在化学电池中，化学能直接转变为电能是靠电池内部自发进行氧化、还原等化学反应的结果，这种反应分别在两个电极上进行。负极活性物质由电位较负并在电解质中稳定的还原剂组成，如锌、镉、铅等活泼金属和氢或碳氢化合物等。

正极活性物质由电位较正并在电解质中稳定的氧化剂组成，如二氧化锰、二氧化铅、氧化镍等金属氧化物，氧或空气，卤素及其盐类，含氧酸及其盐类等。电解质则是具有良好离子导电性的材料，如酸、碱、盐的水溶液，有机或无机非水溶液、熔融盐或固体电解质等。当外电路断开时，两极之间虽然有电位差（开路电压），但没有电流，存储在电池中的化学能并不转换为电能。

当外电路闭合时，在两电极电位差的作用下即有电流流过外电路。同时在电池内部，由于电解质中不存在自由电子，电荷的传递必然伴随两极活性物质与电解质界面的氧化或还原反应，以及反应物和反应产物的物质迁移。电荷在电解质中的传递也要由离子的迁移来完成。因此，电池内部正常的电荷传递和物质传递过程是保证正常输出电能的必要条件。充电时，电池内部的传电和传质过程的方向恰与放电相反；电极反应必须是可逆的，才能保证反方向传质与传电过程的正常进行。

因此，电极反应可逆是构成蓄电池的必要条件。G为吉布斯反应自由能增量（焦）；F为法拉第常数=96500库=26.8安·小时；n为电池反应的当量数。

这是电池电动势与电池反应之间的基本热力学关系式，也是计算电池能量转换效率的基本热力学方程式。实际上，当电流流过电极时，电极电势都要偏离热力学平衡的电极电势，这种现象称为极化。电流密度（单位电极面积上通过的电流）越大，极化越严重。

极化现象是造成电池能量损失的重要原因之一、由于构成锂离子电池的电解质材料各有不同，锂离子电池也被划分为聚合物锂离子电池和液态锂离子电池两种。聚合物锂离子电池与液态锂离子电池的正负极材料相同，电池工作原理相似，而其中的电解质互不相同。聚合物锂电池轻质、储能能力强、放电性能好并且可以造成各种形状，并且寿命较长。聚合物锂电池的电解质为固态电解质，相对于液态锂离子电池的液态电解质，聚合物锂电池可以造成各种形状从而改善电池的比容量。

In a chemical battery, the direct conversion of chemical energy into electrical energy is the result of spontaneous chemical reactions such as oxidation and reduction in the battery, which are carried out on two electrodes respectively. The negative active material is composed of reducing agent with negative potential and stable in electrolyte, such as active metals such as zinc, cadmium, lead, hydrogen or hydrocarbons, etc.

The positive active substance is composed of oxidants with positive potential and stable in the electrolyte, such as manganese dioxide, lead dioxide, nickel oxide and other metal oxides, oxygen or air, halogen and its salts, oxyacid and its salts, etc. Electrolytes are materials with good ionic conductivity, such as acid, alkali, salt aqueous solution, organic or inorganic nonaqueous solution, molten salt or solid electrolyte. When the external circuit is disconnected, although there is a potential difference (open circuit voltage) between the two poles, there is no current, and the chemical energy stored in the battery is not converted into electrical energy.

When the external circuit is closed, a current flows through the external circuit under the action of the potential difference between the two electrodes. At the same time, because there are no free electrons in the electrolyte inside the battery, the transfer of charge must be accompanied by the oxidation or reduction reaction between the bipolar active substances and the electrolyte interface, as well as the migration of reactants and reaction products. The transfer of charge in the electrolyte is also completed by the migration of ions. Therefore, the normal charge transfer and material transfer process inside the battery is a necessary condition to ensure the normal output of electric energy. During charging, the direction of power and mass transfer inside the battery is just opposite to that of discharge; The electrode reaction must be reversible to ensure the normal process of reverse mass transfer and electricity transfer.

Therefore, reversibility of electrode reaction is a necessary condition to form a battery. G is the Gibbs reaction free energy increment (coke); F is Faraday constant=96500 storehouse=26.8 A · h; N is the equivalent number of battery reaction.

This is the basic thermodynamic relationship between the battery electromotive force and the battery reaction, and also the basic thermodynamic equation for calculating the energy conversion efficiency of the battery. In fact, when the current flows through the electrode, the electrode potential will deviate from the thermodynamic equilibrium electrode potential, which is called polarization. The greater the current density (the current passing through the unit electrode area), the more serious the polarization.