聚合物自由基锂二次电池正极材料的合成与电化学性能

SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF POLYRADICAL CATHODE MATERIALS FOR LITHIUM SECONDARY BATTERIES

合成了一种聚合物自由基聚 4 甲基丙烯酸 2 ,2 ,6 ,6 四甲基哌啶 1 氮氧自由基酯 (PTMA) ,并用红外光谱 (IR)、紫外光谱 (UV)、电子顺磁共振 (ESR)等证实了PTMA的结构 .PTMA的循环伏安曲线 (扫描速度为 5mV·s- 1)显示通过阳极的氧化电量和阴极的还原电量相等且氧化峰电流等于还原峰电流 ,表明PTMA的氧化还原反应可逆性很好 .PTMA的氧化峰电位 (Ea ,p=3 6 6VversusLi Li+ )与还原峰电位 (Ec,p=3 58V)之差为 80mV ,比其它锂二次电池的有机正极材料 (如有机二硫化物 )小得多 ,因此PTMA的氧化还原反应速度比较快 .PTMA的最大放电比容量为 78 4mAh·g- 1(以 0 2C充放电 ) ,是它理论比容量 ( 111mAh·g- 1)的 70 6 % ,它的充放电曲线分别在 3 6 5V和 3 56V处有一个很平稳的平台 ,经过 10 0次充放电循环后电池的放电比容量相对于最大放电比容量只衰减了 2 % ,表明PTMA 锂扣式电池具有优良的循环稳定性 .

Poly (2,2,6,6 tetramethylpiperidinyloxymethacrylate)(PTMA) was synthesized fr om 4 hydroxy 2,2,6,6 tetramethylpiperidine and methyl methacrylate by the reaction of esterification,polymerization and oxidation,and its structure wa s determined by infrared,ultraviolet visible,and ESR spectroscopy.Cyclic volt ammograms(scan rate: 5 mV·s -1 ) of PTMA showed that the oxidation pe ak current was equal to the corresponding reduction peak current and the oxidation charge passed duri ng the anodic cycle was almost equal to the reduction charge released during the following cathodic cycle.These results suggest that PTMA possesses excellent reversibilit y,and the difference of the anodic (E a,p =3 66 V versus Li/Li +) and c athodic (E c,p =3 58 V) peak potentials is estimated as 80 mV,which is extremely smaller than that of the other electroactive organic materials in lithium secondary batteries such a s disulfide compounds,which leads to the fast electrode reaction rate of PTMA in the charging and discharging processes of the battery.The maximum discharge spe c ific capacity of PTMA is 78.4 mAh·g -1 at a constant discharge current o f 0 3 m A (0 2 C),the coulombic efficiency is about 95%.In the charging/discharging c u rves,there are obvious voltage plateaus at 3 65 V and 3 56 V,respectively.Th e charging/discharging specific capacity of the batteries was almost unchanged aft er 100 cycles,the decay ratio is about 2% of the maximum specific capacity of P TMA.PTMA/Li button batteries exhibited an excellent stability in the charging d ischarging processes.These results show that PTMA is a promising polyradical c athode materials for lithium secondary batteries.