<figure><img src="image_29.png" /><figcaption>**Figure 24.** The representative set-up for different *in-situ* characterization techniques. (a) *In-situ* XRD set-up (reflection mode). [315] John Wiley & Sons. © 2021 Wiley-VCH GmbH. (b) *In-situ* XAS set-up (transmission mode), [315] John Wiley & Sons. © 2021 Wiley-VCH GmbH. (c) *In-situ* Raman spectroscopy set-up, with few-layered graphene (FLG) foam electrode, [315] John Wiley & Sons. © 2021 Wiley-VCH GmbH. (d) *In-situ* strain analysis set-up, Reprinted with permission from [326]. Copyright (2021) American Chemical Society. (e) *In-situ* visualization set-up, Reproduced from [327], with permission from Springer Nature. (f) *In-situ* TEM set-up, with red phosphorous@N-PHCNFs electrode. Reprinted with permission from [127]. Copyright (2019) American Chemical Society.</figcaption></figure>

remodeling of FeSe$_2$ during potassiation/depotassiation, as well as increased orderliness of the carbon components in the composite electrode [327].

Construction of proper set-ups are also very important for *in-situ* characterizations. As shown in figures 24(a), (b) and (c)–(e), x-ray transparent window (e.g. Beryllium window) and light transparent window (e.g. quartz window) were utilized to construct cells for *in-situ* XRD, XAS [315] and *in-situ* Raman [328] and *in-situ* optical microscopy [327]. An in-plane cell set-up (figure 24(d)) was built with a quartz window for analyzing the strain evolution in FePO$_4$ electrode during charge/discharge by digital image correlation, through tracking the speckle pattern position on the electrode surface. First cycle potassiation of FePO$_4$ lead to volume expansions, increased interplanar spacing and reduced crystallinity, as revealed by *in-situ* strain analysis and *in-situ* XRD characterization. However, in subsequent cycles, reversible volume expansion/shrinkage are still present, while the XRD patterns remain unchanged, indicating potassiation/depotassiation in an amorphized phase in the electrode.

Proper testing parameters are also suggested for *in-situ* characterization. Hard x-rays (5 to ~100 keV) with high penetration depth are often needed for *in-situ* XAS (transmission mode) analysis and can also be used for *in-situ* XRD characterization. Guo *et al*, employed synchrotron x-ray sources (wavelength 0.688273 Å, transmission mode) to track the phases changes in few-layered Sb$_2$S$_3$/carbon sheet (SBS/C) electrode. During initial potassiation, $K^+$ was inserted into Sb$_2$S$_3$, which was then converted into $K_2$S and Sb. Further potassiation resulted in formation of $K_2$S$_6$ intermediate phase and the final discharge product of $K_2$S$_3$ and $K_3$Sb were also detected, revealing the multi-step intercalation, conversion, and alloying reactions in this SBS/C anode [322].
## Concluding remarks

*In-situ* characterization methods are undoubtedly informative and constructive in analyzing the electrochemical mechanisms of PIBs. Albeit the fact that several *in-situ* methods have been adopted in PIBs, further efforts are still needed to advance the proliferation of more *in-situ* characterization techniques. First, it is suggested that proper *in-situ* methods should be selected to match with the electrode properties. Second, appropriate set-ups should be constructed for *in-situ* characterization, suitable testing parameters should also be considered to meet the testing requirements. Third, combination of different *in-situ* methods is suggested to harvest multidimensional and multimodal information, thus corroborating a more comprehensive understanding of PIB electrochemical mechanisms. What's more, aside from focusing on the structural variation of electrode (mostly anode) during charge/discharge, the electrochemical behavior of cathode and the effect of binders, separators and electrolytes on PIB electrochemical mechanism should not be neglected. Last, it is encouraged to explore more possibilities of *in-situ* methods in PIBs, including the emerging *in-situ* NMR, EQCM, SECM, atomic force microscopy etc. Through judicious adoption of the available *in-situ* characterization techniques and exploration of emerging *in-situ* methods, issues existing in PIBs will be resolved and the PIBs performance will be promoted, advancing the development and commercialization of PIBs.

## Acknowledgments

This study was financially supported by the National Natural Science Foundation of China (Nos. 22179123 and 21471139), Shandong Provincial Natural Science Foundation, China (No. ZR2020ME038) and the Fundamental Research Funds for the Central Universities (No. 201941010).
# 19. Cost-effectiveness and techno-economic analysis of PIBs

Laura Lander and Jacqueline Sophie Edge

Imperial College London, London, United Kingdom

## Status

While batteries have an important role to play in decarbonizing our energy and transport systems, they have environmental and social impacts across their lifecycle which need to be assessed and mitigated. These impacts include habitat destruction, pollution, displacement of communities, competition for freshwater and unethical labor practices. In addition, owing to the scarce minerals required in LIBs, there are supply chain risks, due to resource depletion and geographic localization. For this reason, alternative materials are sought to replace, for example, lithium with more abundant materials, such as potassium and sodium (table 3) [124, 329]. PIBs have the potential to outperform both LIBs and SIBs, because K⁺ ions, unlike Na⁺ ions, can intercalate reversibly into a graphite anode [330], K has a lower standard redox potential than Na and Li, resulting in a higher working voltage [330], and K electrolytes exhibit higher conductivity than Li and Na electrolytes [331].

Besides performance, an important criterion for the success of any new battery technology is its economic viability. Here, techno-economic analysis is an important tool to reveal economic benefits and drawbacks and to develop strategies on how to optimize the overall costs.

In this context, Yan and Obrovac conducted a techno-economic analysis of non-aqueous PIBs including current cathode materials (e.g. K₂MnFe(CN)₆, KCrO₂ and KVPO₄F) as well as a hypothetical KNi₀.₆Mn₀.₂Co₀.₂O₂ (KNMC622) cathode [332]. The latter was then benchmarked against LiNi₀.₆Mn₀.₂Co₀.₂O₂ (LNMC622). It was concluded that indeed costs can be reduced by $2.2/kg cathode material using KNMC622 instead of LNMC622 due to the lower price of K compared to Li (figure 25(a), table 3). Further cost savings can be achieved on the anode current collector, which in PIBs, in analogy to SIBs is Al foil, whereas in LIBs Cu foil is used. However, the total PIB cost exceeds the cost of LIBs ($7535.29 and $7359.32, respectively; figure 25(b)). This stems from the lower volumetric capacity of graphite for PIBs compared to LIBs leading to larger amounts of material (i.e. graphite, binder and electrolyte) being required to achieve the set energy storage capacity [332, 334]. The study further evaluated the cost of a PIB over its cycle lifetime ($/kWh·year). It was shown that for PIBs to become economically viable compared to LIBs an increase in battery lifetime to up to 1500 cycles (vs. 1000 for LIBs) is required.

## Current and future challenges

Current and future challenges regarding the cost-competitiveness and techno-economic assessment of PIBs can be divided into three categories as described in the following:

**Technological challenges:** economic drawbacks of PIBs stem primarily from currently low volumetric and gravimetric energies leading to higher materials demand as well as short cycle life [8, 332, 334–336]. PIBs are still in their early development stages and further intensive research efforts are needed to improve the overall battery performance. It should be noted, however, that also the performance and cost-efficiency of LIBs are going to be further optimized, which might make it even harder for PIBs to be a viable contender in the future [337].

**Supply chain challenges:** additional economic issues could arise from the availability and cost of the potassium source—potash. Potash is heavily used for fertilizers in the agricultural sector and its price is sensitive to geopolitical and global economic developments. It has been reported that the potash price has recently significantly increased from $300 per ton in 2021 to $1100 in 2022 [338, 339]. Similar fluctuations in the future would further compromise the cost-competitiveness of PIBs. Moreover, potential supply chain risks might occur for the PIB manufacturing industry as preference probably would be given to food production in case of potash shortages, for instance.

**End of life processing challenges:** like LIBs, spent PIBs will need to be processed, so that these still active, electrochemical devices do not pose an environmental hazard in landfill sites and so as not to waste their component materials. This goes especially for PIBs with critical, expensive and/or toxic materials such as cobalt, chromium, graphite or vanadium. LIBs can be recycled using three main processes: (1) pyrometallurgical, where the battery is shredded and melted down, so that standard metallurgical processes can be applied to extract the valuable materials; (2) hydrometallurgical, where the shredded battery undergoes lower temperature, chemical processes to extract materials and (3) direct recycling, in which component materials are first separated through various mechanical processes and then undergo a series of processes to restore their functionality, for direct use in manufacturing of further batteries. At the time of publishing, no specific research into the recycling of PIBs has been published, but it is expected that the processes will be largely similar to those for LIBs. There will be similar issues to overcome, such as the high
<table><caption>**Table 3.** Comparison between Li, Na and K. Reprinted from [332], Copyright (2020), with permission from Elsevier.</caption><thead><tr><th></th><th>Earth crust<br>abundance (wt%) [329]</th><th>World reserves<br>(ktonne<sup>a</sup>) [333]</th><th>Cost ($/tonne<sup>a</sup>) [333]</th></tr></thead><tbody><tr><td>Li</td><td>0.0017</td><td>22 000</td><td>17 000 (Li<sub>2</sub>CO<sub>3</sub>)<sup>b</sup></td></tr><tr><td>Na</td><td>2.36</td><td>25 000 000 (Na<sub>2</sub>CO<sub>3</sub>)</td><td>155 (Na<sub>2</sub>CO<sub>3</sub>)</td></tr><tr><td>K</td><td>2.09</td><td>35 000 000 (K<sub>2</sub>O eq.)</td><td>980 (K<sub>2</sub>O)</td></tr></tbody></table>

<figure><img src="image_30.png" /><figcaption>**Figure 25.** (a) Cost breakdown for a Li-NMC/G and hypothetical K-NMC/Gr battery. (b) Total cost for a 50 kWh LIB and PIB. Reprinted from [332], Copyright (2020), with permission from Elsevier.</figcaption></figure>

cost and low resource efficiency of pyrometallurgical processing and the development of processes for recovery of a broader range of materials. First studies have reported the usage of graphite recycled from LIBs as anode in PIBs with promising electrochemical performance [340, 341]. This serves as a first proof-of-concept of the manufacturing of PIBs using recycled materials.

*Methodological challenges:* the techno-economic assessment of PIBs is currently facing several obstacles including: (1) lack of input data due to low technology readiness level, (2) unfair comparison between PIBs and LIBs as the latter are produced on industrial scale with optimized manufacturing processes and (3) incoherent assessment metrics [342].

Regarding the last point, it is crucial that a standardized assessment approach is used to be able to compare the costs across battery technologies. Here, cost needs to be paired with performance and results should be presented on a per kg, per kWh and per kWh·lifetime basis. To avoid misleading interpretation of results, economic analyses should consider single cell materials (the focus of interest is often on the electrode materials) as well as the whole battery pack with its defined performance metrics (e.g. kWh) [342]. Indeed, it was shown in several studies that while SIB and PIB cathode materials present lower costs than their LIB counterparts, the overall cell and battery pack costs are higher due to lower performance [332, 334–336].

**Advances in science and technology to meet challenges**

*Materials*

To improve the economic viability of PIBs, the implementation of low-cost materials should be envisaged. In this context, especially the production of anode materials from waste and biomass has attracted attention in recent years [124, 343]. This would not only have a positive impact on the economics of PIBs, but also on their sustainability as environmental impacts associated with mining activities and graphite manufacturing would be avoided. Moreover, the use of biomass-derived anodes could mitigate the use of graphite, which is

<footnote>a Refers to metric tonne.</footnote>

<footnote>b Battery grade Li₂CO₃.</footnote>
classified as critical material. This would increase the supply chain resilience for PIBs, which is one of the major weaknesses of LIBs.

### Performance

An additional strategy to reduce the overall costs for PIBs is the improvement of their performance (i.e. cycling stability and energy density). This can be achieved by understanding the fundamental reaction mechanisms in PIBs, their performance bottlenecks and how to overcome them [343]. In this context, also the application purpose of PIBs should be well-defined to prioritize the correct performance metric for a specific use case and bundle research efforts.

### Manufacturing

An increased efficiency of materials and energy use as well as waste reduction will reduce manufacturing and battery costs. Knowledge transfer from LIB production could accelerate upscaling and facilitate the establishment of optimized manufacturing processes [334]. Also already existing manufacturing lines for LIBs could be used for PIBs thus reducing initial capital expenses [344].

### Techno-economics

Only few studies have dealt with the economics of PIBs due to their early development stages and lack of input data. Here, using the experience of battery manufacturers, for instance, could help overcome uncertainties in terms of battery costing and increase the accuracy of techno-economic models for this emerging technology. Therefore, close collaborations between industry and academia are highly desirable.

### Concluding remarks

PIBs are handled as a promising battery technology and research efforts in this domain have significantly increased in recent years. However, PIBs also need to make a good business case to incentivize their commercialization. In this context, techno-economic analyses are crucial as they can reveal financially non-viable materials that should not be pursued further and highlight areas and metrics that need to be improved to bring down overall costs. Indeed, it was shown that PIBs are currently not cost-competitive to LIBs and further research is needed to achieve cost parity.

In addition to the techno-economics, also the environmental impacts of PIBs should be closely observed. For every technology, it is crucial to match performance and cost with sustainability to avoid environmental crises to the like we can observe currently with LIBs. Therefore, besides techno-economic analysis, also life cycle assessment should be an integral part of the fundamental research in the field of PIBs.

### Acknowledgments

LL thanks the Faraday Institution for their support through the ‘Multiscale Modelling (MSM)’ project (Grant No. FIRG0025).

### Data availability statement

No new data were created or analysed in this study.

### ORCID iDs

Yang Xu https://orcid.org/0000-0003-0177-6348

Magda Titirici https://orcid.org/0000-0003-0773-2100

Jacqueline Sophie Edge https://orcid.org/0000-0003-4643-2426

Jingyu Feng https://orcid.org/0000-0003-3181-4544

Sumair Imtiaz https://orcid.org/0000-0001-7288-2987

Laura Lander https://orcid.org/0000-0001-8128-126X

Phuong Nam Le Pham https://orcid.org/0000-0001-7176-2449

Laure Monconduit https://orcid.org/0000-0003-3698-856X

Gopinathan Sankar https://orcid.org/0000-0001-5152-3424

Lorenzo Stievano https://orcid.org/0000-0001-8548-0231

Chengliang Wang https://orcid.org/0000-0002-1151-3122

Qichun Zhang https://orcid.org/0000-0003-1854-8659

Min Zhou https://orcid.org/0000-0003-2677-5472
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