Long-Duration Energy Storage: The Race to Define the Grid’s Future

At a January 30 press conference held by China’s National Energy Administration, new data revealed a striking milestone: by the end of 2025, the country’s installed new-type energy storage capacity reached 136 million kilowatts (3.51 billion kWh)—a more than 40-fold increase compared to the end of the 13th Five-Year Plan period. In 2025 alone, 62.24 GW / 183 GWh of new storage capacity was added, representing year-on-year growth of 47% in power capacity and 81% in energy capacity.

The primary driver behind this surge is the large-scale integration of renewable energy into the grid. However, the intermittent and fluctuating nature of wind and solar power remains an unresolved challenge. As a result, a more pressing question has emerged beyond simply “whether to deploy storage”: As the grid requires power stability over entire diurnal cycles—or longer—when will long-duration energy storage be ready to meet the demand?

This very question—one tied directly to future energy security—has quietly yet intensely spurred a competition among technology pathways. In this race, early movers in the industry have diverged into two fundamentally different strategic mindsets.

The first is the evolutionary approach. This path pushes the limits of existing technologies to the edges of physics and chemistry, with a focus on deep innovation in cell design and system integration. By developing larger, thicker, and more efficient battery cells, and through systemic integration breakthroughs, this camp aims to push energy storage solutions into the economically viable range of 8 hours or longer.

The opposing camp is the reconstructionist approach, represented by flow battery technologies such as all-vanadium and iron-chromium systems. These solutions operate on a fundamentally different principle. Energy is stored in liquid electrolytes, and to increase storage duration, one theoretically only needs to enlarge the electrolyte tanks. This scalability—along with reduced dependence on scarce metals—has drawn significant attention since the technology’s inception. Yet the challenges are equally foundational: building an entirely new industrial ecosystem distinct from established supply chains.

On the lithium-ion front, companies like Hithium have already launched the world’s first native 8-hour lithium-ion energy storage system. Meanwhile, flow battery technologies saw explosive growth in 2024, and overall progress in that space continues to accelerate.

These two paths are not engaged in a simple zero-sum rivalry. Rather, they represent a competitive dynamic rooted in differing technological philosophies and tailored to distinct application scenarios. The outcome of this competition will profoundly shape the cost, safety, and structure of future power systems.

01
The Cost Reduction Race Defines the Divergence

No matter how promising a technological concept, it must ultimately be tested in the crucible of commercialization.

For long-duration energy storage, the evolutionary and reconstructionist schools start from different baselines and face different obstacles—yet cost reduction is the common goal. Since early 2025, the policy of mandatory storage allocation has been phased out. According to industry media reports, at least eight energy storage projects across China—spanning Shanxi, Hebei, Shandong, Henan, Yunnan, and Xinjiang—have announced tender cancellations in the past month alone, representing a total scale exceeding 4.2 GWh.

This means that every storage project must now prove its own profitability. But the paths to achieving this differ sharply between the two technology camps.

For the evolutionary camp, the cost reduction curve has been repeatedly validated by the photovoltaic and lithium battery industries. As production capacity expands, manufacturing processes improve, and vertical integration deepens, unit costs continue to descend along the learning curve. In practice, companies like Hithium and Envision Energy are pushing cell capacities from the industry-standard 280Ah toward 500Ah, 700Ah, and beyond.

The logic behind this capacity arms race is straightforward: fewer cells mean fewer connectors, lower battery management system complexity, higher system integration efficiency, and ultimately, lower cost per watt-hour. Hithium, for example, leveraged its manufacturing efficiency to become the world’s second-largest energy storage supplier in 2025 and achieve profitability—demonstrating the commercial viability of this path.

Of course, this route has its vulnerabilities, particularly in resource dependence. Even with lithium iron phosphate batteries that utilize cheaper iron, fluctuations in upstream lithium prices introduce uncertainty into the cost curve. This is why industry giants are also exploring sodium-ion technology: sodium is far more abundant than lithium, offers theoretically lower costs, and can leverage existing lithium-ion production lines—a promising cost-reduction branch.

For instance, at the end of October 2025, Hithium showcased its ∞Power N2.28MWh sodium-ion storage system (1-hour duration), alongside its ∞Power 6.25MWh long-duration system and the global-first ∞Cell 1175Ah long-duration battery cell.

For the flow battery camp, the cost equation is more complex. Take all-vanadium flow batteries (VRFB) as an example: their initial capital costs currently exceed those of lithium-ion systems. Cost reduction here is not a simple function of scale but requires simultaneous progress across materials, design, and manufacturing.

On the materials front, the core task is reducing the cost of expensive electrolytes or developing cheaper alternatives. On the design side, increasing power density in stacks can lower the cost per unit of power. On the manufacturing side, the localization and scaling of key components like ion-exchange membranes remain critical.

That said, flow batteries hold distinct advantages. Power and energy are decoupled: extending storage duration theoretically requires only larger, low-cost tanks and more electrolyte—not proportionally more expensive stacks. This gives flow batteries significant long-term cost potential in ultra-long-duration applications (e.g., 8–10 hours or more). Realizing that potential, however, depends on crossing the critical threshold from demonstration projects to cost-competitive commercialization.

02
Technological Fundamentals Determine the Pace of Evolution

The two major long-duration storage pathways are driven by fundamentally different physical principles.

To put it simply: for lithium-ion (and sodium-ion) batteries, energy and power are deeply coupled. Both are integrated into fixed electrode materials. Extending storage duration means proportionally increasing electrode materials, cells, and system scale—like enlarging both the fuel tank and the engine simultaneously.

For flow batteries, the equation is different: energy and power are relatively decoupled, and storage duration scales with electrolyte volume. In this liquid-based system, power is determined by the stack, while energy is determined by the volume of electrolyte tanks—two independent variables. Extending duration theoretically requires only larger tanks and more electrolyte, while the costly power unit can remain unchanged.

Companies like Hithium, which has released 1300Ah ultra-large cells targeting the 8-hour storage market, represent the current frontier of the lithium-ion path. The core logic involves innovations like ultra-thick electrodes to push single-cell energy to its limits without significantly sacrificing efficiency or cycle life, thereby reducing balance-of-system costs and enabling long-duration applications.

Of course, inherent safety risks remain a consideration. Hithium has announced multi-level cell protection systems, including intelligent temperature-control separators that automatically close pores when temperatures rise abnormally, cutting off charging current and suppressing thermal runaway. The company also works to reduce the surface reactivity of LFP cathodes under high temperature and voltage for greater stability.

Flow batteries offer greater peace of mind in this regard. Whether all-vanadium or zinc-bromine systems, their active materials are dissolved in aqueous electrolytes, fundamentally eliminating the combustion and explosion risks associated with organic electrolytes. This gives them a non-negotiable advantage in grid-scale peak shaving and storage projects near densely populated areas.

Still, as noted, overcoming inherent disadvantages—improving energy density, efficiency, and lowering costs—remains the core technological challenge.

A recent example: Shanghai Electric’s newly certified high-performance non-fluoride membrane all-vanadium flow battery stack. By replacing costly traditional fluorinated membranes with innovative non-fluoride alternatives, the company reduced key material costs and, through optimized flow channel design, boosted stack energy efficiency to over 82%—reaching internationally advanced levels.

Meanwhile, Professor Li Xianfeng’s team at the Dalian Institute of Chemical Physics achieved a breakthrough in zinc-bromine flow batteries, developing a novel bromine-based two-electron transfer system that increased cycle life by more than 20-fold while achieving near-zero corrosion and higher energy density.

Both pathways are advancing rapidly toward the long-duration storage frontier, though lithium/sodium-ion technologies maintain a faster commercialization pace, while flow batteries remain largely in the demonstration or early-commercialization phase.

03
Defining Long Duration Means Defining the Application

When we consider the divergent cost curves and inherent technological characteristics, the competition between long-duration storage pathways can be reframed as a single question: Which scenarios are best suited to which technological solutions at what stage of maturity?

The eventual outcome may not be a winner-take-all scenario but rather a coexistence defined by specific application contexts.

Consider grid-scale storage—currently the largest market. For intraday peak shaving in the 4- to 8-hour range, lithium/sodium-ion solutions—with their lower upfront costs and fast response—hold a clear advantage. This is precisely the market Hithium targets with its 8-hour systems. However, as renewable penetration crosses critical thresholds, grids will inevitably face longer-duration energy gaps. If flow battery technologies mature sufficiently, their low marginal cost for capacity expansion could make them invaluable for managing multi-day or multi-week weather events.

In commercial and industrial applications, safety can be a decisive factor. Flow batteries’ inherent safety characteristics give them a natural—and sometimes mandatory—advantage in industrial parks, densely populated areas, or critical infrastructure with stringent fire-safety requirements. If costs can be addressed, this could become a major opportunity for the flow battery camp.

Moreover, the rapidly growing AI and data center sector may not wait for this competition to resolve itself. AI data centers demand safety, fast response, and long cycle life—requirements that may be difficult for any single technology to fully meet. This could give rise to hybrid storage systems combining, for instance, high-power, fast-response lithium/sodium batteries for second-level power fluctuations with inherently safe, long-life flow batteries for longer-duration backup.

In this context, competition may shift from individual product performance to the ability to deliver scenario-specific integrated energy solutions.

This capability is also reflected in Hithium’s strategic evolution. From its early days focusing entirely on energy storage, to continuous cell innovation around grid-centric LCOE reduction, to its strategic entry into sodium-ion for future resource security and scenario diversification, and now to its early deployment of long-duration storage products—each step aligns with evolving customer needs. It is this approach that has enabled Hithium to sustain its momentum in the energy storage market.

04
Epilogue

This is both the best of times and the most demanding of times for energy storage. Installation rates continue to break records, yet numerous projects across China have halted tenders due to unworkable economics. Ultimately, economic viability and scenario-based thinking will be the cornerstones of a healthy business model.

As we dissect the competition between pathways, examine technological differences, and explore application needs, we must return to a fundamental truth: the goal of developing energy storage is not simply deployment for its own sake, but the creation of measurable, sustainable industrial value within the broader context of China’s long-term renewable energy build-out.

The current tension, at its core, is a temporary mismatch between the pace of energy storage technology iteration and the speed at which electricity market value-discovery mechanisms are evolving. Until the grid establishes clear pricing signals, all technology pathways must prove their viability in a market with fuzzy economics. This is the harsh backdrop against which companies like Hithium pursue extreme cost reduction—and the reason flow battery technologies must overcome higher initial barriers.

The story of long-duration energy storage began with anxiety over intermittency. Its conclusion will be defined by control over certainty.

Whoever defines the reliable value of storage will define the future of energy.

Edit by paco

Last Update:2026-02-26 09:10:16