Na-ion type bioabsorbable flexible electrochemical microbattery

Abstract

Na-ion type bioabsorbable flexible electrochemical microbattery. This invention is essentially composed solely of biocompatible materials that can be decomposed and removed by biological fluids, possessing mechanical properties and area capacity, particularly 1 mAh·cm². -2 The sodium-ion microbattery for powering various implantable bioelectronic devices features a 3D electrode design with micropillars that ensure improved electrochemical performance in terms of area capacity, cycle stability, and rate performance.

Description

[Technical Field]

[0001] This invention relates to electrochemical accumulators, and more particularly to sodium-ion (Na-ion) accumulators.

[0002] The main objective of this invention is to propose a novel structure for such a rechargeable battery, thereby making the battery flexible and bioabsorbable within the body of an animal or human.

[0003] A battery according to the present invention can be implemented to supply power to an implantable electronic system. For example, the battery of the present invention can be used to supply power to an organic light-emitting diode (OLED) that can be implanted in the body of an animal or a human. Furthermore, for example, the battery of the present invention is useful in meeting the performance requirements of miniaturized sensors for Internet of Things (IoT) applications such as electronic textiles, skin patches, drug delivery microchips, and cochlear implants. [Background technology]

[0004] As schematically shown in Figures 1 and 2, a lithium-ion battery or storage battery typically comprises an electrolyte component 1 located between a positive electrode or cathode 2 and a negative electrode or anode 3, at least one electrochemical cell consisting of a current collector 20 connected to the cathode 2 and a current collector 30 connected to the anode 3, and finally, a package 4 arranged to tightly house the electrochemical cell while allowing portions of the current collectors 20 and 30 to pass through.

[0005] The structure of a conventional lithium-ion battery comprises an anode, a cathode, and an electrolyte. Several types of conventional structural shapes are known: - A cylindrical shape, such as that disclosed in U.S. Patent Application Publication No. 2006 / 0121348; - Prismatic shapes such as those disclosed in U.S. Patent No. 7,348,098 (B1) and U.S. Patent No. 7,338,733 (B1); - Laminated structures such as those disclosed in U.S. Patent Application Publication No. 2008 / 060189, U.S. Patent Application Publication No. 2008 / 0057392, and U.S. Patent No. 7335448(B1).

[0006] The electrolyte component 1 may be in the form of a solid, liquid, or gel. In this last form, the component may include a polymer, ceramic, or microporous composite separator immersed in an organic electrolyte, aqueous electrolyte, or ionic liquid type electrolyte, thereby allowing lithium ions to move from the cathode to the anode during charging and in the reverse direction during discharging, thereby generating an electric current. The electrolyte is generally a mixture of organic solvents, for example, a carbonate to which a lithium salt, typically LiPF6, is added.

[0007] The positive electrode or cathode 2 is LiFePO4, LiCoO2, or LiNi 0.33 Mn 0.33 Co 0.33 It is composed of lithium cation-inserted materials, which are generally composites, such as O2.

[0008] The negative electrode or anode 3 is very often graphite carbon or Li4TiO5O 12 It is composed of (titanate material) and may also be a composite formed from silicon or a silicon base.

[0009] The current collector 20 connected to the positive electrode is generally made of aluminum.

[0010] The current collector 30 connected to the negative electrode is generally made of copper, nickel-plated copper, or aluminum.

[0011] These electrodes 2 and 3 for lithium-ion batteries are typically manufactured according to a continuous process by coating an active insertion material onto a metal strip acting as a current collector to form an active continuous layer. These coating methods are known by the terms "slot die" or "roll-to-roll transfer."

[0012] Lithium-ion batteries or rechargeable batteries can, of course, comprise multiple electrochemical cells stacked on top of each other.

[0013] Conventionally, lithium-ion batteries or rechargeable batteries use a pair of materials for the anode and cathode, thereby enabling them to operate at a high voltage level, typically equal to 3.6 volts.

[0014] Depending on the intended application, the goal is to manufacture either thin, flexible lithium-ion batteries or rigid batteries, and the package can also be flexible or rigid, in the latter case forming a kind of enclosure.

[0015] Flexible packages are typically manufactured from multilayer composite materials consisting of stacks of aluminum layers covered with one or more polymer films bonded together.

[0016] A rigid package, in itself, offers advantages such as resistance to higher pressures, and is typically 10 -8 It is used in applications requiring a more stringent level of airtightness than mbar·l / s, or in demanding applications where long service life is required in extremely harsh environments such as aerospace.

[0017] In some applications, the main drawback of the conventional shape of the structures described above is that the shape is bulky, heavy, and rigid regardless of the electrochemical properties and the flexible or rigid package. For example, due to the increasing interest in the development of small, fast, and portable electronic devices in recent years, it has become critically important to provide lightweight and flexible energy storage systems suitable for powering them.

[0018] Therefore, lithium-ion batteries (LIBs) called linear fiber-shaped lithium-ion batteries have become increasingly important due to their advantages of miniaturization, compliance, and ease of weaving.

[0019] Biodegradable microbatteries are particularly attractive for powering implantable electronic systems, but such body-safe devices also strongly influence a wider range of Internet of Things (IoT) applications such as electronic textiles, skin patches, drug delivery microchips, and cochlear implants.

[0020] In addition, the concept of biodegradable batteries is very interesting in powering environmentally friendly wearable devices such as discarded sensors and in solving the important issue of material recycling.

[0021] Among all energy solutions for implantable bioelectronics, rechargeable microgenerators for low-power electronics have several advantages such as high energy and power density, versatility, and lifespan: [1], [2]; and in terms of abundant availability, uniform distribution, low cost, and easy recyclability: [3], mainly relying on lithium (Li)-based technologies (LIBs).

[0022] However, these batteries encapsulated with toxic elements cannot be safely decomposed, so they must be surgically removed and recycled after use.

[0023] Therefore, efforts have been directed towards biocompatible self - degrading batteries:[4].

[0024] Currently, most bioabsorbable devices consist of a primary system using metal electrodes such as Mg, Zn, Mo, etc., and a liquid electrolyte which is generally a biological fluid such as blood, saliva, urine, etc., which causes fluctuations in electrochemical performance.

[0025] Solid and gel - like electrolytes have been proposed, but the formation of by - products has hindered electrode characteristics. In any case, this type of battery is not rechargeable, still difficult to handle, and its practical use is limited:[5].

[0026] In addition to electrochemical performance and biodegradability characteristics, an ideal battery for IoT dedicated to medical implants should also be ultra - thin, lightweight, flexible, and fully integrable. Its manufacturing should also be compatible with integrated circuit technology and micro - electronics processes.

[0027] Therefore, designing a flexible energy - storage micro - battery that is decomposable in biological fluids, safely excretable by the body, and exhibits high electrochemical performance is a challenging task.

[0028] Based on a mechanism similar to LIB, very recently, sodium - ion batteries (SIBs) have become a promising option because the main components of the battery can be non - toxic and biocompatible.

[0029] The electrolyte is an important component that governs the electrochemistry of the battery, but the related research in the case of SIBs is still at an initial stage.

[0030] Generally used organic electrolytes have poor thermal stability, high flammability, and low heat capacity. In addition, organic electrolytes are potentially dangerous due to their volatility and toxicity.

[0031] Safer and more sustainable polymer electrolytes are the best option to overcome these limitations:[6].

[0032] Solid polymer electrolytes (SPEs) still suffer from significant drawbacks, including low ionic conductivity and high interfacial resistance. Gel polymer electrolytes (GPEs), on the other hand, combine the advantages of SPEs and conventional liquid electrolytes, offering a path to rational design for SIBs with improved safety performance and, in particular, flexibility. However, to date, their development for SIBs is still in its very early stages.

[0033] Furthermore, since the manufacturing of all-solid-state sodium-ion microbatteries (SIMs) is still in its very early stages, research into developing novel bioabsorbable flexible energy storage devices is justified.

[0034] Among the few complete cells reported to date, the authors of the published publication reported a concentration of 145 μWh·cm². -2 We have fabricated a quasi-solid planar ionogel system SIM that was obtained by a sodium titanate anode and a sodium vanadate phosphate cathode of a separatorless interdigital microelectrode embedded in a three-dimensional interconnected graphene framework:[7].

[0035] SIMs produced by 3D printing have also been studied:[8]. The resulting thick SIM with a thickness of 1200 μm produced 40 mA·cm². -2 3.6mAh·cm -2 It demonstrated high rate performance and a robust long-term cycle life of up to 6000 cycles.

[0036] Regarding biocompatible batteries, efforts have also been focused on aqueous sodium-ion batteries.

[0037] Flexible belt-shaped and fiber-shaped aqueous systems have been studied with a variety of Na+ / - containing aqueous electrolytes, including Na2SO4 solution, ordinary saline, and cell culture medium.[9]

[0038] Symmetrical integrators (SIMs) obtained from Na2VTi(PO4)3 / C comb-type electrodes and different aqueous electrolytes such as simulated body fluids have also been tested:

[10]

[0039] There is a need to further improve sodium-ion microbattery (SIM) solutions to have particularly good electrochemical performance (high energy and / or power density, and / or area capacity, and / or cycle stability, and / or rate performance), and to make them flexible, implantable subcutaneously, and fully bioabsorbable. [Overview of the project] [Problems that the invention aims to solve]

[0040] The object of the present invention is to address such needs, at least in part. [Means for solving the problem]

[0041] Therefore, the present invention relates, in one embodiment thereof, to a sodium-ion microbattery (SIM) comprising the following: - At least one flexible encapsulation substrate made of at least one biocompatible, biodegradable polymer; - First and second electrically conductive biocompatible biodegradable films or foils forming a current collector, each having two main surfaces, one of which is connected to a flexible substrate and the other supporting biocompatible biodegradable electrode active material arranged in the form of a micropillar extending from the current collector to define a 3D electrode, wherein the electrode active material supported by the second current collector is of opposite polarity to the electrode active material supported by the first current collector; - A biocompatible, biodegradable polymer electrolyte positioned between two 3D electrodes, in contact with micropillars and filling the gap between the micropillars.

[0042] According to an advantageous embodiment, the polymer of the flexible encapsulating substrate is selected from poly(lactic-co-glycolic acid) (PLGA), polyester urethane, or mixtures thereof. Other biocompatible and degradable polymers may be implemented.

[0043] Advantageously, the first and / or second current collector is made of magnesium (Mg). Other biocompatible materials may be implementable, such as Mo, Fe, Z, and alloys, for example FeCuZn, etc. The active material of the electrode may be deposited on the current collector. The current collector can also be deposited on the slurry of the active material before subsequent deposition of a sealing material of a substrate such as PLGA.

[0044] Due to the abundance and non-toxicity of Mn, the sodium manganate material can be considered as a cathode material.

[0045] Thereafter, the active material is prepared as an electrode slurry together with a binder and carbon. Aqueous processing using a CMC binder improves the sustainability and environmental impact of battery technology. Na-CMC was selected because it is non-toxic, shows good water solubility, low cost, biodegradability, and biocompatibility. The weight percentages of the active material, conductive carbon, and binder components can be adapted.

[0046] Na 0.44 MnO2 (NMO) has been designated as one of the most promising (SIB) cathodes due to its low cost, simple preparation, high capacity of 121 mAh·g -1 and high stability:

[10] .

[0047] Therefore, according to another advantageous embodiment, the active material of the cathode is made of Na 0.44 MnO2 (NMO). As the active material of the cathode, all sodiated oxide materials with biocompatibility can be implemented.

[0048] According to this embodiment and advantageous modifications, the substance is obtained by mixing 80% by weight of NMO with 15% by weight of acetylene black and 5% by weight of Na-carboxymethylcellulose (Na-CMC) using water as a solvent.

[0049] The orthorhombic structure of NMO is advantageous for transporting relatively large Na+ ions and can withstand the stresses generated during charging and discharging.

[0050] NaTi2(PO4)3(NTP) has a capacity of 133mAh·g -1 It was selected as the anode material because of its large capacity and high performance against NMOs.

[11]

[0051] Because NTP has low electronic conductivity, carbon composite NTP-C is preferred, which is prepared by solid sintering:

[12] .

[0052] In a favorable embodiment, the anode active material is made of a NaTi2(PO4)3 carbon (NTP-C) composite. As the anode active material, any biocompatible material such as oxides or porous silicon can be implemented.

[0053] According to this embodiment and advantageous modifications, the substance is obtained by mixing 80% by weight of NTP-C with 15% by weight of acetylene black and 5% by weight of Na-carboxymethylcellulose (Na-CMC) using water as the solvent.

[0054] According to another advantageous embodiment, the polymer electrolyte is a gel polymer composed of an ion-conducting polymer, a sodium salt, and a plasticizer.

[0055] According to this embodiment and its advantageous modifications, the ion-conducting polymer may be selected from among sodium carboxymethylcellulose (Na-CMC), polyethylene glycol (PEG), and the like. A biocompatible gel polymer electrolyte (GPE) may be implemented as the polymer electrolyte.

[0056] According to this embodiment and its advantageous modifications, the Na salt can be selected from among Na2SO4, Na2SO3, and the like. All biocompatible sodium salts, such as NaCl, can be implemented.

[0057] According to another advantageous embodiment, the microbattery may comprise a further biocompatible and biodegradable film, preferably made of sodium carboxymethylcellulose (Na-CMC), positioned between the two 3D electrodes (2;3) as an electrical insulating separator.

[0058] Preferably, the thickness of the flexible sealing substrate is 1 to 100 μm.

[0059] Therefore, the essence of the present invention is to consist solely of biocompatible materials that can be decomposed and removed by biological fluids, possessing mechanical properties and a surface capacity, particularly 1 mAh·cm². -2 A sodium-ion microbattery exists for powering various implantable bioelectronic devices, featuring a 3D electrode design with micropillars that ensure improved electrochemical performance in terms of area capacity, cycle stability, and rate performance.

[0060] The aforementioned battery design relies on combining two flexible, thin foil films to form a current collector, each having an array of micropillar electrodes into which Na+ ions can be reversibly inserted and which are separated by a polymer electrolyte.

[0061] Ultimately, the present invention offers numerous advantages, some of which can be listed below: Unlike compact thin films for active materials, micropillars provide voids that prevent material fracture under mechanical strain and crack formation in the current collector due to volume fluctuations of the electrodes during Na+ ion insertion / extraction; - 3D structured electrodes using micropillars also improve the energy and power density of microbatteries because the surface area established between the electrode and electrolyte is larger; - The breakdown of micropillars yields small by-products that can be easily released by bodily fluids; - 3D electrodes have a faster resolution than conventional planar electrodes; - As described above, compared to results reported in the literature, the microbattery according to the present invention can be disintegrated and removed by bodily fluids, resulting in a safe and flexible micropower source that exhibits high energy and power density.

[0062] The present invention also relates to the use of the aforementioned microbatteries for supplying power to connected communication objects, biomedical devices, human implants, bioelectronic devices, and human / machine interfaces.

[0063] Therefore, the present invention can truly lay the foundation for future energy solutions for healthcare IoT by powering subcutaneous implantable devices and systems for in vivo sensing that can operate in the body for a predetermined period of time until the entire system is fully and safely absorbed by the body, detect specific disease biomarkers / drugs, and transmit physiologically relevant data on demand and wirelessly (e.g., red / NIR light or radio frequency-RFID) through the skin.

[0064] Because the microbatteries according to this invention can overcome the important challenge of recycling toxic components, they can penetrate deeply into other IoT markets as well.

[0065] Other advantages and features of the present invention will become clearer by reading the detailed description of exemplary implementations of the invention, which are given illustratively and non-limitingly with reference to the following figures. [Brief explanation of the drawing]

[0066] [Figure 1]Figure 1 is an exploded perspective schematic diagram showing various elements of a lithium-ion battery. [Figure 2] Figure 2 is a front view of a lithium-ion battery with a flexible package, based on prior art. [Figure 3] Figure 3 is a perspective view of a partially exploded sodium-ion microbattery according to the present invention. [Figure 4] Figure 4 is a scanning electron microscope (SEM) image of the Na0.44MnO2 substance (NMO) used as a cathode according to the present invention. [Figure 5] Figure 5 shows (a) the XRD pattern of the NMO sample, inset: schematic diagrams of the corresponding structures showing two different sites of sodium, and (b) the Raman spectrum of NMO in the wavenumber region of 100–900 cm⁻¹. [Figure 6] Figure 6 shows (a) the charge-discharge profile and (b) the cycle performance of an NMO-based cathode at 0.1C in the potential range of 2.0 to 4.0V versus Na+ / Na, according to the present invention. [Figure 7] Figure 7 shows a scanning electron microscope (SEM) image of the NaTi2(PO4)3-C composite material used as an anode according to the present invention. [Figure 8] Figure 8 shows (a) the XRD pattern of an NTP-C sample, inset: schematic diagram of the corresponding structure of NTP, and (b) the Raman spectrum of NTP-C in the wavenumber region of 100–1800 cm⁻¹. [Figure 9] Figure 9 shows the charge-discharge profile of the anode of an NTP-C system at 0.1C in the potential range of 1.0 to 3.0V versus Na+ / Na, according to the present invention. [Figure 10] Figure 10 shows the charge-discharge profiles of a porous Si anode in the potential range of 1.0–3.0 V versus Na+ / Na. [Figure 11] Figure 11 shows the biodegradation rates of (c) an NMO-based paste coated with the polymer electrolyte according to the present invention and (d) an NTP-C-based paste coated with the polymer electrolyte according to the present invention. [Figure 12]Figure 12 shows SEM images of the cathode (a) before decay and (b) 6 days later; the polymer electrolyte coated cathode (c) before decay and (d) 6 days later; the anode (e) before decay and (f) 6 days later; and the polymer electrolyte coated anode (g) before decay and (h) 6 days later. [Figure 13] Figure 13 shows the charge-discharge profile of the microbattery according to the present invention, which has an NTP-C anode / polymer electrolyte / NMO cathode. [Modes for carrying out the invention]

[0067] Figures 1 and 2 illustrate different examples of lithium-ion batteries with flexible packages based on prior art.

[0068] Figures 1 and 2 have already been described in the introduction and will not be discussed further here.

[0069] For clarity, in all of Figures 1 to 3, the same reference numerals are used for elements that are identical in the prior art and elements according to the present invention.

[0070] Figure 3 shows a Na-ion microbattery according to the present invention, which is implantable subcutaneously and is configured to be completely bioabsorbable.

[0071] Micro battery A includes the following components: - At least one flexible encapsulating substrate 6 made of at least one biocompatible, biodegradable polymer; - A conductive biocompatible biodegradable film or foil forming a current collector 20, comprising two main surfaces, one of which 22 is connected to a flexible substrate 6, and the other 21 supports a biocompatible biodegradable electrode active material 23 arranged in the form of a micropillar 24 extending from the current collector 20, thereby defining a 3D cathode 2; - A conductive biocompatible biodegradable film or foil forming a current collector 30, each having two main surfaces, one of which 32 is connected to a flexible substrate 6, and the other 31 supports a biocompatible biodegradable electrode active material arranged in the form of a micropillar 34 extending from the current collector, thereby defining a 3D anode 3; - A biocompatible, biodegradable polymer electrolyte 1 is positioned between the 3D cathode 2 and the 3D anode 3, in contact with the micropillars 24 and 34, and filling the gap between the micropillars.

[0072] Electrode preparation The active material is described in detail below. The active material was prepared as an electrode slurry together with a binder and carbon. Aqueous processing using a CMC binder improves the sustainability and environmental impact of the battery technology.

[0073] Na-CMC was selected due to its non-toxicity, good water solubility, low cost, biodegradability, and biocompatibility. The weight percentages of the active material, conductive carbon, and binder components are optimized.

[0074] Assembly of micro batteries The flexible substrate 6 may be made from PLGA or a polyester urethane polymer and may be used to encapsulate the electrochemical cores 1, 2, and 3.

[0075] The thickness of the sealing flexible substrate 6 can be adjusted between 1 μm and 100 μm to control the start date of microbattery decomposition.

[0076] Each electrode preparation is deposited onto a thin Mg film serving as the current collector 20, 30 using a doctor blade method.

[0077] Laser ablation is used to fabricate a vertical array of micropillars 24, 34 extending from current collectors 20, 30. This method can be carried out according to the procedure in

[13] . The size and spacing between adjacent micropillars 24, 34 can be adjusted to increase the capacitance by a factor of five while ensuring the flexibility of electrodes 2, 3.

[0078] Finally, polymer materials are used as electrolytes. Such polymer layers, which also function as separators, can be deposited onto flexible microstructure electrodes by drop casting or spin coating before assembling the full cell. The use of bioabsorbable separators, such as cellulose-based membranes, can also help avoid the risk of short circuits.

[0079] Cathode preparations and characterization preparation The active material 23 of cathode 3 is Na 0.44 This substance is MnO2(NMO). This material is a sodium ion biocompatible cathode, and its advantages are low cost, easy preparation, large capacity (121 mAh·g-1 vs Na+ / Na), and high stability.

[0080] NMO powder was synthesized using the coprecipitation method.

[0081] The SEM image in Figure 4 shows a finely shaped form of NMO particles with a uniform particle size distribution of approximately 3–5 μm in length and 0.5–1 μm in width. This particle size ensures reliable subsequent removal by animals or humans. The uniform grain size suggests favorability for Na migration. The morphological results obtained are in good agreement with those reported in the literature:

[14] .

[0082] As shown in Figures 5 a) and b), the as-prepared NMO was characterized by XRD and Raman spectroscopy. These results are consistent with previous reports such as

[15] .

[0083] Cathode paste was prepared by mixing 80% by weight of the active material (i.e., as-prepared NMO) with 15% by weight of acetylene black (biocompatible conductive agent) and 5% by weight of Na-CMC as a biocompatible binder, using water as the solvent, and deposited on an Al current collector.

[0084] Characteristic evaluation To demonstrate the paste preparation, the cathode performance was investigated using a half-cell configuration with a known organic liquid electrolyte.

[0085] Figures 6a) and 6b) show typical charge / discharge profiles and cycle performance (10 hours of charging or discharging, respectively) at a 0.1C rate. The capacity obtained in the second cycle was 1.1 mAh·cm². -2 (110mAhg -1 ) and after 30 cycles, 94% of the initial volume was observed to be retained.

[0086] Therefore, this paste cathode preparation achieves the inventors' objectives in terms of volume and stability.

[0087] These results validate the preparation of the cathode material.

[0088] Anode preparations and characterization preparation The active material 33 of anode 2 is a titanium-based NASICON compound, typically NaTi2(PO4)3(NTP). This material is considered to be a superionic conductor and biocompatible electrode material with high specific capacity, good structural stability, and cycleability in non-aqueous sodium-ion batteries.

[0089] However, pure NTP has the disadvantage of low electronic conductivity, and therefore, to overcome this limitation, the synthesis of NTP is further optimized by mixing it with carbon to obtain ultrafast rate performance and excellent high-rate cycle stability.

[0090] The synthesis of NTP-C was achieved using the solid-state method.

[0091] Figure 7 shows SEM images of the composite morphology of NTP-C tightly encapsulated in carbon black, with aggregate sizes ranging from 0.1 to 0.4 μm. The NTP crystallites have an equiaxed shape, consistent with those reported in reference

[16] .

[0092] As shown in Figures 8 a) and b), the as-prepared NTP-C was characterized by XRD and Raman spectroscopy. These results are consistent with previous reports such as

[17] .

[0093] For the preparation of the cathode electrode, the negative electrode paste was obtained by mixing 80% by weight of the active material (i.e., as-prepared NTP-C) with 15% by weight of acetylene black (biocompatible conductive agent) and 5% by weight of Na-CMC as a biocompatible binder, using water as the solvent, and then depositing it onto an Al current collector.

[0094] Characteristic evaluation Figure 9 shows 0.1C (1C = 133mA·g -1 The constant current charge / discharge voltage profile for the first cycle within the potential range of 1.0 to 3.0V is shown. The profile is for the first cycle with 125mAhg -1 (1.25mAh·cm -2 It exhibits a flat potential plateau at approximately 2.1V, providing a discharge capacity of ). Therefore, this paste electrode preparation achieves the required performance in terms of capacity and stability.

[0095] These results demonstrate the preparation of the anode material.

[0096] Porous Si films were also tested as a candidate anode material. Unfortunately, as shown in Figure 10, the overall performance was poor due to irreversible insertion of Na ions after the initial discharge, which led to a complete loss of capacity.

[0097] Polyelectrolyte preparation Various polymer electrolytes were prepared using sodium carboxymethylcellulose (Na-CMC) or polyvinyl alcohol (PVA) as the polymer material, sodium sulfate (Na2SO4) as the salt (mass ratio 3:1), glycerin as the plasticizer, and deionized water (DI) as the solvent.

[0098] Table 1 summarizes the composition of each component of the polymer electrolyte and the corresponding electrochemical reactions.

[0099] [Table 1]

[0100] Electrolyte preparations that did not contain plasticizers or had a low amount of glycerin exhibited a rigid morphology, while electrolyte #5 presented a gel-like texture.

[0101] In the electrochemical tests conducted using the anode and cathode described earlier in a half-cell configuration, no electrochemical activity was observed (the battery did not charge) due to the low ionic conductivity of Na+ in the solid electrolyte. Therefore, electrolyte number 5, which promotes rapid Na+ transport, was selected for the design of full electrochemical cells 1, 2, and 3.

[0102] These results demonstrate the feasibility of preparing polymer electrolytes.

[0103] To confirm these results, and in particular to determine whether PVA is ineffective, additional tests may or may not be conducted.

[0104] Disintegration test in simulated biological fluid The disintegration of polymer electrolyte-coated electrodes on aluminum was investigated in 10 mM phosphate buffer (PBS) and 100 mM sodium chloride (NaCl) at 37°C and pH 7.4. The biodisintegration test was conducted in an artificial climate chamber for 15 days.

[0105] Figures 11c) and d) show the biodegradation rates of (c) electrolyte-coated NMO-based paste and (d) electrolyte-coated NTP-C-based paste, respectively.

[0106] The disintegration rates of electrolyte-coated electrodes 2 and 3 in physiological fluid were calculated as the percentage of the mass difference of the electrode material relative to the initial mass of the electrode material.

[0107] It took 12 days for the components of the microbattery to completely disintegrate. These results were confirmed by SEM analysis shown in Figure 12, where the current collector surface is clearly visible after 6 days. Figure 12 shows SEM images of the cathode (a) before disintegration and (b) after 6 days; the electrolyte-coated cathode (c) before disintegration and (d) after 6 days; the anode (e) before disintegration and (f) after 6 days; and the electrolyte-coated anode (g) before disintegration and (h) after 6 days.

[0108] These results demonstrate the biodegradability of all components 1, 2, and 3 of the microbattery according to the present invention.

[0109] Manufacturing of a micro battery prototype A microbattery consisting of an anode 2 material coated with electrolyte 1 and a cathode 3 material was assembled, and its electrochemical properties were evaluated to obtain a charge-discharge profile.

[0110] Figure 13 shows the first three charge-discharge cycles of the first NTP / polymer electrolyte / NMO prototype at a current of 10 μA.

[0111] The discharge capacity of the full micro battery is 138 μAh·cm². -2 Achieve.

[0112] Therefore, the microbattery prototype possesses energy storage properties and is completely biodegradable in a biological medium. A high-performance biodegradable microbattery for implantation applications can be envisioned.

[0113] The present invention is not limited to the examples described so far, and the features of the examples shown can be combined with each other in, in particular, variations not shown.

[0114] Other modifications and extensions can be envisioned without departing from the scope of the present invention.

[0115] For example, it is conceivable to implement an additional biocompatible, biodegradable film as an electrical insulating separator between two 3D electrodes. This additional film is preferably made of sodium carboxymethylcellulose (Na-CMC).

[0116] To avoid oxidation of the current collector, a thin layer of gold may be laminated on the current collector, for example, by vapor deposition.

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[17] : G. Xu et al., Electrochim. Acta 254, 328 (2017). DOI.org / 10.1016 / j.electacta.2017.09.121.

Claims

1. - At least one flexible encapsulating substrate (6) made of at least one biocompatible, biodegradable polymer; - First and second electrically conductive biocompatible biodegradable films or foils forming current collectors (20;30), each comprising two main surfaces (21, 22;31, 32), one of which (22;32) is connected to the flexible substrate (6), and the other (21;31) supports biocompatible biodegradable electrode active material (23;33) arranged in the form of micropillars (24;34) extending from the current collector to define a 3D electrode (2;3), wherein the electrode active material supported by the second current collector is of opposite polarity to the electrode active material supported by the first current collector; - A biocompatible, biodegradable polymer electrolyte (1) is positioned between the two 3D electrodes (2;3), in contact with the micropillars (24;34) and filling the gap between the micropillars. A sodium-ion (Na-ion) microbattery (SIM) equipped with [this feature].

2. The sodium ion (Na ion) microbattery according to claim 1, wherein the polymer of the flexible encapsulating substrate is selected from poly(lactic acid-co-glycolic acid) (PLGA), polyester urethane, or a mixture thereof.

3. The sodium ion (Na ion) microbattery according to claim 1 or claim 2, wherein the first and / or second current collector is made of magnesium (Mg).

4. The electrode active material of the positive electrode is Na ０．４４ MnO ２ A sodium ion (Na ion) microbattery according to any one of claims 1 to 3, manufactured by (NMO).

5. The sodium ion (Na ion) microbattery according to claim 4, wherein the substance is obtained by mixing 80% by weight of NMO with 15% by weight of acetylene black and 5% by weight of Na-carboxymethylcellulose (Na-CMC) using water as a solvent.

6. The electrode active material of the negative electrode is NaTi ２ (PO ４ ) ３ A sodium ion (Na ion) microbattery according to any one of claims 1 to 5, made of a carbon (NTP-C) composite.

7. The sodium ion (Na ion) microbattery according to claim 6, wherein the substance is obtained by mixing 80% by weight of NTP-C with 15% by weight of acetylene black and 5% by weight of Na-carboxymethylcellulose (Na-CMC) using water as a solvent.

8. The sodium ion (Na ion) microbattery according to any one of claims 1 to 7, wherein the polymer electrolyte is a gel polymer composed of an ion-conducting polymer, a Na salt, and a plasticizer.

9. The sodium ion (Na ion) microbattery according to claim 8, wherein the ion-conducting polymer is selected from sodium carboxymethylcellulose (Na-CMC) and polyethylene glycol (PEG).

10. The Na salt is Na ２ SO ４ Na ２ SO ３ The sodium ion (Na ion) microbattery according to claim 8 or claim 9, which is selected from among them.

11. A sodium ion (Na ion) microbattery according to any one of claims 1 to 10, comprising a further biocompatible and biodegradable film, preferably made of carboxymethylcellulose sodium (Na-CMC), disposed between the two 3D electrodes (2;3) as an electrical insulating separator.

12. The sodium ion (Na ion) microbattery according to any one of claims 1 to 11, wherein the thickness of the flexible sealing substrate is 1 to 100 μm.

13. Use of a microbattery according to any one of claims 1 to 12 for supplying power to connected communication objects, biomedical devices, human implants, bioelectronic devices, and human / machine interfaces.

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