Introduction. chemical energy into electrical energy by means of redox reactions.

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1 CHAPTER I

2 Introduction 1. 1 Battery An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy by means of redox reactions History of batteries 1748 Benjamin Franklin first coined the term "battery" to describe an array of charged glass plates Luigi Galvani was dissecting a frog affixed to a brass hook. When he touched its leg with his iron scalpel, the leg twitched. Galvani believed the energy that drove this contraction came from the leg itself, and called it "animal electricity" Volta invented the first true battery which came to be known as the Voltaic Pile. It consisted of pairs of copper and zinc discs piled on top of each other, separated by a layer of cloth or cardboard soaked in brine (i.e. the electrolyte) John Frederic Daniell invented the Daniell cell, which consisted of a copper pot filled with a copper sulphate solution, in which was immersed an unglazed earthenware container filled with sulphuric acid and a zinc electrode William Robert Grove invented Grove cell. It consisted of a zinc anode dipped in sulfuric acid and a platinum cathode dipped in nitric acid, separated by porous earthenware. The Grove cell provided a high current and nearly twice the voltage of the Daniell cell. 1

3 1859 Gaston Plante invented the lead acid battery, the first ever battery that could be recharged by passing a reverse current through it. A lead acid cell consists of a lead anode and a lead dioxide cathode immersed in sulphuric acid Georges Leclanche invented a battery that consisted of a zinc anode and a manganese dioxide cathode wrapped in a porous material, dipped in a jar of ammonium chloride solution. The manganese dioxide cathode had a little carbon mixed into it as well, which improved electrolyte conductivity and absorption Carl Gassner invented the first commercially successful dry cell battery (zinc carbon cell) Waldemar Jungner invented the nickel cadmium battery Thomas Alva Edison invented the alkaline storage battery Jungner invented the nickel iron battery Lithium battery 1989 Nickel/Metal hydride battery An American chemist John B. Goodenough led a research team at Sony that would produce the lithium ion battery, a rechargeable and more stable version of the lithium battery; the first ones were sold in lithium ion polymer battery. 2

4 1. 3 Categories and types of batteries Batteries are classified into two broad categories. Primary batteries irreversibly (within limits of practicality) transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means. eg. Zinc carbon batteries, Alkaline batteries Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition. eg. Lead acid batteries, Lithium ion batteries 1. 4 Battery cell types There are many general types of electrochemical cells, according to chemical processes applied and designs chosen. The variation includes galvanic cells, electrolytic cells, fuel cells, flow cells and voltaic piles Wet cell A wet cell battery has a liquid electrolyte. Other name is flooded cell, since the liquid covers all internal parts, or vented cell, since gases produced during operation can escape to the air. Wet cells may be primary cells (non rechargeable) or secondary cells (rechargeable). eg. Leclanche cell. 3

5 Dry cell A dry cell has the electrolyte immobilized as a paste, with only enough moisture in the paste to allow current to flow. Compared to a wet cell, the battery can be operated in any random position, and will not spill its electrolyte if inverted. eg. Zinc carbon battery Molten salt battery A molten salt battery is a primary or secondary battery that uses a molten salt as its electrolyte. eg. ZEBRA batteries (Na NiCl 2 battery) Reserve battery A reserve battery can be stored for a long period of time and is activated when its internal parts (usually electrolyte) are assembled. For example, a battery for an electronic fuze might be activated by the impact of firing a gun, breaking a capsule of electrolyte to activate the battery and power the fuze's circuits. eg. Water activated battery Components of cell Anode or negative electrode Cathode or positive electrode Electrolyte Separator Current collector Anode The electrode at which the oxidation occurs is called the anode. The charge on the anode is negative. 4

6 Characteristics Efficiency as a reducing agent. High coulombic output (Ah/g) Good conductivity. Stability Example Metals Cathode The electrode at which reduction occurs is termed the cathode. The charge on the cathode is positive. Characteristics Good oxidizing agent. Must stable when contact with electrolyte. To achieve high performance. Should be conductive. Example Metallic oxides Electrolyte The ionic conductor which provides the medium for transfer of charge, as ions, inside the cell between the anode and cathode. Characteristics Good ionic conductivity Low viscosity and high dielectric constant 5

7 Non reactivity with electrode materials Example Sulphuric acid, LiPF 6 in 1: 1 (Ethylene carbonate and diethylene carbonate) Separator An ion permeable and electronically non conductive, spacer or material which prevents electronic contact between electrodes of opposite polarity in the same cell. Characteristics Chemical stability. Low thickness. Mechanical strength. High porosity & permeability. Examples Polypropylene, Glass, Non Woven glass Current collector An inert member of high electrical conductivity used to conduct current from or to an electrode during discharge or charge. Characteristics Excellent bulk electrical conductivity. Minimal thickness / weight. Excellent surface conductivity. Examples Aluminium foil, Copper foil and Nickel mesh. 6

8 1. 6 Operating principle of cell Discharge The operation of a cell during discharge is shown schematically in Fig. 1. 1a. When the cell is connected to an external load, electrons flow from the anode, which is oxidized, through the external load to the cathode, where the electrons are accepted and the cathode material is reduced. The electric circuit is completed in the electrolyte by the flow of anions (negative ions) and cations (positive ions) to the anode and cathode, respectively Charge During the recharge of a rechargeable or storage cell, the current flow is reversed and oxidation takes place at the positive electrode and reduction at the negative electrode, as shown in Fig. 1. 1b. As the anode is, by definition, the electrode at which oxidation occurs and the cathode, the one where reduction takes place, the positive electrode is now the anode and the negative the cathode Lithium batteries Lithium batteries 1 were first proposed by M. S. Whittingham at Binghamton University, at Exxon, in the 1970s. Whittingham used titanium (II) sulfide as the cathode and lithium metal as the anode. The reversible intercalation in graphite and intercalation into cathodic oxides was also already discovered 2 in the 1970s by J.O. Besenhard at TU Munich. He also proposed the application as high energy density lithium cells. In 1979, John Goodenough demonstrated a rechargeable 3 cell with high cell voltage in the 4V range using lithium cobalt oxide (LiCoO 2 ) as the positive electrode and lithium metal as the negative electrode. This innovation provided the positive electrode material which 7

9 made lithium ion batteries (LIBs) possible. LiCoO 2 is a stable positive electrode material which acts as a donor of lithium ions, which means that it can be used with a negative electrode material other than lithium metal. In 1985, Akira Yoshino 4 assembled a prototype cell using carbonaceous material into which lithium ions could be inserted as the anode, and as the cathode lithium cobalt oxide (LiCoO 2 ), which is stable in air. By using an anode material without metallic lithium, safety was dramatically improved over batteries which used lithium metal. The use of lithium cobalt oxide (LiCoO 2 ) enabled industrial scale production to be achieved easily. This was the birth of the current lithium ion battery. In 1991, Sony and Asahi Kasei released the first commercial lithium ion battery Advantages of lithium ion battery High voltage Lithium cells have voltages up to about 4V, depending on the cathode material, compared with 1.5V for most other primary system. High open circuit voltage in comparison to aqueous batteries (such as lead acid, nickel metal hydride and nickel cadmium). This is beneficial because it increases the amount of power that can be transferred at a lower current. High energy density and power density The energy density ( Wh/Kg) and power density (250 Wh/L) of lithium cell is 2 4 or more times better than that of conventional batteries (Lead acid, zinc anode and Ni/MH batteries). 8

10 Operation over a wide temperature range Many of the lithium cells will perform over a temperature range from 40 to 70 C. Flat discharge characteristics A flat discharge curve is typical for many lithium cells. No memory effect Superior shelf life Self discharge rate of approximately 5 10% per month, compared to over 30% per month in common nickel metal hydride batteries, approximately 1.25% per month for low self discharge Ni MH batteries and 10% per month in nickel cadmium batteries Electrochemistry of lithium ion Battery During charge, the positive material is oxidized and the negative material is reduced. In this process, lithium ions are de intercalated from the positive material and intercalated into the negative material. (Intercalated a reaction where lithium ions are reversibly removed or inserted into a host without a significant structural change to the host) The reverse process is present during a discharge cycle. The operation of a Lithium ion cell is shown schematically in Fig The positive electrode half reaction is Charge LiCoO 2 Li 1 x CoO 2 + xli + + xe Discharge 9

11 The negative electrode half reaction is Charge xli + + xe + 6C Li x C 6 Discharge The over all electrode reaction is Discharge CoO 2 + LiC 6 LiCoO 2 + C 6 Charge Classification of lithium batteries Lithium batteries are classified into two broad categories. Lithium battery Li primary battery Li secondary battery Soluble cathode cells Solid cathode cells Solid electrolyte cells Lithium ion battery Lithium ion polymer battery Classification of lithium primary battery material. Lithium primary cells classified on the basis of electrolyte used or cathode 10

12 a. Soluble cathode cells These use liquid or gaseous cathode materials that dissolve in the electrolyte or the electrolyte solvent. Their operation depends on the formation of a passive layer on the lithium anode resulting from a reaction between the lithium and the cathode material. This prevents further chemical reaction (self discharge) between anode and cathode or reduces it to a very low rate. These cells are manufactured in many different configurations and designs (such as high and low rate) and with a very wide range of capacities. They are generally fabricated in cylindrical configuration in the smaller sizes, upto about 35 Ah, using a bobbin construction for the low rate cells and a spirally wound (jelly roll) structure for the high rate designs. Prismatic containers, having flat parallel plates, are generally used for the larger cells upto 10,000 Ah in size. Flator pancake shaped configurations have also been designed. These soluble cathode lithium cells are used for low to high discharge rates. The high rate designs, using large electrode surface areas, are noted for their high power density and are capable of delivering the highest current densities of any active primary cell. Eg. Li/SO 2 Cl 2 cells b. Solid cathode cells The second type of lithium anode primary cells uses solid rather than soluble gaseous or liquid materials for the cathode. With these solid cathode materials, the cells have the advantage of not being pressurized or necessarily requiring a hermetic type seal, but they do not have the high rate capability of the soluble cathode systems. They are designed, generally, for low to medium rate applications such as memory backup, security devices, portable electronic equipment, photographic equipment, watches, 11

13 calculators and small lights. Button, flat, and cylindrical shaped cells are available in low rate and the moderate rate jelly roll configurations. Eg. Li/V 2 O 5 cell. c. Solid electrolyte cells The third type of lithium anode primary batteries uses solid rather than liquid for electrolytes. The solid electrolyte is formed in situ as the discharge product of the cell reaction. However, the viscous liquid phase impart a plasticity to the cathode which makes these solid state cells better able to adapt to volumetric changes during cell discharge. These cells are noted for their extremely long storage life, in excess of 20 years, but are capable of only low rate discharge in the micro ampere range. They are used in applications such as memory backup, cardiac pacemakers, and similar equipment where current requirements are low but long life is critical. Eg. Li/LiI/I 2 (P 2 VP) Classification of lithium secondary batteries Lithium secondary cells classified on the basis of electrolyte used. a. Lithium ion battery The three primary functional components of a lithium ion battery are the anode, cathode, and electrolyte. The anode of a conventional lithium ion cell is made from carbon, the cathode is a metal oxide, and the electrolyte is a lithium salt in an organic solvent. The most commercial popular anode material is graphite. The cathode is generally one of three materials: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate), or a spinel (such as lithium manganese oxide). The electrolyte is typically a mixture of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions. These non aqueous 12

14 electrolytes generally use non coordinating anion salts such as lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate monohydrate (LiAsF 6. H 2 O), lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4 ), and lithium triflate (LiCF 3 SO 3 ). Depending on materials choices, the voltage, capacity, life, and safety of a lithium ion battery can change dramatically. b. Lithium ion polymer battery Lithium ion polymer batteries, polymer lithium ion, or more commonly lithium polymer batteries (abbreviated Li poly, Li Pol, LiPo, LIP, PLI or LiP) are rechargeable batteries (secondary cell batteries). This battery consists of a carbon anode and Li + insertion material cathode and solid polymer electrolyte, in which lithium ions swing between the two electrodes. Lithium polymer batteries have the same basic chemistry as lithium ion batteries. However, the polymer cells use a porous separator that, when exposed to the electrolyte, turns to a gel because the gel isn't flammable, lithium polymer batteries have a different architecture, with the anode and cathode developed as a plate and stacked on top of each other. Polymer electrolytes/separators can be solid polymers (e.g., polyethylene oxide) and LiPF 6, or other conducting salts and SiO 2, or other fillers for better mechanical properties. Lithium polymer batteries do not need a metal shell the way that lithium ion batteries do. In fact, the shell of lithium polymer batteries is often plastic Components of lithium ion cells Anode The anode is the electrode at which oxidation takes place and electrons are fed into the external circuit. Different type of anode materials are used in currently used 13

15 lithium ion batteries such as lithium metal, carbonaceous materials, Sn, SnO based materials and Intermetallic alloys etc., Criteria The potential of lithium insertion and deinsertion in the anode Vs Li must be as low as possible. The amount of lithium which can be accommodated by the anode material should be as high as possible to achieve a high specific capacity. The anode should endure repeated Li insertion and deinsertion without any structural change to obtain long cycle life. Examples. Li, graphite, metal and metal oxides Cathode The cathode is the electrode at which reduction takes place and into which electrons are fed from the external circuit. A guest spaced such as lithium can be inserted interstitially into the host lattice and extracted during recharge with little or no structural modification of the host. The intercalated compounds are classified as follows LiMO 2 based materials (M = Co, Ni, Mn) LiMPO 4 based materials (M = Fe, Co, Ni and Mn) LiMn 2 O 4 based materials Criteria The insertion compound Li x M y X z (X anion) should have a high lithium chemical potential (µ Li(c) ) to maximize the cell voltage. The insertion compound Li x M y X z should allow an insertion/extraction of a large amount of lithium, to maximize the cell capacity. 14

16 The lithium insertion/extraction process should be reversible with no or minimal changes in the host structure over the entire range x of lithium insertion/extraction in order to provide a good cycle life for the cell. The insertion compound should support mixed conduction. It should have good electronic conductivity σ e and lithium ion conductivity σ Li to minimize polarization losses during the discharge/charge process and thereby to support a high current density and power density. The insertion compound should be chemically stable without undergoing any reaction with the electrolyte over the entire range, x of lithium insertion/extraction. Examples. LiCoO 2, LiMn 2 O 4, LiFePO 4 etc Electrolyte Electrolytes can be defined as to serve as the medium for the transfer of charges, which are in the form of ions, between a pair of electrodes. The vast majority of the electrolytes are electrolytic solution types that consists of salts dissolved in either water (aqueous) or organic molecules (nonaqueous) and are in a liquid in the service temperature range. Criteria It should be a good ionic conductor and electronic insulator It should have wide electrochemical window It should also be inert to other cell components It should be robust against other various abuses, such as electrical, mechanical or thermal ones. 15

17 Its components should be environmentally friendly. Classification Electrolytes can be roughly divided into three groups as follows Liquid electrolytes eg. LiPF 6 in 1: 1 (EC: DEC) Solid polymer electrolyte eg. LiClO 4 PEO Gel polymer electrolyte eg. PVDF HFP Separators A separator is a porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electrical contact of the electrodes. Criteria Electronic insulator Minimal electrolyte (ionic) resistance Mechanical and dimensional stability Sufficient physical strength to allow easy handling Chemical resistance to degradation by electrolyte, impurities and electrode reactants and products Effective in preventing migration of particles or colloidal or soluble species between the two electrodes Readily wetted by electrolyte Uniform in thickness and other properties 16

18 Classification Separators for batteries can be divided into different types, depending on their physical and chemical characteristics. They can be molded, woven, non oven, microporous, bonded, papers, or laminates. Eg. Polypropylene, cellulose, nonwoven fabric and celgard etc Current collectors A structural part of a complicated electrode assembly. Its primary purpose is to conduct the electricity between the actual working (reacting) parts of the electrode and the terminals. Current collectors must be electrochemically stable when in contact with the cell component during the potential operation window of an electrode. In lithium batteries Al can be used as current collector for positive electrode and Cu foil for negative electrode. The rough surface of substrate enhanced the adhesive force between an active material and a current collector. Therefore, surface roughness of substrate is an important factor to improve the cycleability of Li ion cell. a. Aluminium foil For high voltage 5 (>3.5 V Vs Li/Li + ) LIBs, Al is the material of choice. It is used extensively with lithiated transition metal oxides upto 5V Vs. Li/Li +. In air and aqueous solutions, Al can be protected by a thin and dense oxide passive layer, Al 2 O 3. Its low price and good electrical conductivity due to a high purity of Al metal expand the potential application for lithium batteries. b. Copper foil Almost all commercial, rechargeable lithium batteries use carbonaceous materials applied to a copper foil substrate as the negative electrode. As lithium ions, which are 17

19 released from the positive electrodes, are intercalated to the carbonaceous negative electrode materials, the resulting potential 6 reaches between 0.25 and 0.01 V Vs. Li/Li +. In this state, the negative electrode materials, the Cu current collector, and the electrolyte are electrochemically reduced. Cu metal surface is likely to reduce the electrolyte at the potential 3 V Vs. Li/Li +, generating the cathodic current beecause of this, Cu metal is stable at a lower narrow potential range and is generally acceptable for negative electrode current collectors Applications of lithium primary and secondary batteries Lithium primary and secondary batteries are widely used in consumer, industrial, medical, automotive and military devices. General usage Lithium ion batteries can be used both in devices that need recharging, such as cell phones, and in products whose batteries are difficult, expensive or impossible to recharge or replace, such as cardiac pacemakers. Portable electronics In portable electronics, batteries needs to be recharged many times, and the lithium ion battery can handle hundreds of recharges. Products that use the lithium ion battery include ipods, cell phones, PCs, laptops, watches and digital cameras. Medical applications Implantable electronic devices cannot be recharged or replaced without great expense, so the batteries used need to be small and able to last for years. Implantable products that use lithium ion batteries include cardiac pacemakers, cardiac defibrillators, neuro stimulators and drug infusion systems. 18

20 Military applications The lithium ion battery's long life and light weight make it the battery used in many military functions, including providing power for the computers in missiles. 19

21 1. 13 References 1. M. S. Whittingham, Science 192 (1976) R. Schallhorn, R. Kuhlmann, J. O. Besenhard, Mater. Res. Bull. 11 (1976) USPTO search for inventions by "Goodenough, John". 4. US , Yoshino; Akira, "Secondary Battery", issued 10 May 1985, assigned to Asahi Kasei. 5. S. T. Myung, Y. Hitoshi, Y. K. Sun, J. Mater. Chem. 21 (2011) K. L. Lee, J. Y. Jung, S. W. Lee, H. S. Moon, J. W. Park, J. Power Sources 129 (2004)

22 Fig Operation of cell a) Discharge b) Charge Fig Lithium ion battery operating principle (source: 21