limit. From the c-rate limit mentioned above, predominantly only the areas that are close to the anode current discharge lug 5 or Kathodenstromableiterfahne 6 have an electrochemical activity, wherein in a central region of the electrochemical cell 1 and thus the anode current collector tab 5 and cathode current collector tab 6 almost no electrochemical activity is recorded. This can, for example, lead to faster cyclic aging of the electrochemical cell 1 to lead.

mit

σ =

spezifische Leitfähigkeit,

U =

elektrische Spannung,

i =

elektrischer Strom.

For an anode current collector 3 and a cathode current collector 4 the following applies one-dimensional differential form of Ohm's law, according to which $$\sigma \cdot GradU\left(x\right)=i\left(x\right)$$

With

σ =

specific conductivity,

U =

electrical voltage,

i =

electrical current.

After a mathematical differentiation of equation (2) to x (= direction x ) surrendered $$\frac{\delta \left(\sigma \cdot GradU\right)}{\delta x}=\frac{\delta i}{\delta x},$$

According to equation (1), a constant and homogeneous current density distribution within the anode current collector 3 and cathode current collector 4 as well as within the respective active material.

gefordert.Furthermore, a linear decrease of the potentials φ along the direction x at the anode current collector 3 and cathode current collector 4 according to $$GradU\left(x\right)=cOnst,$$

required.

The last two conditions for Ohm's law show that $$\frac{\delta \sigma }{\delta x}=cOnst,$$

Thus, it follows that the specific conductivity σ of the respective Anodenstromableiterfahne 5 to the opposite end face or of the respective Kathodenstromableiterfahne 6 must remove to the opposite end.

The equations (1) to (5) mentioned above are also satisfied if the specific conductivity σ is replaced by the effective surface conductivity (= reciprocal of the surface resistance). With this assumption it follows that a topological change of the anode current collector 3 and cathode current collector 4 , which generates a constant gradient of the effective area conductivity in a desired direction, a homogeneous distribution of the current density in the cell 1 causes.

To realize this is in a possible execution of the cell 1 provided that a material thickness of the anode current collector 3 starting from the front side with the Anodenstromableiterfahne 5 decreases linearly to the opposite end face and a material thickness of the cathode current collector 4 starting from the front side with the Kathodenstromableiterfahne 6 decreases linearly to an opposite end face.

That is, anode current collector 3 and cathode current collector 4 each have a triangular cross-section.

In another possible embodiment of the cell 1 is provided that the anode current collector 3 and the cathode current collector 4 each a Stromleitstruktur 9 . 10 comprising one of the anode current collector tab 5 or the Kathodenstromableiterfahne 6 guided electric current I such that a path thereof with increasing distance from the Anodenstromableiterfahne 5 or the Kathodenstromableiterfahne 6 increasingly non-linear is formed. This is in the 5 and 6 shown in more detail.

This shows 5 a plan view of a flat side of an anode current collector 3 with a current conducting structure 9 wherein the anode current collector 3 a length A between the anode current collector tab 5 and the opposite end face.

To the courses of the electrical potentials φ along the direction x for the anode current collector 3 at least nearly linear, includes the Stromleitstruktur 9 several at least substantially parallel to the end face with the Anodenstromableiterfahne 5 arranged rows R1 to rn each with a plurality of spaced-apart Stromablenkelementen 11.1 to 11.M , wherein the current deflection elements 11.1 to 11.M each as a slit-shaped material breakthroughs in the anode current collector 3 are introduced. Here are the current deflection elements 11.1 to 11.M by any method, for example by punching, laser cutting, knife cutting, etc., in the anode current collector 3 brought in. The current deflection elements 11.1 to 11.M each have a length L on, wherein between adjacent Stromablenkelementen 11.1 to 11.M a row R1 to rn one Stromleitbereich each with a width O is trained.

A distance B (x) between each row R1 to Rn thereby provides a width for a path of the electric current I where the distance B (x) of the ranks R1 to Rn from the Anodenstromableiterfahne 5 to the opposite flat side of the anode current collector 3 in the direction x decreases.

The effective surface conductance necessary for the operation of the electrochemical cell 1 is decisive, is proportional to a ratio between the width of the path, ie the respective distance B (x) and a sum of length L the current deflection elements 11.1 to 11.M and the width O of the respective Stromleitbereichs.

wobei x in diesem Fall den Abstand einer Achse des Pfades des Stroms I von der Anodenstromableiterfahne 5 darstellt.For the special case where the width O equal to the distance B (x) is, results as a condition for the distance B (x) $$B\left(x\right)\frac{A-x}{x}*L.$$

in which x in this case, the distance of an axis of the path of the current I from the anode current collector tab 5 represents.

Here are the current deflection elements 11.1 to 11.M adjacent rows R1 to Rn and between the current deflection elements 11.1 to 11.M trained Stromleitbereiche adjacent rows R1 to rn in the direction of a course of the rows R1 to Rn offset from one another. Thus, the Stromleitstruktur forms 9 a kind of labyrinth in which the path of the stream I , that is the current path, with increasing distance x from the anode current collector tab 5 "Delinearized", for example, is converted into a meandering course.

6 shows a plan view of a flat side of a cathode current collector 4 with a current conducting structure 10 , wherein the cathode current collector 4 a length A between the cathode current collector tab 6 and the opposite end face.

To the courses of the electrical potentials φ along the direction x for the cathode current collector 4 at least nearly linear, includes the Stromleitstruktur 10 analogous to the current conducting structure 9 of the anode current collector 3 according to 5 several at least substantially parallel to the end face with the Anodenstromableiterfahne 5 arranged rows R1 to rn each with a plurality of spaced-apart Stromablenkelementen 12.1 to 12.z , wherein the current deflection elements 12.1 to 12.z each as slit-shaped material breakthroughs in the cathode current collector 4 are introduced. Here are the current deflection elements 12.1 to 12.z by any method, for example by means of punching, laser cutting, knife cutting, etc., in the cathode current collector 4 brought in. The current deflection elements 12.1 to 12.z each have a length L on, wherein between adjacent Stromablenkelementen 12.1 to 12.z a row R1 to rn one Stromleitbereich each with a width O is trained.

A distance B (x) between each row R1 to Rn thereby provides a width for a path of the electric current I where the distance B (x) of the ranks R1 to rn starting from the Kathodenstromableiterfahne 6 to the opposite flat side of the cathode current collector 4 in the direction x decreases.

The effective surface conductance necessary for the operation of the electrochemical cell 1 is decisive, is proportional to a ratio between the width of the path, ie the respective distance B (x) and a sum of length L the current deflection elements 12.1 to 12.z and the width O of the respective Stromleitbereichs.

wobei x in diesem Fall den Abstand einer Achse des Pfades des Stroms I von der Kathodenstromableiterfahne 6 darstellt.For the special case where the width O equal to the distance B (x) is, results as a condition for the distance B (x) $$B\left(x\right)\frac{A-x}{x}*L.$$

where x in this case is the distance of an axis of the path of the stream I from the cathode current collector banner 6 represents.

Here are the current deflection elements 12.1 to 12.z adjacent rows R1 to Rn and between the current deflection elements 12.1 to 12.z trained Stromleitbereiche adjacent rows R1 to Rn in the direction of a course of the rows R1 to Rn offset from one another. Thus, the Stromleitstruktur forms 10 a kind of labyrinth in which the path of the stream I , that is the current path, with increasing distance x from the cathode current collector banner 6 "Delinearized", for example, is converted into a meandering course.

The in the 1 to 6 The features illustrated and the description of these figures apply generally to any electrochemical system, wherein the said modifications of the current collector can also be applied to any primary or secondary cell or fuel cell.

LIST OF REFERENCE NUMBERS

1

cell

2

casing

3

Anode current collector

4

Cathode current collector

5

Anodenstromableiterfahne

6

Kathodenstromableiterfahne

7

anode current

8th

cathode current

9

Stromleitstruktur

10

Stromleitstruktur

11.1 to 11.m

Stromablenkelement

12.1 to 12.z

Stromablenkelement

A

length

B (x)

distance

I

electricity

L

length

O

width

R1 to Rn

line

x

direction

y

direction

φ

potential

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2016/0285105 A1 [0002]

Claims (5)

An electrochemical cell (1) having an electrode stack comprising - at least one anode current collector (3) formed at least substantially flat and at least one substantially flat cathode current collector (4) stacked one above the other, and - at least one between the anode current collector (3) and The separator arranged at the cathode current collector (4), wherein - the anode current collector (3) comprises at least one arranged on an end side Anodenstromableiterfahne (5) and the cathode current collector (4) at least one arranged on a front side Kathodenstromableiterfahne (6), characterized in that - a material thickness of the anode current collector (3) starting from the end face with the Anodenstromableiterfahne (5) decreases linearly to an opposite end face and a material thickness of the cathode current collector (4) starting from the front side with the Kathodenstromableiterfahne (6) linearly decreases to an opposite end face, or the anode current collector (3) and the cathode current collector (4) each comprise a current conducting structure (9, 10) which directs an electric current (I) guided by the anode current discharge lug (5) or the cathode current collector lug (6) such that a path thereof increases with increasing current Distance from Anodenstromableiterfahne (5) or the Kathodenstromableiterfahne (6) is increasingly formed non-linear. Electrochemical cell (1) after Claim 1 , characterized in that - the Stromleitstruktur (9, 10) a plurality of at least substantially parallel to the end face with the Anodenstromableiterfahne (5) or to the front side with the Kathodenstromableiterfahne (6) arranged rows (R1 to Rn), each having a plurality of spaced apart arranged Stromablenkelementen (11.1 to 11.m, 12.1 to 12.z), - a distance (B (x)) of the rows (R1 to Rn) starting from Anodenstromableiterfahne (5) or the Kathodenstromableiterfahne (6) to the opposite flat side of the anode current collector ( 3) or to the opposite flat side of the cathode current collector (4) decreases and - the current deflection elements (11.1 to 11.m, 12.1 to 12.z) adjacent rows (R1 to Rn) and between the current deflection elements (11.1 to 11.m, 12.1 to 12.z) formed Stromleitbereiche adjacent rows (R1 to Rn) in the direction of a course of the rows (R1 to Rn) are arranged offset from each other. Electrochemical cell (1) after Claim 2 , characterized in that the Stromablenkelemente (11.1 to 11.m, 12.1 to 12.z) are each formed as slit-shaped material breakthroughs in the anode current collector (3) and the cathode current collector (4). Electrochemical cell (1) according to one of the preceding claims, characterized in that a plurality of anode current collector (3) and cathode current collector (4) are alternately stacked, wherein between the anode current collector (3) and the cathode current collector (4) each having a separator is arranged. Electrochemical cell (1) after Claim 4 , characterized in that the Anodenstromableiterfahnen (5) of the anode current collector (3) are coupled to a common Anodenstromableiter (7) and - the Kathodenstromableiterfahnen (6) of the cathode current collector (4) are coupled to a common cathode current collector (8).

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