  Linear complementary dual (LCD) codes can provide an optimum linear coding
solution for the two-user binary adder channel. LCD codes also can be used to
against side-channel attacks and fault non-invasive attacks. Let $d_{LCD}(n,
k)$ denote the maximum value of $d$ for which a binary $[n,k, d]$ LCD code
exists. In \cite{BS21}, Bouyuklieva conjectured that $d_{LCD}(n+1,
k)=d_{LCD}(n, k)$ or $d_{LCD}(n, k) + 1$ for any lenth $n$ and dimension $k \ge
2$. In this paper, we first prove Bouyuklieva's conjecture \cite{BS21} by
constructing a binary $[n,k,d-1]$ LCD codes from a binary $[n+1,k,d]$
$LCD_{o,e}$ code, when $d \ge 3$ and $k \ge 2$. Then we provide a distance
lower bound for binary LCD codes by expanded codes, and use this bound and some
methods such as puncturing, shortening, expanding and extension, we construct
some new binary LCD codes. Finally, we improve some previously known values of
$d_{LCD}(n, k)$ of lengths $38 \le n \le 40$ and dimensions $9 \le k \le 15$.
We also obtain some values of $d_{LCD}(n, k)$ with $41 \le n \le 50$ and $6 \le
k \le n-6$.
