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Chapter 7

Lithium Micro-Batteries

Batteries store, in the form of electrical energy, chemical energygenerated by electrochemical reactions. A battery, regardless of thetechnology used, is essentially defined by four variables:

– Specific energy density (or specific energy), in Wh/kg,corresponds to the quantity of energy stored per unit mass of thebattery.

– Energy density, in Wh/l, corresponds to the quantity of energystored per unit volume of the battery.

– Specific power density, in W/kg, represents the power that can bedelivered by the battery per unit mass.

– Cyclability, expressed as the number of cycles (one cyclecorresponds to a charge and a discharge), characterizes the battery life,i.e. the number of times the same level of energy is released after eachnew recharge.

The characteristics mentioned above are important, whatever theintended application: electric vehicle, stationary, computers, built-insensors, etc. Improving the performance of these energy storagesystems according to these criteria has led to different generations.

Chapter written by Raphaël SALOT.

Energy Autonomous Micro and Nano Systems Edited by Marc Belleville and Cyril Condemine© 2012 ISTE Ltd. Published 2012 by ISTE Ltd.

186 Energy Autonomous Micro and Nano Systems

The specific energy (expressed in Wh/Kg) has been significantlyincreased according to the chemical compounds used: lead(30−50 Wh/kg), Ni-Cd (45−80 Wh/kg), NiMetalHydride (60−110Wh/kg), and lithium (120−190 Wh/kg).

In the field of micro- and nanosystems, another constraint is addedto the specifications. It is concerned with the possibility of thedeveloped technologies to be miniaturized and integrated into low-dimensional systems. The first consequence is that the available volumeis systematically reduced; it is necessary to turn to the most efficientsystems in terms of storage. Thus, typically, lead batteries have storagevolume properties too low to be of interest in this area. The work isthus focused on lithium-based systems. This is the reason why thedevelopments made on this type of system are described in this chapter.Initially, a general overview of lithium batteries is presented, and thenthe focus turns to specific lithium battery technologies that aim to obtainthe best miniaturization and integration properties.

7.1. Development of lithium batteries over 20 years

The first commercial Li-ion batteries were placed on the market in1991 by Sony. The first compounds used in the 18650-type wereLiCoO2 for the positive electrode and graphite for the negativeelectrode; originally intended for the portable electronics market, theyhad a capacity of approximately 1,000 mAh. Since then numerouscombined developments by the first industries of the sector (Sony,Sanyo, and Panasonic) have allowed continual gains in terms ofspecific energy and volume density. As shown in Figure 7.1, thesevalues have doubled, or even tripled, over 20 years of development,essentially reaching 570 Wh/l and more than 200 Wh/kg.

This development is mainly due to the better manufacturing ofthese types of elements and due to the improved performance of activematerials at the electrode, especially that of the positive electrode. Thelatest development concerning lamellar materials using LiMO2 is tomake composite materials capable of generating the best features ofeach of the individual materials. In this case, the LiCoO2 offers the

Lithium Micro-Batteries 187

highest density but has a high potential instability, so is combinedwith a material of the LiNi1/3Mn1/3Co1/3O4 (NMC) type which iselectrochemically more stable.

100

120

140

160

180

200

220

240

250 300 350 400 450 500 550 600 650 700

Volumetric energy density (Wh/l)

Gra

vim

etric

ener

gyde

nsity

(Wh/

kg)

19941995

1996

19982000

20012002

2004

2005

2008

Typ. 1260mAhTyp. 1370mAh



Typ. 2200mAh

Typ. 2400mAh


> 3000mAh

Current GenerationLiCoO2-Graphite

New GenerationNew Materials

Figure 7.1. Performance development of Li-ion batteries over 20 years

Figure 7.2. Cycling characteristics of previous generations of Li-ion batterymaterials (source: T. Ozhuku [OZH 06])


Simultaneously, with regard to the development of the initial system,Sony also put on the market in 2005 a type of battery (Nexelion) wherethe negative electrode was replaced by a composite material Sn-Co-C,wherein the lithium combines reversibly with tin. This change allowedthe energy density to increase by 30% (478 Wh/l, 158 W/kg in thepotential window 2.5−4.2 V against 395 Wh/l, 144 Wh/l – all in the14430 format). However, the cost of such a material, like graphite,severely limits its outlets.

Alongside the search for better performance in terms of energydensity and power, the search for a decrease in the quantity of cobalt,due to the cost and improving system security, is the subject ofimportant research in this field. These last two points are particularlycrucial for new Li-ion battery applications, such as hybrid and electricvehicles.

Cost

Capacity Power

Availability

Reliability

Lifespan

Safety

Figure 7.3. Main points to take into account in the development andchoice of Li-ion technologies

Over the past 15 years, the prospect of applying families of Li-ionbatteries to completely electric or hybrid modes of transport hasencouraged a number of studies in this field. Alternatives to thestandard organic solvents/graphite-based LiCoO2/liquid electrolytes of18650 format have emerged at all levels.

7.1.1. Alternative materials for the positive electrode

Some alternative materials for the positive electrode are listed inthis section:


LiNi0.85Co0.1Al0.05O2 (NCA): This compound was developed bySAFT 15 years ago as an alternative lamellar material at a lower costand a higher energy density. This compound rich in nickel is stabilizedby a “doping” with aluminum.

LiNi1/3Mn1/3Co1/3O2 (NMC): This compound was also developedafter several years by different teams; it is also commerciallyavailable. The positive electrode is made up of a material with anenergy density similar to LiCoO2 (lower medium voltage but higherspecific capacity), now significantly less reactive in the charged state(deintercalated) and of a lower cost.

LiMn2O4: This compound has been known for about 20 years; itsmain advantage is its low cost and excellent performance in kineticinsertion/removal of lithium. The partial solubility of the compound inthe electrolyte – linked to the presence of manganese III – limits thelifespan of the system mainly at high temperature.

LiFePO4 (LFP): This electronic insulator, “discovered” in 1997,only functions properly at ambient temperature in the nanocompositeLiFePO4 (10−50 nm)/carbon form. The polyanionic skeleton gives it agreat structural and chemical stability even in the completelydeintercalated state. This results in a large cyclability associated witha high safety. However, the relatively weak value for operatingvoltage (3.45 V/Li+/Li) limits the energy density of the battery. It isone of the main candidates for high-capacity batteries.

LiNi0.5Mn1.5O4: This compound with a spinal structure identical toLiMn2O4 in principle only contains manganese IV, involves the couplesNi2+/Ni3+, and Ni3+/Ni4+ functioning at a high potential (4.75 V /Li+/Li)for a specific capacity of 145 mAh/g, which gives it an energydensity/graphite superior to that of LiCoO2. The material functionsintrinsically satisfactorily in terms of cyclability, but it works outsidethe electrochemical stability zone of conventional liquid electrolytes.We can therefore observe a large auto-discharge. Solutions are beingsought through the formulation of the electrolyte or through thetreatment of surface particles.

New emerging compounds: These compounds include FeF3,Li2FeS2, and LiMnPO4.


7.1.2. Alternative materials for the negative electrode

Some alternative materials for the negative electrode are describedin this section:

Sn-Co-C: this nanostructured material allows the use of tin for thereversible insertion of lithium, despite the strong induced volumetricvariations between the states Sn and Li4.4Sn. The choice of Co islinked to the fact that this metal does not produce carbide in thesynthesis conditions and the latter has a large impact on the final costof the material.

Si: this material offers the best prospects in terms of specificcapacity (~3,500 mAh/g) and cost. Similar to tin, strong volumetricvariations are generated between the initial state and the lithiated state(+280%). A satisfactory cyclability and a limited initial irreversibilityare obtained through the attainment of nanocomposites (generallySi/carbon) and a formula adapted to the electrolyte and the electrode.

Li4Ti5O12: the main points of interest concerning this material arethe small dimensional variation between the intercalated anddeintercalated states, its two-phase operation 1.55 V/Li+/Li, and itsspinal structure. Together these properties give it an excellent lifespanand the possibility of a safe and rapid insertion of lithium, attainingbatteries that take on very important charging regimes.

Other emerging compounds: These compounds include phosphidesof transition metals, other compounds, or tin-based nanocomposites.

7.1.3. Alternative materials for the electrolyte

This section describes some alternative materials for the electrolyte:

Ionic liquids: The greatly increased ionic conductivity of thesemolten salts at ambient temperature (imidazolium and pyridinium-based) offers the prospect of substantial gains in terms of reducing theinternal resistance. Moreover, the lack of vapor pressure and solvent isan asset for security systems and for use at higher temperature. Theircost remains prohibitive for now for the majority of the applications.Their high viscosity, the low value of lithium’s transport number, and


their inability to form a solid electrolyte interface (SEI) layer on thenegative electrode are the major obstacles for their usage.

LiSiCON: This compound has been known for decades for the mostpart. They are inorganic solid conductors of crystallized or vitreouslithium ions generally oxide or sulfide-based. These include, forexample, LAGP (Li1+xAlxGe2-x(PO4)3 Nasicon) and LLT (La2/3-xLi3xTiO3perovskite) for crystallized materials.

LiPON (LiPxOyNz): This compound is among the amorphouscompounds. Despite their limited conductivity at ambient temperature(10–6–10–4 S/cm), they can be an adapted response to certain constraints:high functioning temperature, solubility or permeability problems, andhigh reactivity potential of conventional electrolytes.

7.1.4. Positioning of different categories

Currently, Li-ion batteries are still only used marginally fortransport applications with regard to Ni–MH batteries, but recently thecommercial supply has been growing.

Apart from the research aiming to improve Li-ion technologies,work on other lithium-based systems (lithium-air, lithium-sulfur, andaqueous systems with Li encapsulated) is intensifying. In effect, thesesystems theoretically have the power to reach notably higher energydensities (2−10x) because of the use of compounds at the positiveelectrode with notably greater capacities. Although these systems arepresented to the state of realization by several start-ups, includingAmerican (Polyplus and Rayovac); their marketing is not likely toresult for another 10 years.

7.2. The lithium system aiming for strong miniaturization properties

Two strategies are followed globally for the disposal of lithiumbatteries with very small dimensions. The first is based on “classic”technologies presented in the previous chapter and on trying toimprove the different stages of the manufacturing process to reduceclutter. Throughout this chapter, these systems are described as


“mini-batteries”. The second strategy is to completely rethink themanufacturing process and to use methods close to those used inthe world of microelectronics (vacuum deposition of thin films). In thechapter, these systems are described as “micro-batteries”. The termsused here “mini-battery” and “micro-battery” are not a generalconsensus at the international level. Therefore, readers will be able tofind elsewhere descriptions of systems using the qualifier for micro-batteries, but here they are classed under “mini-batteries”.

Pb-Acid

Ni-Cd

MH

LNiiC

oO2/

Graph

ite(L

CO)

Li(No.

85Co0

.1Al0.

05)O

2/Gra

phite

(NCA)

LiFeP

O4/Gra

phite

(LFP)

Li(Ni1/

3Mn1

/3Co1

/3)O

2/G

raph

ite(N

CM)

LiMn2

D4/Gra

phite

(LM

S)

LiMn2

D4/Li4

Ti5O12

(LTO)

LiMn1

.5Ni0.

5O4/

Li4Ti5O

12(M

NS)

Li1.2

Mn0

.6Ni0.

2O2/

Graph

ite(M

N)Zinc

-Air

NaNiC

l(ZEBRA)

Tec

hnol

ogie

s

Performance rating

Low-Cost

Safety

Life

Energy

Power

Lith

ium

Ion

0 1 2 3 4 5 6

Figure 7.4. Positioning of the different groups of batteries and Li-ion batteries withthe potential usage in hybrid and electric vehicles (source: [AXS 08], [NEL 07],

[KRO 07], [KAL 07], and RMI analysis)


7.2.1. Lithium mini-batteries

The medical applications take the development of lithium batteriestoward miniaturization. An example is the Contego Li-ion batterydeveloped by Eagle Picher [EAG 11].

The dimensions of this battery (6.73 mm long × 2.37 mm diameter)are very small compared with standard batteries, but still significantlylarger than those obtained by other techniques (thin-film type). Thisbattery, which is at least 50% smaller and lighter than currentcommercially available products, is based on a new technologypatented by Eagle Picher Medical Power. It has a capacity of 500 µAh,an auto-discharge of 2% per month, and it can support approximately1,000 charge/discharge cycles with a capacity loss of 20%.

Such a system is currently under clinical trials in Europe to limitacts of invasive surgery.

Other thin battery technologies are beginning to make anappearance on the market. These technologies were initially developedfor the field of energy storage (i.e. non-rechargeable). This property islinked to the chemistry of the materials used in these systems(Li/MnO2 or Zn/MnO2). Moreover, these systems function atintermediate voltages, lower than conventional Li-ion batteries thatdeliver a voltage of approximately 4 V.

These systems can be rolled and produced with varied and specificshapes. One part of the production method, which is often of theassembly line type, may include stages of printing of the activematerials. The technology that currently appears to be the cheapest isbased on manganese dioxide and zinc. Power Paper and licensedcompanies such as Graphic Solutions make this type of system.

However, these technologies are limited by their functioningtemperature. Their thicknesses (between 0.3 and 0.5 mm) areinteresting for certain applications even though they do not allowhigher degrees of flexibility or conformability to be attained.


An example of this type of lithium-based system developed bySolicore is shown in Table 7.1 and Figure 7.5.

The capacities are between 1 and 3 mAh/cm². It is importantto note that their behavior is satisfactory only at very weak currents(i.e. for discharges of C/40, equivalent to a current of approximately10−30 µA/cm²).

These systems therefore do not seem the most appropriate fortypical sensor applications for which the energy storage system mustbe capable of supplying peaks of current (during measurement or datatransmission), and it is charged by an energy recovery system.

Technical specifications performances

System Lithium polymer

Cathode Manganese dioxide

Anode Metallic lithium

Nominal voltage 3 V

Nominal capacity (C/40 at 23°C) 10–14 mAh

Maximum continuous discharge (23°C) C/2

Functioning temperature −10°C to 60°C

Storage temperature −20°C to 40°C

Weight 0.3 g

Maximum thickness 0.45 mm

Auto-discharge <1% per month

Anode current collector Copper–Nickel

Cathode current collector Aluminum

Casing Flexible aluminum

Table 7.1. Battery properties for the “Solicore” type [SOL 11]

The companies that sell and develop Zn–Mn batteries areessentially Power Paper, Blue Spark Technology, Enfucell, andGraphic Solutions Incorporated. This type of battery is also integratedinto patches for health applications [POW 11].


0

0.5

1

1.5

2

2.5

3

3.5

Discharge Time (hours)

Vol

tage

(V)

15 20 25 30 35 40 450 5 10

Figure 7.5. Typical properties of a primary lithium system [SOL 11]

The companies that sell lithium-based systems are Solicore andVarta Microbattery. The main applications targeted in this case are theradio frequency identification (RFID) tags and smart cards.

7.2.2. Lithium micro-batteries

7.2.2.1. Micro-battery properties and technologies [SAL 09]

A micro-battery is a completely solid, rechargeable electrochemicalgenerator with a thickness of a few tens of micrometers (typicallybetween 10 and 25 μm), an area ranging from several mm2 to severalcm2 and is formed by the stacking of dozens of thin layers; of thelayers, three are “active” (positive electrode, electrolyte, and negativeelectrode) and the others are protective or insulating layers or serve ascurrent collectors. The best capacities obtained at present areapproximately 100−200 µAhcm2.

The study of micro-batteries that begun in the 1980s has remainedfor a long time as university research, but in recent years these systemshave entered a phase of industrial development, or preindustrialization.Micro-batteries appear to be able to respond to the demand of multipleapplications, being regrouped into three main categories: solutions forbackup power, powering RFID tags, and powering autonomous sensors.


Even if the functioning principle is identical to that of aconventional battery, a micro-battery presents certain specificity. Inreality, a micro-battery is prepared by successive depositions ofdifferent layers whose thickness varies from a few nanometers to afew micrometers; the complete stacking, including the currentcollectors, the active layers, and the encapsulation surpass a fewdozens of microns.

Figure 7.6. Diagram of a micro-battery showing the piling up of different layers

The first specificity of a micro-battery compared to a conventionalbattery comes from the usage of specific deposition techniques thatprepare them: predominantly physical vapor deposition (PVD) butalso occasionally chemical vapor deposition (CVD). Depending on theintended applications, micro-batteries can be deposited onto either aflexible or a rigid substrate and can eventually be integrated into anelectronic microcircuit as a standard compound, provided that they arecompatible with the thermal treatment necessary for the weldingprocess (solder reflow) usually used in microelectronics.

The second specificity concerns the choice of active materials:

– The solid inorganic electrolyte, generally amorphous, allowsthe production of a monolithic system. Compared with a liquidelectrolyte, it shows a weaker ionic conductivity (by a factor of about1,000, going from 10–3 S/cm for a liquid electrolyte to about 10–6 S/cmfor a solid electrolyte), which limits the micro-battery’s use especiallyat low temperature. Using a solid electrolyte whose electronicconductivity can reach 10–12–10–13 S/cm and reactivity toward the


electrodes is minimal, leads to an extremely weak auto-discharge,which is particularly favorable in terms of long-term energy storage.This also leads to very good coulomb yields (an important parameterwhen the micro-battery is associated with an energy recovery system).

– The use of metallic lithium in conventional batteries has beenquickly abandoned, but still remains very attractive in micro-batteriesbecause using a solid electrolyte completely prevents the formation ofdendrites.

– All materials used for the positive electrode in a conventionallithium battery can potentially be used in a micro-battery, and thereare numerous examples of this: LiCoO2, V2O5, TiS2, and LiMn2O4.However, in the case of micro-batteries, there is no real need to have amaterial functioning at a higher voltage.

After the deposition of active materials, it is essential to protect thewhole ambient atmosphere by encapsulation. This can be achievedeither by depositing alternating thin layers of polymers and denselayers (metal or silica), or by rolling a sheet of an adhesive barrier(aluminum + adhesive). It must show the best performance possible interms of a barrier against humidity.

Each thin layer has a particular geometry so that the stack isfunctional. The desired geometry can be obtained either by carryingout the deposit through shadow masks or by means of etchingtechniques after the deposition has been made over the whole surfaceof the substrate.

The mechanical masks are fairly thin plates (a few tenths of amillimeter at most) and allow the production of patterns of successivethin layers in such a way that the mask edges do not create asignificant undesirable effect during deposition of the thin layer(shade effect and thermal effect for the main part). These plates aredrilled with holes corresponding to the desired pattern. It is veryimportant that the masks coat the substrate as perfectly as theypossibly can to limit overflow of the deposit under the masks. Severaltechniques are used for this purpose. Masks can be lined with morerigid counter masks with slightly recessed perforated edges, whichallow the masks to cling to the substrate. A magnetic force may be


applied by the opposite side of the substrate (in the case of nickelmasks). The definition obtained for different patterns with thistechnique is in the region of 100 µm, which is sufficient for a certainnumber of applications (batteries of a few cm²). However, thistechnique creates problems in industrial production (cleaning andpollution of the masks, faults produced on the substrate).

Besides the mechanical masking technique used in the majority ofcases, the use of photolithographic techniques is being studied in somelaboratories. These techniques have the main advantages of enabling abetter resolution of the patterns leading to micro-battery surfaces ofless than 10−2 mm², allowing a greater density of micro-batteries andpreventing drawbacks linked to the management of masks in anindustrial process. They require, however, clean rooms for themanufacture stages and contact with potentially hazardous chemicalsolutions. These constraints are managed by the intermediate depositionof protective layers that are etched after the pattern is defined.

W.C. West [WES 02] also produced micro-batteries using a processinvolving stages of photolithography. In this case, no etching process isused. The patterns have been created by a process called lift-off1 forthe positive electrode (LiCoO2) and the electrolyte (LiPON). Thesemicro-batteries do not include metallic lithium; the negative electrodeis made “in situ” during the charge between the anode current collectorand a covering layer (nickel). The capacity measured is close to halfof that obtained for micro-batteries created by a macroscopic process(using mechanical masks) under the same conditions.

The same group has also carried out another study on micro-batteries using a similar photolithography process, with the onlydifference being the micro-batteries having a negative electrode ofmetallic lithium. This study highlights the difficulty of performingphotolithography on lithium. The lithium patterns were obtained bysimply applying adhesive tape over the layer. A difference in adhesion

1 Instead of creating a pattern by depositing a thin layer over the whole surface of thesubstrate and removing the undesired parts by means of etching through a resin mask,the lift-off consists of making the resin mask before depositing onto the thin layer. Asit disappears, the resin removes the material deposited on the surface leaving only theintended patterns.


allows the removal of excess lithium with the adhesive tape, leavingonly the desired pattern on the substrate [WHI 03].

Finally, S. Oukassi [OUK 08] has recently developed aphotolithography process to produce V2O5/LiPON/Li micro-batteries.Contrary to the previous work, the entire process was carried out in aclean room under non-anhydrous conditions. Moreover, the metalliclithium patterns were created by a Parylene®-based micromaskingprocess.

The electrical performance of these systems clearly depends on thematerials used, even if the orders of magnitude remain close to thesimilar dominating phenomena. Also, the capacity of TiOS/LiPON/Limicro-batteries increases linearly with the thickness of the TiOSpositive electrode. This can be verified up to 10 µm (approximately50 µAh/cm2 per µm thickness). However, it was also observed that theamount of functional micro-batteries decreases quite strongly as thethickness increases beyond 5 µm, and also with the number of cyclesperformed.

The internal resistance of batteries depends on the conductivity of theelectrolyte (and its thickness), the interface resistance between theelectrolyte and the cathode, and the conductivity and the resistance duringinsertion of lithium into the cathode. Globally, the internal resistanceof a micro-battery decreases with temperature, the conductivity of theelectrolyte being an important limiting factor. Typically, a 2D micro-battery can supply a capacity of approximately 50 µAh/cm2 per µmthickness of TiOS between 1.8 and 2.6 V for a current lower than10 µA/cm2. This capacity is typically divided by two for a current of1 mA/cm2:

The main performances of micro-batteries are grouped together inTable 7.2.

Besides the development of industrial means of production, themain developments on this type of system involve an increase inperformance. Two main points are explored: the stacking of unitarysystems and 3D configurations. In the first case, the objective is to


work with very thin substrates (<50 µm) to always produce a finalcomponent of smaller dimensions. In the second case, as the capacityof a battery in thin layers is directly proportional to the surface andthickness of the stacking of the negative electrode/electrolyte/positiveelectrode, the idea is to increase the surface/volume ratio of theelectrodes. For this reason, the substrate is no longer flat but texturedto develop the surface.

0.5

1

1.5

2

2.5

3

3.5

0 20 40 60 80

800 μA cm–2

10 μA cm–2

100 μA cm–2

Vol

tage

(Vol

ts/L

i+/L

i)

Figure 7.7. Potential current charge−discharge curves at different densities of amicro-battery composed of a stack of Li/LiPON/TiO0.6S1.6 (1.5 µm)

Wafer levelpackaging

Electrolyte

C-collector

A-collectorSubstrate

Anode

Cathode

10μm

Figure 7.8. Development in capacity of a Li/LiPON/TiOS (1.5 µm) micro-batterywith a surface area of 5 × 5 mm2, cycled at different currents and in different

potential windows


Characteristic Nominal value Maximum/realisticobjective

Capacity 200 µAh/cm2 700 µAh/cm2/1 mAh/cm2

Maximum current 1 mA/cm2 /3 mA/cm2

Voltage Between 1.8 and 2.6 V Adjustable by changing theelectrochemical couplebetween 0 and 5 V

Auto-discharge No auto-discharge

Useful surface 25−400 mm2 10−1,000 mm

Highest functionaltemperature

60°C 100°C/250°C

Lowest functionaltemperature

−20°C −40°C/−60°C

Number of cycles Several thousand Tens of thousands

Substrate – nature(insulating)

Glass, silica, ceramic,and polymer

25 mm2 prototypes carriedout “above IC”

Substrate – thickness 75 µm 50 µm

Active thickness Approximately 10 µm Works on seriesconnection, in parallel,stacks, cathode thickness.

Encapsulation thicknessof thin layers

<10 µm

Table 7.2. Micro-battery performances

7.2.2.2. Micro-battery applications

Micro-batteries appear to respond to many application requests,which can be grouped into three main categories: backup powersolutions, powering RFID tags, and powering autonomous sensors.


7.2.2.2.1. Micro-batteries as backup power solutions

Having an energy supply at one’s disposal joined to a product thatcan power various basic functions in case the main battery fails or isremoved for replacement is fundamental for numerous electroniccomponents such as real-time clocks (RTCs) or static random accessmemories (SRAM).

Approximately 1 billion RTCs are sold each year. This componentrequires very weak currents (approximately several hundred nA).Currently, this function is assured by the presence of miniature buttonbatteries, oversized in terms of capacity and are still too thick (>1 mm)for optimal integration on printed circuit boards (PCBs). Micro-batteries, due to their completely solid configuration and the materialsthat they are made of, can be integrated into thinner boxes, being ableto withstand thermal stresses accompanying the “solder reflow” andcan be therefore used in the same way as all other electroniccomponents. The cost constraint for this application is particularlyhigh. It involves having industrial tools for mass production of micro-batteries, capable of producing these components on substrates withlarge surface areas by using mechanical masks to define the patternsof the micro-batteries.

This type of application involves a replacement market that is aviable alternative for micro-batteries when produced in large volumeat a competitive cost.

7.2.2.2.2. Micro-batteries for powering RFID tags

Different categories of RFID tags exist: passive, semi-active, andactive. For previous systems, an embedded energy supply is needed tomeasure backup data about the lifespan of a component (temperaturemonitoring for the traceability of a cold chain, e.g. a measure ofshocks). It can be noted that this is a particular case of an autonomousmicrosystem. Moreover, data transmission is fundamental for theuse of these products. An embedded energy supply must allowa significant increase in current transmission distances fromapproximately a centimeter up to a meter.


The market for active tags was $550 billion in 2006 and isestimated to be $6,000 billion in 2015. To enter this market, micro-batteries must respond to large constraints in terms of cost, but alsoconfirm their ability to be produced on a flexible substrate, operate atlow temperature, and provide higher capacities.

7.2.2.2.3. Micro-batteries for powering autonomous sensors

The concept of wireless, therefore autonomous, microsensorsimplies the presence in a small volume of a sensor, a microprocessor,an energy source, and a data transmission system. This intelligentnode has the function of measuring different physical parameters(temperature, pressure, vibration, CO2, etc.), to convert thesemeasurements into quantifiable values and transmit them to beprocessed. In the majority of cases, the aim is to distribute asignificant number of sensors without having to ensure theirmaintenance. From an energy storage point of view, they need to havea system which is not cumbersome, but is capable of power surges(transmission of information) and of assuring a battery life of severalyears. The energy charged in a micro-battery generally appears to berather limited; the most commonly considered scenario consists ofcombining a battery with an energy recovery system. The latter can bebased on a photovoltaic, mechanical (vibration), or thermal(temperature effect via Seebeck effect) energy system. Whatever theenergy recovery system, the element providing the storage shouldhave the following characteristics: long lifespan, higher number ofcharge/discharge cycles, little auto-discharge, higher energetic yield,and low volume. Owing to their completely solid structure and thematerials used (solid inorganic electrolyte), micro-batteries are in avery good position. We can note a particularly higher number ofcycles than in conventional batteries with a greater yield and a weakerauto-discharge. The experts expect a large increase in the market ofwireless sensor networks in the coming years.

Embedded sources of energy are also in demand in the field ofmedicine for supplying implanted microsystems. Examples includepacemakers, defibrillators, insulin pumps, systems to fight againstincontinence, cochlear implants, and neurostimulators. More and morehearing problems are being treated by implanting electrodes into the


cochlea to activate the nerves. The assembly is then connected to ahearing aid. It is estimated that 10,000 systems of this type have beenimplanted. An integrated energy source, such as a micro-battery,would significantly improve the technology. Other types of implants,such as neurostimulators, are currently being studied. The aim in thiscase is to deliver electrical impulses to specific zones of the nervoussystem or directly to the brain. These systems are used in thetreatment of epilepsy and Parkinson’s disease. Developments alsoaddress the problem of paralysis.

7.3. Bibliography

[AXS 08] AXSEN J., BURKE A., KURANI K., Batteries for plug-in hybridelectric vehicles (PHEVs): goals and the state of technology circa 2008,Research Report UCD-ITS-RR-08-14, Institute of Transportation Studies,University of California, Davis, 2008.

[EAG 11] Available at http://www.eaglepicher.com.

[KAL 07] KALHAMMER F.R., KOPF B.M., SWAN D.H., ROAN V.P., WALSHM.P., Status and prospects for zero emissions vehicle technology, Reportof the ARB Independent Expert Panel, 2007.

[KRO 07] KROMER M.A., HEYWOOD J.B., Electric powertrains: opportunitiesand challenges in the U.S. Light-Duty Vehicle Fleet, Publication No. LFEE2007-03 R, Sloan Automotive Laboratory, Massachusetts Institute ofTechnology, May 2007.

[NEL 07] NELSON, P., AMINE, K., ROUSSEAU, A., YOMOTO, H., “Advancedlithium-ion batteries for plug-in hybrid electric vehicles”, InternationalElectric Vehicle Symposium, EVS-23, Anaheim, California, 2–5 December2007.

[OUK 08] OUKASSI S., Développement de microsources d’énergie pouralimentation de microsystèmes radio-fréquence, University Thesis, ParisXII, 2008.

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