EP2095458A1

EP2095458A1 - Electrochemical energy source and electronic device provided with such an electrochemical energy source

Info

Publication number: EP2095458A1
Application number: EP07849440A
Authority: EP
Inventors: Johannes H. G. Op Het Veld; Rogier A. H. Niessen; Remco H. W. Pijnenburg; Petrus H. L. Notten; Youri V. Ponomarev
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2006-12-18
Filing date: 2007-12-12
Publication date: 2009-09-02
Also published as: CN101563806A; JP2010514123A; WO2008075251A1

Abstract

Electrochemical energy sources based on solid-state electrolytes are known in the art. These energy sources, or 'solid-state batteries', efficiently convert chemical energy into electrical energy and can be used as the power sources for portable electronics. Nowadays, new application areas arise like implantables, small autonomous devices, smart cards, integrated lighting solutions or hearing aids. The invention relates to an improved electrochemical energy source and to an electronic device provided with such an electrochemical energy source, and whereby the volume change of the anode and cathode electrode assembly is minimised during charging and discharging of the battery cell.

Description

Electrochemical energy source and electronic device provided with such an electrochemical energy source

FIELD OF THE INVENTION

The invention relates to an improved electrochemical energy source. The invention also relates to an electronic device provided with such an electrochemical energy source.

BACKGROUND OF THE INVENTION

Electrochemical energy sources based on solid-state electrolytes are known in the art. These (planar) energy sources, or 'solid-state batteries', efficiently convert chemical energy into electrical energy and can be used as the power sources for portable electronics. Nowadays, new application areas arise like implantables, small autonomous devices, smart cards, integrated lighting solutions (OLED's) or hearing aids. These low-power and small- volume applications require small batteries with a large volumetric energy/power density. The gravimetric energy/power density is of minor importance due to the small size. In order to obtain an improved volumetric power density, it is conceivable to apply a battery as described in the international patent application WO 2005/027245, wherein a three- dimensionally oriented solid-state thin-film lithium ion battery is disclosed for obtaining an increased surface area between different active layers of the battery. Although this known solid-state battery has an improved volumetric power density, this battery also has several serious drawbacks. A major drawback of this integrated solid-state battery is the stress/strain induced during battery operation as a result of the expansion/contraction of the anode and cathode, which will commonly cause a total volume change of the assembly of the anode and the cathode of over 25%. These mechanical stresses will affect and the reliability and the processability of the integrated battery, and makes stacking of multiple integrated batteries on top of each other relatively difficult and sometimes even non- feasible. It is an object of the invention to provide an improved electrochemical source exhibiting a reduced volume change during operation.

SUMMARY OF THE INVENTION This object can be achieved by providing an electrochemical energy source according to the preamble, comprising: a substrate, and at least one battery cell deposited onto said substrate, the battery cell comprising: an anode, a cathode, and an solid-state electrolyte separating said anode and said cathode, wherein the anode and the cathode are tailored to each other, such that the total volume change of the assembly of the anode and the cathode is less than 20% during charging and discharging of the battery cell. By smartly choosing and constructing a mutually compatible anode and cathode, a volume expansion respectively reduction of the anode during charging can be counteracted substantially by a volume reduction respectively expansion of the cathode, while a volume expansion respectively reduction of the cathode during discharging can be counteracted substantially by a volume reduction respectively expansion of the anode. Hence, the total volume change of the battery cell during battery operation can be reduced substantially, as a result of which the battery cell of the electrochemical energy source can be packaged, integrated, and/or stacked with other components in a more reliable and durable manner. In a preferred embodiment, the anode and the cathode are tailored to each other, such that the total volume change of the assembly of the anode and the cathode is less than 15%, preferably less than 10%, in particularly less than 5% during charging and discharging of the battery cell. Eliminating a volume change of the assembly of the anode and the cathode would also be technically feasible in theory, however this would commonly result in a battery cell having an unsatisfactory volumetric energy density and/or could lead to an impractical excessive battery volume. Hence, the aim to minimize the total volume change of the assembly of the anode and the cathode during battery operation should be balanced against certain predefined boundary conditions, such as a minimum required volumetric energy density, and an acceptable dimensioning and shape of the battery cell. In a preferred embodiment, the materials of the anode and the cathode are chosen such that the total volume change of the assembly of the anode and the cathode is less than 20%, and more preferably as less as practically possible, during charging and discharging of the battery cell. This way of smartly choosing an anode material and a compatible cathode material is also considered as chemical matching. In an alternative preferred embodiment the volume of the anode and the cathode are chosen such that the total volume change of the assembly of the anode and the cathode is less than 20%, and more preferably as less as practically possible, during charging and discharging of the battery cell. The method, wherein the volume of the anode and the volume of the cathode are mutually tailored, is also considered as geometrical matching. In a particular preferred embodiment both chemical matching and geometrical matching are applied to the at least one battery cell to minimise the total volume change of the assembly of the anode and the cathode, while preserving a satisfying volumetric energy density of the battery cell of the energy source according to the invention. Preferably, the energy density reduction ratio (G) between an optimized volumetric energy density ( σ_c ^v ₊ ^e _a ) of the assembly of the anode and the cathode on one side, and the volumetric energy density (σf^e _+a) optimized for a predefined volume change of the assembly of the anode and the cathode on the other side is between 0.25 and 1, preferably between 0.5 and 1, more preferably between 0.75 and 1, and in particularly between 0.9 and 1. The energy density reduction ration is dependent on the characteristics of the anode material and the cathode material used, wherein the energy reduction ratio G as such is preferably practically maximised in order to reduce to loss of volumetric energy density, and hence the loss of battery efficiency.

Preferably, the anode and the cathode of at least one battery cell of the energy source according to the invention are adapted for storage of active species of at least one of following elements: hydrogen (H), lithium (Li), beryllium (Be), magnesium (Mg), aluminium (Al), copper (Cu), silver (Ag), sodium (Na) and potassium (K), or any other suitable element which is assigned to group 1 or group 2 of the periodic table. So, the electrochemical energy source of the energy system according to the invention may be based on various intercalation mechanisms and is therefore suitable to form different kinds of (reserve-type) battery cells, e.g. Li-ion battery cells, NiMH battery cells, et cetera. In a preferred embodiment at least one electrode, more the battery anode, comprises at least one of the following materials: C, Sn, Ge, Pb, Zn, Bi, Sb, Li, and, preferably doped, Si. A combination of these materials may also be used to form the electrode(s). Preferably, n-type or p-type doped Si is used as electrode, or a doped Si-related compound, like SiGe or SiGeC. Also other suitable materials may be applied as anode, preferably any other suitable element which is assigned to one of groups 12-16 of the periodic table, provided that the material of the battery electrode is adapted for intercalation and storing at least one of the abovementioned reactive species. The aforementioned materials are in particularly suitable to be applied in lithium ion based battery cells. In case a hydrogen based battery cell is applied, the anode preferably comprises a hydride forming material, such as ABs-type materials, in particular LaNi₅, and such as magnesium-based alloys, in particular Mg_xTii__x. The cathode for a lithium ion based cell may comprise at least one metal-oxide based material, e.g. LiCoO₂, LiNiO₂, LiMnO₂ or a combination of these such as. e.g. Li(NiCoMn)O₂. In case of a hydrogen based energy source, the cathode may comprise Ni(OH)₂ and/or NiM(OH)₂, wherein M is formed by one or more elements selected from the group of e.g. Cd, Co, or Bi. In a particular preferred embodiment the anode comprises Li_ySi and the cathode comprises Li_xNiO₂. It has been found that this particular combination has beneficial volumetric energy density at a predefined volume change of e.g. 5%.

In a preferred embodiment the electrochemical energy source has a non-planar geometry, being a geometry deviating from a planar geometry, such as for example a curved plane geometry, or a hooked geometry. A major advantage of the electrochemical energy source having a non-planar geometry is that any desired shape of said electrochemical energy source can be realized such that the freedom of choice as regards shape and format of said electrochemical energy source is many times greater than the freedom offered by the state of the art. The geometry of said electrochemical energy source can thus be adapted to spatial limitations imposed by any electrical apparatus in which the battery can be used. From a point of view of space, electronic devices can often be more efficiently configured because of the greater freedom as regards the choice of the geometry of electrochemical energy source; this may lead to a saving of space in and greater freedom of design of the device. It is to be noted that a curved planar geometry results in a curved battery which has a curved planar shape which may be concave/convex or wavy. However, it also imaginable for a person skilled in the art to apply an angular battery which has a hooked shape.

In a preferred embodiment at least one electrode of the anode and the cathode is patterned at least partially. By patterning or structuring one, and preferably both, electrodes of the electrochemical energy source according to the invention, a three-dimensional surface area, and hence an increased surface area per footprint of the electrode(s), and an increased contact surface per volume between the at least one electrode and the electrolyte is obtained. This increase of the contact surface(s) leads to an improved rate capacity of the energy source, and hence to an increased performance of the energy source according to the invention. In this way the power density in the energy source may be maximized and thus optimized. Due to this increased cell performance a small-scale energy source according to the invention will be adapted for powering a small-scale electronic device in a satisfying manner. Moreover, due to this increased performance, the freedom of choice of (small-scale) electronic components to be powered by the electrochemical energy source according to the invention will be increased substantially. The nature, shape, and dimensioning of the pattern may be various, as will be elucidated below. It is preferred that at least one surface of at least one electrode is substantially regularly patterned, and more preferably that the applied pattern is provided with one or more cavities, in particular pillars, trenches, slits, or holes, which particular cavities can be applied in a relatively accurate manner. In this manner the increased performance of the electrochemical energy source can also be predetermined in a relatively accurate manner. In this context it is noted that a surface of the substrate onto which the stack is deposited may be either substantially flat or may be patterned (by curving the substrate and/or providing the substrate with trenches, holes and/or pillars) to facilitate generating a three-dimensional oriented cell.

Preferably, both the anode and the cathode are connected to a current collector respectively, wherein the current collectors are made of at least one of the following materials: Al, Ni, Pt, Au, Ag, Cu, Ta, Ti, TaN, and TiN. Other kinds of current collectors, such as, preferably doped, semiconductor materials such as e.g. Si, GaAs, InP may also be applied to act as current collector.

The invention also relates to an electronic device provided with at least one electrochemical energy source according to the invention, and at least one electronic component connected to said electrochemical energy source. The at least one electronic component is preferably at least partially embedded in the substrate of the electrochemical energy source. In this manner a System in Package (SiP) may be realized. In a SiP one or multiple electronic components and/or devices, such as integrated circuits (ICs), actuators, controllers, sensors, receivers, transmitters, et cetera, are embeddded at least partially in the substrate of the electrochemical energy source according to the invention. The electrochemical energy source according to the invention is ideally suitable to provide power to different kind of electronic devices, like domestic electrical appliances, such as laptops, and relatively small high power electronic applications, such as (bio)implantantables, hearing aids, autonomous network devices, and nerve and muscle stimulation devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of the following non- limitative embodiment, wherein the following figures have been incorporated: Fig. 1 shows a schematic view of chemical electrode matching,

Fig. 2 shows a schematic view of geometrical electrode matching,

Fig. 3 shows a chart of the relative volume expansion as a function of the anode volume expansion factor F, Fig. 4 shows a chart of the energy reduction ratio G as a function of the volume reduction ratio F at a volume change of 5%, and

Fig. 5 shows a comparative chart of the anode and cathode volumes as a function of a lithuim concentration with said anode and said cathode.

DETAILED DESCRIPTION OF THE EMBODIMENT

Chemical electrode matching

The chemical electrode matching method is based on the right combination of anode and cathode materials so that the overall volume expansion is low (see figure 1), wherein the starting point is the situation optimized for volumetric energy density using superscript indexing (^ed) and the end point is the situation optimized for less volume expansion using superscript indexing (^ve). This method is based on the replacement of one or both electrode materials chemistry in order to reduce the overall volume expansion ΑomAV_c]+a] to AV_c2+a2 . Table 1 shows a combination of two anode materials (Si and Li) and two cathode materials [LiCoO 2 and LiNiO 2) of a solid-state battery (comprising a solid-state electrolyte) where V_c+a(chg) is the sum of the cathode and anode volume for a charged battery system and ΔV_c+a the absolute volume expansion between the discharged and charged state. A conventional reference battery system is Li - LiCoθ2. Battery systems with a very high volumetric energy density σ_c+a (0.3 mWh/μmxm²) are Li- Li_xNiθ2 and Li_ySi-

Li_xNiO 2. However, these systems have a relative large expansion of respectively -25.2% and - 12.8%.

Table 1 : Volumes expansion rates and energy densities for several battery systems, wherein each battery system is normalised for delivery of 1 mAh charge. Geometrical electrode matching Geometrical electrode matching means that the volume of at least one of the electrodes is changed in such a way that the total volume expansion of a stack is rather low. Figure 2 shows an example where the anode volume is reduced by a factor F (θ < F < l) .

The volume expansion ratio ΔR_V defined as

ΔV^X

ΛR_V = (1) v;:_a (chg)

and depends on the anode volume reduction factor F as shown in figure 3 for several battery systems. Li based battery systems show a large volumetric expansion ratio compared to Li_ySi based systems. This means that for Li based systems, the volume of the anode should be reduced much more in order to get less volume expansion as for Li_ySi based systems and accordingly, the anode reduction factor ^F will be much closer to 1. As a consequence, the volumetric energy density will be reduced due to the fact that the volume of both electrodes will change. The change in energy density is denoted by

σ_r ed (2) σ „

with σf_+a the volumetric energy density at optimal energy density and σζ₊ ^e _a at reduced volume expansion. The overall impact on the volumetric energy density ratio G c+a for a

volume expansion ratio ΔR_V of -5% is plotted in figure 4.

Table 2: Volume expansion and volumetric energy density before and after reduction of the anode volume in order to get -5% expansion. It can be deduced from Table 2 that the reference battery system Li-Li_xCoθ2 has a relatively poor volumetric energy density (0.203 mWh/μm.cm²) and at the same time a relatively large relative large volume expansion ratio (-12.7 %). Chemical matching will result in that it is more beneficial to apply a battery system with an increased volumetric energy density, such as the Li-Li_xNiθ2 (0.312 mWh/μm.cm²) based battery system or the

LiySi-Li_xNiθ2 (0.306 mWh/μm.cm²) based battery system. In order to get a rather low volume expansion ratio of -5%, the latter two preferred battery systems can be matched geometrically, resulting in a reduction of the volumetric energy density of both battery systems. After geometrical matching the Li-Li_xNiθ2 based battery system will have a volumetric energy density of 0.069 mWh/μm.cm², and the Li_ySi-Li_xNiθ2 based battery system will have a volumetric energy system density of 0.131 mWh/μm.cm². Hence, based on the battery systems listed in Table 2, it will be preferable to apply a Li_ySi-Li_xNiθ2 based battery system having the highest volumetric energy density in case a predefined volume expansion ration of -5% is required. In this embodiment the geometrical matching method is described to obtain less volume expansion of a battery stack consisting of a Si or Li anode (a) and LiCoθ2 or LiNiO 2 cathode (c), see tables 3, 4 and 5 for materials data. The quantities y , U _a (y) ,

V _a (} '_max ) ' ^ _a (y _mm ) ^and ^ ^ _a represent the concentration, the equilibrium potential versus LiZLi⁺ , the volume at maximum concentration, the volume at minimum concentration and the absolute volume expansion, respectively, for the anode material.

Table 3: Anode materials Li and Si for Q = ImAh.

The quantities x , U_c{x) , V_c(x_max) , V_c(x_mm ) and ΔV_C represent the concentration, the equilibrium potential versus LiZLi⁺ , the volume at maximum concentration, the volume at minimum concentration and the absolute volume expansion, respectively, for the cathode material.

Table 4: Li-Metal-Oxide cathode materials for Q = ImAh.

Combination of several cathode-anode materials results in four different battery systems. The quantities of these battery systems represent only the cathode and anode material so electrolyte and other layers are not included (as the electrolyte and the current collectors commonly do not show a noticeable volume change during battery operation). The

AV_^ quantities V_c+a {chg) , ΔV_c+a , U_bat and σ_c+a represent the volume for a charged

battery, the absolute volume expansion from charged to discharged state, the relative volume expansion from charged to discharged state, the battery voltage in both states and the volumetric energy density, respectively.

Table 5 : The resulting battery equilibrium potential range and volumetric energy density for Q = ImAh.

As aforementioned the starting point is the situation optimized for volumetric energy density using superscript indexing (^ed), while the end point is the situation optimized for less volume expansion using superscript indexing (^ve). Figure 5 shows a graphical representation for both these situations. The unbroken lines in figure 5 show the original situation at maximal volumetric energy density and the dashed lines represent the situation after reduction of the anode volume V_a in order to get less volume expansion for the sum of both electrodes Δ V_c+a -I . The anode and cathode volume V_a and V_c depend on the Li concentration y and x respectively. At the left side of the figure, the battery is in the charged state so y = y_max and x = x_mm . At the right side of the picture, the battery is in the discharged state so y = y_mm and x = x_max . The original anode volume at optimal volumetric energy density Vf will be reduced by a factor F (θ < F < l) in order to obtain less volume expansion of both electrodes AV_c+a -I . The cathode (c) is not changed. Optimal volumetric energy density

Changing from the charged (chg) to discharged (dis) state will change the total volume of the electrode materials denoted by AV^* _+a . The volume expansion AV^* _+a for this system is

KiΛchg) = V:^d{x_mm) + V:^d{y_max)

VfΛdis) = V:^d{x_max) + V:^d{y_mm) (3)

Av:t = v;^d _a(dis)-v:^d _a(ch_g) ≠ o

where x_mm and x_max are respectively the minimal and maximal Li content in the Li_xNiθ2 cathode and y_mm and y_max the minimal and maximal Li content in the Li_ySi anode.

Furthermore it is assumed that the volume expansion of an electrode is linear with x and y for the cathode and anode respectively ( a is the slope and K the vertical offset). So the anode volume V_a ^ed{y) is

v:^d(y) = <^d-y + K eel

, eel o._r. = V ^yyaa^ed( W XJvmmaUxX )) )-~V ^Vyaa^ed( XXJJvmmImn )) ) '' J S V mmmm < —— J SV< —— J SV mmaaxx (4) y max y mm

and the cathode volume Vf is

v;^d{x) = a_c ^ed-x+κ ";^eed

= Vf{x_max)-V:^d{x_mm) , x_mm≤x≤x_max

(5) x max — x mm

K^d = V:^d{x_mm)-a_c ^ed-x_mm

Or written in a more explicit notation for the anode (6) and cathode (7), respectively, yields vf(y) = <^d-(y-y_mJ+K^d(y_mΛ a - _ vf(y_max)-vf(y_mm) y_m≤y≤y∞ ) s V ma — V (6 x y mm

and

v?{x) =

Reduced volume expansion

Reduction of the anode volume with a factor F reduces the amount of Li atoms in the anode so the amount of charge that will be shuttled between the anode and cathode is also reduced by the same factor F . This means that the maximum Li concentration in the cathode at reduced anode volume x. will be lower than x_max at optimal volumetric energy density (see figure 5). Forx_* yields

Xmax -X* x max —x mm

^ = ^Xmm ^+Fi^Xmaχ -^Xmm) (8)

Q-F Q Q

Again, changing from the charged (chg) to discharged (dis) state causes a volume expansion J F_c7_a equal to

VllXchg) = V:^d{x_mm) + F-V:^d{y_max)

VrΛdis) = V:^d(x,) + F-V_a ^ed(y_mm) (9)

Av:ι_a = v:ι_a{dis)-v:ι_a{chg)

Substitution of (7) in (9) yields

vzichg) = v:^d(x_mm)+F-v:^d(y_mj

(10) V;:_a {dis) = a? ^■ (x. - x_mm ) + Vf {x_mm ) + F- Vf {y_mm )

and substitution of x. from (8) in (10) to V ^yc^v+^ea V r _c ^v ₊ ^e _a ) I

Substitution of the slope af (7) in (11) results in

vzichg) = v:^d(x_mm)+F-v:^d(y_mj

and after some simplification in

V ^yc^v+^ea iVc-hⁿ&<Λ/ = )) + F ^J -V ^Y a^ed( XJv max ) I

VZXdis) =

The overall volume expansion A V_c ^vl_a when changing from charged to discharged state is

Δv:ι_a = v:ι_a(dis)-v:ι_a(chg) = F-( V(Vv c^ed

The relative volume expansion factor AR_V , defined as the volume expansion AVζl_a divided by the volume in charged state V_c ^vl_a (chg) , is

_{AR =} AV $ _{a =} (v;^d (x_max ) - Vf (x_mm )) - (Vf (y_max ) - Vl^d (y_mm )) r^~ v;:_a(chg) ^{" ■} v;^d(x_mm)_+F.v:^d(y_max) ⁽¹⁵⁾

Solving for F yields

^

Substitution of Vf (y_mm) and Vf(y_max) from table 3 and Vf(x_mm) and Vf (x_max ) from table

4 in (16) gives the relation between the anode volume reduction factor F and the desired relative volume expansion factor ΔR_V . Figure 3 shows the results for the anode-cathode combinations Li-Li_xCoO 2, Li-Li_xNiO 2 , Li_ySi-Li_xCoθ2 and Li_ySi-Li_xNiθ2. In order to obtain less volume expansion, the volumetric energy density will have to become smaller. This reduction is dependent on the anode-cathode materials combination. In the next section, the impact on the volumetric energy density will be calculated.

Volumetric energy density

In general, the volumetric energy density σ_c+a is defined as the electrochemical energy E_bat stored in the battery system divided by the sum of the anode and cathode volume for a charged battery system V_c+a {chg) .

^ bat

°c+a = _τ. T₁ χ (17)

V_c+a [chg)

The energy stored in the battery is equal to

E_bat = dq (18)

with Q₀ as initial charge.

Substitution of (18) in (17) gives a general expression for the volumetric energy density σ_c+a of a battery system

where U_bat is the average battery voltage, Q the amount of charge shuttled between the electrodes and V_c+a{chg) the volume of the sum of the electrodes when the battery is charged. So for the optimal volumetric energy density situation this can be written as c^+a v;i(ch_g)

and for the reduced volume expansion situation as \ The quantities Q^ed , V_c ^e ₊ ^d _a{chg) and u£ will change into Q^ve , V_c ^vl_a{chg) and UZ , respectively, after applying volume modification to one of the electrodes by a factor F in order to achieve a reduced volume expansion. Introduction of some normalising factors like

^Gσ- ' ^GvΛM ^{GQ and 0}^ ^representing σZ_a = G_σc+a ^■ σ$_a , V^ (chg) = <^(_cAg) ^■ Vf₊₁₁ (chg), Q- = G_n ^■ Q- and

UZ_t ⁼ G — ' U _bat respectively gives the energy density ratio depending on the anode volume bat reduction factor F (θ < F < l)

β ve

*~i " c+a J-- ^■ U j j w _bv b_ae a_tt

"^c+a π ^σc^e ₊ ^d _a V ^v c^v+^ea (\c^Lhⁿ&e)⁾ n Q^ed τ Uτ_b ^e _a ^d _t G v_c+a[ ichg \) ^ '

So G ( , _\ , G_n and G — will be calculated in order to obtain the volumetric energy

^Vc₊a \^ChS) ^{Q U}bat density ratio G c+a

Change in volume G i , \

The volume of a charged battery system for both situations is given by (3) and (13)

vzMg) = v:^d{x_mm)+v:^d(y_max)

(23) V ^y c^v+^ea (Vc-hⁿ&e)/ = V ' c^ed ( \x^Λ mm ) I + F ^λ - V ' a^ed ( XJv max ) I

Introduction of the factor G i , \ , defined as Vζ₊ ^e _a {chg) = G i , \ • V_c ^ed _a {chg), gives the

ratio of the change in volume between the reduced volume expansion and optimal volumetric energy density situation.

r

Change in charge G_n The change in the amount of charge that can be shuttled in the battery is directly related to the amount of Li which on its turn is directly related to the change of the anode volume F . So we can write for Q^ve

Q^ve = F Q^ed (25)

Introduction of the factor G_Q , defined as Q^ve = G_Q ^■ Q^ve , gives the ratio of charge transfer in case of the reduced volume expansion and optimal volumetric energy density situation.

G_Q = F (26)

Change in average battery voltage G —

^Ubat

The average battery voltage U_bat is the difference between the average cathode potential

U_c and the average anode potential U _a . In case of the optimal volumetric energy density and reduced volume expansion situation this results respectively into (27) and (28)

U ed bat = u:^a -u I ed (27) uz, = u;^v -u;^v (28)

It is assumed that the electrode voltage is linear with the concentration x and y for the cathode and anode, respectively. For the optimal volumetric energy density situation, this yields

and for the average battery voltage

In case of the reduced volume expansion situation, the concentration in the cathode x is limited tox_* instead of x_max so the average cathode voltage U_c is

The potential of the cathode Uf (x, ) at concentration jc. can be calculated because the voltage of an electrode is assumed to be linearly dependent on the concentration

u:^d(χ_mj-u:^d(x>) _ u:^d{x_max) -Wf[X₁J

Xmax -X* x max — x mm

Solving (30) for Uf (JC. ) yields

Uf (x.) = Uf (x_max ) - ^X- ^{~ X* ■} (Uf (x_max ) - Uf (x_m )) (33) x max — x mm

The relation between x. and F is also known from (8): x, = x_mm + F ■ (x_max - x_mm ) . Substitution of (8) in (33) gives the relation between Uf(x, ) and F

Uf (x.) = Uf(x_max)-(l-F)-{uf(x_max)-Uf(x_mJ (34)

Substitution of (34) in (31) gives the average cathode potential for the reduced volume expansion situation.

The average anode potential is not changed because the concentration limits y_mm and y_max are the same

Substitution of (35) and (36) in (28) gives the average battery voltage

(37) and after simplification using (30), this results in

U bat = Uf_{at +}^ (l-F). {uf(x_mm)-Uf (x_mJ (38)

Introduction of the factor G — , defined as Uζ_a ^e _t = G — ^• U_b ^e _at , gives the ratio of the average

^Jbat cathode voltage between the reduced volume expansion and optimal volumetric energy density situation.

Combining (24), (26) and (39) in (22) gives the overall energy density ratio G_n

Figure 4 shows the energy density reduction ratio G as function of the c+a volume reduction ratio F for a relative volume expansion of ΔR_V = - 0.05 . Table 6 gives the corresponding data for the battery systems: Li-Li_xCoθ2, Li-Li_xNiθ2, Li_ySi-Li_xCoθ2 and Li_ySi- Li_xNiO₂.

Table 6: Volume expansion and volumetric energy density after reduction of the anode volume in order to get -5% expansion.

It should be noted that the above-mentioned embodiment illustrates rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. Although it is chosen to smartly adapt the volume of merely the anode in the embodiment elaborated above, it will also be conceivable to smartly adapt the volume of merely the cathode or to smartly adapt the volume of both the anode and the cathode in order to reduce the total volume change of the assembly of the anode and the cathode during battery operation. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. Electrochemical energy source, comprising: a substrate, and at least one battery cell deposited onto said substrate, the battery cell comprising:

- an anode,

- a cathode, and

- an solid-state electrolyte separating said anode and said cathode, wherein the anode and the cathode are tailored to each other, such that the total volume change of the assembly of the anode and the cathode is less than 20% during charging and discharging of the battery cell.

2. Electrochemical energy source according to claim 1, characterized in that the materials of the anode and the cathode are chosen such that the total volume change of the assembly of the anode and the cathode is less than 20% during charging and discharging of the battery cell.

3. Electrochemical energy source according to claim 1 or 2, characterized in that the volume of the anode and the cathode are chosen such that the total volume change of the assembly of the anode and the cathode is less than 20% during charging and discharging of the battery cell.

4. Electrochemical energy source according to one of the foregoing claims, characterized in that the anode and the cathode are tailored to each other, such that the total volume change of the assembly of the anode and the cathode is less than 15%, preferably less than 10%, in particularly less than 5% during charging and discharging of the battery cell.

5. Electrochemical energy source according to one of the foregoing claims, characterized in that the energy density reduction ratio G between an optimized volumetric energy density of the assembly of the anode and the cathode on one side, and the energy density optimized for a predefined volume change of the assembly of the anode and the cathode on the other side is between 0.25 and 1, preferably between 0.5 and 1, more preferably between 0.75 and 1, and in particularly between 0.9 and 1.

6. Electrochemical energy source according to one of the foregoing claims, characterized in that both the anode and the cathode of at least one battery cell are adapted for storage of active species of at least one of following elements: H, Li, Be, Mg, Cu, Ag, Na and K.

7. Electrochemical energy source according to one of the foregoing claims, characterized in that the anode comprises Li_ySi and the cathode comprises Li_xNiO₂.

8. Electrochemical energy source according to one of the foregoing claims, characterized in that the electrochemical energy source has a non-planar geometry.

9. Electrochemical energy source according to one of the foregoing claims, characterized in that at least one electrode of at least one cell is provided with at least one patterned surface.

10. Electrochemical energy source according to claim 9, characterized in that the at least one patterned surface of the at least one electrode is provided with multiple cavities.

11. Electrochemical energy source according to claim 10, characterized in that at least a part of the cavities form pillars, trenches, slits, or holes.

12. Electrochemical energy source according to one of the foregoing claims, characterized in that the electrochemical energy source comprises multiple battery cells stacked on top of each other.

13. Electrochemical energy source according to one of the foregoing claims, characterized in that a current collector is connected to the anode and the cathode respectively, wherein each current collector is made of at least one of the following materials: Al, Ni, Pt, Au, Ag, Cu, Ta, Ti, TaN, and TiN.

14. Electronic device, comprising at least one electrochemical energy source according to one of the claims 1-13, and at least electronic component connected to said electrochemical energy source.

15. Electronic device according to claim 14, characterized in that the at least one electronic component is at least partially embedded in the substrate of the electrochemical energy source.

16. Electronic device according to claim 14 or 15, characterized in that the electrochemical energy source comprises a control unit for selectively electrically connecting at least two current collectors to the at least one electronic component.

17. Electronic device according to one of claims 14-16, characterized in that the at least one electronic component is chosen from the group consisting of: sensing means, controlling means, communication means, and actuating means.

18. Electronic device according to one of claims 14-17, characterized in that the electronic device and the electrochemical energy source form a System in Package (SiP).