Energy Autonomous Micro and Nano Systems (Belleville/Energy Autonomous Micro and Nano Systems) || Lithium Micro-Batteries

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<ul><li><p>Chapter 7</p><p>Lithium Micro-Batteries</p><p>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:</p><p> Specific energy density (or specific energy), in Wh/kg,corresponds to the quantity of energy stored per unit mass of thebattery.</p><p> Energy density, in Wh/l, corresponds to the quantity of energystored per unit volume of the battery.</p><p> Specific power density, in W/kg, represents the power that can bedelivered by the battery per unit mass.</p><p> 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.</p><p>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.</p><p>Chapter written by Raphal SALOT.</p><p>Energy Autonomous Micro and Nano Systems Edited by Marc Belleville and Cyril Condemine 2012 ISTE Ltd. Published 2012 by ISTE Ltd.</p></li><li><p>186 Energy Autonomous Micro and Nano Systems</p><p>The specific energy (expressed in Wh/Kg) has been significantlyincreased according to the chemical compounds used: lead(3050 Wh/kg), Ni-Cd (4580 Wh/kg), NiMetalHydride (60110Wh/kg), and lithium (120190 Wh/kg).</p><p>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.</p><p>7.1. Development of lithium batteries over 20 years</p><p>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.</p><p>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</p></li><li><p>Lithium Micro-Batteries 187</p><p>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.</p><p>100</p><p>120</p><p>140</p><p>160</p><p>180</p><p>200</p><p>220</p><p>240</p><p>250 300 350 400 450 500 550 600 650 700</p><p>Volumetric energy density (Wh/l)</p><p>Gra</p><p>vim</p><p>etric</p><p>ener</p><p>gyde</p><p>nsity</p><p>(Wh/</p><p>kg)</p><p>19941995</p><p>1996</p><p>19982000</p><p>20012002</p><p>2004</p><p>2005</p><p>2008</p><p>Typ. 1260mAhTyp. 1370mAh</p><p>Typ. 1420mAhTyp. 1700mAh</p><p>Typ. 1900mAhTyp. 2000mAh</p><p>Typ. 2200mAh</p><p>Typ. 2400mAh</p><p>Typ. 2600mAhTyp. 2800mAh</p><p>&gt; 3000mAh</p><p>Current GenerationLiCoO2-Graphite</p><p>New GenerationNew Materials</p><p>Figure 7.1. Performance development of Li-ion batteries over 20 years</p><p>Figure 7.2. Cycling characteristics of previous generations of Li-ion batterymaterials (source: T. Ozhuku [OZH 06])</p></li><li><p>188 Energy Autonomous Micro and Nano Systems</p><p>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 2.54.2 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.</p><p>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.</p><p>Cost</p><p>Capacity Power</p><p>Availability</p><p>Reliability</p><p>Lifespan</p><p>Safety</p><p>Figure 7.3. Main points to take into account in the development andchoice of Li-ion technologies</p><p>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.</p><p>7.1.1. Alternative materials for the positive electrode</p><p>Some alternative materials for the positive electrode are listed inthis section:</p></li><li><p>Lithium Micro-Batteries 189</p><p>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.</p><p>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.</p><p>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.</p><p>LiFePO4 (LFP): This electronic insulator, discovered in 1997,only functions properly at ambient temperature in the nanocompositeLiFePO4 (1050 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.</p><p>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.</p><p>New emerging compounds: These compounds include FeF3,Li2FeS2, and LiMnPO4.</p></li><li><p>190 Energy Autonomous Micro and Nano Systems</p><p>7.1.2. Alternative materials for the negative electrode</p><p>Some alternative materials for the negative electrode are describedin this section:</p><p>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.</p><p>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.</p><p>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.</p><p>Other emerging compounds: These compounds include phosphidesof transition metals, other compounds, or tin-based nanocomposites.</p><p>7.1.3. Alternative materials for the electrolyte</p><p>This section describes some alternative materials for the electrolyte:</p><p>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 lithiums transport number, and</p></li><li><p>Lithium Micro-Batteries 191</p><p>their inability to form a solid electrolyte interface (SEI) layer on thenegative electrode are the major obstacles for their usage.</p><p>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.</p><p>LiPON (LiPxOyNz): This compound is among the amorphouscompounds. Despite their limited conductivity at ambient temperature(106104 S/cm), they can be an adapted response to certain constraints:high functioning temperature, solubility or permeability problems, andhigh reactivity potential of conventional electrolytes.</p><p>7.1.4. Positioning of different categories</p><p>Currently, Li-ion batteries are still only used marginally fortransport applications with regard to NiMH batteries, but recently thecommercial supply has been growing.</p><p>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 (210x) 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.</p><p>7.2. The lithium system aiming for strong miniaturization properties</p><p>Two strategies are followed globally for the disposal of lithiumbatteries with very small dimensions. The first is based on classictechnologies 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</p></li><li><p>192 Energy Autonomous Micro and Nano Systems</p><p>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.</p><p>Pb-A</p><p>cid</p><p>Ni-C</p><p>d</p><p>MH</p><p>LNiiC</p><p>oO2/</p><p>Grap</p><p>hite(</p><p>LCO)</p><p>Li(No</p><p>.85C</p><p>o0.1</p><p>Al0.</p><p>05)O</p><p>2/Gr</p><p>aphit</p><p>e(N</p><p>CA)</p><p>LiFeP</p><p>O4/G</p><p>raph</p><p>ite(L</p><p>FP)</p><p>Li(Ni</p><p>1/3M</p><p>n1/3</p><p>Co1/</p><p>3)O2</p><p>/Gra</p><p>phite</p><p>(NCM</p><p>)</p><p>LiMn2</p><p>D4/G</p><p>raph</p><p>ite(L</p><p>MS)</p><p>LiMn2</p><p>D4/L</p><p>i4Ti5O</p><p>12(L</p><p>TO)</p><p>LiMn1</p><p>.5Ni</p><p>0.5O</p><p>4/Li4</p><p>Ti5O</p><p>12(M</p><p>NS)</p><p>Li1.2</p><p>Mn0</p><p>.6Ni</p><p>0.2O</p><p>2/Gr</p><p>aphit</p><p>e(M</p><p>N)Zi</p><p>nc-A</p><p>irNa</p><p>NiCl</p><p>(ZEB</p><p>RA)</p><p>Tec</p><p>hnol</p><p>ogie</p><p>s</p><p>Performance rating</p><p>Low-Cost</p><p>Safety</p><p>Life</p><p>Energy</p><p>Power</p><p>Lith</p><p>ium</p><p>Ion</p><p>0 1 2 3 4 5 6</p><p>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],</p><p>[KRO 07], [KAL 07], and RMI analysis)</p></li><li><p>Lithium Micro-Batteries 193</p><p>7.2.1. Lithium mini-batteries</p><p>The medical applications take the development of lithium batteriestoward miniaturization. An example is the Contego Li-ion batterydeveloped by Eagle Picher [EAG 11].</p><p>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 Ah,an auto-discharge of 2% per month, and it can support approximately1,000 charge/discharge cycles with a capacity loss of 20%.</p><p>Such a system is currently under clinical trials in Europe to limitacts of invasive surgery.</p><p>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.</p><p>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.</p><p>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.</p></li><li><p>194 Energy Autonomous Micro and Nano Systems</p><p>An e...</p></li></ul>