Research on working principle and characteristics of new energy lithium ion battery

With the development of the global economy, the pollution of environment and energy has become more and more serious, and the environmental crisis that has erupted has become more and more obvious. The global temperature has increased year by year, and the problem of smog is also very serious. In order to reduce unnecessary fuel pollution, the state is vigorously developing sustainable energy. With the strengthening of people's environmental awareness, lithium-ion batteries, as new energy sources, have been widely welcomed as soon as they are launched. Lithium-ion batteries have become a research hotspot in the field of new energy battery applications due to their high energy density, long cycle life, no memory effect and environmental friendliness.

The working principle of lithium-ion batteries

Lithium battery refers to a secondary battery comprising two reversibly intercalated and deintercalated lithium ion compounds as positive and negative electrodes. Lithium-ion batteries have different names according to the cathode material, anode material and electrolyte, but their working principles are similar. As shown in Figure 1. A lithium ion battery is actually a lithium ion concentration battery.

The lithium battery is mainly composed of positive electrode plate, negative electrode plate, electrolyte, separator and outer shell. The active material on the positive electrode plate is generally selected from Li_xCoO₂, Li_xNiO₂ or Li_xMn₂O₄, and the active material on the negative electrode plate is generally selected from the lithium carbon interlayer The electrolyte is a mixed solvent system of an alkyl carbonate such as ethylene carbonate (EC), propylene carbonate (PC) and low viscosity diethyl carbonate (DEC) of LiPF₆ and LiAsF₂. The separator is made of a polyene microporous membrane PE, PP or their composite membrane. The outer shell is made of steel or aluminum. When the battery is charged, lithium ions are deintercalated from the positive electrode and embedded in the negative electrode. When the battery is discharged, lithium ions are deintercalated from the negative electrode and embedded in the positive electrode.

Under normal charge and discharge conditions, lithium ions are intercalated and detached between the layers of the carbon material and the layered oxide, generally causing only a change in the layer spacing, like a rocking chair, so lithium ion battery is also called as "rocking chair battery". The electrode reactions of lithium ion batteries are as follows:

Reactions on positive electrode：

LiMO₂→Li_1-xMO₂+xLi⁺+xe (1)

Reactions on negative electrode：

nC+xLi⁺ +xe→Li_xC_n (2)

in total：

LiMO₂+nC→Li_1-xMO₂+ Li_xC_n (3)

Where M is metal element selected from Co、Ni、W、Mn, etal.

The characteristics of Lithium-ion battery

The main characteristics of the lithium-ion battery are:

(1) High specific energy, the weight specific energy and volume specific energy of lithium-ion battery are 120~200 W•h/kg and 300 W•h/L respectively, which is the highest in the current battery.

(2) discharge voltage is high, the discharge voltage platform is generally above 3.2~4.2V (except lithium titanate battery);

(3) self-discharge is low, under normal storage conditions, the monthly self-discharge rate of lithium-ion battery is usually only ~5%

(4) long cycle life and no memory effect. Ordinary lithium secondary battery at 100% depth of discharge (DOD), charge and discharge is up to 500 times, The cycle life of battery with lithium iron phosphate battery and lithium titanate as the negative exceeds 2000 times and 5000 times respectively;

(5) the charging and discharging efficiency is high, the energy conversion efficiency during charging and discharging can reach more than 90%;

(6) the working temperature range is wide, and the general working range is −20~45°C. The lithium titanate negative battery can work even at −40°C.