**1. Introduction**

The unavoidable consumption of the global fossil fuel reserves in conjunction with the increasing environmental issues, have rendered the storage of electrical energy produced from renewable sources of greater importance than ever before [1]. Rechargeable Lithium-Ion batteries (LIB) have gained considerable attention among various energy storage technologies and are currently widely employed or considered to be deployed in electric devices, electric vehicles (EVs) and grid energy storage systems due to their relatively high energy density, high voltage, better cycle life and environmental friendliness [2–5]. Pyrolysis methods are extensively studied for the synthesis of anode and cathode materials for LIBs [6–11], either as mixed oxide particles [12, 13] or carbon-based structures [14], thereby providing a scalable and sustainable process for the production of electrode materials. The demand for high specific power, energy capacity [15, 16] and safety within the battery lifetime

has led to the importance of "going nano" [17] in order to optimize electrode electrochemical activity and stability towards lithium ion intercalation (insertion within the material lattice) in the framework of the necessary cycling operation.

Aerosol spray pyrolysis synthesis is an established and scalable method for the synthesis of metal oxides [18], metal [19] and carbon-based [20] materials. The atomized droplets undergo controlled evaporation of solvents and subsequent precipitation of precursor materials by regulating the operating conditions of the process to allow tuning of size distribution, morphology, porosity and to achieve uniform multicomponent composition of the synthesized particles and structures. Furthermore, the residence time of the droplets in the heated reactors is in the time frame of seconds, while further (i.e. post-synthesis) calcination can be performed in powder form. The precursor solutions for aerosol spray pyrolysis are mostly aqueous based, leading only to gaseous byproducts that can be in-line processed or captured, thereby contributing further to an environmentally sustainable and cost-effective process.

To meet the demanding battery standards, a wide variety of cathode materials has been thoroughly studied, such as the layered LiMO2 [21–24], the olivine LiMPO4 [25–27] and the spinel structure of LiM2O4. Among the materials of the latter LiM2O4 family, LiNi0.5Mn1.5O4 (LNMO) is considered a very promising candidate as a cathode material in both environmental [28, 29] and operational terms, since it exhibits an operating charge/discharge voltage of ~4.7 V vs. Li/Li<sup>+</sup> , a theoretical capacity of ~147 mAh·g−1 [30] and it does not require the use of cobalt. In this work we investigate the doping of Mg, Al and Fe through partial substitution of Ni in the LNMO structure (Mg-LNMO, Al-LNMO and Fe-LNMO respectively) via the Aerosol Spray Pyrolysis (ASP) synthesis technique for a production capacity of approximately 100 g·h−1. Subsequently, the doping effect on the electrochemical performance of LNMO half cells is assessed experimentally.
