Lithium secondary battery

Abstract

To provide a lithium secondary battery capable of suppressing thermal runaway.SOLUTION: There is provided a lithium secondary battery including an ionic provider added to a positive electrode. The ionic provider does not involve in an electrochemical reaction of the lithium secondary battery during charging and discharging. The ionic provider can absorb thermal energy caused by the rising temperature of the lithium secondary battery to release a reactive anionic group. The reactive anionic group reacts with a positive electrode active material to reduce reversibility of the positive electrode active material. Also, the positive electrode active material becomes to a lower energy state from a higher energy state with lithium-ion extraction to effectively suppress the thermal runaway of the lithium secondary battery.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery capable of suppressing thermal runaway. [Background technology]

[0002] Lithium-ion batteries are widely used in various products such as automobiles, consumer and industrial wearable products, portable devices, energy storage devices, etc., and these lithium-ion batteries are applied in almost all areas of human daily life. However, accidents related to lithium-ion batteries, such as fires or explosions of mobile phone batteries and electric vehicles, are frequently heard. All of these are due to the fact that a comprehensive and effective solution to the safety issues of lithium-ion batteries has not yet been found.

[0003] Thermal runaway is the main cause of dangerous events such as fire or explosion in lithium batteries. The main cause of thermal runaway in lithium batteries is heat as an exothermic reaction caused by thermal decomposition induced by temperature rise of SEI (solid electrolyte interphase) film, electrolyte, binder, and positive and negative active materials in the battery. Currently, methods to suppress thermal runaway are classified into two types, external and internal, according to the location of the safety mechanism. The external type uses a monitoring system using digital computation simulation. The internal type is further divided into physical or chemical methods. The external digital monitoring system uses a dedicated protection circuit and a dedicated management system outside the battery cell to facilitate safe monitoring of the battery during the use process. The internal physical type, such as a thermal cutoff separator, closes the pores of the separator when the battery cell becomes hot to block the passage of ions.

[0004] The chemical type inside the battery cell can be defined as scale-controlled type or electrochemical reaction type. In the scale-controlled type, flame retardants are added to the electrolyte to control the scale of thermal runaway. Examples of electrochemical reaction types include: a. Monomers or oligomers are added to the electrolyte. As the temperature increases, polymerization occurs and ion transfer slows down. Thus, as the temperature increases, the ionic conductivity decreases and the electrochemical reaction rate in the cell slows down. b. A positive temperature coefficient (PTC) resistance material is sandwiched between the positive or negative electrode layer and the adjacent current collecting layer. When the temperature of the battery cell increases, the electrical insulation improves. The power transmission efficiency between the positive or negative electrode layer and the adjacent current collecting layer decreases, and the electrochemical reaction rate also decreases. c. A modified layer is formed on the surface of the positive electrode active material. When the temperature of the battery cell increases, the modified layer transforms into a dense film, which increases the resistance of charge transfer and reduces the electrochemical reaction rate.

[0005] However, the above-mentioned methods only aim to reduce heat generation by passively blocking the ion / electron transfer pathway, and do not target the main cause of the maximum energy generation that causes thermal runaway or the main reactant of the entire electrochemical reaction, i.e., the active material.

[0006] Therefore, the present invention provides a completely new lithium secondary battery that solves the problem of thermal runaway from the active material. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a lithium secondary battery including an ion donor disposed in a positive electrode. The ion donor is not involved in charge / discharge operations. The ion donor can absorb thermal energy and release reactive anionic groups. The reactive anionic groups react with the positive electrode active material and reduce the reversibility of the positive electrode active material. In addition, due to certain reactive anionic groups, the lattice structure of the positive electrode active material changes from a high energy state to a low energy state with the extraction of lithium ions. Therefore, the positive electrode becomes stable with the extraction of lithium ions, effectively suppressing thermal runaway of the lithium secondary battery.

[0008] Another object of the present invention is to provide a lithium secondary battery comprising an ion donor disposed at the positive electrode and a lithium acceptor disposed at the negative electrode. The ion donor can absorb thermal energy, release reactive anion groups, react with the positive electrode active material, and improve the oxygen binding ability in the positive electrode active material accompanying lithium ion extraction. Thus, the release of a large amount of atomic oxygen caused by the lithium ion extraction site is avoided. At the negative electrode, the excess lithium embedded in the negative electrode diffuses to the lithium acceptor, reducing the lithium concentration of the negative electrode. Thus, the negative electrode exhibits a stable state and effectively suppresses thermal runaway. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention discloses a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte system that provides ionic conductivity between the positive electrode and the negative electrode. Lithium ions are transferred between the positive electrode and the negative electrode to perform an electrochemical reaction for charging and discharging. An ion donor that is inactive during the electrochemical reaction is added to the positive electrode. The ion donor includes a reactive anionic group and a cation bonded to the reactive anionic group. The ion donor can absorb thermal energy and release the reactive anionic group. The reactive anionic group reacts with the positive electrode active material to reduce the reversibility of the positive electrode active material. In addition, due to certain reactive anionic groups, the lattice structure of the positive electrode active material changes from a high energy state to a low energy state as lithium ions are extracted. Thus, the positive electrode becomes stable as lithium ions are extracted, preventing the occurrence of a thermal runaway event.

[0010] Further scope of applicability of the present invention will become apparent from the detailed description given below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. The present invention will be more fully understood from the following detailed description, which is given by way of example only and is not intended to be limiting of the invention. [Brief description of the drawings]

[0011] [Figure 1] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. [Diagram 2] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. [Diagram 3] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. [Figure 4] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. [Diagram 5] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. [Figure 6] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. [Figure 7] 1 is a differential scanning calorimeter thermogram with and without the addition of an ion donor in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described with respect to certain embodiments and with reference to certain drawings, but the present invention is not limited to the drawings, but only by the claims. Any reference signs in the claims should not be construed as limiting the scope. The drawings described are only schematic and are non-limiting. In the drawings, the dimensions of some of the elements may be exaggerated and not drawn to scale for illustrative purposes.

[0013] The terms used herein are intended only to describe specific embodiments and are not intended to limit the general inventive concept. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly dictates otherwise. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which the exemplary embodiments belong. It is further understood that terms as defined in commonly used dictionaries should be interpreted to have a meaning consistent with the meaning in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0014] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, but may all refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner, in one or more embodiments, as will be apparent to one of ordinary skill in the art from this disclosure.

[0015] The present invention discloses a lithium secondary battery capable of effectively suppressing thermal runaway. The lithium secondary battery includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and an electrolyte system that provides ionic conductivity between the positive electrode and the negative electrode. Lithium ions can be transferred between the positive electrode and the negative electrode to perform an electrochemical reaction for charging and discharging. An ion donor is added to the positive electrode. The ion donor is inactive during the electrochemical reaction, i.e., does not participate in the electrochemical reaction. The ion donor includes a reactive anionic group and a cation bonded to the reactive anionic group. The ion donor releases the reactive anionic group after absorbing thermal energy. The reactive anionic group reacts with the positive electrode active material to reduce the reversibility / activity of the positive electrode active material. In addition, a certain reactive anionic group stabilizes the lattice structure of the positive electrode active material. Therefore, the positive electrode active material changes from a high-energy state to a low-energy state with the extraction of lithium ions, suppressing thermal runaway of the lithium secondary battery. When the temperature of the lithium secondary battery reaches a first temperature, the thermal energy may be absorbed by the ion donor by the lithium secondary battery. The bond strength between the cation and the reactive anionic group can be adjusted by a person skilled in the art by selecting the material. At the first temperature, the ion donor can obtain sufficient kinetic energy to break the bond between the cation and the reactive anionic group, so that the reactive anionic group can move freely. Therefore, the ion donor of the present invention does not dissociate in a polar solution to release the reactive anionic group, i.e., the ion donor does not dissociate in a polar solution. The reactive anionic group is activated and ionized by thermal energy.

[0016] The reactive anionic group may have at least a boron-oxygen bond, a sulfur-oxygen bond, a silicon-oxygen bond, an aluminum-oxygen bond, or a phosphorus-oxygen bond. The ion donor is disposed on the positive electrode of the lithium secondary battery and is adjacent to or in direct contact with the positive electrode active material particles of the positive electrode. For example, the ion donor is mixed with the positive electrode active material particles of the positive electrode to form a random distribution between the positive electrode active material particles. Alternatively, the ion donor is applied to the surface of the positive electrode. The electrolyte system may be a solid electrolyte, a semi-solid electrolyte, a liquid electrolyte, or a combination thereof. The ion donor is not dissolved in the electrolyte system.

[0017] A reactive anionic group having at least a boron-oxygen bond, a sulfur-oxygen bond, a silicon-oxygen bond, an aluminum-oxygen bond, or a phosphorus-oxygen bond can react with the positive electrode active material to disable the positive electrode and effectively suppress thermal runaway. In this embodiment, the reactive anionic group is AlO2 - , PO4 3- , P2O7 4- , AlSiO4 - , B4O7 2- , SO3‐R - , SO2‐R - , SiO3 - , HPO4 2- , SO3 2- , H2PO2 - , HPO3 2- , P2O6 - , P3O9 3- , BO2 - , B.O. 3- , P4O 13 6- , S2O7 2- , S2O3 2- , SO5 2- , S2O8 2- , S2O6 2- , S2O4 2- , P3O 10 5- , B2O5 4- , H2PO4 - , or S2O5 2-R is selected from any substituent. For example, R is selected from substituents including hydrogen, alkyl, aryl, aralkyl, or alkaryl. The reactive anionic group can be symmetric or asymmetric, with asymmetric reactive anionic groups being preferred over symmetric reactive anionic groups. Take the sulfur-containing oxide as an example: SO7 2- or SO3 2- is SO4 2- The more asymmetric structure, the greater the S2O7 2- is SO3 2- The more asymmetric structure. Therefore, S2O7 2- is SO3 2- More preferably, SO3 2- is SO4 2- It is more preferable for phosphorus oxide to be P2O7 4- is PO4 3- More asymmetric structure. P2O7 4- is PO4 3- More preferred. SO4 2- is a symmetrical type that is almost impossible to separate from the active part. Therefore, SO4 2- However, it is difficult for the reactive anionic group of the present invention to be carried by the positive electrode active material having a reactive anionic group. In addition, when reacting with the positive electrode active material having a reactive anionic group, the selection of the cation can be more diversified, for example, metal ions having a valence in the range of +1 to +3, such as sodium, potassium, copper, magnesium, calcium, or iron, can be selected. Therefore, it is possible to adapt compounds such as copper pyrophosphate (Cu2P2O7) and iron pyrophosphate (Fe4(P2O7)3).

[0018] Additionally, the ion donor may also have a backbone anionic group that is larger in molecular weight than the reactive anionic group, the reactive anionic group being located at the end or side of the backbone anionic group.

[0019] In the present invention, a lithium acceptor, or a so-called new lithium host, is further disposed on the negative electrode of the lithium secondary battery. This lithium acceptor can react with lithium to form a lithium alloy or lithium compound, but does not participate in the electrochemical reactions of the positive and negative electrodes of the lithium secondary battery during charging and discharging. That is, the lithium acceptor is inactive during lithium alloying or lithium ion insertion into the negative electrode. The potential at which the lithium acceptor reacts with lithium is different from the potential at which the negative electrode active material of the negative electrode reacts with lithium. For example, the potential at which the lithium acceptor reacts with lithium to form a lithium alloy or lithium compound is higher than the potential at which the negative electrode active material of the negative electrode reacts with lithium to form a lithium alloy or lithium compound. Therefore, the lithium acceptor does not participate in the charging and discharging of the lithium secondary battery. The lithium acceptor is disposed on the negative electrode of the lithium secondary battery and is adjacent to or in direct contact with the negative electrode active material. For example, the lithium acceptor is mixed with the negative electrode active material particles of the negative electrode, dispersed between the negative electrode active material particles, or coated on the surface of the negative electrode.

[0020] During the charging operation of the lithium secondary battery, lithium ions are excessively deposited and diffused in the negative electrode. The negative electrode exhibits lithium material properties different from those of the raw material. It is very unstable. However, lithium atoms diffuse from the negative electrode to the lithium acceptor activated by the concentration difference and the thermal energy of the lithium secondary battery at the second temperature. The lithium concentration in the negative electrode decreases and the material properties close to those of the original raw material appear. Thus, the negative electrode exhibits a stable state at a lower energy. The second temperature may be the same as or different from the first temperature. The negative electrode active material may be carbon, silicon, or lithium metal. The lithium acceptor may be an inorganic material, such as Li4Ti5O 12 , Fe4(P2O7)3, FeS2, Cu2P2O7, TiS2, or mixtures thereof. For example, FeS2 alloys with lithium at 1.5 to 2.5 volts, while carbon, silicon, or lithium metal electrochemically reacts with lithium at 0 to 0.1 volts. Thus, the lithium acceptor is inactive during lithium alloying or lithium ion insertion into the negative electrode.

[0021] Alternatively, the lithium acceptor may be an organic polymer that can withstand temperatures above 150°C. The organic polymer is alloyed with lithium at 1.5 to 3.5 volts. In order to avoid the above operating voltage of the organic polymer, it is possible to pretreat the negative electrode active material. When the negative electrode active material is carbon or silicon, the carbon or silicon is lithiated to avoid the above operating voltage of the organic polymer. The organic polymer may also be polyimide (PI), a polyimide derivative such as polyetherimide (PEI), polyaryletherketone (PAEK), or a mixture thereof. For example, PI is alloyed with lithium at 2.5 volts.

[0022] The lithium secondary battery may include an ion donor or may further include a lithium acceptor. The lithium secondary battery of the present invention may further include a separator made of an ion-conducting and electrically insulating material such as an electrically insulating material having pores for passing ions, or a solid electrolyte. The negative electrode active material of the negative electrode may be a carbon material, a silicon-based material, a mixture thereof, or lithium metal. Examples of carbon materials include graphitized carbon materials and amorphous carbon materials, such as natural graphite, modified graphite, graphitized mesocarbon microbeads, soft carbon (such as coke), and hard carbon. Examples of silicon-based materials include silicon, silicon oxide, silicon-carbon composites, and silicon alloys. The positive electrode active material of the positive electrode may be a material having a weight percentage of nickel of more than 75%. Lithium oxide containing nickel, cobalt and manganese , for example NCM811.

[0023] In the following, various experiments are carried out to verify the effects of the present invention. The electrolytes used in these experiments are non-aqueous electrolytes such as organic electrolytes, colloidal electrolytes, and polymer electrolytes to which salts such as LiPF6 and LiBF4 have been added, or carbonate solvents such as EC (ethylene carbonate) and PC (polycarbonate).

[0024] Table 1 below shows the difference between samples with and without the addition of an ion donor with respect to the amount of oxygen generated. Sample 1 has a composition of 76.61% NCM811, 3.26% conductive material, 1.63% adhesive, and 18.5% electrolyte by weight. In the method of producing sample 1, 76.61% NCM811, 3.26% conductive material, 1.63% adhesive, and 18.5% electrolyte by weight are mixed, and the mixture is applied onto a positive electrode current collector to form a positive electrode active material layer. Next, a separator, a negative electrode active material layer, and a negative electrode current collector are stacked in this order on the surface of the positive electrode active material layer. A sealing frame is used to seal the positive electrode active material layer, separator, and negative electrode active material layer between the positive electrode current collector, the sealing frame, and the negative electrode current collector, to form a stacked battery sheet. The laminated battery sheet is formed at 100% SOC (state of charge). The formed positive electrode active material layer is then scraped off and pressed at 0.9 N for 1 minute to form a sheet, thereby obtaining sample 1. In the method for producing sample 2, 76.61% NCM811, 3.26% conductive material, 1.63% adhesive, and 18.5% electrolyte are mixed by weight, and the mixture is applied onto a positive electrode current collector to form a positive electrode active material layer. Next, a separator, a negative electrode active material layer, and a negative electrode current collector are stacked in sequence on the surface of the positive electrode active material layer. A sealing frame is used to sandwich the positive electrode current collector and the negative electrode current collector, and the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector, the sealing frame, and the negative electrode current collector are sealed to form a laminated battery sheet. The laminated battery sheet is formed at 100% SOC (state of charge). The formed positive electrode active material layer is then scraped off, mixed with an equal weight of Na2B4O7, and pulverized. This mixture is pressed at 0.9N for 1 minute to form a sheet, obtaining sample 2. In sample 2, Na2B4O7 serves as the ion donor. Samples 3-6 are produced in the same manner as described for sample 2, except that the ion donor, i.e., Na2B4O7, is replaced with Na2SiO3, NaAlSiO4, Na2SO3, and Na2S2O5. Samples 1-6 are analyzed by gas chromatography-mass spectrometry (GC-MS), respectively. In this analysis, samples 1-6 are placed in a dedicated sample bottle for GC-MS analysis. In a glove box, the oxygen in the sample bottle is replaced with argon. The sample bottle is then sealed using parafilm to prevent air from entering.In the GC-MS analysis, the headspace extraction temperature is 200°C and the extraction time is 20 minutes. Then, 1 ml of the sample is heated from 40°C to 250°C. As shown in Table 1 below, after the above GC-MS analysis, the amount of oxygen generated in the sample with the ion donor added can be significantly reduced.

[0025] [Table 1]

[0026] Please refer to Figures 1 to 3. The figures are differential scanning calorimeter thermograms of sample 1 versus sample 3, 5, or 6. An appropriate amount of these samples is taken with a spatula. The samples are then placed on a sample tray dedicated to differential scanning mass spectrometry (DSC), and the sample tray is sealed. The samples are subjected to a DSC test while being heated from 30°C to 300°C at a rate of 5°C / min. It can be seen from the figures that the starting temperature of the exothermic reaction can be shifted to a higher temperature in the sample to which an ion donor is added. Thus, the lithium secondary battery can withstand higher temperatures.

[0027] Table 2 below shows the difference between samples in terms of oxygen evolved with and without the addition of a lithium acceptor.

[0028] Sample 7 has a composition by weight of 76.61% NCM811, 3.26% conductive material, 1.63% adhesive, and 18.5% electrolyte. The method for producing Sample 7 involves mixing NCM811, conductive material, adhesive, and electrolyte to form an electrode film. The electrode film is then used as the positive electrode of a coin cell. The coin cell is formed at 100% SOC (state of charge). The electrode film is then directly adopted as Sample 7. Sample 8 has a composition by weight of 66.61% NCM811, 3.26% conductive material, 1.63% adhesive, 18.5% electrolyte, and 10% Cu2P2O7. In the preparation method of sample 8, 66.61% NCM811, 3.26% conductive material, 1.63% adhesive, 18.5% electrolyte, and 10% Cu2P2O7 are mixed by weight to form an electrode film. The electrode film is used as the positive electrode of a coin cell. The coin cell is prepared at 100% SOC (state of charge). Then, the electrode film is directly adopted as sample 8. In sample 8, Cu2P2O7 serves as the ion donor. Samples 9-11 are prepared in the same manner as described for sample 8, except that the ion donor, i.e., Cu2P2O7, is modified. In sample 9, Fe4(P2O7)3 serves as the ion donor. In sample 10, KAl(SO4)2 serves as the ion donor. In sample 11, NaAIO2 serves as the ion donor. These samples are analyzed by gas chromatography-mass spectrometry (GC-MS). In this analysis, the samples are placed in a special sample bottle for GC-MS analysis. In a glove box, the oxygen in the sample bottle is replaced with argon. The sample bottle is then sealed with parafilm to prevent air from entering. In the GC-MS analysis, the headspace extraction temperature is 200°C and the extraction time is 20 minutes. Then, 1 ml of the sample is heated from 40°C to 250°C. As shown in Table 2 below, after the above GC-MS analysis, the amount of oxygen generated from the sample with the ion donor added can be significantly reduced compared to sample 7.

[0029] [Table 2]

[0030] Please refer to Figures 4 to 7. The figures are differential scanning calorimeter thermograms of Sample 7 and Samples 8, 9, 10, and 11. An appropriate amount of these samples is taken with a spatula. Next, the sample is placed on a DSC-specific sample tray, and the sample tray is sealed. The sample is subjected to a DSC test while increasing the temperature from 30°C to 300°C at a rate of 5°C / min. It can be seen from the figures that the starting temperature of the exothermic reaction can be shifted to the higher temperature side in the sample to which the ion donor is added. Therefore, the lithium secondary battery can withstand higher temperatures.

[0031] Table 3 below shows the difference in gas evolution between samples with and without the addition of a lithium acceptor. Sample 12 has a composition of 62.153% C / SiO, 2.049% conductive material, 4.098% adhesive, and 31.7% electrolyte by weight. Sample 12 is produced by mixing 62.153% C / SiO, 2.049% conductive material, 4.098% adhesive, and 31.7% electrolyte by weight, and applying the mixture onto a negative electrode current collector to form a negative electrode active material layer. Next, a separator, a positive electrode active material layer, and a positive electrode current collector are stacked in order on the surface of the negative electrode active material layer. A sealing frame is used between the positive electrode current collector and the negative electrode current collector to seal the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector, the sealing frame, and the negative electrode current collector to form a stacked battery sheet. The laminated battery sheet is formed at 100% SOC (state of charge). Then, the formed negative electrode active material layer is scraped off and pressed at 0.9 N for 1 minute to form a sheet, and sample 12 is obtained. Sample 13 has a composition of 31.0765% C / SiO, 1.0245% conductive material, 2.049% adhesive, 15.85% electrolyte, and 50% CaHPO4 by weight. In the method of producing sample 13, 62.153% C / SiO, 2.049% conductive material, 4.098% adhesive, and 31.7% electrolyte by weight are mixed, and the mixture is applied onto the negative electrode current collector to form the negative electrode active material layer. Next, a separator, a positive electrode active material layer, and a positive electrode current collector are stacked in order on the surface of the negative electrode active material layer. A sealing frame is sandwiched between the positive electrode current collector and the negative electrode current collector to seal the positive electrode active material layer, the separator, and the negative electrode active material layer between the positive electrode current collector, the sealing frame, and the negative electrode current collector, forming a stacked battery sheet. The stacked battery sheet is formed at 100% SOC (state of charge). The formed negative electrode active material layer is then scraped off, mixed with an equal weight of CaHPO4, and pulverized. This mixture is pressed at 0.9 N for 1 minute to form a sheet, and sample 13 is obtained.

[0032] The preparation method of sample 14 is almost the same as that of sample 13. Only CaHPO4 is replaced with Cu2P2O7. GC-MS is used to analyze oxygen, carbon monoxide, and gaseous alkanes, and GC-TCD (gas chromatography-thermal conductivity detector) is used to analyze hydrogen. In the analysis, the headspace extraction temperature is 200°C and the extraction time is 20 minutes. Then, 1 ml of the sample is heated from 40°C to 250°C. As shown in Table 3 below, after the above analysis, the amount of oxygen generated by sample 13 without the addition of ion donor is increased compared to sample 12, and the amount of oxygen generated by sample 14 with the addition of ion donor is decreased compared to sample 12.

[0033] [Table 3]

[0034] Table 4 below shows the difference between the samples in terms of gas evolution with and without the addition of lithium acceptor. Sample 15 has a composition of 62.153% C / SiO, 2.049% conductive material, 4.098% adhesive, and 31.7% electrolyte by weight. The method for preparing Sample 15 involves mixing 62.153% C / SiO, 2.049% conductive material, 4.098% adhesive, and 31.7% electrolyte by weight to form an electrode film. This electrode film is then used as the positive electrode of a coin cell. The coin cell is formed at 100% SOC (state of charge). The electrode film is then directly adopted as Sample 15. Sample 16 has a composition of 52.153% C / SiO, 2.049% conductive material, 4.098% adhesive, 31.7% electrolyte, and 10% Cu2P2O7 by weight. In the preparation method of sample 16, all the above materials are mixed together to form an electrode film. The electrode film is used as the positive electrode of a coin cell. The coin cell is prepared at 100% SOC (state of charge). Then, the electrode film is directly adopted as sample 16. The preparation method of sample 17 is almost the same as that of sample 16. Only Cu2P2O7 is replaced with Fe4(P2O7)3. Samples 15-17 are analyzed by GC-MS / GC-TCD (gas chromatography-thermal conductivity detector), respectively. In this analysis, samples 15-17 are placed in a dedicated sample bottle for GC-MS / GC-TCD analysis. In a glove box, the oxygen in the sample bottle is replaced with argon. Then, the sample bottle is sealed with parafilm to prevent air from entering. GC-MS is used to analyze oxygen, carbon monoxide, and gaseous alkanes, and GC-TCD is used to analyze hydrogen. In the analysis, the headspace extraction temperature is 200° C. and the extraction time is 20 minutes. Then, 1 ml of the sample is heated from 40° C. to 250° C. As shown in Table 4 below, the amount of gas generated in Samples 16 and 17 to which an ion donor was added can be significantly reduced compared to Sample 15.

[0035] [Table 4]

[0036] Therefore, the present invention provides a lithium secondary battery capable of suppressing thermal runaway. An ion donor is added to the positive electrode, or a lithium acceptor is further added to the negative electrode. The ion donor can absorb thermal energy due to the temperature rise of the lithium secondary battery and release a reactive anionic group. The reactive anionic group reacts with the positive electrode active material and reduces the reversibility / activity of the positive electrode active material. In addition, due to a certain reactive anionic group, the lattice structure of the positive electrode active material changes from a high energy state to a low energy state with the extraction of lithium ions. Therefore, the positive electrode becomes stable with the extraction of lithium ions. In the negative electrode, a lithium acceptor is used to receive excess lithium and exhibit material properties close to the original raw material of the negative electrode. Therefore, the negative electrode exhibits a stable state and effectively suppresses thermal runaway.

[0037] The present invention having been described above, it will be apparent that the same may be varied in many ways. Such variations should not be regarded as departing from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A lithium secondary battery, comprising: a positive electrode having a positive electrode active material; a negative electrode having a negative electrode active material; an electrolyte system that provides ionic conductivity between the positive electrode and the negative electrode, moves lithium ions between the positive electrode and the negative electrode, and performs an electrochemical reaction for charging and discharging; and an ion donor that is added to the positive electrode and is inactive during the electrochemical reaction, the ion donor including a reactive anionic group and a cation bonded to the reactive anionic group, and that releases the reactive anionic group by absorbing thermal energy, reacts with the positive electrode active material, inactivates the positive electrode active material, and stabilizes the lattice structure of the positive electrode active material; Including, The reactive anionic group is AlO ２ － , P ２ O ７ ４－ , AlSiO ４ － , B ４ O ７ ２－ , SiO ３ － , S.O. ３ ２－ , or S ２ O ５ ２－ and The reactive anionic groups are AlO 2 − , AlSiO 4 − , B 4 O 7 2− , SiO ３ － , SO 3 2− , or S 2 O 5 2− , the cation is Na; The reactive anionic group is P ２ O ７ ４－ wherein the cation is Cu or Fe; A lithium secondary battery comprising:

2. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material is a lithium oxide containing nickel, cobalt, and manganese, and the weight percentage of nickel is more than 75%.

3. The reactive anionic group is SO ３ ２－ 2. The lithium secondary battery according to claim 1,

4. The reactive anionic group is P ２ O ７ ４－ 2. The lithium secondary battery according to claim 1,

5. 2. The lithium secondary battery according to claim 1, wherein the ion donor has a main chain anionic group having a molecular weight larger than that of the reactive anionic group, and the reactive anionic group is located at an end or a side of the main chain anionic group.

6. 2. The lithium secondary battery according to claim 1, wherein the ion donor is distributed among positive electrode active material particles or is coated on the surface of the positive electrode.

7. The lithium secondary battery according to claim 1, further comprising a lithium acceptor distributed among particles of the negative electrode active material or coated on the surface of the negative electrode, the lithium acceptor being capable of reacting with lithium to form a lithium alloy or lithium compound, but not participating in the electrochemical reaction, and the potential at which the lithium acceptor reacts with lithium is different from the potential at which the negative electrode active material of the negative electrode reacts with lithium.

8. The lithium acceptor is an inorganic material or an organic polymer, and the inorganic material is Li ４ Ti ５ O １２ , Fe ４ (P ２ O ７ ) ３ , FeS ２ , Cu ２ P ２ O ７ , TiS ２ 8. The lithium secondary battery according to claim 7, wherein the organic polymer comprises polyimide (PI), a polyimide derivative, or a mixture thereof.

9. 2. The lithium secondary battery according to claim 1, wherein the ion donor does not dissociate in a polar solution.

10. 2. The lithium secondary battery according to claim 1, wherein the negative electrode active material is carbon, silicon, or lithium metal.

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