WO2018228806A1

WO2018228806A1 - Method and apparatus for charging a rechargeable electrochemical energy storage cell

Info

Publication number: WO2018228806A1
Application number: PCT/EP2018/063880
Authority: WO
Inventors: Johannes Sieg; Jochen Bandlow; Bernd Spier; Jochen Siehr; Frieder STOEHR; Daniel Dragicevic; Torben Materna
Original assignee: Daimler Ag
Priority date: 2017-06-13
Filing date: 2018-05-28
Publication date: 2018-12-20
Also published as: DE102017005595A1

Abstract

The invention relates to a method for charging a rechargeable electrochemical energy storage cell (6) having an anode (1) and a cathode (3), wherein an electrical charging current (I) is fed into the energy storage cell (6) during the charging operation, wherein the electrical charging current (I) is controlled in such a manner that the cell voltage (U cell(t)) is less than or equal to the concentration-dependent electrochemical potential of the cathode based on the electrochemical potential of the metal reference electrode (ϕ+ (ϰpos t) vs.Me/Men+) in order to avoid an electrochemical reaction at the anode (1). The present invention also relates to an apparatus (4) for carrying out the method.

Description

Method and device for charging a rechargeable electrochemical

Energy storage cell

The present invention relates to a method and a device for charging a rechargeable electrochemical energy storage cell.

In motor vehicles with a (partial) electric drive train (such as hybrid, plug-in hybrid and purely electrically powered vehicles) are currently almost exclusively lithium-ion battery cells as rechargeable electrochemical

Energy storage cells (hereinafter often referred to as battery cells) used for the battery packs that serve as electrical energy storage for the drive train.

Lithium-ion battery cells are known to comprise a negative electrode (anode), a positive electrode (cathode), a lithium ion permeable separator disposed between the anode and cathode, and a liquid electrolyte. The anode and the cathode are each further electrically connected to a current conductor.

The anode and the cathode of a lithium-ion battery cell each consist of or contain active material. During a charging process, lithium ions intercalate into the active anode material; during the discharge process, the lithium ions deintercalate again. In the case of the active cathode material, the opposite action takes place. such

Electrodes are often referred to as intercalation electrodes.

For the anode, graphite is mainly used as the active material in the current state of the art, the cathode is often a mixed oxide.

One reason for using graphite as the anode material is that the electrochemical potential of charged graphite is very low compared to metallic lithium. Thus, the voltage difference between the positive and negative electrodes is close to the energetic optimum of a metallic lithium anode. The small potential difference from lithiated graphite to metallic lithium, however, has the disadvantage that when positive charging power is supplied, deposition of metallic lithium on the surface of the graphite particles can occur, the so-called lithium plating.

Lithium plating leads to an increased degradation of the battery cell (if that

deposited, metallic lithium reacts with the electrolyte or loses electrical contact, it is no longer available for further charging and discharging; only if the metallic lithium is still electrically connected, it can continue to intercalate or re-oxidize during discharge) and it is also discussed in the literature, an impact on the safety of the battery cell. For these reasons, lithium plating must be avoided when charging a lithium-ion battery cell.

From DE 10 2016 007 479 A1, a method and a device are known in order to charge a battery cell with a high charging current in the shortest possible time, without resulting in lithium plating. In the method according to said

Offenlegungsschrift is the charging current from a charging current intensity map in

Depending on the (local) state of charge and the (local) temperature of the battery cell calculated. The charging current strength map is determined in advance experimentally or simulatively. As an application, a full charge was chosen.

During a charging process from the deepest of the system (vehicle / battery)

The maximum charge state permitted by the system with the maximum charge current determined according to this disclosure maximizes the lithium ion concentration gradients in the active material and in the electrolyte. For this reason, the full charge of a battery cell from the lowest to the highest state of charge is the most critical application.

In motor vehicles with a (partial) electric drive train, the battery is not only charged via the mains, but it is also when driving

Braking energy in the form of positive power fed back into the battery (so-called.

Recuperation). The battery cells are thus briefly recharged while driving, usually after a discharge phase (positive acceleration and holding the speed) (during a braking operation or a negative acceleration).

For such charging processes, the method known from DE 10 2016 007 479 A1 is not optimal. Against this background, it is an object of the present invention to provide a method and a device with which a rechargeable,

electrochemical energy storage cell can be charged with a maximum, not to lithium plating leading performance, both in the driving and in the

Network operation.

These objects are achieved by the method according to claim 1 and the

Apparatus according to claim 9. Advantageous developments of the method and the device are the subject of the dependent claims.

According to the invention, a method for charging a rechargeable

proposed electrochemical energy storage cell (battery cell) with an anode and a cathode, wherein during the charging process, an electric charging current (/) is fed into the energy storage cell. The method is characterized in that the electrical charging current (/) is regulated by means of a cell model such that the cell voltage (U _ceU (t)) is less than or equal to the (metal ion) concentration- _dependent electrochemical potential of the cathode based on the electrochemical potential of the metal reference electrode (0j (x _pos , t) vs. Me / Me ^{n +} ) to avoid an electrochemical reaction at the anode.

The method is characterized in particular by the fact that a rechargeable electrochemical energy storage cell (battery cell) with a maximum, not leading to increased damage by deposition of metallic lithium on the surface of the particles of the anode (lithium plating) leading load in driving and mains operation can be, without this, a calculation of the anode potential is required.

In the method mentioned in the opening paragraph DE 1 0 201 6 007 479 A1, it is necessary to determine the maximum charging power at which no deposition of metallic lithium still occurs on the anode, the anode potential (for instance by means of a control unit in a motor vehicle). to calculate. One in one

Motor vehicle, accurate, correct on the aging of the battery cells

However, to the knowledge of the inventors, computation of the anode potential by a physico-electrochemical cell model is currently both in a series product technically and economically not feasible or only with considerable effort. This disadvantage is overcome by the present invention.

As already mentioned above, before charging a battery of a motor vehicle by means of recuperation usually a (short-term) discharge takes place. This previous discharge causes the concentration of lithium ions on the surface of the graphite particles to be less than the average lithium ion concentration of the particles. The charging current of a recuperative charging pulse can thus be selected to be higher than the charging current intensity map according to the published patent application DE 10 201 6 007 479 A1 would allow for the same (local) state of charge and the same (local) temperature.

This also applies to charging operations that are started at a higher than the lowest state of charge, ie in a partially discharged state of the battery cell. Again, the maximum charge current not leading to lithium plating is due to the lower lithium ion concentration at the surface of the graphite particles and the lower

Concentration gradient in the electrolyte at the corresponding state of charge higher than the charge current intensity map from the published patent DE 1 0 2016 007 479 A1 for the same (local) state of charge and the same (local) temperature would allow.

There are no particular restrictions with regard to the cell model used or usable and, for example, known electrical, physical-electrochemical models, models simplified in complexity, for example by a mathematical model order reduction (MOR), can be reduced by reducing the number of simulated particles , by a picture of the

Physic-electrochemical cell model on electrical components, through the use of knowledge-based methods, such as artificial neural networks, support vector methods and fuzzy systems or similar, related methods are implemented to calculate U _C h (t) or to investigate.

For the calculation of the voltage quantities by the cell model, a suitable (digital) computing device is to be provided with (a) memory device (s) in order to provide the parameters necessary for the respective model used. According to a first advantageous development of the method, the electrical charging current (I) is regulated by means of a cell model such that the cell voltage (

is less than or equal to the sum (U _C h (t)) that is formed from the

concentration-dependent electrochemical potential of the cathode based on the electrochemical potential of the metal reference electrode

vs. Me / Me ^{n +} ) and at least one other addend, which represents an overvoltage, preferably the reaction overvoltage at the cathode ^ ⁺ (x _pos , t)) and / or the

Electrolyte overvoltage (η (ί)).

According to a second advantageous development of the method, the calculation of the voltage quantities by the cell model (in addition to the cell current) is performed as a

Input a vector with at least one measured temperature (7) of the rechargeable electrochemical energy storage cell, optionally with an

different locations of the rechargeable electrochemical energy storage cell measured temperature (7) used.

For example. In the case of a large-sized lithium-ion battery cell, the temperature (7) is not homogeneous due to the cell design and / or cooling, but there are warmer and colder areas. Due to the strongly temperature-dependent electrical and ionic conductivities of the materials installed in a battery cell, it follows that the current density in a battery cell is likewise not homogeneous. This results in different states of charge within the battery cell. The method should therefore be carried out in an advantageous manner taking into account the local charge states and the current density distribution.

Likewise, it is advantageous if the cell model, an overvoltage or

Overvoltages are taken into account by an offset value.

Since the models described so far require a lot of computing power and have a high memory requirement, the method can advantageously be carried out using at least one simplifying model approach, for example when carrying out the method in a motor vehicle. Simplifying model approaches are known to the person skilled in the art and are encompassed by the present invention. Furthermore, it is advantageous if the charging current is determined in accordance with the above disclosed method according to the invention or one of its advantageous developments and additionally an empirically or simulatively determined parameter is subtracted from the cell voltage determined by the cell model in order to obtain a model error of the

Cell model to consider.

It is also advantageous if in the used (possibly simplifying) cell model a tracking of the model parameters on the aging of

rechargeable electrochemical energy storage cell is made.

Further advantageous embodiments of the method encompassed by the present application include

the method is carried out with a rechargeable electrochemical energy storage cell which is only partially discharged;

- The method is carried out with a lithium-ion energy storage cell;

- The method is carried out with a lithium-ion energy storage cell with a graphite anode;

- the current, temperature and charge state distribution within the rechargeable electrochemical energy storage cell are taken into account;

- The aging of the rechargeable electrochemical energy storage cell is tracked by an adaptation of the age-dependent model parameters over the service life of the rechargeable electrochemical energy storage cell;

- The method with a rechargeable battery with parallel connected, rechargeable electrochemical energy storage cells or with a

Series connection of one or more parallel connected rechargeable electrochemical energy storage cells is performed, in particular with a battery with lithium-ion energy storage cells, preferably with a battery with lithium-ion energy storage cells, each containing a graphite anode.

Also included in the present invention is an apparatus for charging a rechargeable electrochemical energy storage cell having an anode and a cathode, the apparatus being characterized in that it is designed to regulate the charging current (/) by means of a cell model in such a way that the cell voltage (t / _cell (t)) less than or equal to the concentration-dependent electrochemical potential of the cathode based on the electrochemical potential of the metal reference electrode (Φο ( _χρθ5 , t) vs. Me / Me ^{n +} ) in order to avoid an electrochemical reaction at the anode.

The device can also be set up in an advantageous manner to be able to carry out one of the advantageous developments of the method.

Further advantages, features and details of the invention will become apparent from the following description and from the drawing. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Showing:

1 shows a one-dimensional model of a battery cell; and

2 is a schematic representation of an exemplary device (of an exemplary control loop) for carrying out the method according to the invention or one of its advantageous developments.

For the description of the solution according to the invention is subsequently of a

simplified, one-dimensional view of a battery cell assumed. However, the function of the inventive solution is not limited by this reduced approach.

As shown in Fig. 1, the simplified model of the battery cell 6 consists of an anode 1 of length _n , a separator 2 of length L _Sep and a cathode 3 of length

The current conductors at the anode 1 and the cathode 3 are assumed to be ideally conducting and omitted in this approach. The two electrodes 1, 3 are made of porous active material, so that there is at each location x in the electrodes 1, 3 and at any time t in the solid state the potential φ ₅ (χ, t) and im

Electrolytes the potential φ \ (χ, ί) is given. In the area of the separator 2, only the potential in the electrolyte φ _λ (χ, ί) exists. All sizes in the anode 1 are identified for clarity with a superscript minus (eg. 0 _s ^~~ (x, t)) and all sizes in the cathode 3 with a superscript Plus (eg, 0 _s ⁺ (x, t)) , Furthermore, overvoltages will occur

Cover layers such as e.g. neglected the solid electrolyte interphase (SEI) of the anode 1 and the influence of electrochemical double layers. These simplifications have no influence on the validity and feasibility of the solution according to the invention.

Lithium plating occurs when the potential at the interface surface graphite particles and electrolyte falls below 0 V versus Li / Li ⁺ . In order to avoid lithium plating, it is therefore necessary to apply in the region of the anode 1: φ _Αη (χ, t): = 0 _S - (x, t) -

(χ, t)> OV vs.. Li / Li ⁺

The deposition of metallic lithium on the surface of the graphite particles typically takes place first on the surface of the separator-near graphite particles due to the high electrical conductivity of the active material and the comparatively low transport speed of the lithium ions in the electrolyte by diffusion and migration. Therefore:

^ crit ⁼ ^ An

And thus for the criterion to avoid lithium plating: An (* crit> = s ^~ (* crit> ^~ 0f (crit,> OV vS. Li / Li ⁺

For the cell voltage that can be measured at the terminals of the battery cell 6, the following applies: fceiiC = 0s ⁺ (pos> ^~ 0s ^~ (O. with x _pos = L _An + L _Sep + L _cat

The cathode potential at the cathode particle and electrolyte interface at position x _{pos is} calculated as:

Here, φ £ is the potential of the cathode material versus Li / Li ⁺ as a function of the concentration of lithium ions on the particle surface and η ⁺ the Reaction overvoltage for charge transfer. This is positive at the cathode 3 in the case of a charge of the battery cell 6.

In the following, an electrolyte overvoltage η is defined for further use: ηι (ΐ) ^■ = Φ ( ^Χ _Ρ Ο5> - 0r (* crit>

With these parameters, the basic equation for the inventive solution for avoiding lithium plating can now be derived:

0AnOcrit, = s ^~ (* crit> ^~ ΦΓ

> O VS. Li / Li ⁺

<=> s ^~ (* crit> ^ 0fOcrit, => l {Xpos.t) ^~ Vl (t <=> s ^~ (* crit> ^ 0s ⁺ (pos' - Kat (* pos » ^~ * 7l

<=> s ^~ (* crit> - s ^~ (O, t)> i / cell ( ^~ 0Kat (pos _* ^~ * 7l (

<=> s ^~ (* crit> - s ^~ (O, t)> i / cell (- o (* pos » ^~ * 7 ⁺ Opos _* 0 ^~ * 7l (

Since the electrical conductivity of the anode material is high, the ohmic

Voltage drop across the active material of the anode 1 small, positive in the charging direction and can thus be estimated for the inventive solution advantageous down to zero:

OV <0 _s ^_ (x _kri t, t) - 0 _s ^~ (O, t) «1mV => 0 _s ^_ (x _kri t, t) - 0 _S ^~ (O, t)« OV It follows that to avoid lithium plating: t / cell (0 ^ o (* pos> + V ⁺ {x _P os> t) + Vl () = ^■ U _ch t)

The cell voltage of the battery cell 6 must therefore be controlled by a corresponding setting of the charging current such that it is less than or equal to the

concentration-dependent electrochemical potential of the cathode material based on the electrochemical potential of the metal reference electrode, advantageously less than or equal to the concentration-dependent electrochemical potential of the cathode material based on the electrochemical potential of

Metal reference electrode plus at least one overvoltage, in the illustrated example of the reaction overvoltage at the cathode 3 and / or

Electrolyte overvoltage, so that a deposition of metallic lithium on the Surface of the anode 1 is avoided. The size (s) or the respective sum of the quantities, hereinafter referred to as U _ch , must be continuous (for example by means of a

Control unit of a motor vehicle) are calculated.

Compared to the direct calculation of the anode potential ΦΑΠ ( ^Χ _> (for instance by means of the mentioned control device), it is advantageous that when the variables to be calculated are underestimated (f _C h, calculated ^ch.ist), the control of the cell voltage

^{leads to} a lower charging current and thus lithium plating is excluded. This is particularly helpful if the aging of the battery cell 6 can not be tracked. An aging of a battery cell 6 tends to lead to higher overvoltages, so that the method according to the present invention remains applicable or valid even with aging, ie during the entire life of the battery cell 6.

Another advantage especially with lithium-ion cells with a negative porous

Graphite electrode is that the modeling of the diffusion in the graphite particles is significantly more complex than in the case of the present mixed on the cathode side mixed oxides. Thus, φ (x _pos , t) can match the existing model approaches with a better

Accuracy can be calculated as the concentration-dependent electrochemical potential of the anode (ö (x, t), which is needed to calculate the anode potential ΦΑΠ (. ^Χ _> .

Fig. 2 shows schematically an exemplary device 4 (a control circuit 4) for

Carrying out the method according to the invention, as can be used, for example, in a motor vehicle for the charging of a battery cell 6.

In order to prevent other damage mechanisms in addition to lithium plating, a maximum cell voltage L / _ma x is specified by the manufacturer, which may not be exceeded during a charge of the battery cell 6. For this reason, the minimum (min) between this upper limit voltage U _ma x and the quantity U _ch (t) calculated by the cell model 7 must be formed in the vehicle. The result is a maximum nominal voltage. The difference to the actual cell voltage is the input variable for a controller 5, which has a maximum charging current / _ma x as manipulated variable as the output signal. This value can be reduced by a further minimum education (min) as the maximum charging current l _ma x must be limited, for example, to prevent other damage mechanisms in addition to lithium plating. Also, the desired torque of the drive for speed reduction, for example from the energy management system of the Motor vehicle is converted into a charging current, or limit the maximum charging current of the charger or the charging station. The result is a maximum charging current with which the battery cell 6 can be charged without damaging lithium plating.

The method and the device 4 according to the present invention are also applicable to a direct parallel connection of a plurality of battery cells 6. In the cell model 7 in this case only the changed thermal and electrical

Boundary conditions are adjusted. The calculated maximum voltage t / _ch (t) then applies to the entire composite of parallel-connected battery cells 6. It is also necessary that the controller 5 to the higher capacity and the lower

Internal resistance of the parallel-connected composite is set to battery cells 6.

If several individual battery cells 6 or more parallel connected

Connected battery cell units in series, a maximum voltage U _ch (t) must be calculated for each battery cell unit separately by a cell model 7, as described above. The controller 5 must then ensure that no battery cell unit exceeds the maximum voltage due to an excessively high charging current.

The inventive method and the device 4 and its or their advantageous developments are in all battery cells 6 with a

Intercalation electrode, are stored in the ions during charging, applicable.

Also, the inventive method and the device 4 and its or their advantageous developments in the automotive field, in stationary storage, in the field of "Consumer Electronics", in the field of model making or other areas on or usable in which rechargeable

electrochemical energy storage cells (accumulators) are used. LIST OF REFERENCE NUMBERS

anode

separator

cathode

contraption

regulator

battery cell

cell model

Claims

claims

Method for charging a rechargeable electrochemical

Energy storage cell (6) with an anode (1) and a cathode

(3), wherein an electrical charging current (/) is fed into the energy storage cell (6) during the charging process,

characterized in that

the electric charging current (I) is regulated by means of a cell model such that the cell voltage (U _ceU (t)) is less than or equal to the concentration- _dependent electrochemical potential of the cathode relative to the electrochemical potential of the metal reference electrode (Φο ( _χρθ5 , t) vs. Me / Me ^{n +} ),

to avoid an electrochemical reaction at the anode (1).

Method according to claim 1,

characterized in that

the electrical charging current (/) is regulated by means of a cell model such that the cell voltage (U _ceU (t)) is less than or equal to the sum (U _C h (t)) which is formed from the concentration-dependent electrochemical potential of the cathode based on the electrochemical potential of the metal reference electrode

(Φο (xpos, vs. Me / Me ^{n +} ) and at least one other addend, which represents an overvoltage, preferably the reaction overvoltage at the cathode (j7 ⁺ (x _pos , t)) and / or the electrolyte overvoltage (η (ί)) ,

Method according to claim 1 or 2,

characterized in that

as an input to the cell model (7), a vector having at least one measured temperature (7) of the rechargeable electrochemical

Energy storage cell (6), optionally with at different points of

rechargeable electrochemical energy storage cell (6) measured Temperature (7) is used.

4. The method according to claim 2 or 3,

characterized in that

an overvoltage or overvoltages by an offset value is / are taken into account by the cell model (7).

5. Method according to one of the preceding claims,

characterized in that

the determination of the concentration-dependent electrochemical potential of the cathode based on the electrochemical potential of the metal reference electrode (0o ( ^x pos _< ^vs -Me / Me ^{n +} ) or the sum (U _ch (t)) using at least one simplistic modeling approach.

6. The method according to any one of the preceding claims,

characterized in that

the charging current according to one of claims 1 to 5 is determined and additionally an empirically or simulatively determined parameter is subtracted from the cell voltage determined by the cell model in order to take into account a model error of the cell model.

7. Method according to one of the preceding claims,

characterized in that

in the cell model used (7) a tracking of the model parameters on the aging of the rechargeable electrochemical energy storage cell (6) is made.

8. Method according to one of the preceding claims,

characterized in that

- It is performed with a rechargeable electrochemical energy storage cell (6), which is only partially discharged;

- It is performed with a lithium-ion energy storage cell (6);

- It is performed with a lithium-ion energy storage cell (6) with a graphite anode (1);

- The current, temperature and charge state distribution within the rechargeable electrochemical energy storage cell (6) are taken into account;

- The aging of the rechargeable electrochemical energy storage cell (6) by an adaptation of the age-dependent model parameters on the

Operating time of the rechargeable electrochemical energy storage cell (6) is taken into account;

- it with a rechargeable battery with parallel connected,

rechargeable electrochemical energy storage cells (6) or with a series circuit of one or more parallel connected rechargeable electrochemical energy storage cells (6) is carried out, in particular with a battery with lithium-ion energy storage cells (6), preferably with a battery with lithium-ion energy storage cells ( 6), each containing a graphite anode (1).

9. Device (4) for charging a rechargeable electrochemical

Energy storage cell (6) with an anode (1) and a cathode (3), characterized in that

the device (4) is set up to regulate the charging current (I) by means of a cell model in such a way that the cell voltage (U _ceU (t)) is less than or equal to the concentration- _dependent electrochemical potential of the cathode relative to the electrochemical potential of the metal reference electrode (Φο ( pos ^{vs vs} ^Me / Me ^{n +} ),

to avoid an electrochemical reaction at the anode (1).

10. Device (4) according to claim 9,

characterized in that

it is adapted to carry out a method according to one of claims 2 to 8.