Lithium secondary battery comprising a non-aqueous electrolyte mixture and a cathode comprising a lithium manganese rich oxide

Abstract

The present invention relates to a lithium secondary battery comprising an anode, a cathode and a non-aqueous electrolyte; wherein the non-aqueous electrolyte comprises a lithium salt, a non-aqueous solvent, fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxine (DTD) and tris(trimethylsilyl) borate (TMSB); and the cathode comprises lithium manganese rich oxide.

Description

LITHIUM SECONDARY BATTERY COMPRISING A NON-AQUEOUS ELECTROLYTE MIXTURE AND A CATHODE COMPRISING A LITHIUM MANGANESE RICH OXIDE

[0001] The present invention relates to a lithium secondary battery comprising non-aqueous electrolyte mixture and a cathode comprising a lithium manganese rich oxide.

[0002] The use of high voltage cathode materials, such as lithium manganese-rich oxides (e.g. Li1.34Ni0.35Mn0.65O2, LMR), and carbonate-based electrolyte solutions in electrochemical cells presents two challenges that limit their electrochemical performance. These are the sudden drop in capacity, also known as the roll-over effect, and the poor anodic stability with the electrolyte solution. These issues relate to the type of the cathode and anode materials used in these high-voltage electrochemical cells. Furthermore, anode materials such as silicon (Si) and lithium (Li), undergo a significant volume expansion upon lithium uptake, which limits their performance.

[0003] A non-aqueous electrolyte is composed of solvents, lithium ion conducting salts and additives that are important for the improvement of the cycling stability and electrochemical performance of a lithium ion battery and of a lithium (metal) battery. Such improvement is a consequence of the electrochemical instability of the constituents of the electrolyte composition with the electrode materials (anodes and cathodes) at low and high potentials, which results in the formation of passivation films at the surface of these electrodes. These films are known as the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI).

[0004] Typically, the solvents, salts and additives of an electrolyte are selected to fulfil a specific requirement. For instance, the inclusion of FEC in the electrolyte composition may facilitate the formation of a stable SEI / CEI at the surface of the electrodes. Additionally, the presence of DTD could enhance the properties of the SEI by improving the Coulombic efficiency, while the inclusion of TMSB could prevent the transition metal dissolution. Additionally, the combination of various electrolyte additives is also advantageous. In the case of DTD when used alone as a single electrolyte additive a large amount of gas is evolved in the cell as in the case when DTD is combined with another electrolyte additive, as reported by Xia et al. (J. Electrochem. Soc., 2014, 161, A264). Furthermore, a crucial requirement is that each electrolyte component should be chemically compatibility with each other.

[0005] The use of DTD in electrolyte solutions was already mentioned in Hall et.al. (J. Electrochem. Soc., 2017, 164, A3445). The authors indicated that in binary electrolyte additive mixtures of DTD and PES (prop-1-ene-1,3-sultone) in a base electrolyte 1M LiPF6in EC:EMC 30:70, the composition of the resulting passivation films on the surface of the graphite electrode is a contribution of the synergistic behavior of the two additives. Also, the authors mention that the electrolyte was always freshly formulated prior the cell assembly took place.

[0006] The color change of electrolyte solutions containing DTD was mentioned in Welch et al. (J. Electrochem. Soc., 2022 169 120523). Among many, the following electrolyte formulations were also reported: FEC+DTD, DTD+TTSPi (tris(trimethylsilyl)phosphite), FEC+DTD+TTSPi. Here, the authors mentioned that the binary and ternary electrolyte formulations prepared using DTD as electrolyte additive showed a change in color during storage (after 1.5 months), while all the other electrolytes remained colorless or clear. Such change in color was shown to be also detrimental to the electrochemical performances resulting in fast capacity fading.

[0007] Ternary electrolyte combinations with DTD+TTSPi+PES was also reported by Nelson et al. (J. Electrochem. Soc., 2015, 162, A1046) and Nelson et al. (J. Electrochem. Soc., 2016, 163, A272). Although upon cycling a brown coloration of the separator was observed, the authors mentioned that this was a result of the cell design and Li metal plating on the anode, where the applied cell pressure was crucial.

[0008] The use of TMSB as electrolyte additive for high-voltage cathode materials was mentioned in: Liao et al. (Applied Energy, 2016, 175, 505), Rong et al. (Electrochimica Acta, 2014, 147, 31) and Li et al. (J. Power Sources 2015, 285, 360). In principle, the CEI formed in electrolytes containing TMSB has an ability to effectively suppress the electrolyte decomposition at high voltage that results in a thinner CEI with a lower interfacial resistance. All these effects result in improved cycling performance of the cathode materials. Furthermore, An et al. (Sci. Reports, 2019, 9, 14108) have indicated the performances of either TMSB or DTD in an baseline electrolyte containing among others also FEC.

[0009] Therefore, there is the object of the present invention to provide an electrolyte for use in a lithium secondary battery overcoming drawbacks of the prior art. Especially, it is an object of the present invention to provide an electrolyte for improving the performance of a lithium secondary battery comprising a LMR cathode material.

[0010] The above problem is solved in accordance with the independent claims. Further embodiments result from the sub claims and / or the following detailed description.

[0011] Especially, in order to achieve the above objects, the present disclosure provides, in a first embodiment, a lithium secondary battery comprising an anode, a cathode and a non-aqueous electrolyte;

[0012] wherein

[0013] - the non-aqueous electrolyte comprises a lithium salt, a non-aqueous solvent, fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxine (DTD) and tris(trimethylsilyl) borate (TMSB); and

[0014] - the cathode comprises lithium manganese rich oxide.

[0015] According to a second embodiment of the present disclosure, in the first embodiment, the non-aqueous electrolyte comprises the fluoroethylene carbonate (FEC) in an amount from 0.5 to 35 wt.-%, based on the total weight of the non-aqueous electrolyte.

[0016] According to a third embodiment of the present disclosure, in the first embodiment or in the second embodiment, the non-aqueous electrolyte comprises the 1,3,2-dioxathiolane 2,2-dioxine (DTD) in an amount from 0.5 to 3 wt.-%, based on the total weight of the non-aqueous electrolyte.

[0017] According to a fourth embodiment of the present disclosure, in any of the first to the third embodiments, the non-aqueous electrolyte comprises the tris(trimethylsilyl) borate (TMSB) in an amount from 0.5 to 5 wt.-%, based on the total weight of the non-aqueous electrolyte.

[0018] According to a fifth embodiment of the present disclosure, in any of the first to the fourth embodiments, the lithium salt is LiPF6.

[0019] According to a sixth embodiment of the present disclosure, in any of the first to the fifth embodiments, the non-aqueous solvent comprises ethylene carbonate (EC), ethyl methylcarbonate (EMC) or a mixture thereof.

[0020] According to a seventh embodiment of the present disclosure, in any of the first to the sixth embodiments, the non-aqueous solvent is ethyl methylcarbonate (EMC) or a mixture of a mixture of ethylene carbonate (EC) and ethyl methylcarbonate (EMC) in a ratio (vol.) from 20:80 to 40:60.

[0021] According to an eighth embodiment of the present disclosure, in any of the first to the seventh embodiments, the lithium manganese rich oxide is Li1.34Ni0.35Mn0.65O2.

[0022] According to a ninth embodiment of the present disclosure, in any of the first to the eighth embodiments, the anode comprises silicon.

[0023] According to a tenth embodiment of the present disclosure, in any of the first to the ninth embodiments, the lithium secondary battery further comprises a separator between the anode and the cathode.

[0024] According to an eleventh embodiment of the present disclosure, in any of the first to the tenth embodiments, the separator comprises a polyolefin.

[0025] It was surprisingly found that a non-aqueous electrolyte comprising a lithium salt, a non-aqueous solvent, fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxine (DTD) and tris(trimethylsilyl) borate (TMSB) improves the cycling performance of a battery comprising a cathode comprising lithium manganese-rich oxides (Li1.34Ni0.35Mn0.65O2, LMR), especially in combination with silicon anodes, such as anodes comprising micro-microcrystalline Si.

[0026] Especially electrochemical performances of LMR||μ-Si cells with an electrolyte in accordance with the inventions, such as (as an example) a non-aqueous electrolyte having the formulation of 1M LiPF6in EC:EMC 30:70 (vol. %) and 3 wt.% FEC, 1 wt.% DTD and 1 wt.% TMSB, are superior when compared to electrolyte solutions containing single and / or binary combinations of the electrolyte additives (DTD or TMSB) or the additive-free.

[0027] Furthermore, using TMSB in combination with DTD and FEC was surprisingly found to reduce the chemical decomposition reaction between DTD and FEC.

[0028] Figure 1. shows electrochemical impedance spectroscopy (EIS) results obtained for μ-Si||Li cells using as electrolyte 1M LiPF6in EC:EMC 30:70 (vol.%) with additional 5 wt.% FEC, or 5 wt.% DTD, or 5 wt.% TMSB. The measurement was carried out in the frequency range of 1 MHz to 10 mHz using an alternating voltage of 10mV.

[0029] Figure 2. shows cyclic voltammetry measurement results obtained for μ-Si||Li cells during the first cycle using an electrolyte based on 1.0 M LiPF6in EC:EMC 30:70 (vol.%) that contained additional 10 wt.% FEC, or 5 wt.% DTD, or 5 wt.% TMSB. The measurement was carried out using a potential scan rate of 50 μV s-1starting from OCP to the potential (E) 10 mV. An enlarged area of the current density (J) can be observed in which the electrolyte and its components decomposition takes place with the formation of the SEI.

[0030] Figure 3. shows specific discharge capacity (Qdisch) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture 1.0 M LiPF6in EC:EMC 30:70 (vol.%) and with various amounts of TMSB. The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0031] Figure 4. shows accumulated Coulombic inefficiency (ACI) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture 1.0 M LiPF6in EC:EMC 30:70 (vol.%) and with various amounts of TMSB. The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0032] Figure 5. shows specific discharge capacity (Qdisch) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture 1.0 M LiPF6in EC:EMC 30:70 (vol.%) and with various amounts of FEC, DTD and TMSB as electrolyte additives.

[0033] Figure 6. shows accumulated Coulombic inefficiency (ACI) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture 1.0 M LiPF6in EC:EMC 30:70 (vol.%) and with various amounts of FEC, DTD and TMSB as electrolyte additives.

[0034] Figure 7. shows the specific discharge capacity (Qdisch) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture of 1M LiPF6in EC:EMC 30:70 (vol.-%) and containing 1 wt.% DTD and 3 wt.% FEC, 1 wt.% DTD and 1 wt.% TMSB as well as 1 wt.% DTD, 1 wt.% TMSB and 3 wt.% FEC. The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0035] Figure 8. shows accumulated Coulombic inefficiency (ACI) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture of 1M LiPF6in EC:EMC 30:70 (vol.-%) and containing 1 wt.% DTD and 3 wt.% FEC, 1 wt.% DTD and 1 wt.% TMSB as well as 1 wt.% DTD, 1 wt.% TMSB and 3 wt.% FEC. The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0036] Figure 9. shows the specific discharge capacity (Qdisch) results obtained for LMR||μ-Si cells versus cycle number (X) during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture of 1M LiPF6in FEC:EMC 30:70 (vol.-%) and containing 1 wt.% DTD, 1 wt.% TMSB as well as their mixture. The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0037] Figure 10. shows accumulated Coulombic inefficiency (ACI) versus cycle number (X) results obtained for LMR||μ-Si cells during a constant-current constant-voltage measurement (CCCV) using as electrolyte a mixture of 1M LiPF6in FEC:EMC 30:70 (vol.-%) and containing 1 wt.% DTD, 1 wt.% TMSB as well as their mixture. The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0038] The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and should be construed in a sense and concept consistent with the technical idea of the present disclosure, based on the principle that the inventor can properly define the concept of a term to describe this invention in the best way possible.

[0039] Unless otherwise restricted, a detailed description defining or specifying the elements may be applied to all inventions and is not limited to descriptions of particular inventions. That is, the present disclosure also refers to combinations of the embodiments even if they are disclosed separately.

[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms "a," "an," and "the" comprise plural referents unless the context clearly dictates otherwise. It is to be understood that the terms such as "comprise" or "have" as used in the present specification, are intended to designate the presence of stated features, numbers, steps, operations, components, parts or combinations thereof, but not to preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. The term "comprises" explicitly, even if not necessarily limited accordingly, includes the meaning "essentially comprising" and "consists of".

[0041] The term "essentially comprises" as used herein has the meaning of "comprising at least 70 %", preferably of "comprising at least 80 %", most preferred of "comprising at least 90 %". If reference is made to the amount of a constituent in a mixture of material, % is wt %, relative to the total weight of the respective mixture. For example, a material essentially comprising silicon comprises the silicon in an amount of at least 70 wt% with respect to the total weight of the material.

[0042] Additionally, the terms "about" and "substantially" as used herein are used in the sense of at, or nearly at, when given the manufacturing and material tolerances inherent in the stated circumstances and are used to prevent the unscrupulous infringer from unfairly taking advantage of the present disclosure where exact or absolute figures are stated as an aid to understanding the present disclosure.

[0043] As used herein, "A and / or B" means "A and B, or A or B".

[0044] The anode as referred to herein may also be referred to as negative electrode. The cathode as referred to herein may also be referred to as positive electrode.

[0045] Hereinafter, the present disclosure will be described in more detail.

[0046] The present invention relates to a lithium secondary battery. The lithium secondary battery comprises an anode, a cathode and a non-aqueous electrolyte.

[0047] Non-aqueous electrolyte

[0048] The non-aqueous electrolyte comprises a lithium salt, a non-aqueous solvent, fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxine (DTD) and tris(trimethylsilyl) borate (TMSB).

[0049] The non-aqueous electrolyte may comprise the fluoroethylene carbonate (FEC) in an amount from 0.1 to 35 wt.-%, preferably 0.5 to 35 wt.-%, based on the total weight of the non-aqueous electrolyte.

[0050] In a first embodiment, the fluoroethylene carbonate (FEC) is contained in the non-aqueous electrolyte in an amount from 0.1 to 10 wt.-%, from 0.5 to 10 wt.-%, from 0.5 to 7.5 wt.-%, from 0.5 to 5 wt.-%, from 0.5 to 3 wt.-%, from 1 to 5 wt.-%, from 2 to 4 wt.-%, or from 2.5 to 3.5 wt.-%, such as about 3 wt.%, based on the total weight of the non-aqueous electrolyte. In this first embodiment, the fluoroethylene carbonate (FEC) which is contained in the non-aqueous electrolyte in said amounts can be considered as an electrolyte additive.

[0051] In a second embodiment, the fluoroethylene carbonate (FEC) is contained in the non-aqueous electrolyte in an amount from 15 to 35 wt.-%, or from 25 to 23 wt.-%, such as about 30 wt.-%, based on the total weight of the non-aqueous electrolyte. In this first embodiment, the fluoroethylene carbonate (FEC) which is contained in the non-aqueous electrolyte in said amounts can be considered as a co-solvent.

[0052] The non-aqueous electrolyte may comprise the 1,3,2-dioxathiolane 2,2-dioxine (DTD) in an amount from 0.1 to 10 wt.-%, from 0.5 to 10 wt.-%, from 0.5 to 7.5 wt.-%, from 0.5 to 5 wt.-%, from 0.5 to 3 wt.-%, from 0.5 to 2 wt.-%, from 0.5 to 1.5 wt.-%, from 0.8 to 1.2 wt.-%, such as about 1 wt.-%, from based on the total weight of the non-aqueous electrolyte.

[0053] The non-aqueous electrolyte may comprise the tris(trimethylsilyl) borate (TMSB) in an amount from 0.1 to 10 wt.-%, from 0.5 to 10 wt.-%, from 0.5 to 7.5 wt.-%, from 0.5 to 5 wt.-%, from 0.5 to 3 wt.-%, from 0.5 to 2 wt.-%, from 0.5 to 1.5 wt.-%, from 0.8 to 1.2 wt.-%, such as about 1 wt.-%, from based on the total weight of the non-aqueous electrolyte.

[0054] The non-aqueous electrolyte may comprise FEC:DTD:TMSB in a weight ratio of 0.5 to 5:0.5 to 3:0.5 to 3; from 2 to 4:0.5 to 1.5:0.5 to 1.5; or from 1.5 to 2.5:0.8 to 1.2:0.8 to 1.2; such as about 3:1:1.

[0055] The lithium salt can be used without limitation as long as it is commonly used in an electrolyte solution for a lithium secondary battery. For example, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, LiN(SO2F)2, lithium chloroborane, lithium lower aliphatic carboxylate, tetra-phenyl lithium borate, lithium imide, etc. or a mixture of two or more thereof. Preferably, the lithium salt is LiPF6, LiN(SO2F)2or a mixture thereof. Most preferred, the lithium salt is LiPF6.

[0056] The concentration of the lithium salt may be 0.2 to 2 M, preferably 0.4 to 2 M, more preferably 0.4 to 1.7 M, most preferred from 0.8 to 1.2 M, such as about 1 M, depending on various factors such as the exact composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, the operating temperature, and the like. When the concentration of the lithium salt is less than 0.2 M, the conductivity of the electrolyte may be lowered and thus the performance of the electrolyte may be deteriorated. When the concentration of the lithium salt is more than 2 M, the viscosity of the electrolyte may increase and thus the mobility of the lithium ion may be reduced.

[0057] The non-aqueous solvent may be used without limitation, and for example, may be ether, ester, amide, linear carbonate, cyclic carbonate, etc. may be used alone or in combination of two or more. Among them, linear carbonates and cyclic carbonates are preferred.

[0058] For example, the acyclic ether may be, but is not limited to, at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, ethylpropyl ether, dimethoxyethane, diethoxyethane, ethylene glycol ethylmethylether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methylethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methylethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methylethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methylethyl ether.

[0059] As an example, the cyclic ether may be, but is not limited to, at least one selected from the group consisting of 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3-dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3-dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene, and isosorbide dimethyl ether.

[0060] Examples of the ester of the organic solvent may be, but is not limited to, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, and a mixture of two or more thereof.

[0061] Specific examples of the linear carbonate compound may representatively be, but is not limited to, any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, or a mixture of two or more thereof.

[0062] In addition, specific examples of the cyclic carbonate compound may be any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides comprise, but are not limited to, fluoroethylene carbonate (FEC) and the like. If fluoroethylene carbonate (FEC) is comprised in the non-aqueous electrolyte as a (co-)solvent, the non-aqueous electrolyte comprises at least one further non-aqueous solvent which is different from fluoroethylene carbonate (FEC).

[0063] The non-aqueous solvent may comprise, essentially comprise or consist of ethylene carbonate (EC), ethyl methylcarbonate (EMC) or a mixture thereof.

[0064] The non-aqueous solvent may be ethyl methylcarbonate (EMC) or may be a mixture of a mixture of ethylene carbonate (EC) and ethyl methylcarbonate (EMC) in a ratio (vol.) from 10:90 to 50:50, 15:85 to 45:55, 20:80 to 40:60, 25:75 to 35:65, or 28:72 to 32:68, such as about 30:70.

[0065] If the non-aqueous solvent is ethyl methylcarbonate (EMC), the non-aqueous electrolyte may comprise fluoroethylene carbonate (FEC) as a co-solvent, wherein a in a ratio (vol.) of FEC:EMC may be from 10:90 to 50:50, 15:85 to 45:55, 20:80 to 40:60, 25:75 to 35:65, or 28:72 to 32:68, such as about 30:70.

[0066] Cathode

[0067] The lithium secondary battery according to the present invention comprises a cathode. The cathode comprises a cathode current collector and a cathode active material. The cathode may be manufactured by coating the cathode active material on the cathode current collector.

[0068] The cathode comprises lithium manganese rich oxide (LMR). In detail, the cathode active material may comprise the lithium manganese rich oxide (LMR). The positive electrode active material may comprise, for example, lithium manganese oxide such as formula Li1+xMn2-xO4(x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, LiNi1-xMxO2(M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); lithium manganese composite oxide represented by formula LiMn2-xMxO2(M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8(M = Fe, Co, Ni, Cu or Zn); LiMn2O4with partial substitution of alkali earth metal ion for Li. The lithium manganese rich oxide may be represented by the formula Li1.34Ni0.35Mn0.65O2.

[0069] The cathode active material may further comprise a conductive material which may be added in an amount of 0.1 weight% to 30 weight% based on the total weight of the cathode active material. The conductive material is not limited to any particular type when it has conductive properties while not causing a chemical change to the corresponding battery, and may include, for example, conductive materials, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; fluorocarbon, metal powder such as aluminum powder and nickel powder; conductive whiskers such as oxide zinc and potassium titanate; conductive metal oxide such as titanium oxide; and polyphenylene derivatives.

[0070] The cathode active material may further comprise a binder and may be added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the cathode active material. Examples of the binder may comprise polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regeneratedcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, fluorine rubber and various types of copolymers.

[0071] In general, the cathode current collector may be manufactured with the thickness of 3 ㎛ to 500 ㎛, and is not limited to a particular type and may include any material having high conductivity without causing any chemical change to the corresponding battery, for example, one selected from stainless steel, aluminum, nickel, titanium, and aluminum or stainless steel surface treated with carbon, nickel, titanium or silver, and specifically aluminum. The current collector may have macrotexture on the surface to improve the adhesion strength of the positive electrode active material, and may come in various types, for example, films, sheets, foils, nets, porous bodies, foams and non-woven fabrics.

[0072] Anode

[0073] The lithium secondary battery according to the present invention further comprises an anode. The anode may be an anode comprising an anode active material. The anode active material may be a porous anode active material (= anode active materials having pores). The anode may essentially comprise or consist of the anode active material. Alternatively, only a part of the anode may essentially comprise or consist of the anode active material, for example one or more layers of the anode.

[0074] In one embodiment the anode (= negative electrode) comprises essentially comprises or consists of a current collector and an anode active material layer, wherein the anode active material layer is provided on at least one surface of the current collector. In such a case, the current collector is a negative electrode current collector. The anode active material layer comprises, essentially comprises or consists of the anode active material.

[0075] The anode may be manufactured by coating the anode active material on a negative electrode current collector and drying.

[0076] The negative electrode current collector may be manufactured with the thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not limited to a particular type and may comprise any material having conductive properties without causing any chemical change to the corresponding battery, for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless-steel surface treated with carbon, nickel, titanium or silver, and aluminum-cadmium alloy. The negative electrode current collector may have microtexture on the surface to improve the adhesion strength of the anode active material, and may come in various types, for example, films, sheets, foils, nets, porous bodies, foams and non-woven fabrics.

[0077] For example, the porous anode active material may comprise silicon, silicon-containing alloys; carbons such as non-graphitizing carbon and graphite-based carbon; metal composite oxides such as LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe'yOz(Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Groups 1, 2 and 3 elements of the periodic table, halogen; 0<x＜1; 1≤y≤3; 1≤z≤8); tin-containing alloys; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; and conductive polymers such as polyacetylene; preferably comprises, essentially comprises or consists of silicon, wherein the silicon is preferably microcrystalline silicon (μ-Si). It is preferred that the porous anode active material microcrystalline silicon (μ-Si) in an amount of at least 80 wt.-%.

[0078] The porous anode active material may include a binder. The binder included in the porous anode active material is usually added in an amount of 0.1 weight% to 30 weight% based on the total weight of the mixture comprising the porous anode active material. In an exemplary embodiment of the present application, the negative electrode binder may comprise at least one selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, an ethylene-propylene-diene monomer (EPDM), a sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, polyacrylic acid and a material in which the hydrogen thereof is substituted with Li, Na, Ca, or the like, and may also comprise various polymers thereof.

[0079] The porous anode active material may have a porosity of at least about 10%, at least 20%, or at least 25%. The porous anode active material may have a porosity of 90% or less, 80 % or less, 70% or less, 60% or less, 50% or less 40% or less 35% or less, or 30 % or less. Preferably, porous anode active material has a porosity from 20% to 35%, more preferably from 25% to 30%, such as about 30%. Such a porosity of the porous anode active material is advantageous in view of the amount of Li which can be deposited in the porous anode active material and in view of the achieved capacity of a lithium secondary battery using such a porous anode active material. The term "porosity" used in the present specification refers to a fraction of voids in a structure over the total volume and is indicated in %, and may be used interchangeably with void fraction, degree of porosity or the like. In the present disclosure, the porosity may be measured by mercury permeation method (Hg porosimeter) according to ASTM D-2873 in the version at the priority date of the present application.

[0080] Separator

[0081] The lithium secondary battery according to the present invention may further comprise a separator. The separator may be arranged between the anode and the cathode. The separator may be made of a porous non-conductive or insulating material and enables transport of lithium ions between the anode and the cathode. The separator may be used without special limitation, may be one conventionally used as a separator in a conventional lithium secondary battery. The separator may be an independent member such as a film.

[0082] The separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used for a lithium-sulfur battery, and porous polymer films may be used alone or by laminating them, and for example, a nonwoven fabric or a polyolefin-based porous membrane made of glass fibers, polyethylene terephthalate fibers, etc. having a high melting point may be used, but is not limited thereto.

[0083] The material of the porous substrate is not particularly limited in the present disclosure, and any material can be used as long as it is a porous substrate commonly used in an electrochemical device. For example, the porous substrate may comprise at least one material selected from the group consisting of polyolefin such as polyethylene and polypropylene, polyester such as polyethyleneterephthalate and polybutyleneterephthalate, polyamide, polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, poly(p-phenylene benzobisoxazole), and polyarylate.

[0084] It is preferred that the separator is a porous polypropylene membrane. Even more preferred, the separator is a porous polypropylene membrane.

[0085] The thickness of the separator is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the separator is not particularly limited to the above-mentioned range, when the thickness is excessively thinner than the lower limit described above, mechanical properties are deteriorated and thus the separator may be easily damaged during pre-lithiation.

[0086] The separator may have pores and the average diameter and porosity of the pores present in the separator are also not particularly limited but may be 0.001 μm to 50 μm and 10% by volume to 95% by volume, respectively.

[0087] Lithium secondary battery

[0088] The present invention relates to a lithium secondary battery, especially a lithium-ion secondary battery.

[0089] The lithium secondary battery according to the present disclosure can be manufactured by lamination, stacking, and folding processes of the separator and the electrodes, in addition to the usual winding process.

[0090] The shape of the lithium secondary battery is not particularly limited and may be various shapes such as a cylindrical shape, a laminate shape, and a coin shape.

[0091] Also, the present disclosure provides a battery module comprising the lithium-sulfur battery described above as a unit battery.

[0092] The battery module may be used as a power source for medium to large-sized devices requiring high temperature stability, long cycle characteristics, high capacity characteristics, and the like.

[0093] Examples of such medium to large-sized devices may comprise, but are not limited to, a power tool powered and moved by an electric motor; an electric car including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; an electric two-wheeled vehicle including an electric bike (E-bike) and an electric scooter (E-scooter); an electric golf cart; a power storage system, etc.

[0094] Further aspects of the invention

[0095] The following further aspects of the invention may be, separately or in combination with each other or parts of the forgoing generalized specification of the invention, material for realizing the invention.

[0096] It was surprisingly found that a ternary combination of FEC, DTD and TMSB, such as, for example, 3 wt.% FEC, 1 wt.% DTD and 1 wt.% TMSB, as electrolyte additives to a solution of a lithium salt in a non-aqueous solvent, such as, for example, 1M LiPF6in EC:EMC 30:70 (by vol.), results in superior electrochemical performances as compared to either the individual components (e.g. 1 wt.% TMSB in 1M LiPF6in EC:EMC 30:70 (by vol.)) or the binary mixtures (e.g. 1 wt.% DTD + 3 wt.% TMSB).

[0097] The percentage of TMSB in 1 M LiPF6in EC:EMC 30:70 (vol.-%) or in binary mixtures, for example, 1 wt.-% DTD + 3 wt.-% FEC in 1 M LiPF6in EC:EMC 30:70 (vol.-%) or 1 wt.-% DTD + 1 wt.-% TMSB in 1 M LiPF6in EC:EMC 30:70 (vol.-%), may be favorable in view of SEI and CEI formation during the first cycles on both the negative and positive electrodes. The presence of the three electrolyte additives in the non-aqueous electrolyte is crucial for the formation of the SEI and CEI film during the first cycles on both the negative and positive electrodes. The SEI film may act as a protective layer that prevents further decomposition reactions of the electrolyte at the negative electrode. The CEI may protect the positive electrode from degradation and electrolyte oxidation, which optimizes the cycle life while minimizing the number of side reactions.

[0098] Using an electrolyte solution, where TMSB, DTD and FEC are combined together, results in an enhancement of the capacity retention as compared to the binary mixtures.

[0099] Addition of TMSB to an electrolyte solution that already contains DTD and FEC results in a lower transition metal dissolution from the LMR positive electrode material (Li1.34Ni0.35Mn0.65O2, LG Energy solution) .

[0100] Addition of TMSB to a combination of DTD and FEC results in an increase of the chemical stability of the latter for more than two weeks as compared to the DTD and FEC mixture without TMSB.

[0101] The addition of FEC to a mixture of TMSB and DTD is able to increase the capacity retention of the LMR||μ-Si cells.

[0102] The presence of DTD and FEC in the electrolyte solutions result in the formation of an SEI on the surface of the μ-Si negative electrode preventing further electrolyte decomposition.

[0103] The presence of FEC and TMSB in the electrolyte solution as electrolyte additives result in the formation of a suitable CEI film at the surface of the LMR positive electrode that prevents the structural decomposition of the cathode material by reducing the transition metal dissolution and further reduces the amount of electrolyte decomposition at high voltage.

[0104] An electrochemical cell can be assembled using a LMR cathode (e.g. Li1.34Ni0.35Mn0.65O2), a monolayer microporous membrane separator (e.g. Celgard 2500) and a Si-anode (e.g. μ-Si anode) together with the electrolyte formulated as a solutions of a lithium salt, a non-aqueous solvent, fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxine (DTD) and tris(trimethylsilyl) borate (TMSB) (e.g. 1M LiPF6in EC:EMC 30:70 (by vol) 3 wt.% FEC, 1 wt.% DTD and 1 wt.% TMSB) as electrolyte additives.

[0105] In order to improve the electrochemical performance of the lithium secondary battery, e.g. a LMR||μ-Si cell, it is necessary that the electrolyte contains among the baseline electrolyte components a certain amount of DTD, FEC and TMSB.

[0106] To prepare the electrolyte, it is favorable that electrolyte additives are added to the baseline electrolyte in a certain wt.% amount. The presence of a single or binary mixture will not produce the enhanced electrochemical performances that are reported.

[0107] It is favorable that after the lithium secondary battery (e.g. LMR||μ-Si cell) assembly, a formation cycle is carried out by using a 0.1C current with respect to the cathode active material amount present in the positive electrode.

[0108] When TMSB is used in the electrolyte formulation it improves the electrochemical performance of the cathode material by reducing the amount of transition metal that is dissolving in the electrolyte.

[0109] The amount of TMSB added to the electrolyte solution may be ranging between 0.5 wt.% and 5 wt.%.

[0110] The amount of DTD added to the electrolyte solution may be ranging between 0.5 wt.% and 3 wt.%.

[0111] As electrolyte additive, the amount of FEC in the electrolyte solution may range between 1 wt.% and 5 wt.%.

[0112] The base line electrolyte solution (BE) as referred to herein is 1M LiPF6 in EC:EMC 30:70 (by vol.). In the inventive examples respective amounts of DTD, TMSB and FEC are added to the BE in amounts in wt.% (with respect to the EC:EMC mixture).

[0113] The base line electrolyte solution (BE-F) as referred to herein is 1M LiPF6 in FEC:EMC 30:70 (by vol.). The use of BE-F with DTD and TMSB as electrolyte additives results also in improved electrochemical performances of the lithium secondary battery (e.g. LMR||μ-Si cell) chemistry.

[0114] EXAMPLES

[0115] Examples using FEC as an additive

[0116] Electrolyte solvent mixtures using FEC as an additive was formulated following the procedure:

[0117] To a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) of 30:70 (vol. %), the required amounts of electrolyte additive are added to give a content of 3 wt.% FEC, 1 wt.% DTD and 1 wt.% TMSB. Furthermore, to prepare the electrolyte solution with a concentration of 1M LiPF6, 0.7720 g of LiPF6were added to a volumetric flask (5 mL) and the amount of 5.1895 g of the electrolyte solvent mixture was added until complete dissolution of the salt.

[0118] Different electrolyte solutions were prepared with the amount of electrolyte additives ranging from 0.1 wt.% and 10 wt.%, and electrochemical performance of a LMR||μ-Si cells with FEC, DTD and TMSB electrolyte additives were investigated.

[0119] To analyze the electrochemical performance of the electrode materials with the different electrolyte solutions, electrochemical cells were assembled using an LMR cathode (Li1.34Ni0.35Mn0.65O2, LG Energy Solution), a polyolefin separator (Celgard 2500) and a μ-Si (LG Energy Solution) together with the electrolyte formulated as a solution of 1M LiPF6 in EC:EMC 30:70 (vol. %) containing different amounts of electrolyte additives.

[0120] Examples using FEC as a co-solvent

[0121] Electrolyte solvent mixtures using FEC as a co-solvent were formulated following the procedure:

[0122] To a mixture of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) of 30:70 (vol. %), the required amounts of electrolyte additive DTD and TMSB were added in different amounts. For example, to give a content of 1 wt.% DTD and 1 wt.% TMSB, the electrolyte solvent mixture was prepared by adding 0.1196 g of DTD and 0.1205 g of TMSB to 11.7377 g of FEC:EMC 30:70 (vol. %) solvent mixture. From this electrolyte solvent mixture, 5.3795 g were added to a volumetric flask (5 mL) containing 0.7619 g of LiPF6and stirred until complete dissolution of the salt. Following these steps, the following electrolyte was formulated: 1M LiPF6in FEC:EMC 30:70 (vol. %) with 1 wt.% DTD and 1 wt.% TMSB as electrolyte additives.

[0123] The different non-aqueous electrolytes using FEC as an additive or as a co-solvent were tested, especially in view of lithium secondary battery performance obtained using said electrolytes. The results are shown in Figs. 1 to 9 and summarized in the following.

[0124] Figure 1 shows the impedance evolution of the μ-Si||Li cell after the cell was charged to 10 mV using a C-rate of C / 50. The results indicate that using FEC and DTD as electrolyte additives a lower cell impedance is obtained as compared to the baseline electrolyte (BE: 1M LiPF6in EC / EMC 30 / 70 (Vol.-%). The values for the SEI resistance decrease in the order BE>DTD>FEC (52.15 Ω > 44.04 Ω > 19.96 Ω). These values may vary depending on the specific surface composition of the used electrodes. The amount of DTD in BE was 5 wt.% and the amount of FEC in BE was 5 wt.%. The Impedance spectra were fitted using the Randless electrical equivalent circuit.

[0125] Figure 2 shows the comparison of the cyclic voltammogram during the first lithiation process of the Si electrode recorded in μ-Si||Li cell using a scan rate of 50 μV s-1of the BE electrolyte, BE electrolyte with 5 wt.% of DTD, BE electrolyte with 5 wt.% TMSB and BE electrolyte with 5 wt.% FEC. The shape of the current profiles indicates that both DTD and FEC react with the surface of the μ-Si prior the electrochemical decomposition of EC around 0.75 V vs. Li / Li+. The decomposition of FEC occurs around 1.28 V vs. Li / Li+while the reductive decomposition of DTD occurs around 1.13 V vs. Li / Li+. On the other side, no additional decomposition process (except the EC decomposition) is observed with TMSB electrolyte additive. This implies that both FEC and DTD can be used to form a stable SEI on the μ-Si electrode surface.

[0126] Figure 3 shows a comparison of the discharge capacity over 300 cycles of the LMR||μ-Si cells under constant current and constant voltage cycling using the BE electrolyte with various amounts of TMSB. The amount of TMSB was varied from 0.5 wt.% to 5 wt.%. The results indicate that stable discharge capacity is obtained for almost 150 cycles of the electrolyte solution that contains an amount of TMSB from 0.5 wt.% to 3 wt.%. Furthermore, a stable discharge capacity was obtained for more than 200 cycles if the amount of TMSB was varied from 1 wt.% to 3 wt.%.

[0127] Figure 4 shows a comparison of the accumulated coulombic inefficiency of the cells assembled with various amounts of TMSB as electrolyte additives. The results indicate that the BE electrolyte performs the worst while the cells assembled with the BE electrolyte containing 1 wt.% of TMSB and 3 wt.% TMSB perform the best with the lowest amount of irreversible capacity accumulated over 150 cycles.

[0128] In the Figure 5, the numbers correspond to the following electrolyte formulations:

[0129] 1 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%);

[0130] 2 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 0.1 / 0.1 / 0.1 (wt.%);

[0131] 3 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 0.5 / 0.5 / 0.5 (wt.%);

[0132] 4 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 3 / 3 / 3 (wt.%);

[0133] 5 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 5 / 5 / 5 (wt.%);

[0134] 6 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 10 / 10 / 10 (wt.%).

[0135] The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0136] Figure 5 shows a comparison of the discharge capacity over 160 cycles of the LMR||μ-Si cells under constant current and constant voltage cycling using the BE electrolyte with various amounts of DTD, TMSB and FEC contained in the same electrolyte formulation. The electrolyte formulation is referred to as 1.0 M LiPF6 in EC:EMC 30:70 (Vol. -%) + DTD / FEC / TMSB x / x / x (Gew. -%), where x denotes the amount of electrolyte additive that varies from 0.1 wt.% to 10 wt.%. The results indicate that the content of electrolyte additives is crucial for the cycling stability of the LMR||μ-Si cells. Furthermore, an amount of electrolyte additives in the baseline electrolyte varying from 0.5 wt.% to 3 wt.% results in a stable discharge capacity delivered for more than 150 cycles. Outside these limits, i.e. x<0.5 wt.% or x>5 wt.% results in no beneficial behavior for the cycling stability of the LMR||μ-Si cells.

[0137] In the Figure 6, the numbers correspond to the following electrolyte formulations:

[0138] 1 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%);

[0139] 2 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 0.1 / 0.1 / 0.1 (wt.%);

[0140] 3 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 0.5 / 0.5 / 0.5 (wt.%);

[0141] 4 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 3 / 3 / 3 (wt.%);

[0142] 5 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 5 / 5 / 5 (wt.%);

[0143] 6 - 1.0 M LiPF6in EC:EMC 30:70 (vol.%) + DTD / FEC / TMSB 10 / 10 / 10 (wt.%).

[0144] The coin cells were cycled using a C-rate of 0.1C for the first two cycles and 0.33C for the following cycles. All measurements were carried out at 20 °C.

[0145] Figure 6 shows a comparison of the accumulated coulombic inefficiency of the cells assembled with various amounts of DTD, TMSB and FEC contained in the same electrolyte formulation. The results indicate that the BE electrolyte performs the worst with a significant increase of the accumulated irreversible capacity after already 60 cycles. On the other side, the addition of additive improves the cycles life, however, the best performances with the lowest increase of the irreversible capacity are accounted to an electrolyte formulation where the electrolyte additives range from 0.5 wt.% to 3 wt.%.

[0146] Figure 7 shows a comparison of the discharge capacity over 300 cycles of the LMR||μ-Si cells under constant current and constant voltage cycling using a BE electrolyte formulation including DTD, TMSB and FEC. The amount of the additives electrolyte additives in each formulation was the following: DTD was used in a 1 wt.% amount, TMSB was used in a 1 wt.% amount and FEC was used in a 3 wt.% amount. The results indicate that the electrolyte formulation containing all three electrolyte additives performs the best with the LMR||μ-Si cells resulting in prolonged cycle performance with stable discharge capacity delivered for almost 250 cycles.

[0147] Figure 8 shows a comparison of the accumulated coulombic inefficiency of the LMR||μ-Si cells assembled with a BE electrolyte formulation that includes as electrolyte additives DTD, TMSB and FEC. The results indicate that a binary mixture of electrolyte additives based on DTD and FEC does not improve the cycle performance of the LMR||μ-Si cells as the accumulated irreversible capacity increases after 60 cycles. On the other side, when TMSB is added to the electrolyte formulation in an amount of 1 wt.% little increase of the accumulated irreversible capacity is observed. The electrolyte with the best performance in terms of the lowest amount of irreversible capacity produced was 1M LiPF6in EC:EMC 30:70 (Vol.-%) with 1 wt.% DTD and 3 wt.% FEC and 1 wt.% TMSB.

[0148] Figure 9 shows a comparison of the discharge capacity of the LMR||μ-Si cells under constant current and constant voltage cycling using the electrolyte formulation as follows: 1M LiPF6was dissolved in a mixture of FEC / EMC 30 / 70 and either 1 wt.% of DTD or 1 wt.% TMSB are added. An electrolyte formulation including both electrolyte additives showed the best performances with a stable discharge capacity delivered for more than 400 cycles.

[0149] Figure 10 shows a comparison of the accumulated coulombic inefficiency of the LMR||μ-Si cells assembled with an electrolyte formulation using the electrolyte formulation as follows: 1M LiPF6was dissolved in a mixture of FEC / EMC 30 / 70 and either 1 wt.% of DTD or 1 wt.% TMSB are added. The results indicate that the addition of a single electrolyte additive (e.g. 1 wt.% DTD or 1 wt.% TMSB) does not result in an enhancement of the electrochemical performances. However, it is necessary to assure the presence of DTD and TMSB is the electrolyte formulation.

[0150] The results show that in lithium secondary batteries with LMR cathode and especially μ-Si electrodes it is favorable that the interphases and interfaces of the μ-Si electrodes and LMR cathode are stabilized. This is can be achieved when selected electrolyte additives that suppress the side reactions at the two electrodes are used. The combination of DTD, TMSB and FEC in various electrolyte formulations and in various amounts was identified to provide an enhancement of the LMR||μ-Si cells electrochemical performance.

[0151] The features disclosed in the foregoing description and in the dependent claims may, both separately and in any combination thereof, be material for realizing the aspects of the disclosure made in the independent claims, in diverse forms thereof.

Claims

1.A lithium secondary battery comprising an anode, a cathode and a non-aqueous electrolyte;wherein- the non-aqueous electrolyte comprises a lithium salt, a non-aqueous solvent, fluoroethylene carbonate (FEC), 1,3,2-dioxathiolane 2,2-dioxine (DTD) and tris(trimethylsilyl) borate (TMSB); and- the cathode comprises lithium manganese rich oxide.2.The lithium secondary battery according to claim 1, wherein the non-aqueous electrolyte comprises the fluoroethylene carbonate (FEC) in an amount from 0.5 to 35 wt.-%, based on the total weight of the non-aqueous electrolyte.3.The lithium secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte comprises the 1,3,2-dioxathiolane 2,2-dioxine (DTD) in an amount from 0.5 to 3 wt.-%, based on the total weight of the non-aqueous electrolyte.4.The lithium secondary battery according to any of the preceding claims, wherein the non-aqueous electrolyte comprises the tris(trimethylsilyl) borate (TMSB) in an amount from 0.5 to 5 wt.-%, based on the total weight of the non-aqueous electrolyte.5.The lithium secondary battery according to any of the preceding claims, wherein the lithium salt is LiPF6.6.The lithium secondary battery according to any of the preceding claims, wherein the non-aqueous solvent comprises ethylene carbonate (EC), ethyl methylcarbonate (EMC) or a mixture thereof.7.The lithium secondary battery according to any of the preceding claims, wherein the non-aqueous solvent is ethyl methylcarbonate (EMC) or a mixture of a mixture of ethylene carbonate (EC) and ethyl methylcarbonate (EMC) in a ratio (vol.) from 20:80 to 40:60.8.The lithium secondary battery according to any of the preceding claims, wherein the lithium manganese rich oxide is Li1.34Ni0.35Mn0.65O2.9.The lithium secondary battery according to any of the preceding claims, wherein the anode comprises silicon.10.The lithium secondary battery according to any of the preceding claims, wherein the lithium secondary battery further comprises a separator between the anode and the cathode.11.The lithium secondary battery according to claim 10, wherein the separator comprises a polyolefin.

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