DE102019134633A1 - Cell with optimized performance and energy density - Google Patents

Abstract

The present invention relates to a lithium ion cell which has at least one first electrode arrangement consisting of anode, separator and cathode, which is optimized for high energy density, and at least one second electrode arrangement consisting of anode, separator and cathode, which is optimized for high performance is, as well as an electrolyte and a housing into which the electrode assemblies and the electrolyte are introduced. The ratio of the weight fraction of the first electrode arrangement to the weight fraction of the second electrode arrangement is 99/1 to 1/99.

Description

Technical area

The present invention relates to a secondary cell, in particular a lithium ion cell or a cell composite, with electrode arrangements of different power and energy density, so that the energy / power ratio can be set as desired.

Technical background

To introduce the terminology, the technical background relating to lithium ion cells is first briefly summarized. A lithium ion cell generally comprises at least one negative electrode (anode), one positive electrode (cathode), an intermediate separator and an electrolyte.

The electrodes comprise an active layer, which typically comprises an active material, a binder and possibly also an electrically conductive additive such as conductive carbon black, and is applied to a metal foil (current collector).

The cells can be produced in a wound or stacked construction. In the winding design, a sequence of separator, anode foil, separator and cathode foil, with anode and cathode foil coated on both sides with active material, is wound onto a round or prismatic core. In the stack design, the electrodes are stacked with a separator in between, whereby again different designs are possible, for example in the form of single cells with electrodes coated on one side and a separator in between, bicells with an electrode coated on both sides and a sequence of separator and counter electrode on both sides, or arrangements in which all electrodes except the top and bottom are coated on both sides. The rolls or stacks are in turn placed in a housing, with foil housings (“pouch”) or dimensionally stable metal housings (“hardcase”) being considered.

There may be various requirements for an energy storage device based on lithium ion cells, some of which may conflict with one another. With regard to the energy density, the highest possible active material loading and the lowest possible weight proportion of passive components, e.g. the thinnest possible separators and current collector foils, can be desirable.

To maximize the performance, however, a higher proportion of electrically conductive additive, a larger wetting area between electrodes and electrolyte and a design of the cell, in particular the separator, for high current densities and thus also higher temperatures can be advantageous, which in part contradicts the Requirements for the energy density can be.

The same applies to the temperature dependence of the power. If, in particular, high performance at low temperatures (e.g. 0 ° C or below) is required, an electrolyte is required that has the lowest possible melting point and the lowest possible viscosity, which is achieved by an electrolyte solvent with a high proportion of open-chain carbonic acid esters in the mixture Can be compared to cyclic carbonic acid esters such as ethylene carbonate. However, open-chain carbonic acid esters have a low dielectric constant and thus a low solubility for the conductive salt, so that the performance at normal temperature (e.g. 20 ° C and above) compared to electrolytes with a high proportion of cyclic carbonates can be impaired.

To increase the (peak) performance of a battery system optimized in terms of energy density, for example the energy storage system (ESS) of an electrically operated vehicle, it is possible to provide an additional secondary energy storage device that is designed for high maximum performance, the same voltage as that Main ESS supplies and is connected in parallel to it. A disadvantage of this design, however, is the increased complexity, space requirements and weight that a complete secondary ESS entails.

Alternatively, a parallel connection of different cell types can also be considered at cell level, some of which are optimized with regard to energy density and the other with regard to performance. However, this has the disadvantage that mechanical, electrical and thermal integration is difficult due to the typically different and incompatible cell geometry (hard case in HEV-PEHV2 or HEV-PHEV1 format, combination with pouch cells, etc.).

Summary of the invention

In view of the above problem, the present invention provides a lithium-ion cell or a cell composite with electrode arrangements of different power and energy density, so that the energy / power ratio can be set as desired.

The energy density (E) and the power density (P) are typically expressed in the state of the art as energy (Wh) or maximum drawable power (W) per gross weight or volume of the entire cell (i.e. including housing) specified. The housing can make up, for example, 1-30% of the weight or 3-40% of the volume, depending on the cell type and format. Since electrode arrangements with different energy or power densities (E or P) are used in combination according to the invention, weight-related net energy or power densities, which relate to the weight of the electrode arrangement alone, are expediently used for the following description.

To characterize the electrode arrangements, in particular the ratio of power to energy density (P / E ratio) is used.

• - mindestens eine erste Elektroden-Anordnung aus Anode, Separator und Kathode, die eine erste Leistungsdichte P₁ und eine erste Energiedichte E₁ aufweist, wobei der gewichtsbezogene Anteil der ersten Elektroden-Anordnung an der Gesamtheit der Elektrodenanordnungen in der Zelle G₁ beträgt;
• - mindestens eine zweite Elektroden-Anordnung aus Anode, Separator und Kathode, die eine zweite Leistungsdichte P₂ und eine zweite Energiedichte E₂ aufweist wobei der gewichtsbezogene Anteil der zweiten Elektroden-Anordnung an der Gesamtheit der Elektrodenanordnungen in der Zelle G₂ beträgt;
• - einen Elektrolyten, der ein nichtwässriges Lösungsmittel und ein Leitsalz umfasst, sowie
• - ein Gehäuse, in das die Elektroden-Anordnungen und der Elektrolyt eingebracht sind;

dadurch gekennzeichnet, dass das P/E-Verhältnis der ersten Elektroden-Anordnung (P₁/E₁) kleiner ist als das P/E-Verhältnis der zweiten Elektroden-Anordnung (P₂/E₂); und dass das Verhältnis der Anteile G₁ und G₂ 99/1 bis 1/99 beträgt.Accordingly, the invention relates to a lithium ion cell comprising:

• - At least one first electrode arrangement comprising anode, separator and cathode, which has a first power density P ₁ and a first energy density E ₁ , the weight-related proportion of the first electrode arrangement in the totality of the electrode arrangements in the cell being G ₁ ;
• - At least one second electrode arrangement comprising anode, separator and cathode, which has a second power density P ₂ and a second energy density E ₂ , the weight-related proportion of the second electrode arrangement in the totality of the electrode arrangements in the cell being G ₂ ;
• - An electrolyte, which comprises a non-aqueous solvent and a conductive salt, and
• a housing into which the electrode assemblies and the electrolyte are introduced;

characterized in that the P / E ratio of the first electrode arrangement (P ₁ / E ₁ ) is smaller than the P / E ratio of the second electrode arrangement (P ₂ / E ₂ ); and that the ratio of the proportions G ₁ and G _{2 is} 99/1 to 1/99.

The first electrode arrangement with the lower ratio P _{1 /} E ₁ is designed for a high energy density, and the second electrode arrangement with the larger ratio P ₂ / E _{2 is designed} for a high power density. The total energy or power density of the cell results as a weighted mean value as Eges = G ₁ E ₁ + G ₂ E ₂ or Pges = G ₁ P ₁ + G ₂ P _2. Thus, the cell according to the invention can be selected accordingly of the P / E ratio of the first and second electrode arrangements and the weight ratio G ₁ / G ₂ with a continuously adjustable total P / E ratio.

It can be easily integrated into existing battery systems without requiring additional installation space and without the need for additional mechanical, electrical or thermal integration measures at the module or storage level. This enables increased performance to be provided without incurring additional costs at the module or storage level.

Figure list

• 1 shows schematically a reference cell (left) as well as cells according to the invention, which comprises a single electrode stack with a proportion of the stacking layers of the first electrode arrangement with a low P / E ratio decreasing towards the right and an increasing proportion of the stacking layers of the second electrode arrangement with a high P / E ratio, which is placed in a hardcase housing.
• 2 is a further schematic representation of a reference cell (left) and cells according to the invention with a single electrode stack in a hardcase housing, with an alternative arrangement of the stacking layers.
• 3 shows schematically a reference cell (left) and cells according to the invention, in which the electrode arrangements are designed as coils, which are in turn placed in a hardcase housing, with a proportion of the first electrode arrangements decreasing from left to right and an increasing proportion of the second electrode arrangements.
• 4th shows schematically a reference cell (left) and cells according to the invention, in which a stack of stacked layers of the first electrode arrangement and a stack of stacked layers of the second electrode arrangement are introduced together into a hard case housing.
• 5 shows two possibilities of combining the cells according to the invention with conventional cells.

Detailed description

Design of the electrode arrangements

In general, the cell according to the invention is configured in such a way that the entirety of its electrode _{arrangements comprises at least a portion G 1} of first electrode arrangements which is optimized for high energy density, and at least a portion G ₂ of second electrode arrangements which is optimized for high performance . The proportions are defined based on weight, and the optimization with regard to the energy or power density is characterized on the basis of the P / E ratio.

In this context, an electrode arrangement is understood to mean the sequence of anode, separator and cathode, without their precise configuration (eg winding, stack, coating on one or both sides, etc.) being important.

For example, a part of the stack can consist of layers of the electrode arrangements with high energy density and thus provide the portion G ₁ , while a further part consists of layers of the electrode arrangements with high power and thus make the portion G ₂ available. When using two electrode arrangements with different P / E ratios, the total G _tot is the sum of the proportions G ₁ and G ₂ .

According to the invention, depending on the requirement profile, more than two electrode arrangements with different P / E ratios can also be used; If, for example, different types of load peaks are expected during operation, two or more electrode arrangements with different power optimization can be used in addition to the electrode arrangement optimized for high energy density. Usually, however, electrode arrangements with two different P / E ratios are sufficient and preferred with a view to reducing the complexity and simplifying production.

The choice of the P / E ratios for the performance and energy-optimized electrode arrangements can also depend on the requirement profile. For use as the main energy store in an electrically operated vehicle, the energy-optimized first electrode arrangement can have a P / E ratio of, for example, 8 or less, preferably 6 or less, in particular 4 or less. The P / E ratio of the power-optimized second electrode arrangement can accordingly be more than 8, preferably 10 or higher, in particular 20 or higher. When used in combination with another energy source, for example in connection with conventional lithium ion cells or in a hybrid electric or plug-in hybrid electric vehicle, the P / E ratios can be correspondingly higher.

The ratio of the proportions G ₁ and G ₂ (G ₁ / G ₂ ) also depends on the intended use and the desired total P / E ratio or the total energy and power density, and is generally between 99/1 and 1 / 99, preferably 90/10 to 10/90, in particular 75/25 to 25/75. When used as the main or sole energy store, higher proportions of G _{1 are} preferred; the ratio is then preferably 99/1 to 50/50, more preferably 90/5 to 67/33, in particular 90/10 to 75/25. When used in combination with a further energy source, however, a reduced proportion G ₁ can be used.

Structure of the cell

According to the invention, the first and second electrode arrangements with a high energy or power density are housed together in a cell housing.

Such embodiments are in 1 shown. The left cell serves as a reference and only comprises a stack of first electrode arrangements with a high energy density, which is placed in a hard case housing. In this case, G ₁ corresponds to the totality G _Ges . By replacing individual stack layers with those with high performance, as shown in the middle-left in the figure, the proportion G _{1 is} reduced and the proportion G _{2 is} increased. The high-performance stack layers of the second electrode arrangement can in principle be positioned at any desired position of the stack. Central positioning is selected in the figure. By increasing the reduction in the high-energy stacking layers of the first and increasing the high-performance stacking layers of the second electrode arrangement, the ratio of G ₁ and G ₂ and thus the ratio of energy density and power can be set continuously.

This is shown in the middle-right and right-hand figures.

2 shows an alternative embodiment in which the high-performance stack layers are attached to the edge of the overall stack.

In addition, the cell can also comprise several stacks or several coils, which are accommodated in the same housing connected in parallel. Then, for example, a certain number of the wraps or stacks contained can be made up of electrode arrangements with high energy density and thus provide the portion G ₁ , while the remainder is made up of electrode arrangements with high power and thus make up the portion G ₁ .

3 shows an example of an embodiment in which several prismatic windings are introduced into a hard case housing. In the cell on the left (reference example) only two coils with high energy density are used, which make up the entirety of the electrode arrangements.

In the middle-left cell, two coils with high energy density but reduced electrode area are used, i.e. the coils have the same height and width as in the left cell, but the number of turns and thus the thickness of the coil and consequently the proportion G is ₁ reduced. The space gained in the housing is used by a third Taken with high performance wrap, which provides _{the portion G 2.}

By reducing the number of turns of the high-energy winding and correspondingly increasing the number of turns of the high-performance winding, as sketched in the middle-right and right-hand figures, the ratio of G ₁ and G ₂ and thus the ratio of energy density and power can be continuously adjusted.

The same applies to the stacked construction, as in 4th shown. The figure on the left again outlines the reference case in which the hard case housing only contains a stack with a high energy density.

The figure in the middle-left shows a cell with a high-energy stack, the number of layers (and thus its proportion G ₁ ) is reduced compared to the reference case. The space freed up is taken up by a high-performance stack that provides the _{G 2 portion.} Again, the number of layers in the high-energy stack can be continuously reduced and the number of layers in the high-performance stack can be continuously increased so that the ratio of G ₁ and G ₂ and thus the ratio of energy density and power can be continuously adjusted.

Configuration of the electrode arrangements

The electrode assemblies generally include a negative electrode (anode), a positive electrode (cathode) and a separator therebetween.

The electrodes comprise an active layer, which typically comprises an active material, a binding agent such as PVdF or cellulose ether and possibly also an electrically conductive additive such as carbon black, and is applied to one or both sides of a metal foil (current collector).

Aluminum foil is preferably used as the current collector for the cathode. The cathode active material is not particularly limited, and conventional materials known in the art capable of intercalating and deintercalating lithium can be used. Preferred examples include transition metal oxides with a layer structure of the type LiMO ₂ (M = Co, Ni, Mn) such as LiCoO ₂ (LCO), LiNiO ₂ , LiMnO ₂ or mixed oxides such as LiNi _x Mn _y Co _z O ₂ (with x + y + z = 1; NMC) or LiCo _0.85 Al _0.15 O ₂ (NCA), spinels such as LiMn ₂ O ₄ (LMO) or phosphates that crystallize in the olivine type such as LiFePO ₄ (LFP) or LiFe _0.15 Mn _{0, 85} PO ₄ (LFMP). Another class of cathode materials are conversion materials such as transition metal fluorides such as FeF ₃ , NiF ₂ , CoFeF ₃ , CuF ₂ , etc., or sulfides such as CuS. The use of a mixture of two or more of these materials is also possible.

Copper foil is preferably used as the current collector for the anode, since aluminum tends to form alloys with lithium. Materials customary in the prior art come into consideration as anode active material, for example carbon-based intercalation materials such as graphite, hard carbon or soft carbon, as well as lithium titanate materials, alloying agents such as silicon, aluminum or magnesium or composite materials such as carbon / silicon.

The function of the separator is, on the one hand, to separate the electrodes mechanically and electrically, and, on the other hand, to enable the transfer of lithium ions between the electrodes. Typically, a porous polyolefin film, in particular made of polyethylene (PE) or polypropylene (PP), or a nonwoven material is used. The separator can be designed as a multilayer separator with a shutdown function, in particular with a layer sequence PP / PE / PP, so that the low-melting PE layer lies between the higher melting PP layers and, in the event of an abnormal rise in temperature, melts and closes the pores can to prevent the flow of lithium ions. Optionally, the separator can also have a ceramic coating.

The electrode arrangements are designed for high energy or power density in a manner known per se.

In general, the energy and power density can be regulated by the composition and configuration of the electrodes, in particular the active material coverage or the ratio of active material to passive components.

In addition, it is also possible to use different active materials or active material mixtures for the first and second electrode arrangements. For example, cathode active materials of the layered oxide type such as LCO have a higher maximum lithium content in relation to the stoichiometry and thus a higher charge density than those of the spinel type such as LMO or of the olivine type such as LFP. In contrast, with active materials of the spinel or olivine type, the maximum discharge currents are usually higher than with the layered oxides.

Consequently, a layer oxide such as LCO or an active material mixture with a high layer oxide content can be used for the first electrode arrangement with high energy density, and an oxide with a spinel structure such as LMO or an active material mixture with a high spinel content can be used for the second electrode arrangement with high power density . When using more than two electrode arrangements with different energy densities, it is possible, for example, to use mixtures of layered oxide and spinel active materials in different mixing ratios.

Since the first and second electrode arrangements are connected in parallel, the nominal voltages are preferably the same as possible. This can be achieved on the one hand by using identical combinations of active materials. When using different active material combinations, for example with regard to the above-described optimization of energy and power density, the difference between the potential differences of the first and second electrode arrangements is preferably 0.3 V or less, more preferably 0.2 V or less, in particular 0.1 V or smaller.

Interconnection of the cells

The cells according to the invention can easily be integrated into existing battery systems. For this purpose, the cells provided in the existing battery system (for example cells that are optimized solely for high energy density) can be completely or partially replaced by cells according to the invention. In this way, the energy / power ratio of the battery system can be modified in a simple manner depending on the requirements, without increasing the complexity at the module or storage level. In particular, no additional mechanical, electrical or thermal integration measures are required on the module or storage level.

An example of the partial use of the cells according to the invention is a cell-by-cell use within a strand of serially linked cells. For example, every third cell can be replaced by a cell according to the invention, as in FIG 5 shown above.

In the case of several parallel strands, one or more strands can also be made up of cells according to the invention and the other strands of conventional cells. Such an arrangement is in 5 shown below.

Claims (10)

A lithium ion cell comprising: at least one first electrode arrangement comprising anode, separator and cathode, which has a first power density P ₁ and a first energy density E ₁ , the weight-related proportion of the first electrode arrangement in relation to the totality of the electrode arrangements in the cell G Is _1; - At least one second electrode arrangement comprising anode, separator and cathode, which has a second power density P ₂ and a second energy density E ₂ , the weight-related proportion of the second electrode arrangement in the totality of the electrode arrangements in the cell being G ₂ ; - An electrolyte, which comprises a non-aqueous solvent and a conductive salt, and - a housing into which the electrode arrangements and the electrolyte are introduced; characterized in that the P / E ratio of the first electrode arrangement (P ₁ / E ₁ ) is smaller than the P / E ratio of the second electrode arrangement (P ₂ / E ₂ ); and that the ratio of the proportions G ₁ and G _{2 is} 99/1 to 1/99. Lithium ion cell according to Claim 1 wherein the case is a hard case case. Lithium ion cell according to Claim 1 or 2 wherein the electrode assemblies are each configured as a coil. Lithium ion cell according to Claim 1 or 2 wherein the electrode assemblies are each configured as a single stack. Lithium ion cell according to Claim 1 or 2 wherein the cell comprises at least one stack, which in turn comprises one or more layers of the first electrode arrangement and one or more layers of the second electrode arrangement. Lithium ion cell according to at least one of Claims 1 to 5 wherein P _{1 /} E _{1 is} 8 or less, preferably 4 or less and P ₂ / E _{2 is} more than 8, preferably 20 or more. Lithium ion cell according to at least one of Claims 1 to 6th wherein G ₁ / G _{2 is} 90/5 to 67/33, preferably 90/10 to 75/25. A battery module comprising a plurality of lithium ion cells connected in parallel and / or in series, wherein at least one of the cells is a lithium ion cell according to at least one of the Claims 1 to 7th is. Battery system that includes a lithium ion cell according to at least one of Claims 1 to 7th or a battery module according to Claim 8 as well as a battery management control unit. Use the battery system in accordance with Claim 9 as energy storage for an electrically powered vehicle, selected from a battery-powered vehicle, a plug-in hybrid electric powered vehicle and a hybrid electric powered vehicle.

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