LiFePO4, normally referred to as LFP, is a major cathode material used by lithium-ion battery industry. LFP has its advantage in superior safety and lower material cost compared to other popular chemistries like NMC (LiNixMnyCo1-x-yO2). Though LFP has lower energy density than NMC, this gap is diminishing fast with new battery manufacturing and assembling techniques, like Cell to Pack (CTP) and blade battery designs.
There are several approaches for the manufacturing of LFP, such as high-temperature solid-state fusion of FePO4 precursor with Li2CO3, co-precipitation of LiFePO4 precursor followed with high-temperature sintering, carbothermal reduction of Li, P and Fe precursors, and hydrothermal synthesis. Each approach has its own pros and cons in the process and the final product quality control. Whatever is the manufacturing method, a strict control on the molar ratios of the raw materials and the elemental composition of the final product is critical to the performance of the assembled battery.
X-Ray Fluorescence (XRF) spectroscopy, with its advantage of high stability and simple sample preparation, is an ideal technique to analyze major elements (except Li) in LFP cathode manufacturing, from raw material to the final product. A study is shown in this report as an example.
LiFePO4, normally referred to as LFP, is a major cathode material used by lithium-ion battery industry. LFP has its advantage in superior safety and lower material cost compared to other popular chemistries like NMC (LiNixMnyCo1-x-yO2). Though LFP has lower energy density than NMC, this gap is diminishing fast with new battery manufacturing and assembling techniques, like Cell to Pack (CTP) and blade battery designs.
There are several approaches for the manufacturing of LFP, such as high-temperature solid-state fusion of FePO4 precursor with Li2CO3, co-precipitation of LiFePO4 precursor followed with high-temperature sintering, carbothermal reduction of Li, P and Fe precursors, and hydrothermal synthesis. Each approach has its own pros and cons in the process and the final product quality control. Whatever is the manufacturing method, a strict control on the molar ratios of the raw materials and the elemental composition of the final product is critical to the performance of the assembled battery.
X-Ray Fluorescence (XRF) spectroscopy, with its advantage of high stability and simple sample preparation, is an ideal technique to analyze major elements in LFP cathode manufacturing, from raw material to the final product. A study is shown in this report as an example.
Malvern Panalytical Zetium floor standing WDXRF spectrometer equipped with an Rh anode SST-mAX tube was used in these measurements. Designed to meet the most demanding process control and R&D applications, the Zetium XRF spectrometer leads the market in high-quality design and innovative features for sub-ppm to percentage level analysis of elements ranging from Be to Am. The Zetium is equipped with the latest version of our SuperQ software, including our Virtual Analyst that enables even non-expert users to easily set up applications.
Samples were prepared in two ways: Borate fusion and pressed pellets. Due to the limitation in matrix match, calibration samples were prepared only for the fusion application. The method precision of the pressed pellet application was evaluated with a single-point calibration.
To create a calibration for the fusion method, synthetic reference materials were prepared using Fe2O3 and Li3PO4 mixtures in varying stoichiometric ratios.
To achieve an optimal precision for Fe in the sample, Co was used as an internal standard. A flux doped with 10% Co2O3 is used during the fusion. A dilution ratio of 1:10 was used for the calibration standards, while 0.8:10 was used for the samples in order to match the concentration. The samples were then fused with TheOX automatic fusion machine at 1120℃.
5g of LFP powder was dried and pressed into pellet with boric acid as backing.
Below measurement conditions were used for fuse bead samples. Total measurement time was 160 seconds per sample. Li2O is used as a balanced compound.
Item | Tube | Optical path | Time (s) | |||||
---|---|---|---|---|---|---|---|---|
Compound | Line | kV | mA | Tube filter | Collimator | X-tal | Detector | |
(Co) | KA | 60 | 40 | None | 150 µm | LiF 220 | Scint. | 20 |
Fe2O3 | KA | 60 |
40 |
None | 150 µm | LiF 220 | Scint. | 60 |
P2O5 | KA | 24 | 100 | None | 550 µm | Ge 111-C | Flow | 80 |
Table 1. Measurement conditions
The same measurement conditions were used for press pellet samples, except that Co was not present in these.
Figures 1 and 2 show the calibrations using fuse bead synthetic reference samples. A single-point calibration (not shown here) was made for the pressed pellet samples.
Pressed pellet | Fused bead | ||||||
---|---|---|---|---|---|---|---|
Sample | P2O5 | Fe2O3 | (Li2O) | Sample | P2O5 |
Fe2O3 |
(Li2O)
|
1 | 47.640 | 48.200 | 4.160 | 1 | 47.677 | 48.108 | 4.215 |
2 | 47.679 | 48.129 | 4.193 | 2 | 47.675 | 48.219 | 4.105 |
3 | 47.683 | 48.095 | 4.223 | 3 | 47.677 | 48.106 | 4.217 |
4 | 47.465 | 48.084 | 4.588 | 4 | 47.618 | 48.047 | 4.335 |
5 | 47.789 | 48.164 | 4.047 | 5 | 47.683 | 48.139 | 4.179 |
Average (%) | 47.624 | 48.134 | 4.242 | Average (%) | 47.666 | 48.124 | 4.210 |
Minimum result (%) | 47.465 | 48.084 | 4.047 | Minimum result (%) | 47.618 | 48.047 | 4.105 |
Maximum result (%) | 47.789 | 48.200 | 4.588 | Maximum result (%) | 47.683 | 48.219 | 4.335 |
RMS (%) | 0.174 | 0.048 | 0.204 | RMS (%) | 0.027 | 0.063 | 0.083 |
Relative RMS (%) | 0.37 | 0.10 | 4.82 | Relative RMS (%) | 0.06 | 0.13 | 1.97 |
Pressed pellet | Fused bead | ||||||
---|---|---|---|---|---|---|---|
Measurement | P2O5 |
Fe2O3 |
(Li2O)
|
Measurement | P2O5 |
Fe2O3 |
(Li2O)
|
1 | 47.789 | 48.164 | 4.047 | 1 | 47.736 | 48.106 | 4.158 |
2 | 47.780 | 48.152 | 4.068 | 2 | 47.737 | 48.163 | 4.100 |
3 | 47.759 | 48.177 | 4.064 | 3 | 47.731 | 48.201 | 4.068 |
4 | 47.757 | 48.173 | 4.070 | 4 | 47.740 | 48.155 | 4.105 |
5 | 47.770 | 48.152 | 4.078 | 5 | 47.736 | 48.243 | 4.020 |
6 | 47.779 | 48.152 | 4.069 | 6 | 47.724 | 48.203 | 4.073 |
7 | 47.785 | 48.122 | 4.093 | 7 | 47.721 | 48.243 | 4.037 |
8 | 47.796 | 48.125 | 4.079 | 8 | 47.709 | 48.283 | 4.008 |
9 | 47.762 | 48.158 | 4.080 | 9 | 47.716 | 48.229 | 4.055 |
10 | 47.672 | 48.181 | 4.147 | 10 | 47.686 | 48.247 | 4.067 |
Average (%) | 47.765
|
48.156 | 4.080 | Average (%) | 47.723
|
48.207 | 4.069 |
Minimum result (%) | 47.672
|
48.122 | 4.047 | Minimum result (%) | 47.686 | 48.106 | 4.008 |
Maximum result (%) | 47.796
|
48.181 | 4.147 | Maximum result (%) | 47.740
|
48.283 | 4.158 |
RMS (%) | 0.035
|
0.020 | 0.027 | RMS (%) | 0.017 | 0.053 | 0.044 |
Relative RMS (%) | 0.07
|
0.04 | 0.65 | Relative RMS (%) | 0.04
|
0.11 | 1.09 |