Autonomic, thermally‐induced shutdown of Lithium‐ion (Li‐ion) batteries is demonstrated by incorporating thermoresponsive polymer microspheres (ca. 4 μm) onto battery anodes or separators. When the internal battery environment reaches a critical temperature, the microspheres melt and coat the anode/separator with a nonconductive barrier, halting Li‐ion transport and shutting down the cell permanently. Three functionalization schemes are shown to perform cell shutdown: 1) poly(ethylene) (PE) microspheres coated on the anode, 2) paraffin wax microspheres coated on the anode, and 3) PE microspheres coated on the separator. Charge and discharge capacity is measured for Li‐ion coin cells containing microsphere‐coated anodes or separators as a function of capsule coverage. For PE coated on the anode, the initial capacity of the battery is unaffected by the presence of the PE microspheres up to a coverage of 12 mg cm−2 (when cycled at 1C), and full shutdown (>98% loss of initial capacity) is achieved in cells containing greater than 3.5 mg cm−2. For paraffin microspheres coated on the anode and PE microspheres coated on the separator, shutdown is achieved in cells containing coverages greater than 2.9 and 13.7 mg cm−2, respectively. Scanning electron microscopy images of electrode surfaces from cells that have undergone autonomic shutdown provides evidence of melting, wetting, and resolidification of PE into the anode and polymer film formation at the anode/separator interface.

animals achieve material stasis via highly sophisticated autonomic repair and regenerative responses triggered by damage.Self-healing in synthetic materials has been demonstrated using a variety of methods such as incorporation of healingagent-fi lled capsules (capsule-based), [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] interconnected vascular networks [ 16 , 17 ] or discrete hollow capillaries, [18][19][20][21] or utilizing intrinsic properties of the material. [22][23][24][25][26] Capsule-based self-healing has been demonstrated in bulk thermoset matrices, [1][2][3][4][5][6][7][8][9] fi ber reinforced composite materials [10][11][12][13][14] and elastomers. [ 15 ] In these materials, damage triggers the rupture of the embedded capsules, releasing healing agent into the damaged material through capillary action. Polymerization of the healing agent is initiated by contact with an embedded catalyst or secondary polymerizing liquid.Efforts to develop self-healing fi berreinforced composites have focused on repair of large-scale delaminations and matrix cracking, but little attention has been given to repair of other composite damage modes. Complex damage modes in fi ber-reinforced composites such as matrix cracking, delamination, fi ber debonding, and fi ber rupture [ 27 , 28 ] present challenges beyond those addressed by self-healing in bulk polymers. In particular, debonding of the reinforcement from the matrix leads to a signifi cant loss of strength and stiffness of the composite by preventing effi cient load transfer from fi ber to matrix. [ 29 ] Additionally, small-scale damage, which may initiate at interfacial defects, can coalesce into large-scale damage during fatigue, ultimately leading to failure of the composite.Fiber-matrix adhesion is characterized by a variety of testing methods including single-fi ber pull-out and microbond, [30][31][32][33][34] single-fi ber fragmentation, [35][36][37][38][39] and single-fi ber pushout tests. [40][41][42][43][44] Each of these single-fi ber tests enables the measurement of the interfacial shear strength (IFSS, τ ) between the fi ber and matrix. In this work, the single-fi ber microbond specimen is adopted for assessing the ability to heal interfacial damage and recover IFSS. Microbond samples consist of a single fi ber embedded in a droplet or cylindrical block of matrix material ( Figure 1 ) and were prepared in a manner similar to the fl at cylindrical specimens described by Zhandarov et al. [30][31][32][33][34] During testing of a microbond specimen, the matrix is constrained and stress is transferred to the matrix-reinforcement interface by pulling on the embedded fi ber, which eventually leads to debonding. [30][31][32][33][34] Autonomic Recovery of Fiber/Matrix Interfacial Bond Strength in a Model CompositeAutonomic self-healing of interfacial damage in a model single-fi ber composite is achieved through sequestration of ca. 1.5 μ m diameter dicyclopentadiene (DCPD) healing-agent-fi lled capsules and recrystallized Grubbs' catalyst to the fi ber/m...

A protective polydopamine (PDA) coating is applied to core-shell microcapsule surfaces by the polymerization of dopamine monomers. A neutral aqueous solution and the addition of an oxidant (i.e., ammonium persulfate) are crucial for microcapsule survival and the initiation of PDA polymerization, respectively. The resulting PDA coating is a dense and uniform layer approximately 50 nm thick. The PDA protective coating significantly increases capsule stability at an elevated temperature (180 °C) and in a variety of organic solvents and acidic/basic solutions that otherwise lead to deflation and loss of the core content of uncoated microcapsules.

Flame retardant tris(2-chloroethyl phosphate) (TCP) is successfully encapsulated in core–shell poly(urea-formaldehyde) microcapsules by in situ polymerization. The microcapsules are electrochemically stable in lithium-ion (Li-ion) battery electrolytes and thermally stable to ca. 200 °C. Thermal triggering of these microcapsules at higher temperatures ruptures the shell wall, releasing the liquid core (flame retardant), and NMR spectroscopy confirms the presence of the flame retardant in the electrolyte solution. Li-ion pouch cell experiments demonstrate that microencapsulation of TCP and its incorporation into the battery electrolyte provide latent fire retardants that improve battery safety while maintaining inherent battery performance and cycling capability.

Thermally triggered autonomic shutdown of a Lithium-ion (Li-ion) battery is demonstrated using polydopamine (PDA)-coated polyethylene microspheres applied onto a battery anode. The microspheres are dispersed in a buffered 10 mM dopamine salt solution and the pH is raised to initiate the polymerization and coat the microspheres. Coated microspheres are then mixed with an aqueous binder, applied onto a battery anode surface, dried, and incorporated into Li-ion coin cells. FTIR and Raman spectroscopy are used to verify the presence of the polydopamine on the surface of the microspheres. Scanning electron microscopy is used to examine microsphere surface morphology and resulting anode coating quality. Charge and discharge capacity, as well as impedance, are measured for Li-ion coin cells as a function of microsphere content. Autonomous shutdown is achieved by applying 1.7 mg cm-2 of PDAcoated microspheres to the electrode. The PDA coating significantly reduces the mass of microspheres for effective shutdown compared to our prior work with uncoated microspheres.