Lithium-Ion Batteries Overview
Lithium-Ion (Li-ion) batteries falls under category of rechargeable batteries with high energy and power capabilities,it is an advanced battery technology with lithium ions as a key component of its electrochemistry. Li-ion batteries use an intercalated lithium compound like Lithium Cobalt Oxide (LiCoO2), Lithium Manganese Oxide (LiMn2O4) and Lithium Nickel Oxide (LiNiO2) as the material at the positive electrode and typically graphite intercalation material at the negative electrode. This anode and cathode assembly is isolated electrically with separator and is impregnated in electrolyte typically organic solvent consisting lithium salt. Due to high flexibility in the construction of lithium ion cells with respect to very high electrode surface area and their chemistry, Lithium-Ion batteries find applications from normal electronics gadgets applications to typically high power applications like Electric Vehicles.
Lithium Ion Battery technology is based on Intercalation, which is actually the addition of lithium ions into a host material without significantly changing the host's structure. During a discharge cycle, lithium atoms in the anode are ionized and separated from their electrons. The lithium ions move from the anode via electrolyteas medium and pass through micro-permeable separator which is in between anode and cathode until they reach the cathode, where they recombine with their electrons. The lithium ions are small enough (third only to hydrogen and helium), which translates into faster charge/discharge capabilities and high charge storage capability per unit mass and unit volume. The single cell voltage in Li-ion battery is difference in the energy between the Li+ ions that are present in the crystalline structure of the two electrodes.
Apart from three vital ingridents namely Cathode, Anode,and an electrolyte, an electronic controller, which regulates power, discharge flows, and moniters battery temperature is also an important and integral part of Lithium-Ion Battery. This incorporation of electronics takes care of special safety precautions need to be taken in order to ensure that the operating conditions of the lithium battery are kept in between the safety limits, because of the high reactivity of Lithium-Ion Batteries.
Special precautions have to be taken also in the case of shipment of Lithium-Ion Batteries
Lithium Battery Technologies
Lithium Cobalt Oxide (LCO): Lithium Cobalt Oxide (LiCoO2) is a mature battery technology, characterized by a long cycle life andhigh energy densities.The cathode consists of a cobalt oxide and anode is of graphite carbon. The cathode has a layered structure and during discharge, lithium ions move from the anode to the cathode. The flow reverses on charge. The drawback of Li-cobalt is a relatively short life span, low thermal stability and limited load capabilities (specific power).
Typical Specifications of LCO with Graphite anode
- Voltages: 3.60V nominal; typical operating range 3.0–4.2V/cell
- Specific Energy: 150–200Wh/kg. Specialty cells provide up to 240Wh/kg.
- Charge (C-rate): 0.7–1C, charges to 4.20V
- Discharge (C-rate): 1C; 2.50V cut off. Discharge above 1C shortens battery life.
- Cycle life: 500–1000, related to depth of discharge, load, temperature
- Thermal runaway: 150°C. Full charge promotes thermal runaway
- Applications: Mobile phones, tablets, laptops, cameras
- Note: Charge current above 1C shortens life of LCO battery.
Lithium Polymer (LiPo): Lithium Polymer battery is a rechargeable battery and is different from it's conterpart for reason polymer electrolyte is used instead of a liquid lithium-salt electrolyte (such as LiPF6). This electrolyte is highly conductivity semisolid (gel) polymer, which does not conduct electricity but allows exchange of ions. One of the advantages of this type batteries is simple low cost packaging cases. They are also called Solid State cells. LiPo cells are less sensitive to overcharge or damage. Solid electrolyte cells have a long life but a low discharge rate. They have a low conductivity, because of the high internal resistance.Other advantages of Lithium-ion polymer batteries are very low profile, flexible form factor, lightweight and improved safety.
These batteries provide higher specific energy than other lithium battery types and are used in applications where weight is a critical feature, like mobile devices, Lap Tops, Tablets, and radio-controlled aircraft/Drones.
Typical Specifications of LiPo Cells based on lithium-metal-oxides (such as LiCoO2)
- Voltages: 3.70V nominal; typical operating range 3.0–4.2V/cell
- Specific Energy: 100–158Wh/kg.
- Charge (C-rate): 1C (safest) to 10C, charges to 4.20V
- Discharge (C-rate): 5C to 15C; Burst C rating 80C
- Cycle life: 300-500 to reach tipping point of Swelling
- Thermal runaway: Increase in internal resistance promotes thermal runaway
- Applications: Mobile phones, tablets, laptops, cameras, drones
- Note: Robust & Flexible, but avoid Charging after abuse/swelling
Lithium Manganese (LMO): Lithium Manganese (LiMn2O4) battery cell's cathode is made out of lithium manganese oxide.It forms a three-dimensional spinel structure which improves ion flow on the electrode, which results in lower internal resistance and improved current handling, in comparsion with Cobalt based batteries. This three dimensional spinel architecture also exhibits high thermal stability and enhanced safety, but at the cost of cycle, calendar life, and energy density.Pure Li-manganese batteries are no longer commonly, they may only be used for special applications. Recent trends indicate that most Li-manganese batteries are blended with lithium nickel manganese cobalt oxide (NMC) to improve the specific energy and prolong the life span, and is popular in most Electric Vehicles.
Typical Specifications of LMO with Graphite anode
- Voltages: 3.70V (3.80V) nominal; typical operating range 3.0–4.2V/cell
- Specific Energy: 100–150Wh/kg
- Charge (C-rate): 0.7–1C typical, 3C maximum, charges to 4.20V (most cells)
- Discharge (C-rate): 1C; 10C possible with some cells, 30C pulse (5s), 2.50V cut-off
- Cycle life: 300–700 (related to depth of discharge, temperature)
- Thermal runaway: 250°C typical. High charge promotes thermal runaway
- Applications: Power tools, medical devices, electric powertrains
- Note: Safer than LCO, commonly mixed with NMC for improved performance.
Lithium Nickel Cobalt Aluminum Oxide (NCA): Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) cathode material is highly thermally stable cathode material, doping the lithium nickel cobalt oxide with aluminum both stabilizes its thermal and charge transfer resistance. NCA shares similarities with NMC in offering high specific energy, reasonably good specific power and a long life span.
High energy and power densities, as well as good life span, make NCA a candidate for EV powertrains
Typical Specifications of NCA with Graphite anode
- Voltages: 3.60V nominal; typical operating range 3.0–4.2V/cell
- Specific Energy: 200-260Wh/kg; 300Wh/kg predictable
- Charge (C-rate): 0.7C, charges to 4.20V, 3h charge typical, fast charge possible
- Discharge (C-rate): 1C typical; 3.00V cut-off; high discharge rate shortens battery life
- Cycle life: 500 (related to depth of discharge, temperature)
- Thermal runaway: 250°C typical. High charge promotes thermal runaway
- Applications: Medical devices, industrial, electric powertrain
- Note: High discharge rate of NCA shortens battery life.
Lithium Nickel Manganese Cobalt oxide (NMC): Lithium Nickel Cobalt Manganese (Li(NiCoMn)O2) batteries are made of cathode materials which is combination of nickel, manganese and cobalt, typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. Similar to Li-manganese, NMC can be tailored to serve as Energy Cells or Power Cells, like other lithium-ion battery varieties, NMC batteries can have either a high specific energy density or a high specific power. They however cannot have both properties in the same pack. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh andcan deliver 4A to 5A. NMC in the same cell size can be optimized for specific powerwith capacity of about 2000mAh, but capable of delivering a continuous discharge current of 20A.
Typical Specifications of NMC with Graphite anode
- Voltages: 3.60V, 3.70V nominal; typical operating range 3.0–4.2V/cell, or higher
- Specific Energy: 150–220Wh/kg
- Charge (C-rate): 0.7–1C, charges to 4.20V, some go to 4.30V; 3h charge typical.
- Discharge (C-rate): 1C; 2C possible on some cells; 2.50V cut-off
- Cycle life: 1000–2000 (related to depth of discharge, temperature)
- Thermal runaway: 210°C typical. High charge promotes thermal runaway
- Applications: power tools, e-bikes and other electric powertrains
- Note: Charge current above 1C shortens life of NMC.
Lihium Ion Phosphate (LFP): In Lithium Iron Phosphate (LiFePO4) Batteries phosphate is used as cathode material, Li-phosphate offers good electrochemical performance with low resistance. This nano-scale phosphate material for cathode in Lithium Ion batteries is most viable option because of its low cost,environmental friendliness, long cycle and calendar lives (chemical stability) and good capacity (170 mAh/g). Doping with transition metals results in reduction of internal impedance. LiFePO4 batteries are incombustible in case of misuse during charging ordischarging, they are more stable during overcharge or short circuit conditions and they can withstand high temperatures without decomposing.LFP is more tolerant to full charge conditions and is compartively less vunerable to stress even if kept at high voltage for a prolonged time.
Typical Specifications of LFP with Graphite anode
- Voltages: 3.20, 3.30V nominal; typical operating range 2.5–3.65V/cell
- Specific Energy: 90–120Wh/kg
- Charge (C-rate): 1C typical, charges to 3.65V; 3h charge time typical
- Discharge (C-rate): 1C, 25C on some cells; 40A pulse (2s); 2.50V cut-off
- Cycle life: 2000 and higher (related to depth of discharge, temperature)
- Thermal runaway: 270°C Very safe battery even if fully charged
- Applications: For high load currents & endurance, and electric powertrains
- Note: LFP if discharged lower than 2V can causes damage
Lithium Titanate (LTO): Lithium Titanate ((Li2TiO3)/(Li4Ti5O12)) battery is a modified Li Ion battery in which the graphite in the anode is replaced by Li-titanate which forms a spinel structure. LTO is the safest Anode Material for Lithium Ion Cells. As there is no volume changes upon charging and discharging, LTO chemistry battery exhibits maximum cyclic stability.
The cathode can be LMO or NMC 622 or LFP, or any other regular lithium battery Chemistry. Depending on selected cathode chemistry the LTO single cell voltage would range from 1.5 Vmin to 2.85 Vmax with nominal operating voltage of around 2.2V to 2.40V.
LTO can be fast charged and can deliver a high discharge current of 10C. Even the cycle life is higher than regular Li-ion batteries. LTO exhibits excellent low-temperature discharge characteristics (capacity of 80 percent at –30°C). Thermal stability underhigh temperature is comparitively better, highly tolerant to operational abuses and can comfortably perform up to 55 °C and can go up to 65 °C.
Typical Specifications of LTO (Li2TiO3)/(Li4Ti5O12) as Anode and LMO or NMC as Cathode
- Voltages: 2.2 V to 2.40V nominal; typical operating range 1.5–2.85V/cell (Cathode Chemistry dependent)
- Specific Energy: 35–90Wh/kg (Cathode Chemistry dependent)
- Charge (C-rate): 1C typical; 5C maximum, charges to 2.85V
- Discharge (C-rate): 10C possible, 30C 5s pulse.
- Cycle life: 3000 to 7000
- Thermal runaway: One of safest Li-ion batteries
- Applications: UPS, electric powertrain, solar-powered street lighting
- Note: LTO- Long life, fast charge, safest, wide temperature range but low specific energy
Note: There is nothing like best or not best in the battery technology. It totally depends upon the application, where one is planning to install the battery. The battery that is the best is the one that meets one's requirement of performance and cost. Each type of battery has its own set of pros and cons that exist because of fundamental properties of their basic material/chemistry. The Battery Chemistry is still in mode of optimization for performance, & Safety.
Factors to be considered while choosing a battery for particular application:
- Required Voltage & Capacity (including any pulse/peak current requirement)
- Required Energy Density (Volumetric & Gravimetric)
- Thermal Capability
- Safety Requirement:
- Cycle life
- Calendar life
- Toxicity
- Cost
