钠离子电池——碳中和世界的储能技术

Wandering on the shore of the Sandu Bay,looking at the blue ocean and the green mountains,a question comes to mind:How can we meet humans’energy demand while minimizing its effect on the environment?In other words,how can we ensure a carbon-neutral world in the near future?

Mechanical behavior analysis of high power commercial lithium-ion batteries

In application,lithium-ion cells undergo expansion during cycling.The mechanical behavior and the impact of external stress on lithium-ion battery are important in vehicle application.In this work,18 Ah high power commercial cell with Li Ni_(0.5)Co_(0.2)Mn_(0.3)O_(2)/graphite electrode were adopted.A commercial compress machine was applied to monitor the mechanical characteristics under different stage of charge(SOC),lifetime and initial external force.The dynamic and steady force was obtained and the results show that the dynamic force increases as the SOC increasing,obviously.During the lifetime with high power driving mode,different external force is shown to have a great impact on the long-term cell performance,with higher stresses result in higher capacity decay rates and faster impedance increases.A proper initial external force(900 N)provides lower impedance increasing.Postmortem analysis of the cells with2000 N initial force suggests a close correlation between electrochemistry and mechanics in which higher initial force leads to higher direct current internal resistance(DCIR)increase rate.In addition,for the cell with higher external force,deformation of the cathode and thicker solid electrolyte interface(SEI)film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.In addition,for the cell with higher external force,deformation of the cathode and thicker SEI film on the surface of anode and separator are observed.Porosity reduction and closure was also verified after cycles which is an obstacle to the lithium ion transferring.The largest cause of the observed capacity decline was the loss of active lithium through autopsy analysis.

The feasibility for natural graphite to replace artificial graphite in organic electrolyte with different film-forming additives

The feasibility for natural graphite(NG)to replace artificial graphite(AG)in organic electrolytes with different additives are investigated.Although the strong film-forming additives contributes to form robust solid electrolyte interphase(SEI)film on graphite particle surface,great differences in gas evolution,lithium inventory loss and other side reactions are observed.Lithium bis(oxalato)borate(Li BOB)and fluoroethylene carbonate(FEC)are found more effective and the combination shows to be more promising.In the optimized electrolyte,natural graphite anode exhibits excellent long-term cycling capability.After 800 cycles at high temperature,the capacity retention is comparable to that using artificial graphite.The mechanisms for the capacity-fading of the full cells with AG and NG anode are investigated by ICP,SEM and polarization studies.The results shows that NG electrode consumes more active lithium due to the rough surface and larger volume expansion.The rapid capacity-fading in the initial 100 cycles is related to the instability of the SEI film aroused from large volume expansion.The systematic analysis is inspiriting for the development of high performance lithium ion batteries with reduced cost.

3D amorphous carbon and graphene co-modified LiFePO_4 composite derived from polyol process as electrode for high power lithium-ion batteries

Amorphous carbon and graphene co-modified LiFePO4 nanocomposite has been synthesized via a facile polyol process in connection with a following thermal treatment.Various characterization techniques,including XRD.Mossbauer spectra,Raman spectra,SEM,TEM,BET,O2-TPO,galvano charge-discharge,CV and EIS were applied to investigate the phase composition,carbon content,morphological structure and electrochemical performance of the synthesized samples.The effect of introducing way of carbon sources on the properties and performance of LiFePO4/C/graphene composite was paid special attention.Under optimized synthetic conditions,highly crystalized olivine-type LiFePO4was successfully obtained with electron conductive Fe2P and FeP as the main impurity phases.SEM and TEM analyses demonstrated the graphene sheets were randomly distributed inside the sample to create an open structured LiFePO4 with respect to graphene,while the glucosederived carbon mainly coated over LiFeP04 particles which effectively connected the graphene sheets and LiFePO4 particles to result in a more efficient charge transfer process.As a result,favorable electrochemical performance was achieved.The performance of the amorphous carbon-graphene co-modified LiFePO4 was further progressively improved upon cycling in the first 200 cycles to reach a reversible specificcapacity as high as 97 mAh·g-1 at 10 C rate.

Charge compensation and capacity fading in LiCoO2 at high voltage investigated by soft x-ray absorption spectroscopy

In order to obtain an in-depth insight into the mechanism of charge compensation and capacity fading in LiCoO2, the evolution of electronic structure of LiCoO2 at different cutoff voltages and after different cycles are studied by soft x-ray absorption spectroscopy in total electron（TEY） and fluorescence（TFY） detection modes, which provide surface and bulk information, respectively. The spectra of Co L2,3-edge indicate that Co contributes to charge compensation below 4.4 V.Combining with the spectra of O K-edge, it manifests that only O contributes to electron compensation above 4.4 V with the formation of local O 2 p holes both on the surface and in the bulk, where the surficial O evolves more remarkably. The evolution of the O 2 p holes gives an explanation to the origin of O2^-or even O2. A comparison between the TEY and TFY of O K-edge spectra of LiCoO2 cycled in a range from 3 V to 4.6 V indicates both the structural change in the bulk and aggregation of lithium salts on the electrode surface are responsible for the capacity fading. However, the latter is found to play a more important role after many cycles.

Stable cycling of practical high-voltage LiCoO_(2)pouch cell via electrolyte modification

Nitriles as efficient electrolyte additives are widely used in high-voltage lithium-ion batteries.However,their working mechanisms are still mysterious,especially in practical high-voltage LiCoO_(2)pouch lithium-ion batteries.Herein,we adopt a tridentate ligandcontaining 1,3,6-hexanetricarbonitrile(HTCN)as an effective electrolyte additive to shed light on the mechanism of stabilizing high-voltage LiCoO_(2)cathode(4.5 V)through nitriles.The LiCoO_(2)/graphite pouch cells with the HTCN additive electrolyte possess superior cycling performance,90%retention of the initial capacity after 800 cycles at 25℃,and 72%retention after 500 cycles at 45℃,which is feasible for practical application.Such an excellent cycling performance can be attributed to the stable interface:The HTCN molecules with strong electron-donating ability participate in the construction of cathode-electrolyte interphase(CEI)through coordinating with Co ions,which suppresses the decomposition of electrolyte and improves the structural stability of LiCoO_(2)during cycling.In summary,the work recognizes a coordinating-based interphase-forming mechanism as an effective strategy to optimize the performance of high voltage LiCoO_(2)cathode with appropriate electrolyte additives for practical pouch batteries.

Boosting energy storage performance of low-temperature sputtered CaBi_(2)Nb_(2)O_(9) thin film capacitors via rapid thermal annealing

CaBi_(2)Nb_(2)O_(9) thin film capacitors were fabricated on SrRuO_(3)-buffered Pt(111)/Ti/Si(100)substrates by adopting a two-step fabrication process.This process combines a low-temperature sputtering deposition with a rapid thermal annealing(RTA)to inhibit the grain growth,for the purposes of delaying the polarization saturation and reducing the ferroelectric hysteresis.By using this method,CaBi_(2)Nb_(2)O_(9) thin films with uniformly distributed nanograins were obtained,which display a large recyclable energy density Wrec≈69 J/cm^(3) and a high energy efficiencyη≈82.4%.A superior fatigue-resistance(negligible energy performance degradation after 10^(9) charge-discharge cycles)and a good thermal stability(from-170 to 150℃)have also been achieved.This two-step method can be used to prepare other bismuth layer-structured ferroelectric film capacitors with enhanced energy storage performances.

A pore-scale smoothed particle hydrodynamics model for lithiumion batteries

A mesoscopic pore-scale model of multi-disciplinary processes coupled with electrochemical reactions in lithium-ion batteries is established via a relatively novel numerical method—smoothed particle hydrodynamics(SPH)method.This model is based on mesoscopic treatment to the electrode(including separator)micro-pore structures and solves a group of inter-coupled SPH equations,including charge(ion in electrolyte phase and electron in solid phase),species(Li?in electrolyte phase and lithium in solid active materials),and energy conservation equations.Model parameters,e.g.the physicochemical properties are location-dependent,directly associated with the local component of the medium.The electrochemical reactions are prescribed to occur exactly at the interface of solid active materials and electrolyte.Simulations to isothermal discharge processes of a battery of 2-dimensional idealized micro-pore structure in electrodes and separator preliminarily corroborate the reasonability and capability of the developed SPH model.