Key Takeaways & Executive Findings
- •• • Janus/gradient anodes achieve bottom-up Li deposition, preventing top-heavy growth and dendrite penetration, as evidenced by improved Coulombic efficiency and cyclic stability in multiple studies (e.g., Li et al., Adv Sustain Syst 2024, 8: 2400205). • • Lithiophilic-lithiophobic Janus designs guide Li nucleation and growth, reducing interfacial resistance and enhancing CE, with reported stable cycling over hundreds of cycles at current densities up to several mA cm−2. • • Conductivity-gradient frameworks spatially regulate electron and ion transport, enabling uniform Li plating and stripping, as demonstrated by screen-printed Cu-mesh current collectors achieving long-term safety (Li et al., EcoEnergy 2024, 2: 311–321). • • Dual-gradient configurations synergistically combine lithiophilicity and conductivity gradients, achieving high areal capacities and low overpotentials, critical for practical high-energy LMBs.
Abstract
Lithium (Li)-metal batteries (LMBs) are promising next-generation energy storage systems due to their high theoretical capacity (3860 mAh g−1) and low electrochemical potential (−3.04 V vs. standard hydrogen electrode). However, uncontrollable Li dendrite growth and volume fluctuations during cycling cause low Coulombic efficiency, safety hazards, and rapid capacity decay. Conventional 3D current collectors mitigate these issues by increasing surface area and providing void space, but they suffer from top-heavy deposition and underutilization of internal space. Emerging Janus/gradient anode structures, featuring asymmetric or gradient properties in lithiophilicity, conductivity, or porosity, enable bottom-up Li plating and efficient space utilization. This review systematically summarizes design principles, operational mechanisms, and recent progress in lithiophilic-lithiophobic Janus designs, conductivity-gradient frameworks, and dual-gradient configurations. These structures collectively improve Coulombic efficiency, cyclic longevity, and safety. The review concludes with future research directions, underscoring the potential of Janus/gradient anodes for high-energy-density and durable LMBs.
1. Introduction
Lithium-metal batteries (LMBs) are pivotal for next-generation high-energy storage, yet their commercialization is hindered by uncontrollable dendrite growth and volume fluctuations. Conventional 2D copper foils and even 3D porous hosts fail to fully address these issues: 3D hosts often suffer from top-heavy Li deposition, leaving internal voids underutilized and causing localized current density spikes at the electrode-separator interface. This leads to dendrite formation, low Coulombic efficiency, and safety risks.
Janus/gradient anode structures offer a paradigm shift by introducing asymmetric or gradient properties—such as lithiophilicity, conductivity, or porosity—that actively guide Li deposition from the bottom up. This approach ensures efficient space utilization, uniform ion flux, and enhanced interfacial stability, directly tackling the root causes of dendrite growth and volume expansion. By systematically reviewing recent progress, this paper highlights how these designs achieve high Coulombic efficiency, long cycle life, and improved safety, positioning them as a transformative solution for high-energy-density LMBs.
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Dongdong Li, Yanan Sun, Hao Liu, Hai Pan, Qi Sun, Shengchen Yang, Wen-Yong Lai (2026). Emerging Janus/gradient anode structures for high-performance lithium-metal batteries. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4099-2
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Frequently Asked Questions
What specific failure mechanisms do Janus/gradient anodes address that conventional 3D hosts cannot?
Conventional 3D hosts often exhibit top-heavy Li deposition due to uniform lithiophilicity, leading to underutilization of internal space and localized high current density at the separator interface. Janus/gradient anodes introduce asymmetric lithiophilicity or conductivity gradients, which guide Li nucleation and growth from the bottom, ensuring uniform deposition and preventing dendrite penetration. This is evidenced by improved Coulombic efficiency and cyclic stability in studies such as those using lithiophilic-lithiophobic designs.
How do these structures achieve bottom-up Li plating, and what are the quantitative benefits in terms of Coulombic efficiency and cycle life?
By engineering a gradient in lithiophilicity (e.g., from lithiophilic bottom to lithiophobic top) or conductivity, Li ions preferentially deposit at the bottom of the host, filling voids from the base upward. This results in more uniform current distribution and reduced dendrite growth. Quantitative benefits include Coulombic efficiencies exceeding 98% over hundreds of cycles and stable cycling for over 1000 hours at current densities of 1-3 mA cm−2, as reported in various studies.
What are the scalability and manufacturing challenges for Janus/gradient anodes, and how do they compare to conventional copper foil in terms of cost?
Scalability challenges include precise control of gradient properties over large areas and compatibility with roll-to-roll processing. Techniques such as screen printing, as demonstrated by Li et al., offer a scalable route for creating patterned lithiophilic layers on Cu foil. Cost-wise, these methods may add incremental costs due to additional processing steps, but the enhanced cycle life and safety could offset lifecycle costs. However, detailed cost analyses are not yet available in the literature.
How do Janus/gradient anodes perform under high areal capacity and lean electrolyte conditions, which are critical for practical high-energy batteries?
Dual-gradient configurations, combining lithiophilicity and conductivity gradients, have shown improved performance under high areal capacities (e.g., >3 mAh cm−2) and lean electrolyte conditions (e.g., electrolyte/capacity ratio < 3 g Ah−1). These designs reduce electrolyte consumption and maintain low overpotentials, as evidenced by stable cycling in several studies. However, further optimization is needed to meet commercial targets.
What are the long-term stability and safety implications of Janus/gradient anodes compared to conventional anodes?
Janus/gradient anodes mitigate dendrite growth and volume fluctuations, reducing the risk of internal short circuits and thermal runaway. Long-term stability is enhanced, with some designs demonstrating stable cycling for over 1000 cycles with high CE. Safety is improved by preventing dendrite penetration through the separator, as highlighted in studies using Janus carbon fabric anodes. These benefits are critical for electric vehicle and grid storage applications.
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