Self-poisoning system for lithium secondary batteries and poisoned incapacitated lithium secondary batteries

Abstract

A self-poisoning system for a lithium secondary battery and a poisoned, deactivated lithium secondary battery are disclosed. The self-poisoning system includes a poisoning agent disposed within or outside the electrochemical reaction system of the lithium secondary battery. When the lithium secondary battery is heated to a poisoning initiation temperature in the temperature range of 120°C to 150°C, the poisoning agent is activated and releases a primary poisoning element and an auxiliary poisoning element into the electrochemical reaction system of the lithium secondary battery. This forms an oxide layer on the surface of the positive electrode active material and fills the lithium-deficient vacancies with fluorine, thereby effectively stabilizing the crystal structure of the positive electrode active material, preventing oxygen release, and causing the positive electrode active material to lose its ability to participate in the electrochemical reaction of lithium-ion transfer, effectively terminating the thermal runaway reaction of the lithium secondary battery.

Description

Lithium secondary battery self-poisoning system and poisoned disabled lithium secondary battery Technical Field

[0001] The present invention relates to the safety of lithium secondary batteries, and particularly to a lithium secondary battery self-poisoning system and a poisoned disabled lithium secondary battery that stabilizes the lattice structure and oxygen content of the positive electrode active material by filling lithium vacancies in the positive electrode active material and forming bonds with oxygen and transition metals in the positive electrode active material, thereby suppressing thermal runaway of the lithium secondary battery. Background Art

[0002] Due to their excellent electrochemical properties, lithium-ion secondary batteries have become the preferred energy supply core in various devices. However, in terms of the basic structure of lithium-ion batteries themselves, excessive lithium ion release from the positive electrode active material, followed by deposition on the negative electrode, and excessive embedding or alloying of the negative electrode active material, etc., all of these processes make the positive and negative electrode active materials extremely thermally unstable. Coupled with some rapid exothermic reactions, such as the decomposition of organic electrolytes, or unexpected external factors such as needle puncture and external short circuits, lithium-ion batteries can experience thermal runaway in a very short time, resulting in explosion. Therefore, how to solve thermal runaway has become a key issue in the application of lithium-ion secondary batteries.

[0003] Currently, the methods for suppressing thermal runaway can be divided into two types, namely, outside the lithium secondary battery and inside the lithium secondary battery, depending on the location of the safety mechanism reaction. The methods outside the lithium secondary battery mainly use digital computing simulation monitoring systems, while the methods inside the lithium secondary battery can be divided into physical methods and chemical methods. The digital monitoring system outside the lithium secondary battery is to load a dedicated protection circuit on the outside of the lithium secondary battery and set up a dedicated management system and other technologies to enhance the safety monitoring of the battery during use. The physical methods inside the lithium secondary battery are such as thermal shutdown separators, which close the pores of the separator when the battery core heats up abnormally to block the passage of ions. The chemical methods inside the lithium secondary battery can be divided into degree control type and electrochemical reaction type. The degree control type, for example, adds flame retardants to the electrolyte to control the degree of thermal runaway. Examples of electrochemical reaction types include the following: 1. Adding monomers or oligomers to the electrolyte will cause polymerization when the temperature rises, thereby reducing the speed of ion migration, causing the ionic conductivity to decrease with increasing temperature, and slowing the electrochemical reaction rate in the lithium secondary battery. 2. Inserting a positive temperature coefficient thermistor (PTC) material between the positive electrode layer or negative electrode layer and the adjacent collector layer. When the temperature of the lithium secondary battery rises, the electronic insulation capacity is enhanced, and the electron transfer capacity between the positive electrode layer or negative electrode layer and the adjacent collector layer is deteriorated, reducing the electrochemical reaction rate. 3. By providing additives in the electrolyte or performing surface treatment on the active material, whether the additives or surface treatments are inorganic additives containing sulfur, phosphorus, carbonic acid or halogens, a modified layer is formed on the surface of the active material after formation to improve the thermal stability and structural stability of the active material.

[0004] However, the aforementioned methods only passively block or inhibit the electron or ion conduction pathways within the electrochemical system, and do not address the fundamental driver of thermal runaway, namely, the suppression of thermal runaway by the active material. For example, the aforementioned modification layer is formed during the molding stage, and to avoid affecting the subsequent charge and discharge performance of the lithium secondary battery, the thickness of the modification layer is often only 10 to 50 nanometers. Furthermore, to prevent the modification layer from being too thick, which would affect the electrical properties of the lithium secondary battery (such as charge and discharge capacity, mainly because a too thick passivation layer would affect ion migration and charge transfer), the dosage of these additives is also limited to an amount consistent with forming a modification layer of 10 to 50 nanometers. Although a passivation layer of such thickness, containing specific elements or compounds, can increase the thermal stability temperature of the active material, as the temperature rises, the extremely thin nanoscale modification layer will still collapse, exposing part of the active material. As a result, at the positive end, the oxygen components of the positive electrode active material, whose lattice is unstable, will still be released, and a violent thermal runaway reaction will occur at this higher temperature. In view of this, the present invention proposes a novel lithium secondary battery self-poisoning system and a poisoned disabled lithium secondary battery to effectively solve the above problems. Summary of the Invention

[0005] The main purpose of the present invention is to provide a self-poisoning system for a lithium secondary battery and a poisoned disabled lithium secondary battery. The lithium secondary battery is heated to a poisoning starting temperature, which is approximately in the range of 120°C to 150°C, and an electrochemical reaction system for the lithium secondary battery is initiated to release a main poisoning element and an auxiliary poisoning element. The auxiliary poisoning element forms an oxide layer on the surface of the positive electrode active material. The main poisoning element fills the lithium-deficient vacancies with fluorine elements to occupy the lithium vacancies in the lithium-deficient positive electrode active material of the lithium secondary battery and stabilize the oxygen content, so that the positive electrode active material that is unstable due to lithium deficiency is converted to a stable and disabled state, thereby cutting off the electrochemical reaction pathway for lithium ion transfer and effectively suppressing thermal runaway of the lithium secondary battery.

[0006] To achieve the above-mentioned purpose, the present invention proposes a self-poisoning system for lithium secondary batteries, which includes a lithium secondary battery and a poisoning agent. The lithium secondary battery has an electrochemical reaction system, which includes a positive electrode active material layer, a negative electrode active material layer and an electrolyte for transferring lithium ions between the positive electrode active material layer and the negative electrode active material layer; the poisoning agent is arranged inside or outside the electrochemical reaction system, and the poisoning agent can release a main poisoning element and an auxiliary poisoning element; when the temperature of the lithium secondary battery itself reaches the poisoning starting temperature, the The poisoning starting temperature falls in the range of 120°C to 150°C, and the poisoning agent begins to release the main poisoning element and the auxiliary poisoning element to the electrochemical reaction system. The auxiliary poisoning element first forms an oxide layer on the surface of the positive electrode active material, and then the main poisoning element occupies the lithium vacancy of the positive electrode active material and forms bonds with the cobalt, nickel and manganese in the positive electrode active material. The main poisoning element forms coordination with oxygen to prevent the release of oxygen in the positive electrode active material and stabilize the positive electrode active material; wherein the main poisoning element is fluorine.

[0007] The present invention also proposes a disabled lithium secondary battery after being poisoned by the above-mentioned self-poisoning system, characterized in that an oxide layer is formed on the surface of the positive electrode active material particles of the positive electrode active material layer of the poisoned lithium secondary battery, and the average fluorine content of the positive electrode active material particles at 300°C is more than 1.5 times the average fluorine content at 150°C.

[0008] The present invention also proposes a disabled lithium secondary battery, characterized in that an oxide layer is formed on the surface of the positive electrode active material particles of the positive electrode active material layer of the lithium secondary battery, and the average fluorine content of the positive electrode active material particles at 300°C is more than 1.5 times the average fluorine content at 150°C, and the positive electrode active material is a layered lithium oxide having cobalt, nickel and manganese.

[0009] The following is a detailed description of specific embodiments to facilitate understanding of the objectives, technical content, features, and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1( a ) is a TG-IR chart of the poisoning agent of the present invention, in which the main poisoning element is fluorine and the auxiliary poisoning element is boron.

[0011] FIG1(b) is an FESEM image of the positive electrode active material layer of FIG1(a) at 150°C, 250°C and 300°C, respectively, to detect the diffusion state of the main poisoning elements in the positive electrode active material particles.

[0012] FIG. 2( a ) is a TG-IR chart of the poisoning agent of the present invention, in which the main poisoning element is fluorine and the auxiliary poisoning elements are boron and phosphorus.

[0013] Figure 2(b) is a FESEM image of the positive electrode active material layer sliced ​​at 150℃, 250℃ and 300℃, showing the diffusion state of the main poisoning elements in the positive electrode active material particles.

[0014] FIG3 is a schematic diagram of an embodiment of the present invention in which the poisoning agent is disposed inside the electrochemical reaction system of a lithium secondary battery.

[0015] FIG4 is a schematic diagram of another embodiment of the present invention in which the poisoning agent is disposed inside the electrochemical reaction system of a lithium secondary battery.

[0016] FIG5 is a schematic diagram of another embodiment of the present invention in which the poisoning agent is disposed inside the electrochemical reaction system of a lithium secondary battery.

[0017] FIG6 is a schematic diagram of an embodiment of the present invention in which a poisoning agent is disposed on the surface of positive electrode active material particles in an electrochemical reaction system.

[0018] FIG7 is a schematic diagram of an embodiment of the present invention in which the poisoning agent is disposed outside the electrochemical reaction system of a lithium secondary battery.

[0019] FIG. 8 is a graph showing heat release curves of a lithium secondary battery having a poisoning agent according to the present invention and a lithium secondary battery not having a poisoning agent according to the present invention.

[0020] FIG9(a) and FIG9(b) are heat release curves of a lithium secondary battery having the poisoning agent of the present invention and a lithium secondary battery not having the poisoning agent of the present invention, respectively.

[0021] FIG. 10 is a temperature curve diagram of a thermal runaway test performed on a lithium secondary battery without the poisoning agent of the present invention using a thermal insulation reliability accelerated analysis calorimeter (ARC). DETAILED DESCRIPTION

[0022] To facilitate a clear understanding of the advantages, spirit, and features of the present invention, the following detailed description and discussion will be provided using examples. It should be noted that these examples are merely representative of the present invention and are not intended to limit the scope of the present invention to these examples. These examples are provided solely to make the disclosure of the present invention more thorough and easier to understand.

[0023] The terms used in the various embodiments disclosed in the present invention are only used for the purpose of describing specific embodiments and are not intended to limit the various embodiments disclosed in the present invention. Unless otherwise clearly indicated, the singular form used also includes the plural form. Unless otherwise specified, all terms used in this specification (including technical terms and scientific terms) have the same meaning as those generally understood by those skilled in the art to which the various embodiments disclosed in the present invention belong. The above terms (such as those defined in generally used dictionaries) will be interpreted as having the same meaning as the contextual meaning in the same technical field, and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in the various embodiments disclosed in the present invention.

[0024] Throughout this specification, references to terms such as "embodiment," "specific embodiment," and the like indicate that the specific features, structures, materials, or characteristics described in connection with that embodiment are included in at least one embodiment of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments.

[0025] In this specification, the word "about" is used to describe and illustrate small changes. For example, when used in conjunction with a numerical value, the word may refer to a range of variation less than or equal to ±10% of the stated numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0026] The present invention discloses a poisoning agent for suppressing thermal runaway of a lithium secondary battery. The poisoning agent can be disposed inside or outside the lithium secondary battery. The positive electrode active material of the positive electrode active material layer of the lithium secondary battery using the poisoning agent is a layered oxide particle having cobalt, nickel and manganese. For example, the positive electrode active material is selected from LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (referred to as NCM 111), LiNi 0.4 Co 0.2 Mn 0.4 O2 (referred to as NCM 424), LiNi 0.5 Co 0.2 Mn 0.3 O2 (referred to as NCM 523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (referred to as NCM 622), LiNi 0.8 Co 0.1 Mn0.1 O2 (referred to as NCM 811) or LiNi 0.9 Co 0.05 Mn 0.05 O2 (abbreviated as NCM 955).

[0027] Based on the aforementioned poisoning agent, the present invention proposes a self-poisoning system for a lithium secondary battery, comprising a lithium secondary battery and the aforementioned poisoning agent. The lithium secondary battery includes an electrochemical reaction system, wherein the electrochemical reaction system comprises a positive electrode active material layer; a negative electrode active material layer opposite the positive electrode active material layer; and an electrolyte for transferring lithium ions between the positive electrode active material layer and the negative electrode active material layer. The positive electrode active material layer is a layered lithium oxide containing cobalt, nickel, and manganese. The poisoning agent is disposed within or outside the electrochemical reaction system. Preferably, the activated poisoning agent is disposed closer to the positive electrode active material layer of the lithium secondary battery.

[0028] The poisoning agent releases a primary poisoning element and an auxiliary poisoning element into the electrochemical reaction system of the lithium secondary battery at the poisoning onset temperature. The auxiliary poisoning element forms an oxide layer (also known as a passivation layer) on the surface of the positive electrode active material. This non-dense passivation layer does not completely cover the positive electrode active material. This non-dense passivation layer can provide pores (or pathways) for the primary poisoning element to pass through the passivation layer and diffuse into the lithium-deficient vacancies in the positive electrode active material, thereby reducing the SEI (Solid Electrolyte Interphase) layer barrier on the surface of the positive electrode active material layer. When the lithium-deficient vacancies are occupied by the main poisoning element, the positive electrode active material no longer has vacancies for lithium atoms to fill, so the poisoned positive electrode active material loses the lithium ion insertion and extraction capabilities that it should have as a lithium secondary battery positive electrode active material (that is, it becomes disabled). And after the lithium-deficient vacancies are occupied by the main poisoning element, the lattice distortion of the positive electrode active material caused by the extraction of lithium atoms is resolved, thereby reducing or avoiding the release of oxygen. The above-mentioned main poisoning element is fluorine, and the auxiliary poisoning element can form an oxide layer on the surface of the lithium-deficient positive electrode active material at a high voltage (about 4.2 volts) or at a high temperature of not less than about 120°C. The auxiliary poisoning element can preferably be boron or phosphorus, or both.

[0029] Please refer to Figure 10, which shows a temperature curve graph of a lithium secondary battery thermal runaway test using an Accelerating Rate Calorimeter (ARC) for thermal insulation reliability. This lithium secondary battery uses NCM955 as the positive electrode active material and silicon-carbon as the negative electrode. The figure shows that lithium secondary batteries will enter a thermal chain reaction between approximately 130°C and 170°C, resulting in thermal runaway. Therefore, the present invention controls the starting temperature of the primary and auxiliary poisoning elements introduced into the electrochemical reaction system of the lithium secondary battery to be between 120°C and 150°C. The selection of a temperature range of 120°C for introducing the poisoning elements is intended to effectively prevent thermal runaway; the selection of a temperature range of 130°C to 150°C for introducing the poisoning elements is intended to intervene in the thermal chain reaction and interrupt thermal runaway.

[0030] In the present invention, the temperature that determines whether the poisoning agent releases the main poisoning element and the auxiliary poisoning element into the electrochemical reaction system of the lithium secondary battery can be the temperature fed back from the lithium secondary battery itself. Therefore, when the temperature of the lithium secondary battery during normal charge and discharge is lower than the poisoning starting temperature, the poisoning agent essentially or basically does not release the main poisoning element and the auxiliary poisoning element into the electrochemical reaction system (positive electrode active material layer, negative electrode active material layer and electrolyte) of the lithium secondary battery. Therefore, the poisoning agent does not participate in the electrochemical reaction generated by lithium ion transfer in the lithium secondary battery, and therefore will not affect the normal use process of the lithium secondary battery.

[0031] In addition, the poisoning agent of the present invention can be set outside the electrochemical reaction system of the lithium secondary battery or inside the electrochemical reaction system. When the poisoning agent of the present invention is set outside the electrochemical reaction system, because the main poisoning element and auxiliary poisoning element in the poisoning agent do not affect the operation of the lithium secondary battery, the temperature at which the main poisoning element and auxiliary poisoning element are released and the impact on the components of the electrochemical reaction system can be unlimited, and the poisoning agent can be composed of a compound that can directly release or provide the main poisoning element and auxiliary poisoning element, such as phosphorus pentafluoride (PF5) or boron trifluoride (BF3). However, when the poisoning agent is set inside the electrochemical reaction system, in order to avoid premature poisoning of the active material of the positive electrode active material layer, it is necessary to rely on an appropriate reaction mechanism to generate the main poisoning element and auxiliary poisoning element. In other words, materials must be used within the electrochemical reaction system and be safe at the normal operating temperature or voltage of the lithium secondary battery. These materials must release the primary poisoning element and auxiliary poisoning elements at the poisoning onset temperature through a triggering or other reaction mechanism. For example, the precursors, triggers, and enhancers described later in this application can be used to form the poisoning agent. Of course, the poisoning agent located outside the electrochemical reaction system can also be composed of these precursors, triggers, and enhancers.

[0032] The poisoning agent of the present invention can release the main poisoning element and the auxiliary poisoning element in a solid state, a liquid state or a gaseous state. When the distance between the poisoning agent and the active material layer of the positive electrode is relatively far, it is preferable to release the main poisoning element and the auxiliary poisoning element in the form of a gas. The released main poisoning element and the auxiliary poisoning element may react with the positive electrode active material in the form of ions or atoms. If the original positive electrode active material with the chemical formula Li x1 (Ni a1 Co b1 Mn c1 O z1 ), the positive electrode active material after being poisoned by the poisoning agent of the present invention will become a disabled positive electrode active material rich in the main poisoning element, and its chemical formula is Li x2 F y1 (Ni a2 Co b2 Mn c2 O z2 ), where x1>x2, or x2 <y1。

[0033] When the cathode active material is lithium-deficient, the reactions of the main poisoning element, namely fluoride ions or fluorine atoms, on the lithium-deficient cathode active material include: 1. Lithium substitution: Fluoride ions can enter the position of the original lithium ions in the NCM structure and form lithium fluoride with the residual lithium; 2. Stability enhancement: Fluorine has a high electronegativity (EN) of approximately 3.98, which makes it interact very strongly with transition metals (such as nickel, cobalt, and manganese) and oxygen, forming stable chemical bonds. Therefore, the introduction of fluorine can stabilize the material structure, reduce oxygen release and material decomposition, and thus improve thermal stability and cycle stability.

[0034] The material that provides the main poisoning element in the poisoning agent can be in the form of a single element or a compound, for example, pure fluorine or a fluorine compound. The fluoride portion can be selected from inorganic materials or organic materials. In terms of compound composition, it can be composed of a single element combined with fluorine, or at least two or more elements combined with fluorine. The above-mentioned elements that can be combined with fluorine can be selected except for Group 8A in the periodic table and lithium. In addition, it can also be a polymer that can be used for the embedding and de-embedding of fluorine atoms or fluorine ions, such as polyaniline (PAN), polypyrrole (PPY), polyacetylene (polyacetylene) or polythiophene (PT).

[0035] When the material providing the main poisoning element is selected from the compound type, the released components may include elements selected from boron (B), sulfur (S), silicon (Si) or phosphorus (P) in addition to fluorine. For example, the compound may have a BF bond, an SF bond, a Si-F bond or a PF bond. When the compound has a BF bond, the compound may be boron trifluoride (BF3) or diboron tetrafluoride (B2F4). When the compound has an SF bond, the compound may be sulfur hexafluoride (SF6), sulfur tetrafluoride (SF4), sulfur hexafluoride (SF6), disulfur decafluoride (S2F4). 10), nitrogen sulfur trifluoride (NSF3). When the compound has a Si-F bond, the compound may be silicon tetrafluoride (SiF4), chlorotrifluorosilane (SiClF3), bromotrifluorosilane (SiBrF3), or dichlorodifluorosilane (SiCl2F2). When the compound has a PF bond, the compound may be phosphorus difluoride (PF2), phosphorus trifluoride (PF3), phosphorus pentafluoride (PF5), phosphorus tetrafluoride (P2F4), trifluorophosphorus dichloride (PF3Cl2), sodium hexafluorophosphate (NaPF6), potassium hexafluorophosphate (KPF6), or ammonium hexafluorophosphate (NH4PF6). Furthermore, the compound may have the above bonds and further contain an oxygen element, for example, sulfuryl fluoride (SO2F2), sulfur tetrafluoride (SOF4), or sulfur difluoride (SOF2). In addition to fluorine, the fluorine-releasing compound may further contain an element from the alkali metal group, such as sodium (Na) or potassium (K). For example, the compound may be sodium fluoride (NaF) or potassium fluoride (KF). Alternatively, it may be an element from the alkaline earth group, such as magnesium fluoride (MgF2), strontium fluoride (SrF2), calcium fluoride (CaF2), or barium fluoride (BaF2). Furthermore, it may be a CF compound, an Al-F compound, a Cl-F compound, an As-F compound, a Se-F compound, a Br-F compound, a Mo-F compound, a Te-F compound, an IF compound, a WF compound, a Re-F compound, and the like. The metal portion may be a single metal element, an alloy, or a metal oxide. Examples of alloys include lanthanum barium (LaBa)-F compounds, bismuth tin (BiSn)-F compounds, lead tin (PbSn)-F compounds, and aluminum titanium (AlTi)-F compounds. The compound can also be nitrogen trifluoride (NF3), fluorine azide (FN3), tetrafluorohydrazine (N2F4), cis-nitrogen difluoride (N2F2), trans-nitrogen difluoride (N2F2), chlorine monofluoride (ClF), chlorine trifluoride (ClF3), chlorine pentafluoride (ClF5), arsenic pentafluoride (AsF5), selenium hexafluoride (SeF6), bromine monofluoride (BrF), molybdenum hexafluoride (MoF6), tellurium hexafluoride (TeF6), iodine heptafluoride (IF7), tungsten hexafluoride (WF6), rhenium hexafluoride (ReF6), etc.

[0036] Compounds composed of fluorine in combination with at least two different elements, for example, nitrogen sulfur trifluoride (NSF3), silicon chlorotrifluoride (SiClF3), silicon bromine trifluoride (SiBrF3), silicon dichlorodifluoride (SiCl2F2), phosphorus dichlorotrifluoride (PCl2F3), cyanogen fluoride (CNF), nitrogen difluorochloride (NClF2), nitrosyl fluoride (NOF), nitryl fluoride (NO2F), trifluoroamine oxide (NOF3), fluorine nitrate (FNO3), difluoromonochloride of phosphorus (PF2Cl), difluoromonobromide of phosphorus (PF2Br), tetrafluorochlorophosphorus (PClF4), dichlorophosphorus monofluoride (PFCl2), monofluoromonoisocyanate of phosphorus (PF2(NCO)), trifluorodichloride of phosphorus (PF3Cl2), difluorochlorosulfuryl phosphorus (PSF2Cl), difluorobromosulfuryl phosphorus (PSF2Br), Sulfur chloride pentafluoro (SF5Cl), sulfuryl fluoride (SO2FCl), sulfur bromide pentafluoro (SBrF5), difluorogermanium dichloride (GeCl2F2), trifluorogermanium chloride (GeClF3), monofluorogermanium trichloride (GeCl3F), difluoroselenium dioxide (SeO2F2), perbromoyl chloride (BrO3F), sulfur chloride pentafluoro (SF5Cl), difluoroamine sulfur pentafluoride (F2NSF5), 1,1,1,2-tetrafluoroethanesulfane (FSSF3), sulfur bromide pentafluoro (SBrF5), sulfurous fluoride (SOF2), sulfur tetrafluoride (SOF4), sulfur hypofluorite pentafluoride (SF5OF), sulfuryl fluoride (SO2F2), (repeated) trifluorosilane (SiHF3), difluorosilane (SiH2F2), monofluorosilane (SiH3F), difluoroamine (HNF2), chloroyl fluoride (ClO2F).

[0037] When the main poisoning element is in the form of an organic compound, for example, the poisoning agent can be formyl fluoride (FCHO), carbonyl fluoride (COF2), nitrosotrifluoromethane (CF3NO), fluoromethane (CH3F), difluoromethane (CH2F2), chlorofluoromethane (CH2ClF), trifluoromethane (CHF3), difluorochloromethane (CHClF2), bromodifluoromethane (CHBrF2), carbon tetrafluoride (CF4), trifluorochloromethane (CClF3), trifluorobromomethane (CBrF3), trifluoroiodomethane (CF3I), difluorodichloromethane (CCl2F2), difluorochlorobromomethane (CBrClF2), fluoroethane (C2H5F), 1,1-difluoroethane (CHF2CH3 ), 1,1,1-trifluoroethane (CF3CH3), 1,1,1,2-tetrafluoroethane (CF3CFH2), 1-chloro-1,2,2,2-tetrafluoroethane (CF3CFHCl), 1-chloro-1,1-difluoroethane (CH3CF2Cl), pentafluoroethane (C2HF5), pentafluorobromoethane (C2BrF5), hexafluoroethane (C2F6), vinyl fluoride (C2H3F), 1,1-difluoroethylene (C2H2F2), chlorotrifluoroethylene (C2ClF3), tetrafluoroethylene (C2F4), trifluoroacetyl chloride (C2ClF3O), trifluoroisoacetonitrile (CF3NC), trifluoromethyl hypofluorite (CF3OF), trifluoromethyldifluoromethyl ether (C2HF5O), 1-fluoro Propane (C3H7F; 1-fluoropropane), 2-fluoropropane (C3H7F; 2-fluoropropane), 1,1,1-trifluoropropane (C3H5F3), heptafluoropropane (C3F7H), octafluoropropane (C3F8), 3,3,3-trifluoropropylene (C3H3F3), 1,3,3,3-tetrafluoropropylene (C3H2F4), hexafluoropropylene (C3F6), 3,3,3-trifluoro-1-propyne (C3HF3), trifluoromethyl-1,1,2,2-tetrafluoroethyl ether (C3F7HO), octafluorocyclobutane (C4F8), hexafluoroacetone (C3F6O), trifluoromethylmercaptan (CF3SH), trifluoromethyl sulfur pentafluoride (CF3SF 5), hexafluoropropanethione ((CF3)2CS), monofluoromonobromomethane (CH2BrF), monofluorodichloromethane (CHCl2F), chlorofluorobromomethane (CHBrClF), difluorodibromomethane (CBr2F2), monofluorotrichloromethane (CCl3F), 12-difluoroethane (CH2FCH2F), 1-chloro-1,1,2-trifluoroethane (C2H2ClF3; 1-chloro-1,1,2-trifluoroethane), 1-chloro-1,2,2-trifluoroethane (C2H2ClF3; 1-chloro-1,2,2-trifluoroethane), 2-chloro-1,1,1-trifluoroethane (C2H2ClF3;2-chloro-1,1,1-trifluoroethane), 1,1-dichloro-1,2,2,2-tetrafluoroethane (C2Cl2F4; 1,1-dichloro-1,2,2,2-tetrafluoroethane), 1,2-dichloro-1,1,2,2-tetrafluoroethane (C2Cl2F4; 1,2-dichloro-1,1,2,2-tetrafluoroethane), 1,1-dichloro-2,2-difluoroethylene (CCl2CF2), cis-1,2-dichloro-1,2-difluoroethylene (C2Cl2F2; cis-1,2-dichloro-1,2-difluoroethylene ), trans-1,2-dichloro-1,2-difluoroethylene (C2Cl2F2; trans-1,2-dichloro-1,2-difluoroethylene), 1,1,1-trifluoroacetone (CF3I), acetyl fluoride (C2H3FO), difluorodimethylsilane (C2H6F2Si), 1,2-dichlorohexafluoropropane (C3Cl2F6; 1,2-dichlorohexafluoropropane), 1,3-dichlorohexafluoropropane (C3Cl2F6; 1,3-dichlorohexafluoropropane), 2-iodoheptafluoropropane (C3F7I), 1-chloroheptafluorocyclobutane (C4ClF7), perfluoropentane (C5F; 12 ), tetramethylammonium fluoride (TMAF), and tetrafluoroboric acid.

[0038] Among the materials of the above-mentioned main poisoning elements, those that can also contain auxiliary poisoning elements are preferred. For example, boron trifluoride (BF3) or phosphorus pentafluoride (PF5) are preferred because both materials are Lewis acids that easily eject F atoms, with boron trifluoride being the best. Take BF3 as an example. Because the electronegativity difference between its elements is high, it is relatively unstable and easier to eject F atoms. Moreover, the boron atom in BF3 has only six valence electrons (forming three covalent bonds with three fluorine atoms) instead of eight electrons, which makes the boron atom electron-deficient and can accept electrons to achieve an octet configuration. BF3 will adsorb on the surface of the lithium-deficient positive electrode active material and is a strong Lewis acid that can react with the active sites on the surface of the positive electrode active material (such as the -O- or -OH groups on the oxide surface). This reaction can induce polarization or even breakage of the BF bond, releasing F- ions, as shown in the reaction formula: BF3+-O - →-OBF3 - , if it is connected to high voltage or high temperature, it will cause -OBF3 - Formation of bond breaking, producing F - Ion: -OBF3 -→-O-B+3F - Li+ vacancies or oxygen vacancies in lithium-deficient cathode active materials (NCMs) provide migration channels for the insertion of F-. Because F- ions are negatively charged, they can form stable MF bonds (M=Ni, Co, Mn) with transition metal cations (such as Ni2+, Co3+) in NCMs, or with -O - The formation of strong coordination and stabilization of metal cations and oxygen at the same time, the formation of this coordination bond can further promote the migration and diffusion of F- into the lithium-deficient NCM. Compared with F ions, the highly active particles of F atoms will interact with the active points on the lattice surface -O - Or transition metal ions react to form compounds (such as NiF2), so it is easier to react on the NCM surface and not diffuse into the crystal interior. F2 molecules are even more difficult to diffuse into the lithium-deficient NCM crystal, mainly because they are too large to diffuse. Therefore, the strong Lewis acid of BF3 makes it easy to generate F - ions, and then quickly diffuse F ions into the lithium-deficient NCM crystal. At the same time, boron atoms (B) easily form stable BO bonds or coordination structures with the surface active points of NCM. This stabilization effect can inhibit the decomposition of the surface oxide layer under high voltage, thereby improving the stability of the material and is also beneficial to the thermal stability of the crystal at high temperature. At the same time, the presence of B will change the electronic structure in the NCM lattice, - Provide a low-energy migration channel and increase its embedding kinetic rate.

[0039] However, for compounds that easily eject F atoms, such as boron trifluoride or phosphorus pentafluoride, it is feasible to place them outside the electrochemical reaction system (positive electrode, negative electrode, and electrolyte, etc.) of a lithium secondary battery. However, if they are placed inside the electrochemical reaction system of a lithium secondary battery, there is still a risk of gradual release, even if the poisoning starting temperature has not been reached and a protective layer is provided on the outer surface, and then the F atoms can attack the positive electrode active material, resulting in reduced performance or even failure of the lithium secondary battery. Therefore, as mentioned above, it is necessary to reduce this risk by selecting an appropriate combination of precursors, triggers, and enhancers.

[0040] For example, when boron is used as the auxiliary poisoning element, the present application uses lithium tetrafluoroborate (LiBF4), sodium tetrafluoroborate (NaBF4), potassium tetrafluoroborate (KBF4), or ammonium tetrafluoroborate (NH4BF4) as a precursor of the poisoning agent, and a triggering agent is used to trigger the reaction, thereby forming BF3 at the poisoning starting temperature and releasing it onto the surface of the positive electrode active material. Furthermore, a reinforcing agent can be used to allow the reaction to proceed at a lower temperature, increase the reaction rate, or increase the amount of the primary poisoning element and the auxiliary poisoning element formed. For example, when sodium tetrafluoroborate (NaBF4) is used as a precursor, boron trioxide (B2O3) can be used as a reinforcing agent, mixed in a weight ratio of 7:3. The triggering agent can be selected from hydrofluoric acid (HF), sodium thiosulfate (Na2S2O3), or sulfur oxides containing free radicals. The aforementioned enhancer can be boron trioxide (B2O3), iodine halogen, or boric acid (H3BO3). The iodine halogen can be provided by potassium iodate (KIO4), strontium iodate (Sr(IO3)2), or sodium periodate. For example, sodium tetrafluoroborate (NaBF4) and sodium periodate are mixed in a 7:3 ratio. Ammonium tetrafluoroborate (NH4BF4) and potassium iodate (KIO4) are mixed in a 5:5 ratio. Sodium tetrafluoroborate (NaBF4) and sodium metabisulfite (Na2S2O5), which contains free radical sulfur oxides, are mixed in a 7:3 ratio.

[0041] In the embodiment where the auxiliary poisoning element is phosphorus, the precursor can be selected from tetrasodium pyrophosphate (Na4P2O7), phosphorus pentoxide (P2O5), copper pyrophosphate (Cu2P2O7), iron pyrophosphate (Fe2P2O7), magnesium pyrophosphate (Mg2P2O7), pentasodium tripolyphosphate (Na5P3O 10 ), calcium pyrophosphate (Ca2P2O7), aluminum phosphate (AlPO4), aluminum hydrogen phosphate (Al(HPO4)3), calcium hydrogen phosphate (Ca(HPO4), sodium dihydrogen phosphate (NaH2PO4), sodium phosphate (Na3PO4), lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6), potassium hexafluorophosphate (KPF6) or ammonium hexafluorophosphate (NH4PF6), etc.

[0042] In embodiments where the auxiliary poisoning element comprises both boron and phosphorus, one of the precursors is at least one of lithium tetrafluoroborate (LiBF4), sodium tetrafluoroborate (NaBF4), potassium tetrafluoroborate (KBF4), or ammonium tetrafluoroborate (NH4BF4), combined with the aforementioned auxiliary poisoning element that provides phosphorus as another precursor, and combined with the aforementioned enhancer and trigger to form the poisoning agent of the present application. In this embodiment, because lithium tetrafluoroborate (LiBF4), sodium tetrafluoroborate (NaBF4), potassium tetrafluoroborate (KBF4), or ammonium tetrafluoroborate (NH4BF4) already contains fluorine, the triggering agent does not need to contain fluorine, and instead sodium thiosulfate (Na2S2O3) or a sulfur oxide containing free radicals can be used. However, if only tetrasodium pyrophosphate (Na4P2O7), phosphorus pentoxide (P2O5), copper pyrophosphate (Cu2P2O7), iron pyrophosphate (Fe2P2O7), magnesium pyrophosphate (Mg2P2O7), pentasodium tripolyphosphate (Na5P3O 10 When calcium pyrophosphate (Ca2P2O7), aluminum phosphate (AlPO4), aluminum hydrogen phosphate (Al(HPO4)3), calcium hydrogen phosphate (Ca(HPO4), sodium dihydrogen phosphate (NaH2PO4), sodium phosphate (Na3PO4), etc. are used as precursors, hydrofluoric acid must be used as the trigger as a source of fluorine.

[0043] The hydrofluoric acid can be generated by compounds such as lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6), potassium hexafluorophosphate (KPF6), ammonium hexafluorophosphate (NH4PF6), lithium tetrafluoroborate (LiBF4), potassium tetrafluoroborate (NaBF4), potassium tetrafluoroborate (KBF4), or ammonium tetrafluoroborate (NH4BF4) under a heated environment. The hydrofluoric acid must reach a certain critical concentration. For example, in a single lithium secondary battery cell, the critical concentration of HF is the concentration of lithium hexafluorophosphate released at a dosage of 1.0 mole to 1.6 mole at 120°C.

[0044] The structure of the above-mentioned free radical sulfur-oxygen bond can be or The aforementioned sulfur-oxygen bond can be located at the free end of the compound, for example, such as sodium trifluoromethanesulfinate (CF3SO2Na), perfluorobutanesulfonic acid (C4F9SO3H), sodium perfluorobutanesulfonate (C4F9SO3Na), or potassium perfluorobutanesulfonate (C4F9SO3K). The sulfur-oxygen bond can also be within the structure of the compound, such as LiFSi (lithium bis(fluorosulfonyl)imide) or sodium salt F-(SO2)-N-(SO2)-FM + , M represents lithium or sodium, Peroxydisulfuric acid, potassium peroxydisulfate, sodium peroxydisulfate. In a method where the sulfur-oxygen bond is not exposed at the free end, a bond-breaking catalyst, such as a fluoroborate, aluminum halide, or hydrohalide, can be added to break the bond on the side of the sulfur-oxygen bond at a default temperature, converting the sulfur-oxygen bond into a state with free radicals, which react with a thermal runaway inhibitor precursor that releases BF3 to release BF3. The fluoroborate can be potassium fluoroborate (KBF4), sodium fluoroborate (NaBF4), or ammonium fluoroborate (NH4BF4), and the aluminum halide can be aluminum chloride (AlCl3) or aluminum bromide (AlBr3). The hydrohalide can be hydrofluoric acid, and the hydrofluoric acid can be generated from lithium hexafluorophosphate (LiPF6) under a heated environment.

[0045] have The first compound of the structure can be sodium octyl sulfate, hexyl sulfate, sodium salt, sodium ethyl sulfate, sodium 1-octanesulfonate monohydrate, 1-octanesulfonic acid sodium salt, sodium 1-heptanesulfonate, sodium hexanesulfonate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium 2-ethylhexyl sulfate, sodium ethyl sulfate, potassium nonafluoro-1-butanesulfonate, trifluoromethanesulfonyl chloride, chloride), 4-(3-butyl-1-imidazolio)-1-butanesulfonate, 3-(1-Pyridinio)-1-propanesulfonate, Dimethyl-2-hydroxyethylammoniumpropane sulfonate, 3-(Decyldimethylammonio)-propane-sulfonate inner salt, [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 1-Ethyl-3-methylimidazolium ethyl sulfate sulfate), copper(I)trifluoromethanesulfonate benzene complexcomplex), 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-Fluoropyridinium triflate, 4-Formyl-1-methylpyridinium benzenesulfonate, 3-Hydroxynaphthalene-2,7-disulfonic acid disodium salt, Potassium benzene-1,2-disulfonate, Lithium trifluoromethanesulfonate, Potassium trifluoromethanesulfonate, Sodium bisulfite solution, Sodium metabisulfite, Sodium thiosulfate thiosulfate), sodium 1-butanesulfonate, potassium diphenylsulfone sulfonate, heptadecafluorooctanesulfonic acid potassium salt, or a mixture of at least two of the above materials.

[0046] For example, having The compound having the structure can be phenyl vinyl sulfoxide, propyl sulfoxide, methyl phenyl sulfoxide, diisobutyl sulfoxide, dodecyl methyl sulfoxide, benzyl phenyl sulfoxide, dimethyl sulfite, benzenesulfinic acid sodium salt, sodium methanesulfinate, sodium p-toluenesulfinate, sodium bisulfite solution, or a mixture of at least two of the above materials.

[0047] For example, having The compound of the structure can be acyl chloride (4-(Trifluoromethyl)benzenesulfonyl chloride), 4-chlorobenzenesulfonyl chloride, 3-(Trifluoromethyl)benzenesulfonyl chloride, 4-fluorobenzenesulfonyl chloride, trifluoromethanesulfonic anhydride, methanesulfonyl chloride, p-toluenesulfonyl chloride, 4-toluenesulfonyl chloride, 3-Hydroxynaphthalene-2,7-disulfonic acid disodium salt, isobutanesulfonyl chloride, cyclohexanesulfonyl chloride. chloride), 4-Methoxybenzenesulfonyl chloride, 4-bromobenzenesulfonyl chloride, 4-(trifluoromethyl)benzenesulfonyl chloride, 4-iodobenzenesulfonyl chloride, 4-fluorobenzenesulfonyl chloride, 4-nitrobenzenesulfonyl chloride, biphenyl-4-sulfonyl chloride, biphenyl-4,4'-disulfonyl chloride, 4-(aminosulfonyl)benzenesulfonyl chloride, or a mixture of at least two of the above materials.

[0048] Furthermore, the aforementioned precursors, enhancers, or triggers may be co-melted and then ground into particles. For example, boron trioxide (B2O3) and sodium tetrafluoroborate (NaBF4) may be co-melted in a weight ratio of 3:7 and then ground into particles; or boron trioxide (B2O3), sodium tetrafluoroborate (NaBF4), and LiFSi may be co-melted in a weight ratio of 3:7:2.5 and then ground into particles. Alternatively, boron trioxide (B2O3) and sodium tetrafluoroborate (NaBF4) may be co-melted in a weight ratio of 3:7 and then ground into particles to form a first eutectic, and boron trioxide (B2O3), sodium tetrafluoroborate (NaBF4), and LiFSi may be co-melted in a weight ratio of 3:7:2.5 and then ground into particles to form a second eutectic. The first and second eutectics are then mixed in a weight ratio of 1:1.

[0049] In practice, the material particles of the poisoning agent of the present application can have an average particle size of 0.1 micrometers (μm) to 150 micrometers (μm). When the poisoning agent is mixed between the particles of the positive electrode active material, in order to avoid the agglomeration effect caused by the small particle size during the mixing process, the particle size of the poisoning agent is about one-third of the thickness of the positive electrode active material layer. For example, the average particle size of the poisoning agent particles is 0.1 micrometers to 100 micrometers, and preferably 0.1 micrometers to 10 micrometers. When the poisoning agent is coated on the outer surface of the positive electrode collector layer of the lithium secondary battery, because there is no need to consider the agglomeration effect and the impact on the electrochemical system, the particle size of the poisoning agent can be more flexible and can be set according to needs. In addition, the poisoning agent of the present application can also be selected in a way that part of the material has a shell-core structure. For example, the core part is selected from the precursor, enhancer or trigger, and a shell layer is provided on the outer surface of the core for protection. The shell layer can be a single layer formed by a polar material, or a multilayer film composed of non-polar materials and polar materials interlaced and stacked. The polar material can be selected from polyacrylic acid (PAA), and the non-polar material can be selected from silicone (-SiO-). x, in order to avoid the influence of the electrolyte on the poisoning agent when the poisoning agent is set in the lithium secondary battery. Furthermore, a shell layer can also be provided on the surface of the particles of the eutectic. For example, the surface of the particles of the first eutectic or the second eutectic is coated with a shell layer, or some particles of the particles of the same eutectic have a shell layer. For example, when tetrafluoroborate (NH4BF4) is used as a precursor and is matched with a sulfur-oxygen bond supplier with a free radical (LiFSI), and mixed in a weight ratio of 7:3, the surface of the particles of tetrafluoroborate (NH4BF4) is coated with silicone, and the surface of the particles of lithium bis(fluorosulfonyl)imide (LiFSI) can be first coated with PAA, and then the surface of the PAA is coated with silicone to form an alternating multilayer membrane shell. For example, sodium tetrafluoroborate (NaBF4) and boron trioxide (B2O3) are eutectic at a weight ratio of 7:3 and then ground into particles to form a first eutectic. Sodium tetrafluoroborate (NaBF4), boron trioxide (B2O3) and LiFSI are eutectic at a weight ratio of 7:3:2.5 and then ground into particles to form a second eutectic. Sodium tetrafluoroborate (NaBF4) and boron trioxide (B2O3) are eutectic at a weight ratio of 7:3 and then ground into particles, and the surface is coated with silicone to form a third eutectic. The first eutectic, the second eutectic, and the third eutectic are then mixed at a weight ratio of 1:1:4.

[0050] Next, a F-based poison with B as the auxiliary poison was synthesized using NaBF4 as a precursor, HF as a trigger, and B2O3 as a booster. Testing was performed with a poisoning onset temperature of 150°C. The results are shown in the TG-IR (thermogravimetry-infrared) chart in Figure 1(a) and the FESEM (field emission scanning electron microscope) in Figure 1(b). The NaBF4 surface was coated with silicone, and the B2O3 surface was also coated with silicone. A F-based poison with B and P as auxiliary poison elements was synthesized using LiBF4 and Na4P2O7 as dual precursors and HF as a trigger. Testing was performed with a poisoning onset temperature of 150°C. The results are shown in the TG-IR chart in Figure 2(a) and the FESEM in Figure 2(b). As shown in the TG-IR graphs of Figures 1(a) and 2(a), the poison releases the largest amount of the main poisoning element between 200°C and 300°C. The LiBF4 surface is coated with silicone, and the Na4P2O7 surface is also coated with silicone. The TG-IR test mode is powder, and the test conditions are a temperature range of 30°C to 500°C, a heating rate of 10°C / min, and a wavelength range of 4000-600cm. -1 .

[0051] Furthermore, Figures 1(b) and 2(b) show that as the temperature increases from 150°C to 300°C, the diffusion of fluorine into the lithium-deficient vacancies in the positive electrode active material becomes more pronounced. Consequently, the positive electrode active material no longer has vacancies for lithium atoms to relocate and fill, resulting in a disabled state. Consequently, the poisoned positive electrode active material loses the lithium ion insertion and extraction capabilities required for a lithium secondary battery positive electrode active material. These FESEM analysis images show that the average fluorine concentration in the positive electrode active material particles treated with the poisoning agent of the present invention is ≥1% at 150°C.

[0052] When the auxiliary poisoning elements are boron and phosphorus, the average concentration of fluorine in the positive electrode active material particles is 1.5% at 150°C, the average concentration of fluorine in the positive electrode active material particles is 2.7% at 250°C, and the average concentration of fluorine in the positive electrode active material particles is 2.8% at 300°C. Therefore, it can be found that when the auxiliary poisoning elements are boron and phosphorus, the average concentration of fluorine in the positive electrode active material particles at 300°C is more than 1.5 times that at 150°C.

[0053] When the auxiliary poisoning element is boron and there is a reinforcing agent, the average concentration of fluorine in the positive electrode active material particles is 1.0% at 150°C, the average concentration of fluorine in the positive electrode active material particles is 5.0% at 250°C, and the average concentration of fluorine in the positive electrode active material particles is 5.8% at 300°C. The average concentration of fluorine in the positive electrode active material particles at 300°C is more than 5 times that at 150°C.

[0054] Furthermore, these FESEM images reveal that the presence of an auxiliary poisoning element forming an oxide on the surface of the positive electrode active material particles provides an excellent channel for fluorine to diffuse into the interior of the positive electrode active material particles to the core region of the particles, rather than just on the outer surface.

[0055] The FESEM test conditions used were a coin cell, with a temperature ramp of 300°C / 20 minutes and a voltage of 15 kV, using a gas shield. Sample preparation involved cutting the sample to the appropriate size, securing it with aluminum tape, and then performing ion beam cross-sectioning. The positive electrode active material used in this test was NCM955.

[0056] The poisoning agent of the present application can be applied to various types of lithium secondary batteries, such as cylindrical batteries, angular batteries and soft-pack batteries. When the poisoning agent of the present application is set in the electrochemical reaction system of the lithium secondary battery, such as applied to the lithium secondary battery structure shown in Figure 3, the lithium secondary battery 10 includes a positive electrode collector layer 12; the positive electrode active material layer 13 located on the inner surface 121b of the positive electrode collector layer 12; a negative electrode collector layer 14; a negative electrode active material layer 15 located on the inner surface 141b of the negative electrode collector layer 14 and corresponding to the positive electrode active material layer 13; an isolation layer 16 located between the positive electrode active material layer 13 and the negative electrode active material layer 15; and a residual inner surface of the positive electrode collector layer 12 adhered to the positive electrode collector layer 12. A polymer frame 18 is formed on a portion of the surface or called the outer periphery 121a and the remaining portion of the inner surface of the negative electrode collector layer 14 or called the outer periphery 141a. The positive electrode collector layer 12, the frame 18 and the negative electrode collector layer 14 form a closed space 19 to accommodate the positive electrode active material layer 13, the isolation layer 16 and the negative electrode active material layer 15, and the positive electrode collector layer 12, the frame 18 and the negative electrode collector layer 14 serve as the packaging structure of the lithium secondary battery 10 to block the influence of the external environment on the positive electrode active material layer 13, the isolation layer 16 and the negative electrode active material layer 15. The above-mentioned lithium secondary battery includes an electrolyte system (not shown in the figure), which is also contained in the closed space 19. The electrolyte system can be selected from various forms of electrolytes in the prior art, such as pure liquid electrolytes, pure gel electrolytes, pure condensed electrolytes or pure solid electrolytes, or a mixture thereof. In addition, the above-mentioned electrolyte can also be arbitrarily mixed with an oxide solid electrolyte. Furthermore, when the electrolyte system is a solid electrolyte, the electrolyte system can also be used directly as a separator. The poisoning agent 17 of the present invention can be disposed on the surface of the positive electrode active material layer 13 (i.e., the positive end), adjacent to the separator 16, as shown in FIG3 ; or, the poisoning agent 17 is disposed on the separator 16 used to block electrical contact between the positive electrode active material layer 13 and the negative electrode active material layer 15, and the distribution position of the poisoning agent 17 is closer to the positive electrode active material layer 13 than to the negative electrode active material layer 15, as shown in FIG4 ; or, the poisoning agent 17 is mixed with the positive electrode active material particles 131 of the positive electrode active material layer to form a state of being added to the positive electrode active material layer 13, i.e., between the positive electrode active material particles 131, as shown in FIG5 ; or, the poisoning agent 17 is coated on the surface of the positive electrode active material particles 131 to form a shell, as shown in FIG6 .

[0057] When the poisoning agent is disposed outside the electrochemical reaction system of the lithium secondary battery, at least one perforation may be provided on the component of the lithium secondary battery used to encapsulate the electrochemical reaction system, which may be connected from the external environment of the lithium secondary battery to the electrochemical reaction system of the lithium secondary battery. The perforation may be pre-formed and be in a closed state when the set temperature (e.g., 150°C) or a certain pressure is not reached, or the perforation is not pre-formed but may be formed by some means or reactions, such as the increase in pressure caused by the gas generated by the electrochemical system during a high-temperature process, which destroys the sealed packaging component of the lithium secondary battery, such as the shell, or the shell may be destroyed by an additional gas-generating component to cause a pressure increase, thereby generating a perforation. For example, as shown in FIG7 , the poisoning agent 17 of the present invention is disposed on the outer surface of the positive electrode current collector layer 12. The positive electrode current collector layer 12 has several through-holes 122 extending through the positive electrode current collector layer 12 and connecting to the electrochemical reaction system of the lithium secondary battery 10. The through-holes 122 are filled with a filler 22 that melts or depolymerizes near the poisoning onset temperature. When the temperature of the lithium secondary battery 10 reaches or approaches the poisoning onset temperature, the filler 22 melts, becomes fluid, and carries the poisoning agent 17 into the electrochemical reaction system of the lithium secondary battery 20. The filler 22 then releases primary and secondary poisoning elements that attack the positive electrode active material layer 13 adjacent to the positive electrode current collector layer 12, disabling the positive electrode active material in the positive electrode active material layer 13 and achieving safety. Furthermore, the outer surface of the poisoning agent 17 may be partially coated with a protective layer 24 to prevent environmental substances, such as moisture, from damaging or affecting the poisoning agent 17. Furthermore, after the filler 22 melts, the protective layer 24 can also serve as a sealing member for the through-hole 122, thereby preventing oxygen from entering the lithium secondary battery 10 through the through-hole 122. Furthermore, the lithium secondary battery 10 can be placed in an aluminum bag, forming a so-called soft pack battery. The poisoning agent 17 can also be placed between the lithium secondary battery and the aluminum bag.

[0058] The aforementioned isolation layer 16 can be formed by stacking inorganic particles with an adhesive, either without or with a substrate. The substrate here refers to a porous woven fabric formed from a polymer material. The inorganic particles can be in the form of a solid electrolyte that can transport ions, or in the form of a non-ion-transporting material, such as aluminum oxide or titanium oxide; or other salt particles, such as sulfates, phosphates, or halides, or a mixture of at least two of the above. When the inorganic particles are selected from aluminum oxide, their crystalline phase can be selected from α, β, or γ phases, or multiple crystalline phases or polymorphs formed by a mixture of two or more of the above, with α phase being preferred, or the isolation layer can be formed in a manner where the α phase accounts for a higher proportion. The material of the solid electrolyte that can transport lithium ions can be an oxide such as LATP, LAGP, LLZO, or LiAlSiO4. Since the poisoning agent of the present application begins to activate before the critical temperature at which the lithium secondary battery heats up, the isolation layer preferably does not collapse at temperatures between 150°C and 200°C.

[0059] Furthermore, two lithium secondary batteries with a 100% SOC (state of charge) were tested, one with the poisoning agent of this application and the other without. As shown in Table 1 below, when observing the location of the primary poisoning element invading the positive electrode active material, the ratio of T (NiMnCo) to oxygen in the positive electrode active material remained virtually unchanged. This indicates that doping with the poisoning agent of this application does not alter the ratio of NMC to oxygen, meaning that the thermal runaway inhibitor of this application does not occupy oxygen positions but rather fills or occupies vacant lithium atoms, stabilizing the crystal lattice and preventing oxygen from escaping. The oxygen to nickel, cobalt, and manganese ratios of the poisoned lithium secondary battery's positive electrode active material were within 10% of those of the lithium secondary battery without the poisoning agent. The compositional analysis of each sample in Table 1 was obtained by sectioning and analyzing a portion of the sample, so there may be slight differences. Boron was used as the auxiliary poisoning element in this experiment.

[0060] Please refer to Figure 8, which shows the heat release curves of lithium secondary batteries containing the poisoning agent of the present invention and lithium secondary batteries without the poisoning agent of the present invention. As can be seen from the figure, the lithium secondary battery without the poisoning agent of the present invention (control group) begins to release heat at 170°C and reaches maximum heat release at 200°C-250°C. The lithium secondary battery containing the poisoning agent of the present invention begins to generate heat of material conversion reaction at the poisoning starting temperature (set at 150°C) and effectively suppresses the heat release reaction of the control group before reaching 250°C. In this experiment, the positive electrode active material is NCM955 and the negative electrode material is silicon carbon. The poisoning agent is NaBF4 and B2O3 co-melted in a weight ratio of 7:3 and then ground into particles, and the surface of the particles is then coated with silicone.

[0061] Please refer to Figures 9(a) and 9(b), which show the exothermic curves of a lithium secondary battery containing the poisoning agent of the present invention and a lithium secondary battery without the poisoning agent. Figure 9(a) shows that the lithium secondary battery containing the poisoning agent of the present invention may exhibit one to three exothermic peaks, with the exothermic temperature occurring between 100°C and 250°C. In contrast, as shown in Figure 9(b), the lithium secondary battery without the poisoning agent of the present invention exhibits a small peak at 170°C and begins to experience thermal runaway at 200°C, with the high temperature exceeding 400°C. These two figures demonstrate that the lithium secondary battery containing the poisoning agent of the present invention effectively suppresses thermal runaway. In this experiment, the positive electrode active material is NCM955, and the negative electrode material is silicon carbon. The poisoning agent is a co-melted mixture of NaBF4 and B2O3 in a weight ratio of 7:3, which is then pelletized and coated with silicone.

[0062] As can be seen from the above, the present invention also provides a self-poisoning method for a lithium secondary battery, the steps of which include providing a lithium secondary battery having an electrochemical reaction system, the electrochemical reaction system including a positive electrode active material layer, a negative electrode active material layer, and an electrolyte for transferring lithium ions between the positive electrode active material layer and the negative electrode active material layer; then, disposing the aforementioned poisoning agent inside or outside the electrochemical reaction system, wherein the poisoning starting temperature is in the range of 120°C to 150°C; then, when the temperature of the lithium secondary battery reaches the poisoning starting temperature, the poisoning agent begins to release the main poisoning element and the auxiliary poisoning element into the electrochemical reaction system, the auxiliary poisoning element first forming an oxide layer on the surface of the positive electrode active material of the positive electrode active material layer, and then the main poisoning element diffuses inwardly through the oxide layer to the surface of the positive electrode active material particles of the positive electrode active material layer, occupying the lithium vacancy of the positive electrode active material of the positive electrode active material layer, so that the positive electrode active material reaches the aforementioned disabled state, thereby suppressing thermal runaway of the lithium secondary battery.

[0063] In summary, the present invention provides a self-poisoning system for a lithium secondary battery and a poisoned, disabled lithium secondary battery. When the lithium secondary battery is heated to the poisoning starting temperature, the poisoning agent releases a primary poisoning element and an auxiliary poisoning element into the electrochemical reaction system of the lithium secondary battery, thereby forming a non-dense oxide layer on the surface of the lithium-deficient positive electrode active material. This allows the primary poisoning element to diffuse into the interior of the positive electrode active material and occupy the lithium-deficient vacancies in the lithium-deficient positive electrode active material, thereby disabling the lithium-deficient positive electrode active material and forming a lower energy state, thereby reducing the voltage of the entire battery and simultaneously cutting off the electrochemical reaction pathway, effectively terminating the thermal runaway of the lithium secondary battery. Compared to existing thermal runaway suppression methods, the present invention directly suppresses thermal runaway from the end with the maximum energy release of thermal runaway and the main body driven by the entire electrochemical reaction, that is, the active material end, and utilizes the temperature of the lithium secondary battery as the spontaneous leading mechanism for the poisoning agent to perform the poisoning action, thereby more effectively improving the safety of the lithium secondary battery.

[0064] The above are only preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, any equivalent changes or modifications based on the features and spirit of the present invention should be included in the scope of the present invention.

[0065] Explanation of Symbols 10 lithium secondary battery 12 positive electrode current collecting layer 121a outer periphery 121b inner part of the surface 13 positive electrode active material 14 negative electrode current collecting layer 141a outer periphery 141b inner part of the surface 15 negative electrode active material 16 separator 17 poisoning agent 18 polymer frame 19 closed space 22 filler 24 protective layer 122 perforation 131 positive electrode active material particle

Claims

1. A lithium secondary battery self-poisoning system, comprising: A lithium secondary battery having an electrochemical reaction system, wherein the electrochemical reaction system comprises: positive electrode active material layer; a negative electrode active material layer; and an electrolyte for transferring lithium ions between the positive electrode active material layer and the negative electrode active material layer; and a poisoning agent disposed within or outside the electrochemical reaction system, the poisoning agent being capable of releasing a primary poisoning element and an auxiliary poisoning element at a poisoning onset temperature, the poisoning onset temperature being within a range of 120° C. to 150° C.; When the temperature of the lithium secondary battery reaches the poisoning starting temperature, the poisoning agent begins to release the main poisoning element and the auxiliary poisoning element to the electrochemical reaction system, the auxiliary poisoning element first forms an oxide layer on the surface of the positive electrode active material of the positive electrode active material layer, and then the main poisoning element diffuses into the surface of the positive electrode active material particles of the positive electrode active material layer through the oxide layer, occupying the lithium desorption vacancies of the positive electrode active material of the positive electrode active material layer; The main poisoning element is fluorine. 2 . The lithium secondary battery self-poisoning system as claimed in claim 1 , wherein the auxiliary poisoning element is boron and / or phosphorus.

3. The lithium secondary battery self-poisoning system as claimed in claim 1, wherein when the poisoning agent is disposed outside the electrochemical reaction system, the poisoning agent is composed of a compound that can directly release the main poisoning element and the auxiliary poisoning element. 4 . The lithium secondary battery self-poisoning system as claimed in claim 3 , wherein the poisoning agent is boron trifluoride (BF 3 ), phosphorus pentafluoride (PF 5 ) or a mixture thereof.

5. The lithium secondary battery self-poisoning system as claimed in claim 1 , wherein when the poisoning agent is disposed in the electrochemical reaction system, the outer surface of the poisoning agent is coated with a protective layer for resisting the electrolyte, which can be selected from a single-layer film type formed by a non-polar material, or a multi-layer film type formed by stacking polar and non-polar materials. 6 . The lithium secondary battery self-poisoning system as claimed in claim 5 , wherein the non-polar material is silicone. 7 . The lithium secondary battery self-poisoning system as claimed in claim 1 , wherein the poisoning agent comprises a precursor and a trigger, which react to form a compound that releases the main poisoning element and the auxiliary poisoning element. 8 . The lithium secondary battery self-poisoning system as claimed in claim 7 , wherein the compound is a Lewis acid compound. 9 . The lithium secondary battery self-poisoning system as claimed in claim 8 , wherein the Lewis acid compound is boron trifluoride (BF 3 ), phosphorus pentafluoride (PF 5 ) or a mixture thereof. 10 . The lithium secondary battery self-poisoning system as claimed in claim 7 , wherein the poisoning agent is formed by melting the precursor and the triggering agent together and then grinding them into particles.

11. The lithium secondary battery self-poisoning system as claimed in claim 7, wherein the precursor and / or the trigger are coated with a protective layer for resisting the electrolyte, which can be selected from a single layer formed by a non-polar material or a multilayer film stacked by polar and non-polar materials. 12 . The lithium secondary battery self-poisoning system as claimed in claim 7 , wherein the triggering agent is hydrofluoric acid (HF), sulfur oxides with free radicals, or sodium thiosulfate.

13. The self-poisoning system for lithium secondary batteries as claimed in claim 7, wherein the precursor is selected from lithium tetrafluoroborate (LiBF4), sodium tetrafluoroborate (NaBF4), potassium tetrafluoroborate (KBF4), ammonium tetrafluoroborate (NH4BF4), tetrasodium pyrophosphate (Na4P2O7), phosphorus pentoxide (P2O5), copper pyrophosphate (Cu2P2O7), 7) , ferric pyrophosphate (Fe2P2O7), magnesium pyrophosphate (Mg2P2O7), pentasodium tripolyphosphate (Na5P3O 10 ), calcium pyrophosphate (Ca2P2O7), aluminum phosphate (AlPO4), aluminum hydrogen phosphate (Al(HPO4)3), calcium hydrogen phosphate (Ca(HPO4)), sodium dihydrogen phosphate (NaH2PO4), sodium phosphate (Na3PO4), lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6), potassium hexafluorophosphate (KPF6) or ammonium hexafluorophosphate (NH4PF6), or a mixture of the above materials.

14. The lithium secondary battery self-poisoning system as claimed in claim 13, wherein the poisoning agent further comprises a enhancer for reducing the reaction temperature of the precursor and the trigger or increasing the reaction rate of the reactant and the trigger, wherein the enhancer is boron trioxide, and when the precursor is sodium tetrafluoroborate (NaBF4), the mixing weight ratio of the precursor to the enhancer is 7:

3. 15 . The lithium secondary battery self-poisoning system as claimed in claim 7 , wherein the poisoning agent further comprises an enhancer for reducing a reaction temperature of the precursor and the trigger or increasing a reaction rate of the reactant and the trigger. 16 . The lithium secondary battery self-poisoning system as claimed in claim 15 , wherein the poisoning agent is formed by melting at least two of the precursor, the enhancer, and the trigger and then grinding them into particles.

17. The lithium secondary battery self-poisoning system as claimed in claim 16, wherein the surface of the part of the particles ground after eutectic melting is coated with an electrolyte-resistant protective layer, and the electrolyte-resistant protective layer can be a single layer formed by a non-polar material, or a multilayer film composed of a stack of polar and non-polar materials. 18 . The lithium secondary battery self-poisoning system as claimed in claim 15 , wherein the enhancer is boron trioxide, boric acid (H 3 BO 3 ), or a compound capable of releasing halogen iodine.

19. The lithium secondary battery self-poisoning system as claimed in claim 15, wherein any outer surface of the precursor, the trigger and the enhancer is coated with an anti-electrolyte protective layer, which can be a single layer formed by a non-polar material, or a multilayer film composed of polar and non-polar materials.

20. The lithium secondary battery self-poisoning system as claimed in claim 1, wherein the positive electrode active material is a layered lithium oxide having cobalt, nickel and manganese.

21. The lithium secondary battery self-poisoning system as claimed in claim 1, wherein the lithium secondary battery further comprises: a separation layer located between the negative electrode active material layer and the positive electrode active material layer; and a positive electrode current collecting layer, which is located on the outer side of the positive electrode active material layer away from the negative electrode active material layer; When the poisoning agent is disposed outside the electrochemical reaction system, the poisoning agent is disposed outside the positive electrode current collecting layer; When the poisoning agent is disposed in the electrochemical reaction system, the poisoning agent is disposed on the surface of the positive electrode active material layer, between the active material particles of the positive electrode active material layer, or covers the surface of the active material particles of the positive electrode active material layer.

22. The lithium secondary battery self-poisoning system as claimed in claim 21, wherein when the poisoning agent is disposed outside the positive electrode collector layer, the positive electrode collector layer has a plurality of high-temperature through-holes that can be connected to the positive electrode active material layer, and the through-holes are filled with hot-melt fillers. 23 . The lithium secondary battery self-poisoning system as claimed in claim 21 , wherein the isolation layer is formed by inorganic particles bonded together by an adhesive, and the isolation layer does not collapse at 150° C. to 200° C.

24. A disabled lithium secondary battery poisoned by the self-poisoning system according to claim 1, characterized in that: The oxide layer is formed on the surface of the positive electrode active material particles of the poisoned positive electrode active material layer of the lithium secondary battery, and the average fluorine content of the positive electrode active material particles at 300° C. is more than 1.5 times the average fluorine content at 150° C.

25. A disabled lithium secondary battery, characterized in that: An oxide layer is formed on the surface of the positive electrode active material particles of the positive electrode active material layer of the lithium secondary battery, and the average fluorine content of the positive electrode active material particles at 300° C. is more than 1.5 times the average fluorine content at 150° C., and the positive electrode active material is a layered lithium oxide having cobalt, nickel and manganese, and the oxide layer contains boron and / or phosphorus.

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