INFLUENCE COMPARISON OF PRECURSORS ON LiFePO4/C CATHODE STRUCTURE FOR LITHIUM ION BATTERIES

Electricity is the most energy demanded in this era. Energy storage devices must be able to store long-term and portable. A lithium ion battery is a type of battery that has been occupied in a secondary battery market. Lithium iron phosphate / LiFePO4 is a type of cathode material in ion lithium batteries that is very well known for its environmental friendliness and low prices. LiFePO4/C powder can be obtained from the solid state method. In this study the variables used were the types of precursors : iron sulfate (FeSO4), iron oxalate (FeC2O4) and FeSO4+charcoal. Synthesis of LiFePO4/C powder using Li:Fe:P at 1:1:1 %mol. Based on the XRD results, LiFePO4/C from FeSO4+charcoal shows the LiFePO4/C peaks according to the JCPDS Card with slight impurities when compared to other precursors. XRD results of LiFePO4/C with precursors of FeSO4 or FeC2O4 shows more impurities peaks. This LiFePO4/C cathode is paired with lithium metal anode, activated by a separator, LiPF6 as electrolyte. Then this arrangement is assembled become a coin cell battery. Based on the electrochemical results, Initial discharge capacity of LiFePO4/C from the FeSO4 precursor is 19.72 mAh/g, while LiFePO4/C with the FeC2O4 precursor can obtain initial discharge capacity of 17.99 mAh/g, and LiFePO4/C with FeSO4+charcoal exhibit initial discharge capacity of 21.36 mAh/g. This means that the presence of charcoal helps glucose and nitrogen gas as reducing agents.


INTRODUCTION
In this era, electricity is the most increased energy need due to the demand for all economy sectors [1][2]. Electrical energy can be found everywhere but still a challenge due to it is not portable or can't be carried anywhere easily, while the amount of electricity need are always increasing. So, in this case we need an electrical energy storage device.
Battery is an such of device that is capable of storing electrical energy and can be applied to many electronic devices such as mobile phones, laptops, remote controls to   [9] , The raw material is quite easy to obtained and LiFePO4 does not produce impurities during the delithiation process [10].
However, LiFePO4 has shortcomings such as the low conductivity of 10 -9 -10 -10 S/cm and the low diffusion coefficient of 10 -13 -10 16 /s. The aims of addition the reducing agent to reduce / eliminate the possibility of oxidized iron. The reducing agent added are activated carbon [13], metal oxides [14] or the presence of dopants with supervalent metal ions [15]. The addition of carbon is intended to increase the value of battery conductivity due to carbon has a higher conductivity value of 1.25-2x10 3 S/cm [16].

Characterization
The obtained LiFePO4/C was charac-

Test
The obtained LiFePO4/C powder were tested using XRD diffraction to determine its crystallinity. Electrochemical properties were tested to determine the initial discharge capacity of the batteries.

Reaction of LiFePO4
There Charging : Discharging :  Based on the appearance of product shows a black color on the inside but there are still red dots on the outside which means oxidation reaction still occurs due to the formation of Fe2O3 [40]. Oxidation reaction caused by the presence of oxygen content during the heating/sintering process in the furnace.   The presence of charcoal is intended as an additional reducing agent apart from the presence of nitrogen (inert) gas and glucose. The oxidation number in Charcoal or C will increased when charcoal is burned so that it automatically becomes a reducing agent.

XRD diffraction pattern
Based on the appearance of product shows a grayish black color which means it matches the color of LiFePO4 in the commercial.

Electrotrochemistry
Electrochemical testing was carried out using a battery analyzer (Neware, China).  [12]. Initial discharge capacity can be seen on the figure below : Figure 3. LiFePO4/C electrochemical test results with precursor variables.