[Paper Review] Revealing the interfacial kinetic mechanisms in high-entropy doped Na$_3$V$_2$(PO$_4$)$_3$ through electrochemical investigation and distribution of relaxation times

Manish Kr. Singh, R. S. Dhaka|arXiv (Cornell University)|Feb 4, 2026

Advancements in Battery Materials0 citations

TL;DR

The paper designs a high-entropy doped NASICON cathode Na3V1.9(CrMoAlZrNi)0.1(PO4)3 and uses electrochemical methods including distribution of relaxation times to elucidate interfacial kinetics and diffusion in SIBs, reporting high capacity and long-term stability.

ABSTRACT

We designed a high-entropy doped NASICON cathode, Na$_3$V$_{1.9}$(CrMoAlZrNi)$_{0.1}$(PO$_4$)$_3$ and investigate its electrochemical performance for sodium-ion batteries (SIBs) to understand the diffusion mechanism including distribution of relaxation times analysis of interfacial kinetics. This trace doping induces high-entropy mixing at the vanadium site, tuning the lattice and enhancing specific capacity, activating V$^{4+}$/V$^{5+}$ redox couple 3.95~V. Interestingly, it delivers a reversible capacity of 119~mAh~g$^{-1}$ at 0.1~C, and demonstrate excellent stability of 68\% after 1000 cycles at 10~C. The calculated diffusion coefficient values are found within the range of \(10^{-11}\)--\(10^{-13}~\mathrm{cm^2\,s^{-1}}\). The systematic investigation of temperature and voltage-dependent impedance data using the distribution of relaxation times provides deeper insights into the underlying charge-transfer and transport processes. The full cells with hard carbon delivers 326~Wh~kg$^{-1}$ (with respect to cathode mass) at $\approx$3.2~V and retained $\sim$79\% capacity after 100 cycles at 2~C. Our study opens new avenues for developing high-entropy doped cathodes for enhanced structural stability, extended redox activity, and optimized electrochemical kinetics for practical implementation of SIBs.

Motivation & Objective

• Motivate the use of high-entropy doping to enhance structural stability and multi-electron redox activity in NASICON cathodes for SIBs.
• Aim to understand diffusion mechanisms and interfacial kinetics via distribution of relaxation times (DRT) analysis of impedance data.
• Demonstrate improved electrochemical performance including activation of V4+/V5+ redox couple and enhanced cycling stability.
• Explore structure–property relationships with multi-dopant incorporation at the vanadium site.

Proposed method

• Synthesize NVP-HE via sol–gel method with trace dopants (Cr, Mo, Al, Zr, Ni) and CNTs; calcine under Ar/H2.
• Characterize structure and composition by XRD with Rietveld refinement, Raman, HR-TEM/SAED, SEM-EDS, ICP-MS, XPS.
• Evaluate electrochemical performance with CV, galvanostatic charge–discharge (GCD), GITT, and EIS; perform in-situ EIS and DRT analysis.
• Estimate diffusion coefficients using Randles–Ševčík analysis and Warburg fits; apply GITT for thermodynamic diffusion coefficients.
• Use DRT (Tikhonov regularization) to deconvolute EIS spectra and assign relaxation-time peaks to specific processes.
• Validate EIS data with Kramers–Kronig consistency checks.

Figure 1: (a) The XRD pattern with Rietveld refinement profile of the NVP-HE sample; (b) an isosurface representation of Na + ion diffusion pathways in the NVP-HE structure, and (c) the corresponding energy profile of migration barriers along the minimum energy path Na1–Na2–Na1, calculated using the

Experimental results

Research questions

• RQ1 How does high-entropy doping affect Na+ diffusion and interfacial kinetics in Na3V2(PO4)3 NASICON cathodes?
• RQ2 What are the activation energies and diffusion coefficients for Na+ transport in the HE-doped framework under varying voltages and temperatures?
• RQ3 Can distribution of relaxation times distinguish charge-transfer, SEI/interfacial, and diffusion processes in NVP-HE during operation?
• RQ4 What electrochemical performance improvements (capacity, stability, rate capability) arise from trace HE doping?

Key findings

• NVP-HE delivers 119 mAh g−1 at 0.1 C, with a ~0.05 V polarization and activation of the V4+/V5+ couple around 3.95 V/3.93 V.
• Cycling stability shows 68% capacity retention after 1000 cycles at 10 C (and 78% after 800 cycles at 10 C) for NVP-HE.
• Diffusion coefficient values from CV/GITT lie in the 10−11 to 10−13 cm2 s−1 range, with DNa+ about 7.5×10−11 cm2 s−1 during charging and 3.1×10−11 cm2 s−1 during discharging from GITT; Warburg analysis yields 10−11 to 10−12 cm2 s−1 in redox-active regions (EIS).
• Full cells with hard carbon deliver ~326 Wh kg−1 (cathode-based) at ~3.2 V and retain ~79% capacity after 100 cycles at 2 C.
• In-situ impedance and DRT analysis reveal distinct relaxation-time peaks corresponding to charge transfer, interfacial polarization, and bulk diffusion, clarifying interfacial kinetics beyond conventional Nyquist plots.
• XRD and BVSE analyses indicate slight lattice expansion and widened Na+ diffusion pathways, with an activation energy ~0.465 eV for Na+ migration, lower than pristine NVP.

Figure 2: (a) The CV curves at 0.1 mV s -1 , (b) the GCD profiles at 0.1 C for the second cycle of NVP and NVP-HE in 2.0–4.3 V; (c) the first five cycles of GCD profile of NVP-HE at 0.1C; (d) the rate performances; (e) the corresponding GCD profiles for second cycle at each current rate; (f) the cyc