富锂镍酸锂(Li_(2)NiO_(2))作为预锂化剂对活性炭//硬碳型锂离子电容器电化学性能的影响

Influence of lithium-rich nickel oxide(Li_(2)NiO_(2))as pre-lithiation agent on electrochemical performances of activated carbon//hard carbon lithium ion capacitor

锂离子电容器(LIC)兼具大容量、高功率、长循环和宽温度特性,但在规模化制备中受限于预锂化这一“卡脖子”难题,导致应用推广受限。相较于负极预锂化,正极预锂化具有操作简便、产线适配性强、工艺成本低等优势。Li_(2)NiO_(2)(LNO)作为一种典型的正极预锂化剂具有储锂容量高、首次效率低、不可逆容量大、释放锂离子后相对稳定的特性,受到广泛关注。本文组装了以活性炭(AC)为正极、硬碳(HC)为负极的LIC,系统研究了正极活性材料组分中LNO的添加量(质量分数为0%,2%,5%,10%,分别命名为AC-Li0、AC-Li2、AC-Li5、AC-Li10)对LIC电化学性能的影响,发现添加量为10%时器件综合性能最佳。同AC-Li0相比,AC-Li10的循环伏安(CV)和恒流充放电曲线均呈现近似EDLC的容性行为,界面阻抗明显减小,高低温性能得以改善,在-40℃超低温环境仍具备10C放电能力,循环10000次(2.0~3.8 V)后容量保持率高达96.3%。此外,LNO的引入使得AC-Li10的额定电压可从3.8 V提升到4.0 V,器件在2.0~4.0 V测得的最大能量密度为61.21 Wh·kg^(-1),在最大功率密度20575.13 W·kg^(-1)下测得的能量密度为16.34 Wh·kg^(-1),优于商业化LIC。在LIC正极制浆过程中直接添加LNO作预锂化剂,能够显著改善器件的电化学性能并降低制程工艺成本,具有重要的科研和实用价值。

Lithium ion capacitor(LIC)possesses the characteristics of high capacity,high power,long cycle and wide temperature adaptability,but is limited by the bottleneck problem of pre-lithiation technology in large-scale preparation,which leads to restricted application potential.Compared with the negative pre-lithiation,the positive pre-lithiation has the advantages of simple operation,strong production adaptability and low process cost.Li_(2)NiO_(2)(LNO),as a representative positive pre-lithiation agent,attracts widespread attention due to the features of high lithium storage capacity,low initial efficiency,large irreversible capacity and relative stability after releasing lithium ions.Here in this paper,the LIC pouch cell was assembled with an activated carbon(AC)cathode and a hard carbon(HC)anode,the effect of LNO addition in the positive components(LNO accounts for 0,2%,5%,10% by mass fraction,samples correspondingly named as AC-Li0,AC-Li2,AC-Li5 and AC-Li10)on the electrochemical performances of LIC was systematically investigated.Specially,10% addition of LNO was proven to be the optimal amount.Compared with AC-Li0,the cyclic voltammetry(CV)and constant-current charging-discharging curves of AC-Li10 showed the capacitive behaviors similar to those of EDLCs.ACLi10 also had the lower interface impedance and possessed better high and low temperature adaptability.Even in the ultra-low temperature of-40℃,AC-Li10 still maintained the discharge capability at the rate of 10C.The capacity retention of 96.3% after 10000 cycles(2.0-3.8 V)reflected the good electrochemical stability of AC-Li10.In addition,the introduction of LNO broadened the voltage window from 3.8 V to 4.0 V of the LIC.For AC-Li10,the maximum energy density between 2.0 V and 4.0 V was 61.21 Wh·kg^(-1) at the power density of 51.26 W·kg^(-1),and still maintained 16.34 Wh·kg^(-1) at the maximum power density of 20575.13 W·kg^(-1),revealing the superior performances compared to the commercial lithium-ion capacitors.The direct addition of LNO pre-lithiation agent in the slurry process for LIC cathode plate production can significantly improve the electrochemical performances of the device and simultaneously reduce the production cost,which has important scientific research and practical value.