#Lithium ion polymer battery overview portable#

( B) Bifunctional separators for early detection of lithium dendrites. Bottom: The novel smart electrolyte with shear thickening effect under pressure or impact demonstrates excellent tolerance to crushing, which could significantly improve the mechanical safety of batteries. Top: For normal electrolyte, mechanical impact can lead to battery internal shorting, causing fires and explosions. It is well known that dendrite can be easily formed if the battery is charged (i) at high current densities where the deposition of Li metal is faster than the diffusion of Li ions in the bulk graphite ( 20, 21) (ii) under overcharging conditions when graphite is overlithiated ( 22) and (iii) at low temperatures, due to the increased viscosity of the liquid electrolyte and the increased Li-ion diffusion resistance ( 23).

In addition, the improper operation conditions of the LIBs can also result in Li metal deposition with dendrite growth. For example, in commercial LIBs, dendrite deposition occurs preferentially at graphite electrode edges if the anodes and cathodes are not well paired ( 19). Although this issue has been alleviated in the anodes of commercial LIBs (for example, carbonaceous anodes), Li dendrite formation has not been entirely inhibited. The Li dendrite formation on the anode of LIB initiates the first stage of thermal runaway. The debris penetrated the polymer separators and directly connected the cathode and anode, causing the battery to short-circuit and to catch fire ( 16) in 2016, the Samsung Note 7 battery fires were due to the aggressively ultrathin separator that was easily damaged by outside pressure or the welding burrs on the positive electrode, causing the battery to short-circuit ( 17). For example, in early October 2013, a Tesla car near Seattle hit metal debris that pierced the shield and the battery pack. Internal shorting can happen in circumstances of cell crush such as external metal debris penetration vehicle collision lithium dendrite formation under high current density charging, under overcharging conditions or at low temperatures and flawed separators created during battery assembly, to name a few. Among them, internal shorting is the predominant reason for thermal runaway and is relatively hard to control. The initial overheating can occur as a result of the battery being charged beyond the designed voltage (overcharging), exposure to excessive temperatures, external short circuits due to faulty wiring, or internal short circuits due to cell defects.

Thermal runaway starts from the overheating of the battery system.

These incidents remind us continuously that safety is a prerequisite for batteries, and serious issues need to be resolved before future applications of high-energy battery systems. For example, the Tesla electric car battery fire, the Boeing 787 Dreamliner battery problems, Samsung Note 7 fires and explosions, etc. Some have caused serious threats to human life and health and have led to numerous product recalls by manufacturers. Accidents related to fires and explosions of LIBs occur frequently worldwide, especially involving cell phones, laptops, electric vehicles, and airplanes. However, if operated improperly, chemical energy can be abruptly released in the form of fire or explosions ( 9– 15). Li-S and Li-air systems can further boost the specific energy to ~650 Wh kg −1 (2.34 MJ kg −1) and ~950 Wh kg −1 (3.42 MJ kg −1), respectively. State-of-the-art Li-ion cells can reach a specific energy of ~250 Wh kg −1 (900 kJ kg −1). Since the commercialization of LIBs in 1991 by Sony Inc., the energy density of LIBs has been aggressively increased.

#Lithium ion polymer battery overview portable#

Lithium-ion batteries (LIBs) have been widely used in electric vehicles, portable devices, grid energy storage, etc., especially during the past decades because of their high specific energy densities and stable cycling performance ( 1– 8).