Lithium Ion Battery Technology
Lithium batteries are a great choice for powering electric and recreational vehicles. They also work well in emergency power backup systems.
A battery’s cathode is a carefully crafted crystal that is its most expensive component and key to supplying the correct voltage. Wang and his team have developed a recycling method that keeps the old cathode’s crucial composition intact–an important distinction from current methods.
Anode
Lithium-ion batteries provide a safe and green source of chemical energy. The lithium ions are stored in carbon electrodes which cannot generate dendritic lithium during charging and discharging, preventing short circuits within the battery pack. It can be charged and discharged repeatedly (cycles) without loss of capacity, which makes it ideal for mobile phones, laptops and hybrid electric cars.
The main drawbacks of lithium-ion batteries are low initial coulombic efficiency and fast capacity fade during cycling, which can be mitigated by using improved anode materials. Early research discovered that alloy materials, conversion-type transition metal compounds and silicon-based anodes had promising electrochemical properties but faced many challenges that limited their full performance.
Alloy anode materials experience huge volume changes during lithiation and delithiation, which leads to an unstable SEI layer, disconnecting the active material from the current collector, and eventually pulverization of the electrode [1,2].
In order to solve this problem, a group of researchers at MIT created a composite anode using graphene and silicon nanoparticles encased in ultrathin cellulose foam. This new anode is able to store Lithium Ion Battery more lithium ions than previous research, while maintaining high cyclability. The team’s patented design combines the advantages of carbon-based anodes with those of transition-metal oxides, resulting in a battery with a higher specific capacity and power density. The composite also has a wide operating temperature range, which is critical for commercial applications.
Cathode
Cathodes (positive electrodes) are currently the primary limitation to higher energy density in Li-ion batteries. They also account for a significant portion of battery cost. This is why much of the research activity in LIBs is focused on finding materials that offer a balance between performance and safety.
Traditionally, lithium cobalt oxide and lithium manganese oxide have been used as cathode materials. However, they both present downsides such as limited stability at high discharge voltages and poor cycling efficiency. Recent studies have found that the addition of sulfur or potassium doping to Li-rich layered transition metals oxides and spinel can significantly improve their cycling behavior. This enables them to preserve their high capacity throughout the charging/discharging progression.
The development of new cathode material with enhanced properties is critical for the success of lithium-ion batteries. It requires a concerted effort to advance the fundamental solid-state chemistry of these materials and the establishment of a deep understanding of the structure-composition-property relationship.
The cathode and anode active materials are synthesized into a mixture known as a slurry before being coated onto metal foils – aluminum for the anode and copper for the cathode. These are then dried in an oven to secure the coating and remove any solvents. The final anode and cathode foils are then cut to size to assemble into the cell.
Electrolyte
The electrolyte is what ferries lithium ions back and forth between the cathode and anode. The electrolyte’s chemical structure, conductivity and interactions with the electrodes determine battery performance. The electrolyte is a critical part 24V Lithium Iron Phosphate Battery of the battery, and if it fails to meet stringent conditions can cause dangerous side reactions.
The chemistry of the electrolyte is complex and varies by manufacturer and model. It is usually a liquid solution of lithium salts and organic solvents such as ethylene carbonate. The salts are often mixed with different types of carbonates to improve conductivity and expand the temperature range where the battery can operate. Other additives can be used to reduce gassing or improve high-temperature cycling. These are typically kept proprietary to prevent the discovery of the chemical composition and quantity used in a battery.
During charging, lithium ions move from the positive to the negative electrode. This is followed by the formation of a solid electrolyte interface (SEI) layer. The SEI is comprised of an outer and inner layer of lithium ions, as well as organic species such as acetone and toluene.
The ohmic internal resistance of the battery – which is the sum of the redox internal resistance of the anode and cathode and the electrode/electrolyte interface resistance – is determined by the chemistry of the SEI. The more complex the redox couple and the higher the voltage of the battery, the greater the internal resistance.
Battery Management System
The Battery Management System (BMS) built into lithium batteries monitors a number of aspects of the battery and is vital for its performance. For instance, it limits the peak voltage of each cell during charge as too much voltage can damage the cells. It also prevents the battery from discharging too low on discharge as this can damage the cells too. The BMS also protects the batteries from temperature extremes, opening and closing valves to maintain a safe temperature range.
The BMS also monitors the state of the battery by estimating its SOC based on current measurements. This enables it to predict when the battery will reach its current limit during charging or discharging and then shut off the process. The BMS can also detect overvoltage or undervoltage, preventing it by limiting the charging current or stopping the charge altogether.
In addition to these safety features, the BMS can monitor cell balancing, ensuring that all of the battery cells are equally charged. This is important for the overall performance of a battery pack as well as for minimizing memory effects and prolonging battery lifespan. A good BMS should also be able to respond quickly to changes in load conditions, with a latency time of just 10 microseconds. This is particularly important when dealing with a vehicle or any other application that requires a high level of response to sudden power demands.