Construction And Electrochemical Performance Study For Carbon-Based Metal-Ion Capacitors With High Energy/Power Density

In order to quickly achieve national goals of the peak carbon emission and carbon neutrality,it is urgent to realize the structural transformation of energy systems and exploit the new clean and renewable energy technologies.Nowadays,limited by energy storage mechanism,metal ion batteries（MIBs）and supercapacitors（SCs）have been encountered with the issues of low power density and insufficient energy density,respectively.Therefore,developing a new energy storage system with high energy/power densities and long cycle life is the vital support to realize the peak carbon emission and carbon neutrality,which possesses importantly strategic significances.Generally,carbon-based metal ion capacitors（MICs）are mainly composed of battery-type carbon anode and capacitor-type carbon cathode.Benefited from the ingenious combination of two different energy storage mechanisms,carbon-based MICs can still maintain high energy density characteristics under large power density.However,construction of advanced carbon-based MICs is mainly limited by key bottlenecks such as the sluggish kinetics of battery-type carbon anode,unclear storage mechanism of capacitor-type carbon cathode,and uncontrollable pre-metallation technology.Focusing on these problems,boosting the sodium storage kinetics of carbon anode,analyzing the capacitive storage mechanism of carbon cathode and exploiting new pre-metallation technology have been studied in this thesis for the construction of advanced carbon-based MIC.The main contents have been summarized as following:（1）In terms of the the kinetic mismatching between battery-type carbon anode and capacitor-type carbon cathode,it is demonstrated that establishiong a pseudocapacitance approach can effectively improve the sodium storage kinetics of battery carbon anode.Designed by the nanoconfined self-activation strategy,three-dimensional nitrogen-doped hierarchical porous carbons（NHPCs）exhibit the enlarged interlayer distance,nitrogen doping,unique morphology and suitable porous structure.Moreover,the obtained NHPC-800 anode with prominent pseudocapacitive feature,delivering the relatively high initial coulombic efficiency of 73.2%and a large reversible specific capacity of 197 m Ah g^-1 at 2 A g^-1,respectively.Triggered by the faster kinetic of anode and outstanding electrochemical performances of electrodes,the assembled carbon-based sodium-ion capacitor can achieve a great energy density of115 Wh kg^-1 at 200 W kg^-1 as well as excellent long-term cyclability.（2）At present,the lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors,limiting the advancement of lithium-ion capacitors（LICs）.Here,an orientated-designed pore size distribution and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed,which is beneficial for deeply evaluating the capacitive storage mechanism.It is uncovered that the electrical double-layer capacitive performances of carbon cathode could be prominently enhanced,resulted from the controlled pore size of 1.5～3 nm.Note that the rate capability of carbon cathode could be further boosted by improving the graphitization degree.Triggered with synergistic effect of graphitization and appropriate pore size distribution,the optimized carbon cathode(Zn₉₀Co₁₀-APC)displays excellent capacitive performances with a reversible specific capacity of 50 m Ah g^-1 at 5 A g^-1.Furthermore,the assembly pre-lithiated graphite（PLG）//Zn₉₀Co₁₀-APC LIC could deliver a large energy densitiy of 108 Wh kg^-1 and a high power density of 15 k W kg^-1 as well as excellent long-term ability with 10000 cycles.（3）High-performance carbon-based LICs have been seriously hindered by the very low capacity and unclear dual capacitive mechanism of carbon cathode.Therefore,the dual capacitive storage mechanism of carbon cathode has been elucidated by centralized pore size range based on in-situ confined self-activation method.It is verifed that the desired pore size（≥0.8 nm）and electrochemical active C=O group play the crucial roles in the electrical double-layer capacitive and pseudocapacitive behaviors,respectively,which holds the key to greatly boost the absorption/desorption process of desolvated PF₆^-ions.Attributed to the synergistic effect of dual capacitive mechanism,porous carbon sheet（PCS）cathode shows a reversible specific capacity of 53.6m Ah g^-1 even at a high current density of 50 A g^-1.Significantly,when paired with PLG anode,the quasi-solid-state LIC manifests state-of-the-art electrochemical performances with an integrated maximum energy density of 163 Wh kg^-1 and an outstanding power density of 15000 W kg^-1.（4）Sacrificial cathode additive as a pre-metallation method could ensure adequate metal sources for anode.However,this pre-metallation technique is seriously suffered from the precise regulation of decomposition potential of additive,further restricting the development of high-perfromance carbon-based MICs.In view of this,a molecularly compensated pre-metallation（Li/Na/K）strategy has been successfully achieved through Kolbe electrolysis,in which the electrochemical oxidation potential of metal carboxylate is manipulated by the bonding energy of oxygen-metal（O-M）moiety.Notably,the electron-donating effect of substituent and low charge density of cation can dramatically weaken the O-M bond strength,further bringing out the reduced potential.Thus,sodium acetate bearing with the weakening O-M bond delivers a large irreversible specific capacity of 301.8 m Ah g^-1 accompanied with a low oxidation platform of 4.18 V.Importantly,this methodology triggered by organic electrochemistry has been profoundly broadened to accomplish pre-lithiation/sodiation/potassiation for fabricating high-performance carbon-based MICs and MIBs.（5）Low oxidation potential of pre-sodiation cathode additive intrinsically prevents the decomposition of electrolyte,ensuring the high stability of carbon-based SICs.Although the introduction of electron-donating substitution reduces the oxidation potential,the additional molecular weight restricts the output capacity.In view of this,a optimized pre-sodiation chemistry triggered by substituent has been demonstrated,in which the electrochemical oxidation potential of sodium carboxylate is manipulated by the electronic effect and regiochemistry of functionality.Notably,the stronger electron-donating substituent,p-πconjugation and optimized regiochemistry can dramatically lead to the lower potential of pre-sodiation additive originated from the elevation of highest occupied molecular orbital level.Therefore,benefiting from the para-NH₂ unit accompanied with conjugated aromatic architecture,molecularly engineered sodium para-aminobenzoate（PABZ-Na）presents a reduced oxidation plateau of 3.45 V.Triggered by the positive compensation merit of PABZ-Na,it is noticed that the carbon-based SIC and SIB systems equipped with cathode additive both show enhaced eletrochemcial performances.