General introduction on Lithium Ion Batteries

History of battery…. Pioneering work for the lithium battery began in 1912 by G. N. Lewis but it was not until the early 1970’s when the first non-rechargeable lithium batteries became commercially available. Attempts to develop rechargeable lithium batteries followed in the eighties, but failed due to safety problems. the first commercial lithium-ion battery was released by Sony in 1991. The cells utilised layered oxide chemistry, specifically lithium cobalt oxide. These batteries revolutionised consumer electronics.

Michael Faraday Charles-Augustin de Coulomb demonstrated the relation between electricity and chemical bonding, capacity (mAh/g) = [F × nLi) / ( M×3600)] × 1000 Where, F = Faraday’s constant( 96,500 coulombs per gm equivalent) n Li = Number of Li per formula unit of the electrode material M = Molecular mass of the electrode material.

Cell – Energy storage device that converts chemical energy present in to electrical energy. Battery: Combination of one or more cell; The cell components: Cathode, Anode and Electrolyte, seperator and current collector. Primary Battery Secondary Battery Zinc- MnO2: Inexpensive, small in size, voltage ~ 1.5V, use in watches, calculators etc, use and dispose, Rechargeable cell , Ni- Cd, Li -Ion battery Energy storage of the battery is means that How much charge a battery can deliver to the external circuit. coulomb is defined as the quantity of electricity transported in one second by a current of one ampere. Named for the 18th–19th-century French physicist Charles-Augustin de Coulomb

Why Li-based power sources? Li is the lightest metal (specific gravity ρ=0.53 g/cm3) high energy density Theoretical capacity of Li : 3860 Ah/kg (Li Li+ + e-) Extremely high compared to Zn (820 Ah/kg) and Pb (200 Ah/kg).

Salient Features of LIB High Energy density, Light weight, design flexibility Preferred choice for portable appliances present world production per year is ~ 300 million cells. Market value ~ US $ 200 Billion expected growth up to 2010 ~ 40% Courtesy of Panacenia.com.

Specification for the Commercial Battery fabricated by Panasonic. Size (DWH) 3.83562 mm Weight 15g Nominal capacity 760 mAh Nominal voltage 3.7 V Charge voltage 4.2 V Charge time 150 min. Energy density (Volumetric) 375 Wh/dm3 Energy density(Gravimetric) 190 Wh/kg Cycle performance 85% at 1000th cycle Temperature range -20C to + 60C Cathode LiCoO2 Anode Graphite Courtesy of Panasonic website

Principle of Operation Discharging Co4+ Co3+ Charging Co3+ Co4+ Cathode: LiCoO2 Li1-xCoO2 + xLi+ + xe- (Oxidation: E° = 0.6V) Anode: C + xLi+ + xe- LixC (Reduction: E°=-3.0V) Overall rxn: C + LiCoO2 LixC + Li1-xCoO2; x=0.5 (Ecell=3.6V) (during charging)

LIB Technology Different configurations : a) cylindrical b) coin c) prismatic d) thin and flat (pLiON) [ref. Nature 2001, Tarascon et al .]

Material Considerations Anodes Carbon anodes Capacity~372 mAh/g Graphite – layered, low capacity, high reversibility Hard Carbon- Non-layered, high capacity. Irreversible capacity loss Metal coating (Ag,Zn or Sn) of anodes tried

Amorphous Tin Composite Oxides (ATCO) SnMxOy (x≥1), M = glass-forming elements (e.g. a mixture of B and P) Gravimetric capacity- high (>600 mAh/g) Sn2+,Sn4+/Sn redox couple SnO + 2 (Li+ + e-) → Sn + Li2O SnO2 + 4 (Li+ + e-) → Sn + 2Li2O Sn + 4.4 (Li+ + e-) ↔ Li4.4Sn Capacity-fading need to be solved before these materials can be used commercially Irreversible loss of Li in Sn formation Reversible capacity

Other options Lithium metal nitrides Inter-metallics Oxides Pros: High capacity(~900 mAh/g), low average voltage Cons: High moisture sensitivity, lack of economic manufacturing processes Inter-metallics Cu6Sn5 – Capacity fading InSb – In (high cost), Sb (toxic) Oxides Spinel-type oxides- Li4Ti5O12, Li4Mn5O12 and Li2Mn4O12 Low voltage spinels + high-voltage cathodes= intermediate voltage Li-ion cells. Do not produce metallic Li which is a safety concern in LiC6 or metallic lithium anodes.

Electrolytes Li salt dissolved in a solvent. LIB Operation range : 3.0-4.2 V, Decomposition potential of H2O = 1.23 V Aqueous electrolyte not used 4 types of non-aqueous electrolytes in use: liquid, gel, polymer and ceramic-solid electrolytes.

Liquid electrolytes Highly ionizable Li-salts - LiPF6, LiAsF6 etc dissolved in organic carbonates - ethylene carbonate (EC), dimethyl carbonate (DMC) etc Organic carbonates - aprotic, polar, high K, solvate Li salts at high concentration (>1M), good ionic conduction. Problems : leakage, sealing, non-flexibility of the cells, side reactions with charged electrodes

Solid electrolytes Crystalline or glassy matrix - Li ions move through vacant/interstitial sites - high σionic (~10-3 - 10-4 S/cm at 25°C) Crystalline : Nasicon framework phosphates – LiM2(PO4)3 and perovskite-based oxides, (Li,La)MO3 (M = Ge, Zr, Hf) Glasses : oxides or sulfides Advantages : (i) No leakage, (ii) Wide operating temperature range (iii) Better charge-discharge cycling profile (iv) Long life – little self discharge.

Polymer electrolyte A salt dissolved in a high-molecular-weight polar polymer matrix E.g. PEO (Poly-ethylene oxide) Chemically stable – contains only C-O, C-C and C-H bonds. Cation mobility - cation-ether-oxygen co-ordination bonds, regulation - local relaxation and segmental motion of the PEO polymer chains -> high σionic of the electrolyte. Pros : ease of fabrication, flexibility, lightweight, leak proof Cons: low conductivities at or below room temperature Addressed by plasticized or gel electrolytes - polymer electrolytes with a component (solid or liquid): to enhance the ionic conductivity.

Layered Cathodes Layered materials Facile Intercalation / deintercalation – high reversibility α-NaFeO2 structure( sp grp R3m) LiNiO2, LixCoO2 (widely in use, 140 mAh/g) – thermally stable : High cost, toxicity LiMnO2 – cheap, substitution needed to stabilize the structure (Li1+x Mn0.5Cr0.5O2, 190 mAh/g )

NaSICON materials Oxyanion scaffolded structures built from corner-sharing MO6 octahedra (where M is Fe, Ti, V or Nb) and XO4n tetrahedral anions (where X is S, P, As, Mo or W) Polyoxyanionic structures possess M-O-X bonds Altering the nature of X -> change (through an inductive effect) the iono-covalent character of the M-O bonding Possible to tune M redox potentials. Promising candidate - LiFePO4

Spinels LiMn2O4 - cubic spinel structure with sp grp Fd3m Spinels - 3D hosts with Li ions occupying 8a tetrahedral sites. Capacity fading and poor recyclability Cost, non-toxicity and availability

Advanced Applications Mars Exploration rover” spirit” Koizumi taking a 10 minute spin www.nasa.gov Eliica, Japan Speed – 90km/hr

Mechanical grinder Tubular Furnace Hydraulic press

Preparation of Composite Electrodes ( Cathode or Anode). Fine powders of the active materials (LiCoO2, CaSnO3, etc) mixed with conducting carbon (Super PMMM) and PVDF in N-methyl pyrolidinone (NMP) solvent. PVDF acts as binder that helps the thick film coating to adhere well to the metal foil. This mixture of active material : conducting carbon :PVDF in fixed proportion ( in my case 70:15:15) was stirred to get the homogenous paste like slurry. The Slurry was coated on to a clean Al or Cu foil. Thick film was dried at 100oC in an air. Thick film coater Furnace

5. Electrode was then pressed between spherical twin roller at about 5. Electrode was then pressed between spherical twin roller at about 1500 KPa pressure. This ensures that the film of the composite electrode adheres to the Al/Cu foil. 6. Electrode was cut into circular discs (16mm). Thickness ~ 0.05 – 0.12mm 7. Electrode- discs were dried in vacuum oven at 800C for ~ 12 hrs.

8. Electrode disc then transferred to the Glove Box. O2 and H2O content < 1ppm Glove Box

Fabrication of Lithium - Ion Cell Diameter of coin cell ( 2016) ~ 16mm and height 2.0mm Parts of Coin cell – Cup > 16mm diameter and plastic ring, separators ( polypropylene separators; Electronically nonconducting but solution/ion permeable) Steel spring for close packing. Finally cell was sealed using a press and transferred out the glove box Punching Machine Li ion - coin Cell Micropipette

Electrochemical Characterization : Galvanostatic Cycling and Potentiostatic Cycling: Galvanostatic Mode: The output voltage of the cell is monitored at constant current. Potentiostatic Mode: The current is monitored at a particular voltage Multi cell analyzer BITRODE

Specific Capacity of the cell : The capacity of the electrode material in the battery depends on the amount of Li that can be intercalated / deintercalated into the host structure. Capacity: Number of Coulombs (Charge) in (amperes-hours) delivered by a battery. Specific capacity: Amount of charge delivered per unit weight of electrode active material (Ah/g or mAh/g ). Theoretical specific capacity of a Li – containing oxide is calculated by assuming that all the Li per formula unit of the oxide participate in the electrochemical reaction and is given by Specific Theoretical capacity (mAh/g) = [F × nLi) / ( M×3600)] × 1000 Where, F = Faraday’s constant( 96,500 coulombs per gm equivalent) nLi = Number of Li per formula unit of the electrode material M = Molecular mass of the electrode material.

Theoretical Capacity of the Electrode Material: Weight of the active electrode material × its theoretical specific capacity Experimental Capacity: Our experimental value observed by BITRODE (mAh) Specific Capacity: Experimental capacity / weight of Electrode Material. Number of Lithium Ions de – intercalated from the cathode active material during charging process, Charging Capacity of Electrode / Theoretical Capacity Where charging capacity = Charging current × Charging time In Coin – type cell the weights of electrodes ~ 8-15mg hence the current will be small.