First patented in the early 1940s, lithium greases rapidly captured the grease market by 1970. The superior performance and ease of manufacturing compared to peer technologies led to this dominance of lithium greases. Lithium greases still dominate the worldwide grease market with approximately 70% of market share.^1,2 Most of the surge in lithium grease volumes since the 1970s has been in lithium complex greases, which are considered superior in performance over conventional lithium and other multipurpose greases.

STLE member Dr. Anoop Kumar, a senior staff scientist with Chevron Products Co., a division of Chevron USA, in Richmond, Calif., notes that lithium grease refers to both simple lithium grease and lithium complex grease. He says, “In general, simple lithium greases are used as multi-purpose and extreme pressure (EP) greases in moderate operating environments, whereas lithium complex greases are used in high performance and severe operating conditions.” Simple lithium greases account for about 50% of the world grease market, while lithium complex greases account for about 20%.²

Currently, the future of lithium greases is at a crossroads due to several challenges: 
1. The use of lithium in batteries. The unprecedented growth in electric vehicles (EVs) may challenge the availability of lithium for greases.
2. Supply challenges and price. From 2017 to 2018, a severe shortage of lithium supplies led to an exponential increase in the price of lithium. Although supplies appear to be improving, prices are still increasing.
3. Toxicological concerns. A recent proposal from the European Union (EU) to classify lithium salts as a Category 1A substance could cause concerns for the lithium grease industry.³ Under EU regulations, carcinogenic, mutagenic or toxic for reproduction (CMR) substances are of concern because of long term and serious effects they may exert on human health. Category 1A substances include known human carcinogens, mutagens or reproductive toxicants that have been identified based on human evidence.

These issues have led to a push to develop alternate grease technologies that can potentially substitute for lithium greases.

Historic dominance of lithium grease
STLE member Wayne Mackwood, head of detergents and grease at LANXESS Canada Co. in West Hill, Ontario, Canada, notes, “Lithium grease, properly formulated, can be an all-round high performing technology.” With the possible exception of food contact, lithium greases have probably either been used or considered for use in nearly all grease applications. Mackwood says lithium greases “are relatively straight-forward to produce, there is a large body of research in the public domain to draw upon, and the products can be produced in very large quantities with good cycle times.” The thickener content in lithium greases also is relatively low, which Mackwood says “until recent times made them a very cost-effective technology, especially for large consumers of grease.”

In addition, Mackwood notes, “Lithium 12-hydroxystearate (12HSA) soap also can be used as a pre-formed soap.” While this pre-formed soap may not be as cost effective as direct, large-scale production, “it has proven to be a very effective thickening system for specialty formations and for hard to process greases, such as those based on esters.”

Lidan Yao, senior engineer for lubricating grease with SINOPEC China (China Petroleum & Chemical Corp.) in Beijing, China, projects, “In China in the EV era, the ratio of lithium series grease will decrease in the future but is still the most important type of grease.” Yao notes that calcium-based alternatives have some shortcomings compared to lithium greases, including the complexity of their manufacturing processes, the low usage temperature of calcium grease and that calcium complex greases tend to harden. These limitations make effective lithium grease replacements difficult to find.

Replacements for lithium greases
Mackwood notes that calcium sulfonate can be a potential replacement for lithium greases, and can even outperform most lithium products, “except for very low temperatures and very high speed/high temperature bearing applications.” Sulfonate greases can offer enhanced corrosion protection and improved mechanical stability in wet conditions when compared to lithium products. He says that a transition has been observed over the last several years to the use of these alternatives to lithium grease.

Mackwood says, “In recent years, quite a number of research papers have been presented at the various lubricant conferences and by many different companies on the subject of the development or use of sulfonate grease.” This activity shows that product development has been occurring with the technology. Mackwood reports that over the past decade the annual NLGI production survey clearly shows the global production of calcium sulfonate grease growing at a high rate, while the lithium grease production numbers have been declining. In addition, he notes, “The equipment used to make lithium complex grease, for the most part, is perfectly suited to the manufacture of calcium sulfonate grease.”

Yao notes that anhydrous calcium grease at medium temperatures and sulfonate calcium complex grease at higher temperatures can substitute for lithium greases. Calcium sulfonate complex grease has better extreme pressure function, antiwear (AW) characteristics and antioxidant (AO) particularity than lithium greases. However, with so much thickener in the mixture with correspondingly less oil, this may result in poorer lubrication.

Kumar identifies potential alternatives to lithium greases currently being studied as including hybrid lithium-calcium, calcium sulfonate, polyurea and aluminum complex greases. He says, “Recent market trends indicate that there is a growing trend to use high-performance long-life greases.” Alternatives to lithium greases include “alternative technologies based on clay, aluminum complex, polyurea and calcium sulfonate thickeners.” When considering the replacement of lithium greases, Kumar notes that it is important “that when someone is considering the replacement of lithium greases with any other technology, the compatibility of lithium greases with the candidate grease plays an important role in decision making.” He observes, “Overall, for long and fill-for-life type applications, polyurea-based greases have an edge over other technologies. However, for heavy-duty industrial applications, calcium sulfonate-based greases generally stand out.”

EV greases
For the sake of simplicity, Kumar broadly classifies EV greases into two categories: wheel bearing greases and electric motor (EM) greases. He notes that while lithium-based greases may still be the preferred choice for wheel bearing applications, other types of grease also may perform well. For electric motor and other fill-for-life type applications, suitably modified lithium greases may still be successfully used; however, polyurea-based greases seem to be the preferred choice.



Future of lithium grease
Kumar says that the increasing demands for lithium for batteries is resulting in lithium prices skyrocketing, raising serious concerns in the grease industry. Additionally, he says, “There is growing concern due to proposed harmonization and classification of lithium compounds, including lithium hydroxide, under the Classification, Labelling and Packaging (CLP) regulations.” These factors are increasing the trend to find alternatives for lithium greases. He noted, “The latest NLGI production survey indicated that the volumes of lithium greases are declining, whereas the volumes of lithium complex greases have slightly increased though at a slower pace.”

Prior to the dominance of lithium greases, Kumar says, “Calcium and sodium greases were the most commonly used greases, especially for automotive and wheel bearing applications.” While calcium greases have excellent water resistance characteristics, they have limited high temperature capability. Sodium-based greases have comparatively superior high temperature characteristics but comparatively inferior water resistance characteristics.

In contrast, Kumar observes, “Lithium greases possess both superior high temperature, as well as water resistance, characteristics.” This combination of properties led to the widespread application of lithium greases. On top of that, he says, “The response of lithium greases toward performance additives is excellent and allows them to easily be customized for specific applications.” The lithium grease manufacturing process is both simple and robust, making lithium grease the preferred choice for grease producers.

Yao sees the price of lithium greases continuing to increase in the future as lithium battery storage energy technologies continue to develop. Lithium-ion batteries are known to be better than nickel-cadmium batteries as they have better energy density and better memory-effect. However, lithium-ion batteries also have limitations, including that they are inadequate for the energy industry, have poor energy conversion efficiency at low temperatures and have poor safety records.

Mackwood believes that the lithium grease technology “remains a viable platform for the development of new grease formulations.” When properly formulated, he notes that lithium-based greases “perform very well in the applications that they are tailored to.” While recognizing the concerns about rising costs and future availability of raw materials, Mackwood believes that “lithium chemistry remains perfectly viable as a thickener for a wide range of applications.”

Recent research has been published and patented (U.S. 20170335223 A1) by Andy Waynick, who has been looking at ways to enhance the thickening efficiency of lithium greases. This research appears to use lithium hydroxide to form a grease.⁴

Conclusions
Kumar says, “Although lithium-based greases are still the most popular and preferred greases, the ever increasing prices and availability concerns have compelled the industry to look for alternate technologies.” In addition, the development of widely accepted specifications for EVs is another challenge facing the industry.

REFERENCES
1. Pistilli, M. (Aug. 12, 2019), “Top lithium-producing countries,” Investing News. Available here.
2. GlobeNewswire (July 20, 2022), “Insights on the lithium grease global market to 2027 - Increase in demand for automotive in emerging economies to create lucrative opportunities,” GlobeNewswire. Available here.
3. Todorović, I. (June 9, 2022), “Lithium salts could be declared health hazard in EU,” Balkan Green Energy News. Available here.
4. Waynick, J.A. (2021), “A fresh look at lithium complex greases part 2: One possible path forward,” NLGI Spokesman, 85 (4), pp. 10-31.

FOR FURTHER READING
McGuire, N. (2020), “Lithium’s changing landscape,” TLT, 76 (2), pp. 32-39. Available here.

Andrea R. Aikin is a freelance science writer and editor based in the Denver area. You can contact her at pivoaiki@sprynet.com.