Electrochemical device and electric device

Abstract

The application provides an electrochemical device and an electric device, and belongs to the technical field of secondary batteries. a Co b M 1 1‑a‑b O2 and LiMn 2‑c M 2 c O4; the positive electrode active material layer comprises a positive electrode material and a lithium supplementing agent; the lithium supplementing agent comprises a matrix and a coating layer, the matrix comprises a lithium-rich metal oxide; and the coating layer comprises poly(3,4-ethylenedioxythiophene). In the electrochemical device, the PEDOT coating layer is coated on the surface of the lithium supplementing agent to reduce the byproduct gas generated by the side reaction between the residual lithium supplementing agent and the electrolyte after lithium supplementing, thereby improving the gas generation and cycle performance of the electrochemical device.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to an electrochemical device and an electrical device. Background Technology

[0002] During the first week of charging of electrochemical devices such as lithium-ion batteries, a solid electrolyte interface (SEI) is formed on the surface of the negative electrode. This consumes the active lithium in the positive electrode, resulting in irreversible capacity loss. The most widely used graphite negative electrode can suffer irreversible capacity loss of up to 10%, while for silicon-based and tin-based negative electrodes with high specific capacity, the irreversible capacity loss can be as high as 30% or more. This means that some of the active lithium extracted from the positive electrode material is irreversibly consumed. The loss of lithium will lead to a decrease in battery capacity, a decrease in coulombic efficiency, and a deterioration in cycle performance.

[0003] In existing technologies, electrochemical devices typically add lithium replenishing agents to the positive electrode active material layer of the positive electrode to compensate for the active lithium consumed during the formation of the SEI film during the initial charging process. However, using widely used lithium replenishing materials such as Li₂NiO₂ and Li₆CoO₄ in ternary chemical system batteries (such as lithium nickel cobalt manganese oxide LiNiO₂) presents challenges. x Co y Mn 1-x-y O2 batteries (and similar products) can exacerbate gas production in batteries, thereby deteriorating battery performance.

[0004] Therefore, an electrochemical device needs to be designed to solve the above problems. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides an electrochemical device and an electrical device to solve the technical problem that, during the charging and discharging process of existing electrochemical devices, the surface conductivity and structural stability of the lithium replenishment material after delithiation are poor, and it is easy to generate gas by side reaction with the electrolyte, which further aggravates the gas generation problem of the electrochemical device.

[0006] To achieve the above and other related objectives, the present invention provides an electrochemical device, the electrochemical device comprising a positive electrode plate, the positive electrode plate comprising a positive electrode active material layer; the positive electrode active material layer comprising a positive electrode material and a lithium supplementing agent;

[0007] The cathode material includes LiNi. a Co b M 1 1-a-b O2 and LiMn 2-c M 2 c One or more of O4, wherein 0 < a < 1, 0 < b < 1, 0 ≤ c < 2, a + b ≤ 1, M1 Includes at least one of Mn, Al, Ti, Zr, Cu, Ca, Ta, and Mg, M 2 Including at least one of Ni, Co, Mg, Al, Cu, Ta, Zr, Ti, and Ca;

[0008] The lithium replenishing agent comprises a matrix and a coating layer; wherein the matrix comprises a lithium-rich metal oxide; and the coating layer comprises poly(3,4-ethylenedioxythiophene).

[0009] In one example of the present invention, the lithium-rich metal oxide is Li2NiO2 or Li6CoO4.

[0010] In one example of the present invention, the thickness of the coating layer is 20-40 nm.

[0011] In one example of the present invention, the thickness of the coating layer is 25-35 nm.

[0012] In one example of the invention, the average particle size D50 of the lithium supplement is 0.4–40 μm. The average particle size (D50) can be defined as the particle size corresponding to the 50% volumetric size in the particle size distribution curve. The average particle size (D50) can be measured, for example, by laser diffraction. Laser diffraction is typically capable of measuring particle sizes from submicron to several millimeters, thus providing highly reproducible and high-resolution results.

[0013] In one example of the present invention, in the positive electrode material, M 1 It includes at least Mn and / or Al; and / or, the M 2 It includes at least Ni.

[0014] In one example of the present invention, the cathode material includes LiNi. a1 Co b1 Mn 1-a1-b1 O2, LiNi a2 Co b2 Al 1-a2-b2 O2 and LiNi c1 Mn 2-c1 One or more of O4, wherein 0 < a1, a2 < 1, 0 < b1, b2 < 1, 0 < c1 < 2, a1 + b1 < 1, a2 + b2 < 1.

[0015] In one example of the present invention, the lithium supplement agent accounts for 0.1 to 10 wt% of the positive electrode active material layer.

[0016] In one example of the present invention, the lithium supplement agent accounts for 2 to 7 wt% of the positive electrode active material layer.

[0017] The present invention also provides an electrical device comprising the electrochemical device described in any of the above examples.

[0018] This invention provides an electrochemical device in which a lithium-rich metal oxide lithium supplement is used in conjunction with a layered or spinel structure positive electrode material in the positive electrode active material layer of the positive electrode sheet. The surface of the lithium supplement is coated with a coating layer containing poly(3,4-ethylenedioxythiophene). The coating layer, which is both conductive and elastic, can accommodate the volume change caused by the shrinkage and cracking of the lithium supplement during high-voltage delithiation, thus providing a continuous and good protective effect on the surface of the lithium supplement. This reduces the surface area of ​​the lithium supplement exposed to the electrolyte after delithiation, thereby ensuring smooth electron transport at the lithium supplement interface while reducing side reactions at the lithium supplement / electrolyte interface, thereby improving the gas generation and circulation performance of the electrochemical device. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of the present invention is for describing specific implementation schemes and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0020] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as part of the scope of the invention.

[0021] Typically, electrochemical devices (such as secondary batteries) include a positive electrode material, a negative electrode material, an electrolyte, a separator, and corresponding connecting components and circuits. During battery charging and discharging, active ions (lithium ions) repeatedly insert and extract between the positive and negative electrode plates. The separator, positioned between the positive and negative electrode plates, primarily prevents short circuits while allowing lithium ions to pass through. The electrolyte, located between the positive and negative electrode plates, mainly serves to conduct the active ions.

[0022] During the initial charging of a battery, lithium ions are released from the positive electrode active material, conducted through the electrolyte, and intercalated into the negative electrode active material. During this process, some lithium ions participate in the formation of a solid electrolyte intercalation (SEI) film on the surface of the negative electrode active material, resulting in the loss of active lithium. Furthermore, during subsequent charge-discharge cycles and storage, the repair and growth of the SEI film, as well as side reactions of the electrolyte on the lithium-intercalated negative electrode surface, may irreversibly consume lithium ions.

[0023] Therefore, additional active lithium can be provided through pre-lithiation schemes to compensate for the loss of active lithium. Existing cathode lithium replenishment schemes typically involve adding a lithium replenishing agent compatible with the battery chemistry to the cathode electrode, such as a lithium-rich metal oxide with a surface oxide layer. Lithium-rich metal oxides, such as Li2NiO2 and Li6CoO4, are compatible with the battery's charge and discharge voltage range. During battery charging, they release lithium ions, compensating for the irreversible loss of active lithium during the initial charge to form the SEI film and during subsequent cycling and storage. The metal oxide layer also enhances the interfacial stability of the lithium replenishing agent, reducing interfacial side reactions between the agent and the electrolyte, thereby minimizing negative impacts on battery performance.

[0024] Lithium replenishers can compensate for lithium ion losses in batteries caused by the formation of SEI films, thereby ensuring battery energy. However, in practical applications, the addition of lithium replenishers can have additional negative effects on the performance of secondary batteries. For example, for cathode lithium replenishment schemes of ternary layered or spinel structure cathode material systems, the lithium replenishers currently used will greatly increase battery gas production, thereby affecting battery cycle performance and safety performance. The above effects are more severe under high temperature conditions (e.g., above 45°C, such as 45°C~80°C or 45°C~60°C).

[0025] The inventors discovered that during the delithiation process in the high-voltage range, the lithium replenishing agent, due to its own characteristics, is unable to adapt to the higher voltage of the battery, and after delithiation, it undergoes a side reaction with the electrolyte to generate additional gas. For secondary batteries using layered or spinel-structured materials as the main cathode material, they have higher charge and discharge voltages compared to batteries using lithium iron phosphate as the cathode material. For example, the full charge voltage of ternary materials is 4.2V to 4.4V, and that of nickel-manganese spinel materials is 4.7V to 5.0V. Under such high voltage, the lithium replenishing agent will experience excessive delithiation, resulting in significant surface collapse and deep cracks. Conventional coatings such as metal oxides cannot adapt to such large volume changes and are easily torn during the lithium insertion / extraction process, exposing the surface cracks of the lithium-rich metal oxides to the electrolyte. After excessive delithiation, the lithium-rich metal oxides are prone to leaving residual compounds such as metal oxides or Li-MO (lithium-containing metal oxides) on the surface. These residual substances have extremely strong reactivity with the electrolyte. When these residual substances are directly exposed to the electrolyte, they will undergo side reactions with the electrolyte, causing gas production and thus worsening the gas production problem of the secondary battery. Therefore, for pre-lithiation solutions of secondary batteries using layered or spinel structure materials as the main cathode materials, how to maintain high energy density of the battery while suppressing gas generation during storage is an urgent problem to be solved.

[0026] To address the aforementioned problems, this invention provides an electrochemical device in which a lithium-rich metal oxide coated with poly(3,4-ethylenedioxythiophene) is used as a lithium replenishing agent in the positive electrode. The conductive and elastic coating layer on the surface of the lithium replenishing agent can adapt to the volume changes caused by the shrinkage and cracking of the lithium replenishing agent during high-voltage lithium insertion / extraction, thus providing continuous and good protection for the surface of the lithium replenishing agent. This ensures smooth electron transport at the lithium replenishing agent interface while reducing side reactions at the lithium replenishing agent / electrolyte interface, greatly improving the gas generation and circulation performance of the electrochemical device. As a result, the gas generation and circulation performance of the electrochemical device with the added lithium replenishing agent reaches the level of that without the added lithium replenishing agent.

[0027] This invention provides an electrochemical device, one specific embodiment of which is a battery comprising one or more "cells". A "cell" refers to a single battery cell capable of independent charging and discharging. Each "cell" includes a positive electrode, a negative electrode, an electrolyte, a separator, and corresponding connecting components and circuits. The positive electrode includes a positive current collector and a positive active material layer disposed on the current collector. The positive active material layer includes a positive electrode material, a lithium replenishing agent, a conductive agent, and a binder. The negative electrode includes a negative current collector and a negative active material layer disposed on the current collector. The negative active material layer includes a negative electrode material, a conductive agent, a thickener, and a binder. In the electrochemical device, the positive and negative electrode materials can intercalate and deintercalate lithium ions to achieve energy storage and release. The electrolyte is the carrier for lithium ion transport between the positive and negative electrode plates. The separator is permeable to lithium ions but non-conductive, thus separating the positive and negative electrode plates to prevent short circuits. It should be noted that the type of negative electrode material used in the negative electrode sheet can be any negative electrode active material known in the art. For example, the negative electrode material can be a carbon-based material (such as graphite, hard carbon or soft carbon), a silicon-based material (such as silicon oxide) or a carbon-silicon composite material.

[0028] The aforementioned cathode materials include layered structure materials, such as LiNi. a Co b M 1 1-a-b O2, and spinel structure materials, such as LiMn 2-c M 2 c O4, one or more of the following, where 0 < a < 1, 0 < b < 1, 0 ≤ c < 2, a + b ≤ 1, M 1 Includes at least one of Mn, Al, Ti, Zr, Cu, Ca, Ta, and Mg, M 2 It includes at least one of Ni, Co, Mg, Al, Cu, Ta, Zr and Ca.

[0029] Among them, the electrochemical device has a high energy density and full charge voltage under the above-mentioned cathode material system. For example, when the cathode material is a layered structure material (such as ternary material), the full charge voltage of the electrochemical device can reach 4.2V to 4.4V; when the cathode material is a spinel structure material (such as nickel manganese spinel material), the full charge voltage of the electrochemical device can reach 4.7V to 5.0V.

[0030] Layered structure material LiNi a Co b M 1 1-a-b In O2, M 1 The element is selected from at least one of Mn, Al, Ti, Zr, Cu, Ca, Ta, and Mg. That is, M 1The element can be any of the elements listed above, such as Mn, Al, Ti, Zr, Cu, Ca, Ta, or Mg, etc.; M 1 An element can also be any two or more combinations of the element types listed above, such as M. 1 The elements can be combinations of Mn and Al, or combinations of Mn and Zr, or combinations of Mn and Mg, or combinations of Al and Ti, or combinations of Al and Zn, or combinations of Mn, Al and Ga, or combinations of Mn, Al, Cu and Mg, etc., which will not be listed here.

[0031] Spinel structural material LiMn 2-c M 2 c In O4, M 2 The element is selected from at least one of Ni, Co, Mg, Al, Cu, Ta, Zr, Ti, and Ca. That is, M. 2 The element can be any of the elements listed above, such as Ni, Co, Mg, Al, Cu, Ta, Zr, Ti, or Ca, etc.; M 2 An element can also be any two or more combinations of the element types listed above, such as M. 2 The elements can be combinations of Ni and Al, or combinations of Ni and Co, or combinations of Ni and Mg, or combinations of Ni and Cu, or combinations of Al and Ta, or combinations of Ti and Cu, or combinations of Ti, Ta and Zr, or combinations of Ni, Co and Al, or combinations of Ni, Co and Zr, or combinations of Ni, Co, Cu and Mg, etc., and will not be listed here.

[0032] Furthermore, when M 1 Elements and M 2 When there are two or more elements in a combination, the proportion of each element within the combination is not limited. In other embodiments, M 1 Elements and M 2 Elements can also be element types not listed above.

[0033] The aforementioned lithium supplement includes a matrix and a coating layer. The coating layer covers at least a portion of the matrix surface. For example, the coating layer covers the entire surface of the matrix particles, or the coating layer covers a portion of the surface of the matrix particles. The matrix includes lithium-rich metal oxides, and the coating layer includes poly(3,4-ethylenedioxythiophene), abbreviated as PEDOT.

[0034] Among them, lithium-rich metal oxides have higher lithium insertion / extraction capacity, and can release more active lithium during battery charging. This can more effectively compensate for the irreversible loss of active lithium in the battery, thereby enabling the battery to have a higher cycle life or storage life under high temperature conditions. It should be noted that the lithium-rich metal oxide can be any lithium metal oxide material known in the art, depending on the type of cathode material used. For example, in a specific embodiment of the present invention, in order to match the cathode material mainly composed of layered structure materials and / or spinel structure materials in the electrochemical device, the lithium-rich metal oxide is Li2NiO2 or Li6CoO4.

[0035] PEDOT possesses excellent elastic modulus. The PEDOT-accumulated coating layer can adapt to the volume changes caused by particle shrinkage and fracture during the lithium-rich metal oxide matrix during lithium insertion / extraction, thus continuously adhering to the surface of the lithium-rich metal oxide to provide a long-lasting protective effect at the lithium supplement interface. Due to its good compatibility with the electrolyte, the PEDOT adhering to the substrate surface can prevent direct contact between the substrate and the electrolyte while ensuring that it does not react with the electrolyte during electron transport. This effectively reduces side reactions at the lithium supplement / electrolyte interface, significantly improving the battery's high-temperature gas generation and cycle performance. Furthermore, since lithium-rich metal oxides themselves have poor electronic conductivity, existing metal oxide coatings may worsen the battery's DC internal resistance and affect its rate performance. PEDOT, as a high-quality conductive polyelectrolyte composite, has excellent conductivity and will not excessively increase the battery's internal resistance.

[0036] In some embodiments, the coating thickness is 20–40 nm, for example, the coating thickness can be 20 nm, 25 nm, 30 nm, 35 nm, or 40 nm. The coating within the above thickness range exhibits both good conductivity and elastic modulus. However, if the coating thickness is too thin, the elastic modulus may be insufficient to accommodate the volume changes caused by particle shrinkage and breakage during the initial lithium insertion / extraction process. This makes it difficult to completely cover the substrate surface after lithium extraction by the lithium replenisher, leaving part of the substrate surface exposed to the electrolyte, resulting in poor improvement of the lithium replenisher / electrolyte interface side reactions. Conversely, if the coating thickness is too thick, the PEDOT coating can affect the extraction of lithium ions from the lithium replenisher, hindering ion transport and increasing the internal resistance of the electrochemical device.

[0037] In some embodiments, the thickness of the coating layer can be selected from 25 to 35 nm, for example, the thickness of the coating layer can be 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, or 35 nm. Further, the coating layer thickness can be selected as 30 nm. When the coating layer thickness is within the above range, the elastic modulus and conductivity of the coating layer on the lithium supplement surface achieve the optimal balance.

[0038] In some embodiments, the elastic modulus of the coating layer is 2 to 4 GPa, for example, the elastic modulus of the coating layer can be 2 GPa, 2.5 GPa, 3 GPa, 3.5 GPa or 4 GPa. Because the coating layer has an elastic modulus within the above range, it can adapt to the volume change of the lithium replenishing agent under high voltage, so that the coating layer can maintain a large area of ​​coating on the substrate surface after the lithium replenishing agent is delithiated.

[0039] In some embodiments, the layered structure material LiNi a Co b M 1 1-a-b In O2, M 1 The elements include at least Mn and / or Al. Optionally, the layered structure material is a ternary material, such as LiNi. a1 Co b1 Mn 1-a1-b1 O2, LiNi a2 Co b2 Al 1-a2-b2 O2, where 0 < a1, a2 < 1, 0 < b1, b2 < 1, a1 + b1 < 1, a2 + b2 < 1; furthermore, the ternary material can be LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Al 0.1 O2 and LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0040] In some embodiments, spinel-structured materials LiMn 2-c M 2 c In O4, M 2 The element must include at least Ni. Optionally, the spinel structure material is a nickel-manganese spinel, i.e., LiNi. c1 Mn 2-c1 O4, where 0 < c1 < 2; furthermore, the nickel-manganese spinel material can be LiNi 0.5±0.2 Mn 1.5±0.2 O4.

[0041] In the above embodiments, the cathode material includes LiNi. a1 Co b1 Mn 1-a1-b1 O2, LiNi a2 Co b2 Al1-a2-b2 O2 and LiNi c1 Mn 2-c1 One or more of O4, wherein 0 < a1, a2 < 1, 0 < b1, b2 < 1, 0 < c1 < 2, a1 + b1 < 1, a2 + b2 < 1.

[0042] In some embodiments, the lithium replenishing agent accounts for 0.1 to 10 wt% of the positive electrode active material layer, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%. Optionally, the lithium replenishing agent accounts for 2 to 7 wt% of the positive electrode active material layer, for example, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, or 7 wt%. When the mass content of the lithium replenishing agent in the positive electrode active material layer is within the above range, the loss of active lithium in the positive electrode active material layer can be compensated as much as possible without excessively affecting the battery energy density. When the mass content of the lithium replenishing agent is lower than the above range, it may not be able to make up for the loss of active lithium in the positive electrode active material layer; when the mass content of the lithium replenishing agent is higher than the above range, it may cause insufficient reversible lithium intercalation vacancies in the positive electrode active material layer, affecting the energy density of the battery.

[0043] In addition, the present invention also provides an electrical device, which includes the electrochemical device described in any of the above embodiments. The electrochemical device can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0044] The composition and preparation method of the electrochemical device provided by the present invention are described in detail below:

[0045] Positive electrode preparation: Positive electrode material, lithium supplement, conductive agent, and binder are mixed in a mass ratio of (87 to 97):(0.1 to 10):1.5:1.5, with a selectable mass ratio of 94:3:1.5:1.5. N-methylpyrrolidone (NMP) solvent is added, and the mixture is thoroughly stirred to obtain a positive electrode slurry. The positive electrode slurry is coated onto a positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, a positive electrode sheet is prepared. The conductive agent can be at least one of the following: carbon black (Super P), acetylene black, carbon nanotubes (CNTs), graphene, and carbon nanofibers (VGCF). For example, the conductive agents can be SP and CNTs, with a mass ratio of SP to CNTs of 1:0.5. The binder can be at least one of PVDF, PTFE, etc.

[0046] The preparation method of the above-mentioned lithium supplement includes the following steps:

[0047] S1. The metal precursor and lithium source are mixed and sintered to obtain a lithium-rich metal oxide matrix;

[0048] S2. 3,4-ethylenedioxythiophene monomer (EDOT) and initiator are purged through the substrate, and a poly(3,4-ethylenedioxythiophene) coating layer, namely PEDOT, is deposited on the substrate surface by oxidative chemical vapor deposition (CVD) to obtain the lithium supplement.

[0049] In step S1, the lithium source is at least one of Li2O, LiOH, Li2CO3, LiNO3, Li2C2O4, and CH3COOLi. Optionally, LiOH is used as the lithium source. The metal element of the metal precursor is Ni or Co. The precursor of Ni can be an oxide, hydroxide, organic salt, or inorganic salt of Ni, such as at least one of NiO, Ni(OH)2, NiSO4, Ni(NO3)2, and Ni(CH3COO)2. The precursor of Co can be an oxide, hydroxide, organic salt, or inorganic salt of Co, such as at least one of Co3O4, Co(OH)2, CoCO3, CoOOH, and Co3(PO4)2.

[0050] In step S2, the thickness of the coating layer deposited on the substrate surface is controlled by adjusting the flow rate of EDOT and initiator purging the substrate or the deposition reaction time.

[0051] Negative electrode preparation: Negative electrode materials such as graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.4:1:1.2:1.4, and deionized water is added. The mixture is stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet is prepared.

[0052] Membrane preparation: The membrane is made of PE or PP porous membrane, and PP / PE / PP porous membrane can be selected. The thickness is 9μm to 18μm, such as 9μm, 12μm, 16μm or 18μm; the air permeability is 180s / 100mL to 380s / 100mL, such as 180s / 100mL, 280s / 100mL or 380s / 100mL; the porosity is 30% to 50%, such as 30%, 40% or 50%.

[0053] Electrolyte preparation: Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0054] Assembling the electrochemical device (secondary battery): The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film is wrapped around the separator, dried, and the electrolyte prepared above is injected. After encapsulation, settling, and formation processes, a 1Ah soft-pack battery (i.e., a lithium-ion secondary battery) is finally produced.

[0055] The specific steps and conditions for electrolyte formation are as follows: After injecting the electrolyte, maintain a hot pressure environment of 0.1 MPa, charge at 0.02C for 17 minutes at 45°C in a static state, let it stand for 5 minutes, and then charge it to 0.3Ah at 0.02C. After that, cut off the gas bag and vacuum seal it, and let it stand at room temperature for 48 hours to complete the electrolyte formation.

[0056] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by conventional methods in the art.

[0057] Example 1

[0058] This embodiment provides a secondary battery, the positive electrode of which includes a positive electrode material and a lithium replenishing agent. The positive electrode material is LiNi. 0.8 Co 0.1 Mn 0.1The lithium supplement uses Li2NiO2 as a base and deposits a 15nm thick PEDOT coating layer on the surface of the base.

[0059] The preparation process of this lithium supplement is as follows:

[0060] S1. The dehydrated Ni(OH)2 precursor and LiOH are mixed, and Al2O3 accounting for 0.2wt% of the mass fraction of the matrix is ​​added. After mixing, the mixture is sintered at 800℃ in a nitrogen atmosphere for 20h to obtain the sintered material. Then the sintered material is crushed and sintered at 800℃ in a nitrogen atmosphere for 10h to obtain the Li2NiO2 matrix.

[0061] S2. 3,4-ethylenedioxythiophene monomer (EDOT) and initiator are purged through the substrate, and a 15 nm thick PEDOT coating layer is deposited on the substrate surface by CVD to obtain the lithium replenishing agent.

[0062] The preparation process of this secondary battery is as follows:

[0063] (1) Preparation of positive electrode sheet: The positive electrode material is mixed with the lithium supplement agent, conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) prepared above at a weight ratio of 94:3:1.5:1.5. The solvent N-methylpyrrolidone (NMP) is added and the mixture is stirred thoroughly to obtain a positive electrode slurry. The mixture is stirred under vacuum until the system is homogeneous and transparent to obtain the positive electrode slurry. The positive electrode slurry is uniformly coated onto a 16μm aluminum foil current collector. The aluminum foil current collector is then dried at room temperature and transferred to an oven to dry at 80℃~120℃ for 6h. After cold pressing and slitting, the positive electrode sheet is obtained, wherein the thickness of the positive electrode active material layer is about 50μm.

[0064] (2) Preparation of negative electrode sheet: The negative electrode material graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.4:1:1.2:1.4. Deionized water is added to adjust the slurry solid content to 55%. The mixture is then thoroughly stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on both sides of an 8μm negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for drying. Then, the negative electrode sheet is obtained through cold pressing, slitting and other processes. The thickness of the negative electrode active material layer is about 50μm.

[0065] (3) Electrolyte preparation: In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1mol / L.

[0066] (4) Separator preparation: The diaphragm is a 9μm polyethylene diaphragm with a ceramic coating of 2μm thickness on both sides.

[0067] (5) Battery assembly: The positive electrode, separator, and negative electrode obtained above are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. Then, an aluminum-plastic film is wrapped around the outside, and the battery is transferred to a vacuum oven to dry at 120°C. After injecting 3.0 g / Ah of electrolyte, the battery is sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a soft-pack battery (i.e., a lithium-ion battery) with a capacity of 1Ah is finally obtained.

[0068] The specific steps and conditions for electrolyte formation are as follows: After injecting the electrolyte, maintain a hot pressure environment of 0.1 MPa, charge at 0.02C for 17 minutes at 45°C in a static state, let it stand for 5 minutes, and then charge it to 0.3Ah at 0.02C. After that, cut off the gas bag and vacuum seal it, and let it stand at room temperature for 48 hours to complete the electrolyte formation.

[0069] Example 2

[0070] This embodiment provides a secondary battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step S2, the thickness of the PEDOT coating layer deposited on the surface of the lithium replenishment substrate is 20 nm by controlling the deposition time.

[0071] Example 3

[0072] This embodiment provides a secondary battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 27 nm by controlling the deposition time.

[0073] Example 4

[0074] This embodiment provides a secondary battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 30 nm by controlling the deposition time.

[0075] Example 5

[0076] This embodiment provides a secondary battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 40 nm by controlling the deposition time.

[0077] Example 6

[0078] This embodiment provides a secondary battery with the same system as that in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 50 nm by controlling the deposition time.

[0079] Example 7

[0080] This embodiment provides a secondary battery similar to that of Embodiment 4. The difference between this embodiment and Embodiment 4 is that the positive electrode material used in the secondary battery of Embodiment 7 is LiNi. 0.8 Co 0.15 Al 0.05 O2 material.

[0081] Example 8

[0082] This embodiment provides a secondary battery similar to that of Embodiment 4. The difference between this embodiment and Embodiment 4 is that the positive electrode material used in the secondary battery of Embodiment 8 is LiNi. 0.5 Mn 1.5 O4 material.

[0083] Example 9

[0084] This embodiment provides a secondary battery with the same system as Example 1. The difference between this embodiment and Example 1 is that the lithium replenishing agent in this secondary battery uses Li6CoO4 as the substrate, and a 15nm thick PEDOT coating layer is deposited on the substrate surface. The preparation process of this lithium replenishing agent is as follows:

[0085] S1. The dehydrated Co(OH)2 precursor and LiOH are mixed, and Al2O3 accounting for 0.2wt% of the matrix is ​​added. After mixing, the mixture is sintered at 800℃ under nitrogen atmosphere for 20h to obtain the sintered material. Then the sintered material is crushed and sintered at 800℃ under nitrogen atmosphere for 10h to obtain Li6CoO4 matrix.

[0086] S2. 3,4-ethylenedioxythiophene monomer (EDOT) and initiator are purged through the substrate, and a 15 nm thick PEDOT coating layer is deposited on the substrate surface by CVD to obtain the lithium replenishing agent.

[0087] Example 10

[0088] This embodiment provides a secondary battery with the same system as that in Embodiment 9. The difference between this embodiment and Embodiment 9 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 20 nm by controlling the deposition time and other methods.

[0089] Example 11

[0090] This embodiment provides a secondary battery with the same system as that in Embodiment 9. The difference between this embodiment and Embodiment 9 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 30nm by controlling the deposition time and other methods.

[0091] Example 12

[0092] This embodiment provides a secondary battery with the same system as that in Embodiment 9. The difference between this embodiment and Embodiment 9 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 40 nm by controlling the deposition time and other methods.

[0093] Example 13

[0094] This embodiment provides a secondary battery with the same system as that in Embodiment 9. The difference between this embodiment and Embodiment 9 is that in step S2, the thickness of the PEDOT coating layer deposited on the substrate surface is 50 nm by controlling the deposition time and other methods.

[0095] Example 14

[0096] This embodiment provides a secondary battery similar to that of Embodiment 11. The difference between this embodiment and Embodiment 11 is that the positive electrode material used in the secondary battery of Embodiment 14 is LiNi. 0.8 Co 0.15 Al 0.05 O2 material.

[0097] Example 15

[0098] This embodiment provides a secondary battery similar to that of Embodiment 11. The difference between this embodiment and Embodiment 11 is that the positive electrode material used in the secondary battery of Embodiment 15 is LiNi. 0.5 Mn 1.5 O4 material.

[0099] Comparative Example 1

[0100] Comparative Example 1 provides a secondary battery with the same system as Example 1. The lithium replenishing agent assembled in the secondary battery uses Li2NiO2 as the substrate, without a PEDOT coating layer on the substrate surface, but instead with an Al2O3 coating layer. The preparation process of this lithium replenishing agent is as follows:

[0101] S1. The dehydrated Ni(OH)2 precursor and LiOH are mixed, and Al2O3 accounting for 0.2wt% of the mass fraction of the matrix is ​​added. After mixing, the mixture is sintered at 800℃ in a nitrogen atmosphere for 20h to obtain the sintered material. Then the sintered material is crushed and sintered at 800℃ in a nitrogen atmosphere for 10h to obtain the Li2NiO2 matrix.

[0102] S2. The matrix is ​​uniformly mixed with 0.2 wt% Al2O3, and then sintered at 400°C for 8 hours under a nitrogen atmosphere to obtain the lithium supplement.

[0103] Comparative Example 2

[0104] Comparative Example 2 provides a secondary battery similar to Comparative Example 1, except that the positive electrode material used in Comparative Example 2 is LiNi. 0.8 Co 0.15 Al 0.05 O2 material.

[0105] Comparative Example 3

[0106] Comparative Example 3 provides a secondary battery similar to Comparative Example 1, except that the positive electrode material used in Comparative Example 3 is LiNi. 0.5 Mn 1.5 O4 material.

[0107] Comparative Example 4

[0108] Comparative Example 4 provides a secondary battery with the same system as Example 9. The lithium replenishing agent assembled in the secondary battery uses Li6CoO4 as the substrate, but instead of coating the substrate surface with a PEDOT coating layer, it is coated with an Al2O3 coating layer. The preparation process of this lithium replenishing agent is as follows:

[0109] S1. The dehydrated Co(OH)2 precursor and LiOH are mixed, and Al2O3 accounting for 0.2wt% of the mass fraction of the matrix is ​​added. After mixing, the mixture is sintered at 800℃ in a nitrogen atmosphere for 20h to obtain the sintered material. Then the sintered material is crushed and sintered at 800℃ in a nitrogen atmosphere for 10h to obtain the Li2NiO2 matrix.

[0110] S2. The matrix is ​​uniformly mixed with 0.2 wt% Al2O3, and then sintered at 400°C for 8 hours under a nitrogen atmosphere to obtain the lithium supplement.

[0111] Comparative Example 5

[0112] Comparative Example 5 provides a secondary battery similar to Comparative Example 4, except that the positive electrode material used in Comparative Example 5 is LiNi. 0.8 Co 0.15 Al 0.05 O2 material.

[0113] Comparative Example 6

[0114] Comparative Example 6 provides a secondary battery similar to Comparative Example 4, except that the positive electrode material used in Comparative Example 6 is LiNi. 0.5 Mn 1.5 O4 material.

[0115] The specific capacity of the lithium replenishing agents prepared in Examples 1 to 15 and Comparative Examples 1 to 6 was tested. Gas generation performance and DCR (Directive Current Resistance) tests were performed on the lithium-ion secondary batteries assembled with the preparations of Examples 1 to 15 and Comparative Examples 1 to 6 to verify the excellent gas generation performance and cycle performance of the electrochemical devices corresponding to the different examples and comparative examples. The test results are shown in Table 1, and the test methods are as follows:

[0116] (1) Lithium supplement specific capacity test:

[0117] The lithium-supplementing material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) prepared in the above embodiments and comparative examples were mixed in a weight ratio of 85:10:5. N-methylpyrrolidone (NMP) solvent was added and the mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was coated on a positive electrode current collector aluminum foil and then dried, cold-pressed, and slit to prepare a positive electrode sheet. A 2032 coin cell was assembled using lithium metal as the negative electrode sheet.

[0118] At 25°C, with a current density of 0.02 A / g, the test voltage range was from 3V (discharge cutoff voltage) to 4.3V (charge cutoff voltage) (when the lithium replenishment agent is in a layered ternary material, such as LiNi). 0.8 Co 0.1 Mn 0.1 O2 (when used in the system), or 3V (discharge cutoff voltage) to 4.95V (charge cutoff voltage) (when the lithium replenisher is in LiNi). 0.5 Mn 1.5 When used in the O4 system, the coin cell is subjected to its first charge / discharge test. The charge / discharge capacity of the coin cell is measured and then divided by the mass of the lithium replenisher to obtain the specific capacity of the lithium replenisher.

[0119] (2) Gas generation performance test of pouch battery:

[0120] After fully charging the prepared secondary battery, the initial volume V1 was measured. Then, the secondary battery was stored in a 60°C high-temperature cabinet. The secondary battery was recharged and its volume was measured every 7 days. After 56 days, the volume of the secondary battery was measured as V2. (V2-V1) / V1 is the gas production growth.

[0121] (3) DCR test method for soft-pack batteries:

[0122] The secondary battery prepared above was adjusted to 50% SOC (State of Charge), and then the DCR of the secondary battery was tested by discharging at a constant current rate of 4C for 30s.

[0123] Table 1: Specific capacity test results of the lithium replenishing agents prepared in Examples 1 to 15 and Comparative Examples 1 to 6, and corresponding gas generation and DCR test results of the secondary batteries.

[0124]

[0125]

[0126] Comparing the test results of Examples 1 to 8 and Comparative Examples 1 to 3, as well as Examples 9 to 15 and Comparative Examples 4 to 6, it can be seen that using lithium-rich metal oxides coated with PEDOT as lithium supplements in secondary batteries can effectively improve the gas generation performance of ternary cathode systems and spinel cathode systems. Because the PEDOT coating layer has a good elastic modulus, it can accommodate the particle shrinkage and cracking of the lithium supplement during the initial lithium insertion / extraction process at high voltage, forming a continuous and good protective effect on the surface of the lithium supplement, reducing side reactions at the lithium supplement / electrolyte interface, and effectively improving the gas generation problem during storage in high-energy-density secondary batteries.

[0127] The test results show that, compared to the over 30% gas production growth rate of secondary batteries using Al2O3-coated lithium supplements after 56 days of storage, using PEDOT-coated lithium supplements reduces the gas production growth rate by at least 10% after 56 days of storage. For example, after using PEDOT coating, the gas production growth rate of NCM ternary secondary batteries with Li2NiO2 as the lithium supplement matrix decreased from 34.7% to below 23.9% after 56 days of storage. The gas production growth rate of the nickel-manganese spinel secondary battery with O2 as the lithium supplement matrix decreased from 42.9% to 23.1% after 56 days of storage; while the gas production growth rate of the NCM ternary secondary battery with Li6CoO4 as the lithium supplement matrix decreased from 34.7% to below 23.9% after 56 days of storage, and the gas production growth rate of the nickel-manganese spinel secondary battery with Li6CoO4 as the lithium supplement matrix decreased from 44.6% to below 21.5% after 56 days of storage.

[0128] Comparing the test results of Examples 1 to 6 and Examples 9 to 13, it can be seen that with the increase of the thickness of the PEDOT coating layer on the surface of the lithium replenisher, the protective effect of the coating layer on the substrate is further improved, and the gas generation during secondary battery storage is reduced accordingly, thus further improving the gas generation problem of the secondary battery. For example, in the NCM ternary system secondary battery with Li2NiO2 as the lithium replenisher substrate, the gas generation growth rate after 56 days of secondary battery storage gradually decreased from 23.9% when the lithium replenisher coating layer thickness was 15nm to 12.6% when the lithium replenisher coating layer thickness was 50nm; in the NCM ternary system secondary battery with Li6CoO4 as the lithium replenisher substrate, the gas generation growth rate after 56 days of secondary battery storage gradually decreased from 29.3% when the lithium replenisher coating layer thickness was 15nm to 13.2% when the lithium replenisher coating layer thickness was 50nm.

[0129] Furthermore, due to the excellent electronic conductivity of PEDOT material itself, the reaction kinetics of the positive electrode are improved by using PEDOT-coated lithium replenishment agents. After using PEDOT-coated lithium replenishment agents, the DCR of the secondary battery decreased by 3.9%.

[0130] Comparing the test results of Examples 1 to 6 and Examples 9 to 13, it can be seen that when the coating thickness on the surface of the lithium replenisher is within an appropriate range, i.e., when the coating thickness is 15 to 30 nm, the storage gas generation and DCR of the secondary battery both decrease with the increase of the lithium replenisher coating thickness. However, since PEDOT is not a good lithium-ion conductor, when the coating thickness on the surface of the lithium replenisher is greater than 30 nm, the excessively thick PEDOT coating layer will affect the extraction of lithium ions from the lithium replenisher, reduce the charge-discharge specific capacity of the lithium replenisher, and deteriorate the conductivity of the positive electrode, leading to an increase in the internal resistance of the electrochemical device and affecting the cycle performance of the electrochemical device. Therefore, when the coating thickness of the lithium replenisher is 25 nm to 35 nm, especially 30 nm, the improvement effect of the lithium replenisher on gas generation and DCR of high-capacity secondary batteries is optimal.

[0131] Comparing Example 7 with Comparative Example 2, Comparative Example 8 with Comparative Example 3, Comparative Example 14 with Comparative Example 5, and Comparative Example 15 with Comparative Example 6, it can be found that the above-mentioned lithium supplement coating layer still has a significant effect on improving gas production in secondary batteries of NCA ternary cathode system and spinel cathode system.

[0132] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode plate, and the positive electrode plate includes a positive electrode active material layer; The positive electrode active material layer includes a positive electrode material and a lithium supplement agent; The cathode material includes LiNi. a Co b M 1 1-a-b O2 and LiMn 2-c M 2 c One or more of O4, wherein 0 < a < 1, 0 < b < 1, 0 ≤ c < 2, a + b ≤ 1, M 1 Includes at least one of Mn, Al, Ti, Zr, Cu, Ca, Ta, and Mg, M 2 Including at least one of Ni, Co, Mg, Al, Cu, Ta, Zr, Ti, and Ca; the LiNi a Co b M 1 1-a-b The full charge potential of O2 is 4.2V to 4.4V, and the aforementioned LiMn 2-c M 2 c The O4 has a full charge capability of 4.7V to 5.0V; The lithium supplement includes: The matrix comprises lithium-rich metal oxide; The coating layer comprises poly(3,4-ethylenedioxythiophene) and the coating layer has a thickness of 20-40 nm.

2. The electrochemical device according to claim 1, characterized in that, The lithium-rich metal oxide is Li2NiO2 or Li6CoO4.

3. The electrochemical device according to claim 2, characterized in that, The coating layer has a thickness of 25–35 nm.

4. The electrochemical device according to claim 1, characterized in that, The average particle size D50 of the lithium supplement is 0.4–40 μm.

5. The electrochemical device according to claim 1, characterized in that, In the positive electrode material, M 1 It includes at least Mn and / or Al; And / or, the M 2 It includes at least Ni.

6. The electrochemical device according to claim 5, characterized in that, The cathode material includes LiNi. a1 Co b1 Mn 1-a1- b1 O2, LiNi a2 Co b2 Al 1-a2-b2 O2 and LiNi c1 Mn 2-c1 One or more of O4, wherein 0 < a1, a2 < 1, 0 < b1, b2 < 1, 0 < c1 < 2, a1 + b1 < 1, a2 + b2 < 1.

7. The electrochemical device according to claim 1, characterized in that, The lithium supplement agent accounts for 0.1 to 10 wt% of the positive electrode active material layer.

8. The electrochemical device according to claim 7, characterized in that, The lithium supplement agent accounts for 2-7 wt% of the positive electrode active material layer.

9. An electrical device, characterized in that, The electrical device includes the electrochemical device according to any one of claims 1 to 8.

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