Battery Knowledge

A battery is a common device of energy storage that uses a chemical reaction to transform chemical energy into electric energy. It is composed of tiny individual electrochemical cells. Batteries are typically classified into primary batteries and secondary batteries, according to the structure of electrochemical cells they hold. Primary batteries are disposable and nonchargeable, which can only convert chemical energy into electrical energy at one time, and can not restore electrical energy back to chemical energy, such as lithium manganese dioxide primary battery and lithium thionyl chloride primary battery. Rechargeable batteries are called secondary batteries. They can convert electric energy into chemical energy for storage, and then convert chemical energy into electric energy when in use. They are reversible, such as lithium ion, nickel metal hydride, nickel cadmium and lead acid batteries.

Lithium ion(li-ion) batteries are a form of rechargeable battery made up of an electrochemical cell, in which the lithium ions move from the anode through the electrolyte and towards the cathode during discharge and then in reverse direction during charging. Due to their high energy density, long cycle life, high open-circuit voltage, and low self-discharge rate, lithium ion batteries have now been conclusively shown to be the finest secondary batteries available. Lithium polymer(li-po, li-polymer, li-ion polymer, pouch) batteries are based on lithium ion technology with a polymer electrolyte instead of a liquid electrolyte, which is the primary difference between lithium ion and lithium polymer. Lithium polymer batteries provide higher specific energies than other lithium batteries.

Composition of Lithium Ion Batteries

A lithium ion battery is made of some components with one or more cells together. The basic structure comprises:

Cathode: positive electrode made up of lithium metal oxide as the cathode on aluminum foil.

Anode: negative electrode made up of carbon as the anode on copper foil.

Electrolyte: lithium salt in organic solvent.

Separator: made up of polyethylene or propylene.

During charging, the Li ion moves from the cathode to the anode through the electrolyte and electrons through the external circuit. Thus, the external power is used to store energy chemically. During energy utilization, i.e. discharging, the electrons move from the anode to cathode through the external circuit and at the same time the Li ions move back to the cathode via the electrolyte. Thus, lithium ion batteries are rechargeable due to the ease with which lithium ions and electrons can be transferred back into negative electrodes. A separator is used to avoid direct contact of the electrodes and only allows the working ion to freely pass through it.

The positive electrode, i.e. cathode, is typically made from a chemical compound called layered lithium metal oxide, for example: lithium–cobalt oxide (LiCoO2), and the negative electrode, i.e. anode, is generally made from carbon/graphite compounds.

The cathode material that stores lithium ions via electrochemical intercalation must contain suitable lattice sites to store and release ions reversibly, hence material with layered structures may offer stable cyclability and high specific capacity. In addition to this, differential electrochemical potential between the cathode and anode is necessary to obtain a high energy density battery with a given anode. The role of the electrolyte is to act as a medium for the transfer of ions between the two electrodes and to block the electrons.

Charging and Discharging Process

During charging, the positive electrode gives up some of its lithium ions, which move through the electrolyte towards the negative, carbon/graphite electrode and remain there. Electrons also flow from the positive electrode to the negative electrode through the external circuit. The electrons and ions combine at the negative electrode and deposit lithium there. Once the moment of most of the ions takes place, decided by the capacity of the electrode, the battery is said to be fully charged and ready to use. When the battery is discharging, the lithium ions move back across the electrolyte to the positive electrode from the carbon/graphite, producing the energy that powers the battery. In both cases, electrons flow in the opposite direction to the ions around the external circuit. Electrons do not flow through the electrolyte: it is effectively an insulating barrier, so far as electrons are concerned.

Types of Lithium Ion Batteries

The cathode is made of a composite material (an intercalated lithium compound) and defines the name of the li-ion battery cell. There are two kinds of electrodes: intercalation and conversion electrodes. The intercalation electrodes are materials that function as host materials where lithium ions can intercalate. A typical example is LiCoO2 and its derivatives. Conversion-type cathode materials are some of the key candidates for the next generation of rechargeable lithium and li-ion batteries. One of the most common lithium batteries is:

Lithium Cobalt Oxide (LiCoO2). LiCoO2 is the most commonly used cathode material. LiCoO2 batteries have very stable capacities, although their capacities are lower than those based on nickel-cobalt-aluminum (NCA) oxides. However, cobalt is relatively expensive compared to other transition metals, such as manganese and iron, despite the attractive electrical properties of LiCoO2 cathodes. Currently, we can find this type of battery in mobile phones, tablets, laptops, and cameras.

Lithium Manganese Oxide (LiMn2O4). LiMn2O4 is a promising cathode material with a cubic spinel structure. LiMn2O4 is one of the most studied manganese oxide-based cathodes because it contains inexpensive materials. A further advantage of this battery is enhanced safety and high thermal stability, but the cycle and calendar life is limited. This type of battery is found in power tools, medical devices, and powertrains.

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2/NMC). Nickel manganese cobalt (NMC) batteries contain a cathode made of a combination of nickel, manganese, and cobalt. NMC is one of the most successful cathode combinations in lithium ion systems. It can be tailored to serve as energy cells or power cells like Li-manganese. NMC batteries are used for power tools, e-bikes, and other electric powertrains.

Lithium Iron Phosphate (LiFePO4/LFP). LiFePO4 is one of the most recent cathode materials to be introduced. 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. The energy density of a LFP battery is lower than that of other common lithium ion battery types, such as Nickel Manganese Cobalt (NMC). Because of their lower cost, high safety, low toxicity, long cycle life, and other factors, LFP batteries are finding a number of roles in vehicle use, utility-scale stationary applications, and backup power. Working voltage 3.0 ~ 3.6V. Cycle life ranges from 2,700 to more than 10,000 cycles depending on conditions.

Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2/NCA). In 1999, Lithium nickel cobalt aluminum oxide battery, or NCA, appeared in some special applications, and it is similar to the NMC. It offers high specific energy, a long life span, and a reasonably good specific power. NCA’s usable charge storage capacity is about 180 to 200 mAh/g. The capacity of NCA is significantly higher than that of alternative materials such as LiCoO2 with 148 mAh/g, LiFePO4 with 165 mAh/g, and NMC 333 (LiNi0,33Mn0,33Co0,33O2)with 170 mAh/g. The voltage of these batteries is between 3.6 V and 4.0 V, at a nominal voltage of 3.6 V or 3.7 V. Another advantage of NCA is its excellent fast charging capability. Nevertheless, its weak points are the limited resources of cobalt and nickel and the high cost.

Lithium ion cells are available in various shapes, which can generally be divided into three groups:

Cylindrical cells with solid bodies without terminals, such as those used in older laptop batteries. Cells with a cylindrical shape are made in a characteristic “jelly roll” manner, which means it is a single long “sandwich” of the positive electrode, separator, negative electrode, and separator rolled into a single spool. One advantage of cylindrical cells compared to cells with stacked electrodes is the faster production speed. One disadvantage of cylindrical cells can be a large radial temperature gradient inside the cells developing at high discharge currents.

Flat or pouch cells with a soft, flat body, such as those used in cell phones and newer laptops; are lithium polymer batteries. Pouch cells do not have a rigid enclosure and use a sealed flexible foil as the cell container. This is a somewhat minimalistic approach to packaging; it reduces weight and leads to flexible cells that can easily fit the available space of a given product. For pouch batteries, the absence of a case gives pouch cells the highest gravimetric energy density. These batteries are increasingly popular with smartphone manufacturers. Their soft, lightweight design also offers more safety measures than hard metal casings. When a critical issue with a pouch cell occurs – often due to internal pressure overheating or shortening the batteries – the pack will noticeably expand with gas.

Prismatic cells with rigid plastic case. Lithium ion (li-ion) battery prismatic cells are thinner and lighter than cylindrical cells. These cells, coming in rectangular aluminum or steel casing, have fairly long lifespans but aren’t as easy to keep cool compared to their cylindrical counterparts.

Advantages of Lithium Ion Batteries

Lithium ion batteries has quickly become popular in modern technology, due to their high energy density, light weight and ability to hold a charge for long periods of time. The following are some of the main advantages of lithium ion batteries:

High energy density. Lithium ion batteries have high energy densities, meaning they can store more energy for a given weight and size compared to other types of rechargeable batteries. This makes them especially suitable for portable electronics applications. They have an impressive energy density of between 150 to 200 Wh/kg, which is up to four times greater than lead acid batteries and five times greater than NiCd (Nickel Cadmium) and NiMH (Nickel Metal Hydride) batteries. Lithium-ion cells also deliver a good cycle life and retain 85-90% of initial capacity over 500 charge cycles or more. This is much longer than alternative chemistries such as lead acid or nickel-cadmium that are known to need frequent replacement due to their significantly shorter lifespans.

Low self-discharge rate. One of the most attractive features of lithium ion batteries is their low self-discharge rate. In comparison to other rechargeable battery chemistries, lithium ion cells lose charge at a much slower rate. This means that they don’t need to be recharged as often and will provide long periods of responsive performance and consistent charge retention. The low self-discharge rate also makes them well-suited for applications where standby power might be needed, such as in security systems and medical instruments.

No memory effect. When using ni-mh or ni-cd batteries, a phenomenon known as “memory effect” occurs where the battery develops a decreased capacity to retain a charge when not fully discharged before recharging. Lithium ion batteries, on the other hand, do not suffer from this issue which allows for the battery to consistently discharge and recharge without losing its optimal performance. Since lithium ion batteries do not experience memory depletion, there is much less wastage than what is expected with other battery technologies. This means that you can be sure you will get maximum performance each and every time.

Load characteristics. Lithium ion batteries have a high operating voltage of 3-5 volts, depending on the specific chemistry. This allows for an equivalent power operation at a lower current draw, and the battery will last longer on a single charge. The load characteristics of a lithium ion battery are reasonably good, providing a reasonably constant 3.6 volts per cell before falling off as the last charge is used.

Disadvantages of Lithium Ion Batteries

There are several specific drawbacks associated with lithium ion battery technology.

Possible safety risks when cells are mishandled incorrectly such as short circuit due to high voltages involved. Good understanding of usage requirements such as charging procedure, charging voltage cutoff points etc is essential for safe use. A battery management system is required. Lithium ion batteries use protection circuilt modules to ensure over-charge, over-discharge, over current and over heat protection.

More easily affected by external temperatures which can reduce performance and lifespan. A thermal management system is required. Batteries generate heat when being charged or discharged, especially at high currents. Large battery packs, such as those used in electric vehicles, are generally equipped with thermal management systems that maintain a right temperature range.

Higher cost compared to other battery types. Typically they are around more costly to manufacture than NiMH cells.

Applications of Lithium Ion Batteries

Lithium ion batteries are particularly popular and effective in consumer electronics, such as mobile phones, wearables, bluetooth due to their high specific energy. However, they are also increasingly used in other applications such as renewable energy storage, backup power, electric vehicles, specialist industrial and medical equipments, power tools and even jet engines.