Unit 1- Battery Technology 1.pdf

Unit 1- Battery Technology Introduction Batteries are essential for various daily applications such as: Clocks, watches, motor vehicles, UPS systems, remote controls, cameras, laptops, cell phones, pacemakers, children's toys, etc. Different applications require batteries with...

Unit 1- Battery Technology Introduction Batteries are essential for various daily applications such as: Clocks, watches, motor vehicles, UPS systems, remote controls, cameras, laptops, cell phones, pacemakers, children's toys, etc. Different applications require batteries with different properties: Car batteries: Deliver large electrical current for a short time. Pacemaker batteries: Small, rugged, leak-proof, deliver a steady current for extended periods. UPS systems: Require long and consistent backup. Hearing aids: Require tiny batteries. Torpedoes and submarines: Need stable, high-power, rechargeable batteries. Laptops: Prefer batteries in a flexible sheet form. Types of Batteries 1. Primary Batteries: Definition: Galvanic cells producing electricity from sealed-in chemicals. Non-rechargeable: Cell reaction cannot be efficiently reversed; once equilibrium is reached, they are discarded. Known as "throw-away" or irreversible batteries. Examples: Dry cell, Lithium copper sulfide cell. 2. Secondary Batteries: Definition: Rechargeable batteries by passing current through them. Recharging reverses the spontaneous cell reaction, restoring a non-equilibrium mixture of reactants. Can be used in multiple cycles of discharging and charging.  Also known as rechargeable cells, storage cells, or accumulators. Examples: Lead-acid batteries, Nickel-cadmium cell, Lithium-ion battery. Requirements of Batteries 1. Primary Batteries: Compact and lightweight. Fabricated from easily available raw materials. Economical with benign environmental properties. High energy density, longer shelf life. Constant voltage and long discharge period. 2. Secondary Batteries: Long shelf-life in both charged and discharged conditions. Longer cycle life and design life. High power-to-weight ratio. Short recharge time. High voltage and high energy density. Basic Principle Behind Battery Operation Battery Operation: Involves exchange of electrons between two chemical reactions (oxidation and reduction) that are physically separated. Key Aspects: Physical separation of oxidation and reduction reactions allows insertion of a load between them. Electrochemical potential difference corresponds to the battery's voltage, driving the load. Exchange of electrons corresponds to the current passing through the load. Components of a Battery:  Electrode and electrolyte for both oxidation and reduction reactions. Means to transfer electrons (wire connecting each electrode). Means to exchange charged ions between the two reactions. Materials: Choice of electrode and electrolyte materials greatly influences battery properties. Electrode Functions: Anode: Where oxidation occurs (positive voltage). Cathode: Where reduction occurs (negative voltage). Battery Definition and Function Battery: Stores energy in chemical form, converts it into electrical energy through electrochemical reactions. Electron Flow: From one electrode to another through an external circuit, generating an electric current. Ions Transport: Charged ions move through an electrolyte to maintain electrical neutrality. Battery Structure Electrochemical Cells: Consist of two electrodes (anode and cathode) separated by an electrolyte. Anode (negative) releases electrons; Cathode (positive) receives electrons. Electrolyte: Allows transport of charged ions toward electrodes. Separator: Porous, electronically insulating, improves mechanical strength of the electrolyte, prevents short circuits. Current Collectors: Made of thin aluminum or copper foils, ensure efficient electron transfer and heat removal. Electrodes (Anode and Cathode) Requirements for Electrodes: Cathode:  High redox potential (efficient oxidizing agent). High specific capacity. Reversibility and stability with the electrolyte. Anode: Low redox potential (efficient reducing agent). High specific capacity. Reversibility and good conductivity. Cell Potential: Difference in electrical potentials of cathode and anode gives the cell potential: Ecell = Ecathode − Eanode Greater potential difference results in higher voltage. Electrode Potential: Measured by assigning zero potential to a reference electrode. Electrolytes, Redox Reactions 1. Electrolytes Definition: An electrolyte in a battery can be a liquid, solid, polymer, or a composite (hybrid), facilitating the movement of ions between the electrodes. Key Requirements of Electrolytes: High ionic conductivity. No electrical conductivity (to prevent short circuits). Non-reactive with electrode materials. Wide operational temperature range. Types of Electrolytes: 1. Liquid Electrolytes:  Properties: Low viscosity, high energy density. Suitable for high charge/discharge rates. Operational temperature: -40 °C to 60 °C. Low flammability. Advantages: Fast ion transport due to low viscosity, resulting in high energy output. 2. Polymeric Electrolytes: Forms: Can be gel or solid. Solid Polymeric Electrolytes: Advantages: High flexibility, energy density, multifunctional applications, good safety, mechanical and thermal stability. Limitations: Low ionic conductivity at room temperature (10⁻⁵ to 10⁻¹ mS/cm). Gel Polymeric Electrolytes: Advantages: Higher ionic conductivity (around 1 mS/cm), high flexibility, chemical stability, multifunctional applications. Limitations: Poor mechanical strength and interfacial properties. Key Advantages of Solid Polymeric Electrolytes: No electrolyte leakage. High safety (non-flammable). Non-volatile. Thermal and mechanical stability. Ease of fabrication. High achievable power density and cyclability. 2. Redox Reactions and Electron Transfer Definition: A redox (reduction-oxidation) reaction involves the exchange of electrons between species. In electrochemical cells, this is split into two half-reactions, occurring at different electrodes: Oxidation: Loss of electrons (occurs at the anode). Reduction: Gain of electrons (occurs at the cathode). Operational Mechanism in Batteries: During discharge: Anode: Electrochemical reaction R → O + ne produces electrons and ions. − Electrons: Transferred through an external circuit to the cathode. Ions: Transferred to the cathode through the electrolyte. Cathode: Electrons and ions react at the cathode/electrolyte interface (O + ne − → R) Key Points: The anode undergoes oxidation and is said to be oxidized during the reaction. The cathode undergoes reduction and is said to be reduced during the reaction. Each redox reaction has a standard potential, indicating its ability to accept or produce electrons. Key Battery Perfomance Metrics The performance of a battery is determined by several factors, which in turn decide its suitability for specific applications. Here are the key metrics: a. Cell Potential (Voltage) Formula: E cell = (E C − E A ) − |η A − η C | − iR cell (E C )and(E A ) : Reduction potentials of the cathode and anode, respectively. (η A )and(η C ): Overpotentials at the anode and cathode, respectively. : Internal resistance of the cell. (iR cell ) Maximizing Cell Voltage: High Electrode Potential Difference: Use materials with a large difference in electrode potentials. Fast Electrode Reactions: Quick reactions reduce overpotential. Low Internal Resistance: Can be achieved by: Keeping electrodes close to each other. Using an electrolyte with high conductivity. Electrode Design: The positive electrode should deplete its active mass easily, while the negative electrode should accumulate active mass efficiently. b. Current Definition: The rate of flow of electrons during discharge, measured in amperes (A). It represents the charge flow per unit time. Uniform Current Flow: Efficient discharge requires a uniform flow of electrons, which depends on the high conductivity of the electrolyte. Output Type: Batteries provide direct current (DC). c. Capacity Definition: The charge (in ampere-hours, Ah) that a battery can deliver. Calculation: m×n×F C = M ( C ): Capacity in Ah. ( m ): Mass of active material. ( n ): Number of electrons involved. ( F ): Faraday's constant. ( M ): Molar mass of the active material. Dependence: Amount of active materials consumed during discharge. Discharge conditions (current, temperature). Measurement: Determined by the time taken for the battery to reach a minimum voltage (considered dead) at a fixed current discharge. Capacity Curve: A longer flat portion in the voltage-time discharge curve indicates better capacity. d. Electricity Storage Density Definition: The charge stored per unit mass of the battery, including the electrolyte, current collectors, terminals, casing, and other elements. Maximizing Storage Density: Minimize the mass of subsidiary elements (e.g., using lighter anode materials like lithium). Example: 7g of lithium can store the same charge as 65g of zinc, indicating lithium’s higher storage density. e. Energy Efficiency Formula: Dependence: Current efficiency of electrode processes. Overpotentials during discharge and charge. Internal resistance. Requirement: A battery should have high energy efficiency for optimal performance. f. Cycle Life Definition: The number of charge-discharge cycles a battery can undergo before failure. Applicability: Relevant for secondary (rechargeable) batteries. Influencing Factors: Chemical composition and morphological changes.  Distribution of active materials within the cell. Corrosion at contact points. Shedding of active material from plates. Short-circuiting due to irregular crystal growth and changes in morphology. g. Shelf Life Definition: The storage duration during which a battery retains its performance. Influencing Factors: Self-Discharge: Caused by reactions between anode and cathode materials or corrosion of current collectors. Commercial Requirements: Tolerance to temperature variations, vibration, and shock. Reliable output over the storage period. h. Energy Density Definition: The ratio of the energy available from a battery to its mass (Wh/kg) or volume (Wh/L). Determination: Measure the capacity. Record the average voltage during discharge. Consider the total mass (or volume) of the battery. Requirement: A battery should provide a high continuous energy density or very high energy density for short durations. i. Power Density  Definition: The ratio of the power available from a battery to its mass (W/kg) or volume (W/L). Requirement: Batteries should provide a continuous power density above a certain threshold or very high power density for brief periods. Emerging Battery Technologies Emerging battery technologies are evolving to meet the increasing demands of industries like consumer electronics, electric vehicles (EVs), renewable energy storage, and grid stabilization. Below are several key developing battery technologies: a. Solid-State Batteries Description: Solid-state batteries replace the liquid or gel electrolytes in traditional lithium-ion batteries with a solid electrolyte. Advantages: Increased Energy Density: Higher capacity for storing energy. Enhanced Safety: Reduced fire risk due to the non-flammable nature of solid electrolytes. Extended Longevity: Potential for a longer battery lifespan. Applications: Expected to significantly impact electric vehicles (EVs) and portable electronics. Challenges: Research is ongoing to improve the performance, reduce the cost, and enhance the scalability of solid-state batteries for commercial use. b. Lithium-Sulfur Batteries Description: These batteries use sulfur as the cathode material and lithium as the anode. Advantages: Higher Energy Density: Potential to exceed the energy density of conventional lithium-ion batteries.  Cost-Effectiveness: Sulfur is an abundant and inexpensive material, potentially reducing production costs. Challenges: Low Electrical Conductivity of Sulfur: Requires additives or engineering solutions to enhance conductivity. Polysulfide Dissolution: Sulfur can dissolve into the electrolyte, reducing efficiency and cycle life. Applications: Could be ideal for electric vehicles and portable electronics once the technical challenges are resolved. c. Lithium-Air Batteries Description: Lithium-air batteries utilize lithium metal as the anode and oxygen from the air as the cathode. Advantages: Extremely High Theoretical Energy Density: Potential to surpass even the energy density of gasoline. Challenges: Stability: Lithium metal anodes have limited cycle life and stability issues. Practical Obstacles: Need to address rechargeability and manage the reactions between lithium and air components effectively. Applications: If practical challenges are overcome, they could revolutionize energy storage for EVs and other high-energy applications. d. Flow Batteries Description: These batteries store energy in liquid electrolytes contained in external tanks, separate from the battery cell itself. Advantages: Scalability: Energy capacity can be adjusted by changing the size of the electrolyte tanks. Flexibility: Suitable for large-scale energy storage applications like grid stabilization. Types: Vanadium Redox Flow Batteries (VRFBs) are the most prominent.  Challenges: Energy Density: Research is focused on exploring new chemistries to improve energy density and reduce costs. Applications: Ideal for stationary energy storage, renewable energy systems, and grid support. e. Metal-Air Batteries Description: Metal-air batteries use a metal anode (e.g., zinc, aluminum) and oxygen from the atmosphere as the cathode. Advantages: High Theoretical Energy Densities: Capable of providing large energy storage capacities. Cost-Effectiveness: The materials (zinc, aluminum) are abundant and inexpensive. Challenges: Reversibility: Issues with efficient recharging. Cycle Life and Efficiency: Need to address problems related to longevity and operational efficiency for commercial viability. Applications: Can be used in various power-intensive applications once technical challenges are addressed. f. Sodium-Ion Batteries Description: These batteries use sodium minerals as a more abundant and economical alternative to lithium. Advantages: Cost-Effectiveness: Sodium is widely available and cheaper than lithium. Challenges: Lower Energy Density: Typically lower than that of lithium-ion batteries. Applications: Suitable for stationary energy storage where cost is a higher priority than energy density (e.g., grid storage, renewable energy systems). Key Takeaways Electrolytes play a crucial role in battery performance, affecting safety, ion conductivity, and operating temperature range. Redox reactions are fundamental to battery operation, where oxidation occurs at the anode and reduction at the cathode. Development Stages: These technologies are at various stages, from initial research to commercial implementation. Research Focus: Ongoing research and innovation are crucial to overcoming challenges and maximizing the potential of these emerging battery technologies for future energy solutions. Maximizing Performance: Design and material selection are crucial in optimizing battery potential, current flow, capacity, energy storage, and power output. Battery Lifespan: Efficient battery usage requires attention to cycle life, shelf life, energy efficiency, and mitigating factors affecting performance and storage. Lead Acid Battery/Storage Battery (Lead Accumulator or Car Battery or Acid Battery) Construction Electrodes: The electrodes are made of lead grids, designed to maximize the surface area. Anode: Filled with finely divided spongy lead (Pb). Cathode: Packed with lead dioxide (PbO₂). Electrolyte: The electrodes are submerged in a sulfuric acid solution (H₂SO₄) with a specific gravity of about 1.25. This acts as the electrolyte in the battery. Insulators: The anode and cathode grids are separated by insulating materials like strips of wood, rubber, or glass fiber to prevent contact between the electrodes. Container: The entire assembly is enclosed in a plastic container or hard vulcanized rubber vessel. Electrolyte Type: It is a wet cell because it uses an aqueous sulfuric acid solution as the electrolyte.  Common Electrolyte: Since both oxidizing (PbO₂) and reducing (Pb) agents are solids, separate compartments for anode and cathode are not needed. Discharging Reactions At the Anode: Lead atoms (Pb) lose electrons and form lead ions (Pb²⁺): [ Pb(s) → Pb 2+ (aq) + 2e − ] Lead ions react with sulfate ions (SO₄²⁻) to form lead sulfate (PbSO₄): (aq) + SO₄ (aq) → PbSO₄(s)] 2+ 2− [Pb Overall reaction at the anode: [ Pb(s) + SO₄ 2− ₄ (aq) → PbSO (aq) + 2e − ] At the Cathode: Lead dioxide (PbO₂) gains electrons, releasing oxygen that reacts with hydrogen ions (H⁺) to form water: [ PbO (s) + 4H (aq) + 2e → Pb (aq) + 2H O(l) ] 2 + − 2+ 2  Lead ions then combine with sulfate ions to form lead sulfate: [ Pb (aq) + SO₄ (aq) → PbSO₄(s) ] 2+ 2− Overall reaction at the cathode: *\ [PbO2(s) + 4H + (aq) + SO ₄ 2− (aq) + 2e − → PbSO4(s) + 2H2O(l)] Overall Discharging Reaction: + 2− [Pb(s) + PbO 2 (s) + 4H (aq) + 2SO (aq) → 2PbSO 4 (s) + 2H 2 O(l)] 4 Explanation: Anode: Lead atoms lose electrons, become positively charged lead ions (Pb²⁺), which then react with sulfate ions to form lead sulfate (PbSO₄). Cathode: Lead dioxide gains electrons, forming water and lead ions, which further react with sulfate ions to produce lead sulfate. During discharge, lead sulfate forms on both electrodes, and sulfuric acid concentration decreases as water increases. This results in the gradual depletion of lead and lead dioxide. Charging Reactions At the Anode: − 2− [PbSO 4 (s) + 2e → Pb(s) + SO (aq)] 4 At the Cathode: 2− + − [PbSO 4 (s) + 2H 2 O(l) → PbO 2 (s) + SO (aq) + 4H (aq) + 2e ] 4 Net Charging Reaction: [2PbSO 4 (s) + 2H 2 O(l) → Pb(s) + PbO 2 (s) + 2H 2 SO 4 (aq)] Explanation: During charging, an external power source (voltage > 2V) is applied to reverse the discharge reactions. This converts the lead sulfate back into lead (Pb) and lead dioxide (PbO₂), while regenerating sulfuric acid. The specific gravity of the sulfuric acid serves as an indicator of the battery's charge level.  A charged battery at room temperature with its electrolyte at normal concentration supplies a potential difference of 2.1 to 2.2 V. The complete reaction cycle of a lead acid storage battery is as follows: In automobiles, the generator driven by the engine supplies the energy for recharging. Key Features of the Lead Acid Battery Voltage: Each cell provides a nominal voltage of about 2.1 V. Reversibility: Designed to be rechargeable, allowing for the storage of electrical energy. Indicator of Charge: The concentration of sulfuric acid, measured by its specific gravity, indicates the operational condition of the battery. Use in Vehicles: Commonly used in cars, where the energy for recharging is supplied by the vehicle's generator. Overcharging Discharge and Charge Reaction: [Pb(s) + PbO 2 (s) + 2H 2 SO 4 (aq) ⇌ 2PbSO 4 (s) + 2H 2 O(l)] Electrolysis of Water: The net reaction of water electrolysis: [2H 2 O(l) + electrical energy → 2H 2 (g) + O 2 (g)] No gas is released during charging if lead ions are present in the solution. If the electrolysis continues further, hydrogen gas forms at the cathode and oxygen gas evolves at the anode. Cathode Reaction: + − [2H (aq) + 2e → H 2 (g)]  Anode Reaction (Water Oxidation): + − [2H 2 O(l) → O 2 (g) + 4H (aq) + 4e ] Consequences of Overcharging 1. Acid Level Reduction: Excessive charging can reduce the sulfuric acid level, damaging the exposed electrode grids. 2. High-Pressure Build-up: In extreme cases, overcharging can lead to dangerous high-pressure build-up, increasing the risk of explosion. 3. Older Battery Maintenance: Older versions of lead-acid batteries require "topping up" with water to maintain electrolyte levels. Maintenance-Free Batteries Gassing Control: Use a specific composition of lead alloys (e.g., Pb-Ca with 0.1% calcium) to inhibit water electrolysis. Catalyst Integration: Some modern batteries use a catalyst (98% cerium oxide and 2% platinum) to recombine hydrogen and oxygen back into water, preventing water loss. These batteries are sealed and require no maintenance. Applications of Lead Acid Batteries 1. Automotive: Used in cars and trucks to provide power for starting engines (Starting, Lighting, and Ignition - SLI). 2. Industrial: Used in electric trucks, submarines, and mine locomotives. Provide backup power for telecommunication systems, hospitals, railway signal centers, and other essential facilities. 3. Consumer: Used in emergency lighting systems, alarm systems, power tools, Uninterruptible Power Supplies (UPS), and vehicles. Advantages of Lead Acid Batteries Voltage Efficiency: The formula for voltage efficiency is: ] Average Voltage During Discharge [Voltage Ef f iciency = × 100 Average Voltage During Charge This gives the efficiency as a percentage, indicating how much of the charging voltage is effectively utilized during discharge. High Efficiency: Voltage efficiency of about 80%. Reversibility: The anode oxidizes and the cathode reduces easily, leading to a high negative free energy change. Long Service Life: Can withstand 300 to 1500 recharge cycles, with sealed versions supporting up to 2000 cycles. Fast Recharge Time: Typically requires 2-8 hours to recharge. Low Self-Discharge: Holds its charge well when not in use. High Current Capability: Can provide a large current (over 10 A) without being damaged. Nominal Voltage: A typical car battery provides around 12 V. Disadvantages of Lead Acid Batteries 1. Sulfation: If left partially charged, large PbSO₄ crystals form, which are hard to reduce or oxidize, ruining the battery. 2. Low Energy Density: Relatively heavy, with an energy density of approximately 35 Wh/kg. 3. Voltage Decrease: The cell potential decreases as sulfuric acid concentration drops during discharge. 4. Temperature Sensitivity: Not efficient at low temperatures due to increased electrolyte viscosity, which reduces cell potential. 5. Overcharging Risks: Can lead to electrode damage, explosion, and hazardous acid spray. 6. Environmental Concerns: Lead is toxic, posing health and environmental risks if improperly disposed of. 7. Corrosion: The lead grid corrodes, particularly at the lead dioxide electrode, leading to battery failure. Nickel-Metal Hydride (NiMH) Battery Overview: NiMH batteries use nickel hydroxide as the positive electrode and hydrogen-absorbing alloys as the negative electrode. They have about twice the energy density of Ni-Cd batteries and a similar operating voltage. The NiMH battery's structure is similar to that of Ni-Cd batteries, featuring a metal case, alkaline electrolyte, and a self- resealing safety vent. Construction: The positive electrode is made of nickel hydroxide. The negative electrode uses hydrogen-absorbing alloys capable of high-density hydrogen absorption. A separator made of fine fibers separates the positive and negative plates, which are then coiled and sealed in a metal case.  Structure: Hydrogen-Absorbing Alloys:  Alloys like NiFe, MgNi, and LaN i can absorb hydrogen up to a thousand times their volume. 5 Alloys are classified into types like AB (e.g., TiFe), AB (e.g., ZnM n ), AB (e.g., LaN i ), and A 2 2 5 5 2B (e.g., M g ). 2N i NiMH batteries commonly use AB alloys for electrodes due to their durability and charge-discharge efficiency. 5 Metals suited for use as electrodes in storage batteries is now being narrowed down to AB type alloys in which rare-earth 5 metals, especially metals in the lanthanum group, and nickel serve as the host metals; and to AB type alloys in which the 2 titanium and nickel serve as the host metals. Operating Principle: Nickel-metal hydride batteries employ nickel hydroxide for the positive electrode like Ni-Cd batteries. Hydrogen is stored in a hydrogen-absorbing alloy for the negative electrode, and an aqueous solution consisting mainly of potassium hydroxide for the electrolyte. Their charge and discharge reactions are shown below: During charge, hydrogen moves from the positive to the negative electrode; during discharge, it moves in the opposite direction.  The electrolyte (usually potassium hydroxide) does not participate in the reaction, so its concentration remains unchanged. - The hydrogen-absorbing alloy negative electrode effectively reduces gaseous oxygen released from the positive electrode during overcharge. This is achieved by increasing the capacity of the negative electrode. This method is similar to the one used in NiCd batteries. Maintaining the internal pressure of the battery in this way allows it to be sealed. Advantages of NiMH Batteries 1. High Energy Density: NiMH batteries provide higher energy density than Ni-Cd batteries, with capacities ranging from 1000 mAh to 3000 mAh. 2. Rechargeability and Long Cycle Life: Can endure hundreds to thousands of charge-discharge cycles, making them cost- effective for long-term use. 3. Environmentally Friendly: Contains fewer harmful materials, reducing environmental impact upon disposal.  4. Enhanced Safety: Lower risk of thermal runaway or fire hazards compared to other chemistries. 5. Cost-Effective: Can be recharged multiple times, reducing the need for frequent replacements. Disadvantages of NiMH Batteries 1. High Self-Discharge Rate: NiMH batteries lose around 1-5% of their charge per day when idle, requiring regular recharging. 2. Memory Effect: Can suffer from memory effect if not fully discharged before recharging, impacting performance. 3. Temperature Sensitivity: Performance decreases in extreme temperatures, affecting battery life and efficiency. 4. Limited Fast Charging: Slower charging rates compared to newer battery technologies. 5. Reduced Voltage Output: Lower voltage output can limit compatibility with devices requiring higher voltage. Applications of NiMH Batteries Consumer Electronics: Cameras, remote controls, portable devices. Power Tools: Drills, saws, and other cordless equipment. Medical Devices: Portable monitoring systems and equipment. Hybrid Vehicles: Used in electric and hybrid cars for power storage. Emergency Lighting and Backup Power: Provides reliable power in critical situations. Renewable Energy Storage: Supports solar and wind energy systems. Electric Bicycles and Scooters: Lightweight and high-capacity power solutions. Lithium-Ion (Li-Ion) Battery Overview: Revolutionized portable electronics and is gaining prominence in electric vehicles and grid storage. Features an anode of lithium-carbide intercalate (LixC6) and a cathode made of a transition metal oxide (e.g., MnO2, CoO2). Electrolyte is typically an inert polar dry ether or carbonate with dissolved conductivity salts like LiPF6. Construction: Anode: A lithium-carbide intercalate (LixC6). Cathode: A metal oxide (e.g., CoO2) capable of intercalating lithium. Electrolyte: Inert polar solvent, such as diethyl carbonate or propylene carbonate, containing lithium salts for conductivity, in which a conductivity salt such as LiPF6 or LiBF4 is dissolved. Working Principle: During charging, lithium ions intercalate into the graphite anode. During discharging, lithium ions migrate back to the cathode (CoO2), enabling current flow. Both electrodes are intercalation compounds, meaning no metallic lithium is present, emphasizing safety. Charge and Discharge Reactions: Anode: Li x C 6 → xLi + (solv) + 6C(s) + xe − Cathode: CoO 2 + xLi + (solv) + xe − → Li x CoO 2 Net Reaction: Explanation: Called a lithium-ion battery to emphasize the absence of lithium metal. Both electrodes are intercalation compounds. During discharge, the left electrode acts as the anode, consisting of a graphite host with lithium ions inserted between carbon layers (LixC6). Lithium ions are extracted from the lithiated graphite compound during discharge. The cathode during discharge is usually cobalt dioxide (CoO2). The reduction half-reaction involves cobalt being reduced from its IV to III oxidation state. During discharge, lithium ions migrate from the graphite anode to the CoO2 cathode, allowing current to flow through the external circuit. During charging, cobalt ions are oxidized, and lithium ions migrate back into the graphite. The anode during discharge becomes the cathode during charging. Advantages of Li-Ion Batteries 1. Safety: Designed to mitigate risks associated with reactive lithium metal.  2. Long Cycle Life: Lasts between 400 to 1200 charge-discharge cycles. 3. High Energy Density: Smaller and lighter with greater energy storage compared to Ni-Cd or NiMH batteries. 4. Wide Temperature Range: Operates efficiently across a variety of temperatures. 5. Convenience: Can be recharged in the device without requiring an external charger. 6. High Voltage: Average voltage equivalent to three Ni-Cd cells. 7. High Energy Storage: Can store 150 watt-hours of electricity per kilogram, compared to 25 watt-hours for lead-acid batteries. Limitations of Li-Ion Batteries 1. Poor Charge Retention: Self-discharge rate is about 10% per month. 2. High Cost: More expensive compared to other rechargeable batteries.