Ionomer Binders Can Improve Discharge Rate Capability in Lithium-Ion Battery Cathodes

Abstract

A lithium-ion form of a perfluorosulfonate ionomer was used as a binder in LiFePO 4 -based lithium-ion battery cathodes. Carboncoated LiFePO 4 and acetylene carbon black were blended with ionomer to prepare composite cathodes having a composition 60% LiFePO 4 , 20% acetylene carbon black, and 20% binder by weight. Cathodes were tested against Li 4 Ti 5 O 12 anodes using 1.0 M and 0.1 M LiPF 6 -ethylene carbonate/diethyl carbonate ͑EC/DEC͒ electrolytes. Comparison was made with cathodes prepared using poly͑vinylidene͒ difluoride ͑PVDF͒ as binder. At low discharge rates ͑e.g., C/5͒ both cathode types exhibited similar chargedischarge capacities and voltage profiles. However, under higher rate discharge conditions ͑e.g., Ͼ1C, up to 5C͒ cathodes prepared using ionomer binder showed better discharge rate capability than cathodes having PVDF binder. This phenomenon was more pronounced when the salt concentration in the electrolyte was low ͑e.g., 0.1 M LiPF 6 -EC/DEC͒. These findings suggest that use of ionic binders can help to compensate for electrolyte depletion from the electrode porous space as lithium ions are intercalated into lithium-deficient LiFePO 4 particles during rapid discharging. Potential uses for electrodes having ionomer binders in enabling lower cost battery electrolytes ͑because of the reduced need for salt͒ and in developing high rate cathodes that are nonporous or have low porosity are discussed.Lithium-ion batteries are being aggressively developed for hybrid electric vehicle, plug-in hybrid electric vehicle, and electric vehicle applications. For many of these applications, a high rate performance ͑e.g., fast charge and discharge reactions͒ is essential. 1-3 Typical lithium-ion battery electrodes are composite mixtures obtained by blending electroactive material particles with non-electroactive additives such as carbon black and a polymeric binder. Lithium-ion transfer at the interface between the electrode and the electrolyte, as well as lithium transport inside the active materials and in the porous spaces of the electrode, are essential processes during battery charging and discharging, and the rates of these processes in part determine the overall battery performance. Therefore, it is important for the battery electrodes to possess high lithium ion and electron conductivity in order to efficiently transport lithium ions and electrons to and from each active material particle and the current collector, respectively. 4 In a typical lithium-ion battery electrode, the binder provides structural integrity at relatively low mass fractions ͑e.g., Ͻ10 wt %͒, bringing together the electroactive material and the carbon black. Nonionic polymers such as Teflon ͓poly͑tetrafluoroethyl-ene͒, PTFE͔ or poly͑vinylidene͒ difluoride ͑PVDF͒ which do not have any intrinsic ionic functionality are commonly used as electrode binders. Rapid and full penetration of liquid electrolytes into the accessible pores in the composite electrode and rapid transport of lithium ions into and out of the pores, are necessary in s...

Generalized Analytical Model for Capacity Evaluation of Automotive-Grade Lithium Batteries

“…As the battery temperature decreases, the available capacity decreases due to increase of internal resistance of the battery and retardation of the chemical metabolism of the batteries effectively hindering the chemical reaction rate. 30,31 So the capacity C released by the battery will be equal to zero at least at temperatures not less than an electrolyte congelation point. By T k let us denote a temperature, at which C = 0.…”

“…30,31 Nevertheless it is evident that the capacity cannot increase constantly with temperature growth. At reasonably large temperatures, active materials of electrodes start degrading and so does an electrolyte.…”

Screen printed cathode for non-aqueous lithium–oxygen batteries

“…As shown in Fig. S1, the lithiated Nafion ionomer shifts the band assigned to ÀSO 3 À symmetric stretch from 1056.1 to 1072.6 cm À1 due to the interaction between Li ion and oxygen, indicating that Li is substituted for hydrogen in the sulfonate group [32,33]. Subsequently, carbon black powder (EC-600 JD, Akzo Nobel) and lithiated Nafion dispersion are added into a solvent of 2-propanol to achieve a binder-to-carbon ratio of 1:4 (m/m).…”

A facile and generic method to improve cathode materials for lithium-ion batteries via utilizing nanoscale surface amorphous films of self-regulating thickness

“…To make the electrolyte, EC/DEC/DMC (1 : 1 : 1 vol, BASF) solvent was used for LiCoO 2 batteries that were charged up to 4.3 V, and EC/DMC (1 : 1 vol, BASF) solvent was used for LiCoO 2 batteries that were charged up to 4.5 V and LiMn 1.5 Ni 0.5 O 4 batteries that were charged to 5.0 V. To probe whether the interfacial polarization of the electrolyte near the particle surfaces is the rate control step in LiCoO 2 -based cathodes, we also prepared and tested coin cells using the 0.1 M LiPF 6 electrolyte following a procedure developed by Creager and co-workers. 55 Electrochemical cycling tests were carried out on an Arbin 2143 tester. The rate capabilities of LiCoO 2 were tested at charge and discharge rates of C/5 for 4 cycles, followed by discharging at 1 C, 2 C, 5 C, 10 C, and 25 C sequentially (2 cycles at each discharge rate) while keeping the charge rate at C/5.…”

“…22 In this study, we found the processing conditions to form significantly more uniform Li 3 PO 4 -based SAFs on LiCoO 2 with an equilibrium thickness of B2.9 nm. Furthermore, we adopted a special technique developed by Creager and co-workers 55 to show that the enhanced rate capability is not due to reduction in the concentration polarization; further impedance measurements suggested that these nanoscale SAFs may enhance the rate performance by reducing the interfacial charge transfer resistance. We further demonstrated that Li 3 PO 4 -based SAFs can enhance the rate performance of an even more isotropic material, spinel LiMn 1.5 Ni 0.5 O 4 , as well as significantly improve its cycling stability at an elevated temperature by protecting the electrode surfaces and suppressing the SEI growth.…”