DS-transformer: a dual-stream transformer for lithium-ion battery state-of-health estimation via cross-attention fusion of discharge curves and impedance features

Accurate and reliable estimation of the State of Health (SOH) of lithium-ion batteries is a fundamental requirement for the safe operation of Battery Management Systems in electric vehicles. Existing methods are broadly limited by the underutilization of complementary multi-modal information, overly simplistic fusion strategies that neglect cross-modal interactions, and the absence of explicit modeling between macroscopic temporal degradation signals and microscopic electrochemical impedance parameters. To address these limitations, this paper proposes DS-Transformer (Dual-Stream Transformer), an end-to-end dual-stream Transformer network. The model processes heterogeneous inputs through two parallel encoding paths: Stream 1 employs a multi-scale one-dimensional convolutional neural network to extract local degradation features from voltage, current, and temperature time-series signals recorded during discharge; Stream 2 uses a multi-layer perceptron to semantically encode the internal resistance (Rₑ) and charge transfer resistance (Rct). Unlike prior multi-modal methods that rely on simple feature concatenation, the two streams are dynamically aligned and explicitly fused through the proposed Cross-Stream Cross-Attention (CSCA) module, which uses temporal embeddings as Query and impedance embeddings as Key/Value to achieve semantic-level interaction modeling between degradation patterns and electrochemical states. A Transformer Encoder then captures global sequence dependencies, ultimately yielding SOH regression predictions. Systematic validation is conducted on the publicly available NASA AMES lithium-ion battery aging dataset (34 batteries, 7,565 experiments, covering five temperature conditions from 4^∘C to 44^∘C). DS-Transformer achieves MAE = 1.24%, RMSE = 1.67%, and R² = 0.9782, improving over the best baseline by 28.3%, 27.1%, and 1.90%, respectively. Ablation studies quantitatively demonstrate that the CSCA module is the most critical contributor (MAE increases by 37.9% upon removal, outperforming simple concatenation by 27.5%), while the dual-stream architecture and Transformer encoder are each independently indispensable. Multi-temperature robustness experiments further validate the stable generalization capability of the proposed model. This work establishes, for the first time, an explicit cross-modal interaction framework between discharge temporal signals and electrochemical impedance parameters for battery SOH estimation, offering significant theoretical insights and practical engineering value.