Week 1 Understanding Different Battery Chemistry
1.Prepare a table which includes materials & chemical reactions occurring at the anode and cathode of LCO, LMO, NCA, NMC, LFP and LTO type of lithium ion cells.Give your detailed explanation on it
2.Compare the differences between each type of Li+ion batteries based on their characteristics
Answer:-
A lithium-ion battery or Li-ion battery is a type of rechargeable battery composed of cells in which lithium ions move from the negative electrode through an electrolyte to the positive electrode during discharge and back when charging. Li-ion cells use an intercalated lithium compound as the material at the positive electrode and typically graphite at the negative electrode. Li-ion batteries have a high energy density, no memory effect (other than LFP cells) and low self-discharge. Cells can be manufactured to prioritize either energy or power density. They can however be a safety hazard since they contain flammable electrolytes and if damaged or incorrectly charged can lead to explosions and fires.
M. Stanley Whittingham discovered the concept of intercalation electrodes in the 1970s, and invented the first rechargeable lithium-ion battery, which was based on a titanium disulfide cathode and a lithium-aluminum anode, patented in 1977, and assigned to Exxon.John Goodenough expanded on this work in 1980 by using lithium cobalt oxide as a cathode. A prototype Li-ion battery was developed by Akira Yoshino in 1985, based on the earlier research by John Goodenough, M. Stanley Whittingham, Rachid Yazami and Koichi Mizushima during the 1970s–1980s, and then a commercial Li-ion battery was developed by a Sony and Asahi Kasei team led by Yoshio Nishi in 1991.Lithium-ion batteries are commonly used for portable electronics and electric vehicles and are growing in popularity for military and aerospace applications.
Research on rechargeable Li-ion batteries dates to the 1960s; one of the earliest examples is a CuF2/Li battery developed by NASA in 1965. The breakthrough that produced the earliest form of the modern Li-ion battery was made by British chemist M. Stanley Whittingham in 1974, who first used titanium disulfide (TiS2) as a cathode material, which has a layered structure that can take in lithium ions without significant changes to its crystal structure. Exxon tried to commercialize this battery in the late 1970s, but found the synthesis expensive and complex, as TiS2 is sensitive to moisture and releases toxic H2S gas on contact with water. More prohibitively, the batteries were also prone to spontaneously catch fire due to the presence of metallic lithium in the cells.
In 1980 working in separate groups Ned A. Godshall et al., and, shortly thereafter, Koichi Mizushima and John B. Goodenough, after testing a range of alternative materials, replaced TiS2 with lithium cobalt oxide (LiCoO2, or LCO), which has a similar layered structure but offers a higher voltage and is much more stable in air. This material would later be used in the first commercial Li-ion battery, although it did not, on its own, resolve the persistent issue of flammability. The same year, Rachid Yazami demonstrated the reversible electrochemical intercalation of lithium in graphite, and invented the lithium graphite electrode (anode).
Types Of Lithium Ions Batteries:-
Electrochemistry:-
The reactants in the electrochemical reactions in a lithium-ion cell are materials of anode and cathode, both of which are compounds containing lithium atoms. During discharge, an oxidation half-reaction at the anode produces positively charged lithium ions and negatively charged electrons. The oxidation half-reaction may also produce uncharged material that remains at the anode. Lithium ions move through the electrolyte, electrons move through the external circuit, and then they recombine at the cathode (together with the cathode material) in a reduction half-reaction. The electrolyte and external circuit provide conductive media for lithium ions and electrons, respectively, but do not partake in the electrochemical reaction. During discharge, electrons flow from the negative electrode (anode) towards the positive electrode (cathode) through the external circuit. The reactions during discharge lower the chemical potential of the cell, so discharging transfers energy from the cell to wherever the electric current dissipates its energy, mostly in the external circuit. During charging these reactions and transports go in the opposite direction: electrons move from the positive electrode to the negative electrode through the external circuit. To charge the cell the external circuit has to provide electric energy. This energy is then stored as chemical energy in the cell (with some loss, e. g. due to coulombic efficiency lower than 1).
Both electrodes allow lithium ions to move in and out of their structures with a process called insertion (intercalation) or extraction (deintercalation), respectively.
Battery types with chemical reaction difference:-
As the lithium ions "rock" back and forth between the two electrodes, these batteries are also known as "rocking-chair batteries" or "swing batteries" (a term given by some European industries).
The following equations exemplify the chemistry.
The positive electrode (cathode) half-reaction in the lithium-doped cobalt oxide substrate is
- {\displaystyle {\ce {CoO2 + Li+ + e- <=> LiCoO2}}}
The negative electrode (anode) half-reaction for the graphite is
- {\displaystyle {\ce {LiC6 <=> C6 + Li+ + e^-}}}
The full reaction (left to right: discharging, right to left: charging) being
- {\displaystyle {\ce {LiC6 + CoO2 <=> C6 + LiCoO2}}}
The overall reaction has its limits. Overdischarging supersaturates lithium cobalt oxide, leading to the production of lithium oxide, possibly by the following irreversible reaction:
- {\displaystyle {\ce {Li+ + e^- + LiCoO2 -> Li2O + CoO}}}
Overcharging up to 5.2 volts leads to the synthesis of cobalt (IV) oxide, as evidenced by x-ray diffraction:[53]
- {\displaystyle {\ce {LiCoO2 -> Li+ + CoO2 + e^-}}}
In a lithium-ion cell, the lithium ions are transported to and from the positive or negative electrodes by oxidizing the transition metal, cobalt (Co), in Li1-xCoO
2 from Co3+ to Co4+
during charge, and reducing from Co4+to Co3+
during discharge. The cobalt electrode reaction is only reversible for x < 0.5 (x in mole units), limiting the depth of discharge allowable. This chemistry was used in the Li-ion cells developed by Sony in 1990.
The cell's energy is equal to the voltage times the charge. Each gram of lithium represents Faraday's constant/6.941, or 13,901 coulombs. At 3 V, this gives 41.7 kJ per gram of lithium, or 11.6 kWh per kilogram of lithium. This is a bit more than the heat of combustion of gasoline but does not consider the other materials that go into a lithium battery and that make lithium batteries many times heavier per unit of energy.
The cell voltages given in the Electrochemistry section are larger than the potential at which aqueous solutions will electrolyze.
Liquid electrolytes in lithium-ion batteries consist of lithium salts, such as LiPF6, LiBF4 or LiClO4 in an organic solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. A liquid electrolyte acts as a conductive pathway for the movement of cations passing from the negative to the positive electrodes during discharge. Typical conductivities of liquid electrolyte at room temperature (20 °C (68 °F)) are in the range of 10 mS/cm, increasing by approximately 30–40% at 40 °C (104 °F) and decreasing slightly at 0 °C (32 °F). The combination of linear and cyclic carbonates (e.g., ethylene carbonate (EC) and dimethyl carbonate (DMC)) offers high conductivity and solid electrolyte interphase (SEI)-forming ability. Organic solvents easily decompose on the negative electrodes during charge. When appropriate organic solvents are used as the electrolyte, the solvent decomposes on initial charging and forms a solid layer called the solid electrolyte interphase, which is electrically insulating, yet provides significant ionic conductivity. The interphase prevents further decomposition of the electrolyte after the second charge. For example, ethylene carbonate is decomposed at a relatively high voltage, 0.7 V vs. lithium, and forms a dense and stable interface. Composite electrolytes based on POE (poly(oxyethylene)) provide a relatively stable interface. It can be either solid (high molecular weight) and be applied in dry Li-polymer cells, or liquid (low molecular weight) and be applied in regular Li-ion cells. Room-temperature ionic liquids (RTILs) are another approach to limiting the flammability and volatility of organic electrolytes.
Recent advances in battery technology involve using a solid as the electrolyte material. The most promising of these are ceramics. Solid ceramic electrolytes are mostly lithium metal oxides, which allow lithium-ion transport through the solid more readily due to the intrinsic lithium. The main benefit of solid electrolytes is that there is no risk of leaks, which is a serious safety issue for batteries with liquid electrolytes.] Solid ceramic electrolytes can be further broken down into two main categories: ceramic and glassy. Ceramic solid electrolytes are highly ordered compounds with crystal structures that usually have ion transport channels. Common ceramic electrolytes are lithium super ion conductors (LISICON) and perovskites. Glassy solid electrolytes are amorphous atomic structures made up of similar elements to ceramic solid electrolytes but have higher conductivities overall due to higher conductivity at grain boundaries. Both glassy and ceramic electrolytes can be made more ionically conductive by substituting sulfur for oxygen. The larger radius of sulfur and its higher ability to be polarized allow higher conductivity of lithium. This contributes to conductivities of solid electrolytes are nearing parity with their liquid counterparts, with most on the order of 0.1 mS/cm and the best at 10 mS/cm. An efficient and economic way to tune targeted electrolytes properties is by adding a third component in small concentrations, known as an additive. By adding the additive in small amounts, the bulk properties of the electrolyte system will not be affected whilst the targeted property can be significantly improved. The numerous additives that have been tested can be divided into the following three distinct categories: (1) those used for SEI chemistry modifications; (2) those used for enhancing the ion conduction properties; (3) those used for improving the safety of the cell (e.g. prevent overcharging).
Details explanation about Anode & Cathode And types of lithium ions batteries:-
Charging and discharging:-
During discharge, lithium ions (Li+
) carry the current within the battery cell from the negative to the positive electrode, through the non-aqueous electrolyte and separator diaphragm.
During charging, an external electrical power source (the charging circuit) applies an over-voltage (a higher voltage than the battery produces, of the same polarity), forcing a charging current to flow within each cell from the positive to the negative electrode, i.e., in the reverse direction of a discharge current under normal conditions. The lithium ions then migrate from the positive to the negative electrode, where they become embedded in the porous electrode material in a process known as intercalation.
Energy losses arising from electrical contact resistance at interfaces between electrode layers and at contacts with current collectors can be as high as 20% of the entire energy flow of batteries under typical operating conditions.
The charging procedures for single Li-ion cells, and complete Li-ion batteries, are slightly different:
- A single Li-ion cell is charged in two stages:
- Constant current (CC).
- Constant voltage (CV).
- A Li-ion battery (a set of Li-ion cells in series) is charged in three stages:
- Constant current.
- Balance (not required once a battery is balanced).
- Constant voltage.
During the constant current phase, the charger applies a constant current to the battery at a steadily increasing voltage, until the voltage limit per cell is reached.
During the balance phase, the charger reduces the charging current (or cycles the charging on and off to reduce the average current) while the state of charge of individual cells is brought to the same level by a balancing circuit, until the battery is balanced. Some fast chargers skip this stage. Some chargers accomplish the balance by charging each cell independently.
During the constant voltage phase, the charger applies a voltage equal to the maximum cell voltage times the number of cells in series to the battery, as the current gradually declines towards 0, until the current is below a set threshold of about 3% of initial constant charge current.
Periodic topping charge about once per 500 hours. Top charging is recommended to be initiated when voltage goes below 4.05 V/cell.
Cathode:-
Cathode materials are generally constructed from LiCoO2 or LiMn2O4. The cobalt-based material develops a pseudo tetrahedral structure that allows for two-dimensional lithium-ion diffusion. The cobalt-based cathodes are ideal due to their high theoretical specific heat capacity, high volumetric capacity, low self-discharge, high discharge voltage, and good cycling performance. Limitations include the high cost of the material, and low thermal stability. The manganese-based materials adopt a cubic crystal lattice system, which allows for three-dimensional lithium-ion diffusion. Manganese cathodes are attractive because manganese is cheaper and because it could theoretically be used to make a more efficient, longer-lasting battery if its limitations could be overcome. Limitations include the tendency for manganese to dissolve into the electrolyte during cycling leading to poor cycling stability for the cathode. Cobalt-based cathodes are the most common, however other materials are being researched with the goal of lowering costs and improving cell life.As of 2017, LiFePO4 is a candidate for large-scale production of lithium-ion batteries such as electric vehicle applications due to its low cost, excellent safety, and high cycle durability. For example, Sony Fortelion batteries have retained 74% of their capacity after 8000 cycles with 100% discharge. A carbon conductive agent is required to overcome its low electrical conductivity.
Anode-
Negative electrode materials are traditionally constructed from graphite and other carbon materials, although newer silicon-based materials are being increasingly used (see Nanowire battery). These materials are used because they are abundant and are electrically conducting and can intercalate lithium ions to store electrical charge with modest volume expansion (~10%). Graphite is the dominant material because of its low voltage and excellent performance. Various materials have been introduced, but their higher voltage reduces low energy density. Low voltage is the key requirement; otherwise, the excess capacity is useless in terms of energy density.
As graphite is limited to a maximum capacity of 372 mAh/g much research has been dedicated to the development of materials that exhibit higher theoretical capacities, and overcoming the technical challenges that presently encumber their implementation. The extensive 2007 Review Article by Kasavajjula et al. summarizes early research on silicon-based anodes for lithium-ion secondary cells. In particular, Hong Li et al. showed in 2000 that the electrochemical insertion of lithium ions in silicon nanoparticles and silicon nanowires leads to the formation of an amorphous Li-Si alloy. The same year, Bo Gao and his doctoral advisor, Professor Otto Zhou described the cycling of electrochemical cells with anodes comprising silicon nanowires, with a reversible capacity ranging from at least approximately 900 to 1500 mAh/g.
To improve stability of the lithium anode, several approaches of installing a protective layer have been suggested.Silicon is beginning to be looked at as an anode material because it can accommodate significantly more lithium ions, storing up to 10 times the electric charge, however this alloying between lithium and silicon results in significant volume expansion (ca. 400%), which causes catastrophic failure for the cell. Silicon has been used as an anode material but the insertion and extraction of {\displaystyle {\ce {\scriptstyle Li+}}}
can create cracks in the material. These cracks expose the Si surface to an electrolyte, causing decomposition and the formation of a solid electrolyte interphase (SEI) on the new Si surface (crumpled graphene encapsulated Si nanoparticles). This SEI will continue to grow thicker, deplete the available {\displaystyle {\ce {\scriptstyle Li+}}}, and degrade the capacity and cycling stability of the anode.
Difference Between Lithium ions battery type regarding material and other specification and application:-
Characteristics based difference:-
Cycle no Vs Depth of Discharge Performnace char.:-
Conclusion:-
Understand the Different battery types its material,characteristics,benefits in Electric vehicle.
References:-
Google,
Video No 3,4,5,6
You tube etc.
| Content and types | LFP | NMC | LMO | NCA | LCO |